Does coronavirus spread more easily in cold temperatures? Here’s what we know



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Sarah Pitt, University of Brighton

Why is the reported number of COVID-19 cases rising across Europe now? Many countries ended their full lockdowns at the start of the summer, but it wasn’t until the autumn that most places began to see a significant increase in the spread of the virus again. The re-opening of schools and universities led to greater mixing of individuals from different households, but could the fall in outside temperatures also be playing a part?

We know that more people get colds and flu in the winter (the colds can be caused by types of coronavirus), but there are several potential reasons for this. It’s often attributed to the fact that people spend more time indoors when it’s colder, coughing, sneezing and breathing on each other.

You are more likely to choose the option of travelling on a crowded bus or train than walking or cycling to work when the weather is cold and wet. Another theory is that people produce less vitamin D when there is less sunlight and so have weaker immune systems.

However, studies have shown that the annual increase in colds and flu particularly coincides with when the temperature outside and relative humidity indoors are lower. Flu viruses survive and are transmitted more easily in cold, dry air. So it’s reasonable to think that the same may be true for the COVID-19 coronavirus, SARS-CoV-2, which has a similar size and structure.

Laboratory experiments with coronaviruses and similar viruses have shown that they do not survive well on surfaces when the temperature and relative humidity are high, but comfortable room temperature could be an ideal environment for them to last for several days. And at refrigeration temperatures (4℃) and low relative humidity, they could last a month or more.

As it happens, there have been repeated reports of outbreaks of COVID among workers in meat-packing factories, which operate under these kind of conditions. However, such factories also contain large numbers of people working close together and shouting to be heard above the noise of machinery, which evidence suggests may be more likely to spread the virus. Their shared living conditions may also encourage transmission.

Old and young man sat talking outside
Flu viruses are transmitted more easily in cold, dry air.
Halfpoint/Shutterstock

The lessons from the other coronaviruses that have appeared during the 21st century (SARS-CoV and MERS-CoV) also tell a slightly different story. A study tracking the weather during the 2003 Sars epidemic in China suggested that the peak of the infections occurred during spring-like weather conditions. (There was no way of confirming this through follow-up studies since the virus later died out.)

Regular outbreaks of Mers also happen in the spring (March to May) in the Middle East. However, this may be less to do with the weather and more related to camel biology. Humans can acquire Mers from each other or from camels. Young camels are a major source of infection and new animals are born during March.

Southern hemisphere

We can also look at what happened in the southern hemisphere during winter there. South Africa has reported over 700,000 cases and experienced a large peak in July, but New Zealand controlled the infection very well and had fewer than 2,000 cases of COVID-19.

These two countries are very different in many respects, so it’s not that useful to directly compare them. But it does seem like the colder weather during July and August was probably not the main factor in deciding their infection rates. New Zealand seems to have kept the spread of SARS-CoV-2 at bay due to geography, the quality of the healthcare system and the effectiveness of the public health response. It might have been able to do that whatever the weather.

Early data from Australia suggested that low humidity would be a factor to look out for and was a better guide to risk of increases in COVID-19 than temperature. However, in Melbourne, there was a large outbreak in July coinciding with a spell of cold weather. This led to a strict lockdown, although it was only fully eased in October.

In all, it seems like a good idea to be prepared for more COVID-19 cases during the colder months. But the one thing we have learned for sure from SARS-CoV-2 is that new viruses can surprise us.

We also know that coming into close contact with others provides an opportunity for the virus to spread, whatever the weather. So we must keep physical distance between people who do not live in the same household and continue to wear face coverings in enclosed spaces whenever possible.

Unfortunately, we will only learn exactly how changes in the weather affect the pandemic by living through it.The Conversation

Sarah Pitt, Principal Lecturer, Microbiology and Biomedical Science Practice, Fellow of the Institute of Biomedical Science, University of Brighton

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mobile phones are covered in germs. Disinfecting them daily could help stop diseases spreading



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Lotti Tajouri, Bond University; Mariana Campos, Murdoch University; Rashed Alghafri, Bond University, and Simon McKirdy, Murdoch University

There are billions of mobile phones in use around the globe. They are present on every single continent, in every single country and in every single city.

We reviewed the research on how mobile phones carry infectious pathogens such as bacteria and viruses, and we believe they are likely to be “Trojan horses” that contribute to community transmission in epidemics and pandemics.

This transfer of pathogens on mobile phones poses a serious health concern. The risk is that infectious pathogens may be spreading via phones within the community, in workplaces including medical and food-handling settings, and in public transport, cruise ships and aeroplanes.

Currently mobile phones are largely neglected from a biosecurity perspective, but they are likely to assist the spread of viruses such as influenza and SARS-CoV-2, the novel coronavirus responsible for the COVID-19 pandemic.




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What the research shows

We reviewed all the studies we could find in peer-reviewed journals that analysed microbes found on mobile phones. Our conclusions are published in the Journal of Travel Medicine and Infectious Disease.

There were 56 studies that met our criteria, conducted in 24 countries around the world between 2005 and 2019.

Most of the studies looked at bacteria found on phones, and several also looked at fungi. Overall, the studies found an average of 68% of mobile phones were contaminated. This number is likely to be lower than the real value, as most of the studies aimed to identify only bacteria and, in many cases, only specific types of bacteria.

The studies were all completed before the advent of SARS-CoV-2, so none of them could test for it. Testing for viruses is laborious, and we could find only one study that did test for them (specifically for RNA viruses, a group that includes SARS-CoV-2 and other coronaviruses).

Some studies compared the phones of healthcare workers and those of the general public. They found no significant differences between levels of contamination.

What this means for health and biosecurity

Contaminated mobile phones pose a real biosecurity risk, allowing pathogens to cross borders easily.

Viruses can live on surfaces from hours to days to weeks. If a person is infected with SARS-CoV-2, it is very likely their mobile phone will be contaminated. The virus may then spread from the phone to further individuals by direct or indirect contact.

Mobile phones and other touchscreen systems – such as at airport check-in counters and in-flight entertainment screens – may have contributed to the rapid spread of COVID-19 around the globe.

Why phones are so often contaminated

Phones are almost ideal carriers of disease. We speak into them regularly, depositing microbes via droplets. We often have them with us while we eat, leading to the deposit of nutrients that help microbes thrive. Many people use them in bathrooms and on the toilet, leading to faecal contamination via the plume effect.

And although phones are exposed to microbes, most of us carry them almost everywhere: at home, at work, while shopping, on holidays. They often provide a temperature-controlled environment that helps pathogens survive, as they are carried in pockets or handbags and are rarely switched off.

On top of this, we rarely clean or disinfect them. Our (unpublished) data suggests almost three-quarters of people have never cleaned their phone at all.




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What this means: clean your phone

While government agencies are providing guidelines on the core practices for effective hand hygiene, there is little focus on practices associated with the use of mobile phones or other touch screen devices.

People touch their mobile phones on average for three hours every day, with super-users touching phones more than 5,000 times a day. Unlike hands, mobile devices are not regularly washed.

We advise public health authorities to implement public awareness campaigns and other appropriate measures to encourage disinfection for mobile phones and other touch screen devices. Without this effort, the global public health campaign for hand washing could be less effective.

Our recommendation is that mobile phones and other touch screen devices should be decontaminated daily, using a 70% isopropyl alcohol spray or other disinfection method.

These decontamination processes should be enforced especially in key servicing industries, such as in food-handling businesses, schools, bars, cafes, aged-care facilities, cruise ships, airlines and airports, healthcare. We should do this all the time, but particularly during a serious disease outbreak like the current COVID-19 pandemic.The Conversation

Lotti Tajouri, Associate Professor, Biomedical Sciences, Bond University; Mariana Campos, Lecturer and researcher, Murdoch University; Rashed Alghafri, Honorary Adjunct Associate Professor, Bond University, and Simon McKirdy, Professor of Biosecurity, Murdoch University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We don’t know for sure if coronavirus can spread through poo, but it’s possible



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Vincent Ho, Western Sydney University

While we most commonly associate COVID-19 with fever and cough, gastrointestinal symptoms including diarrhoea, vomiting and abdominal pain are not unheard of in people who contract coronavirus.

This is likely because SARS-CoV-2, the virus that causes COVID-19, is found in the gut as well as the respiratory tract.

Importantly, the gut’s involvement in coronavirus illness points to the possibility COVID-19 could spread through faeces.

At this stage we don’t know for certain whether or not that occurs – but we can take precautions anyway.




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Coronavirus and the gut

SARS-CoV-2 gains entry into human cells by latching onto protein receptors called ACE2, which are found on certain cells’ surfaces.

Around 2% of the cells lining the respiratory tract have ACE2 receptors, while they’re also found in the cells lining the blood vessels.

But the greatest numbers of ACE2 receptors are actually found in the cells lining the gut. Around 30% of cells lining the last part of the small intestine (called the ileum) contain ACE2 receptors.

Coronavirus gets into our cells by latching on to ACE2 receptors.
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Clinicians have detected coronavirus in tissue taken from the lining of the gut (oesophagus, stomach, small bowel and rectum) through routine procedures such as endoscopy and colonoscopy, where we use cameras to look inside the body. They found abundant ACE2 receptors in those tissue samples.

While some researchers have proposed alternative explanations, it’s likely people with COVID-19 experience gastrointestinal symptoms because the virus directly attacks the gut tissue through ACE2 receptors.

How common are gastrointestinal symptoms?

Data from 55,000 COVID-19 cases in China has shown the most common gastrointestinal symptom, diarrhoea, occurs in only 3.7% of those affected.

But there’s emerging evidence gastrointestinal symptoms such as diarrhoea may actually be more common, particularly among patients who develop more serious disease.

In one study of 204 patients diagnosed with COVID-19 at three different hospitals in the Hubei province in China, almost 20% of patients had at least one gastrointestinal symptom (diarrhoea, vomiting or abdominal pain).




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The researchers found gastrointestinal symptoms became more severe as the COVID-19 illness worsened. And patients with gastrointestinal symptoms were less likely to recover than those without gastrointestinal symptoms.

The reason for this is not clear but one possibility is patients with a higher density of virus, or viral load, are more likely to have coronavirus wreak havoc in their gut.

Coronavirus in our poo

The presence of coronavirus in the gut and the gastrointestinal symptoms associated with COVID-19 suggest coronavirus could be spread via faecal-oral transmission. This is when virus in the stool of one person ends up being swallowed by another person.

A recent study from China found just over half of 73 hospitalised patients with COVID-19 had virus in their faeces. Many of them did not have gastrointestinal symptoms.

While testing stool samples may not be an efficient way to diagnose COVID-19 in individuals – it’s normally slower than testing samples from the respiratory tract – researchers are looking at poo to detect population outbreaks of coronavirus.

More than a dozen research groups worldwide are collaborating on a project analysing wastewater for the presence of coronavirus in target populations.

But just because the virus is found in faeces, it doesn’t mean it’s necessarily infectious when shed from the stool. We need more research to ascertain whether this is the case.




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The virus seems to last longer in faeces

One study in China followed 74 COVID-19 patients in hospital by taking throat swabs and faecal samples daily or every second day.

The researchers found in over half of patients, their faecal samples remained positive for coronavirus for an average of just over 11 days after their throat swabs tested negative. Coronavirus was still detected in one patient’s faeces 33 days after their throat swab had turned negative.

This suggests the virus is still actively reproducing in the patient’s gastrointestinal tract long after the virus has cleared from the respiratory tract.

So if coronavirus can transmit via the faecal-oral route, we’ll want to know about it.

Sewage could offer clues about coronavirus transmission.
Shutterstock

In order to prove coronavirus can transmit via the faecal-oral route we’d need to see larger cohort studies.

These studies would include gathering more information on how well the coronavirus survives in the gut, how it causes gastrointestinal symptoms like diarrhoea and how the virus survives in faeces at different temperatures.

Researchers have found live coronavirus in faecal cultures grown in the lab, but this was only in two patients, so other research teams will need to reliably confirm the presence of infectious virus in faeces.

Take precautions anyway

In one study, researchers collected samples from the bathroom of a COVID-19 positive patient with no diarrhoea. Samples from the surface of the toilet bowl, sink and door handle returned positive for the presence of the coronavirus.

So effective handwashing, particularly after using the toilet, is critical.

We know coronavirus can survive for up to three days on plastic and stainless-steel surfaces. So it’s sensible to regularly disinfect surfaces that will be touched when using shared toilets including doorknobs, door handles, taps, support rails and toilet control handles.




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Finally, flush the toilet with the lid closed. This is particularly important for public toilets in communities where there is sustained transmission of coronavirus.

Flushing a toilet creates a phenomenon known as toilet plume where up to 145,000 aerosolised droplets can be released and suspended in the air for hours.

Scientists believe the infectious viral gastroenteritis caused by norovirus can be transmitted in aerosol form through toilet plumes. Coronavirus may be able to do the same. Closing the lid when flushing can prevent around 80% of these infectious droplets from escaping into the air.The Conversation

Vincent Ho, Senior Lecturer and clinical academic gastroenterologist, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

More testing will give us a better picture of the coronavirus spread and its slowdown


Haydar Demirhan, RMIT University

Many states are now ramping up the number of tests by relaxing the criteria for who can get tested for COVID-19. This should give us a better idea of whether the spread is easing or getting worse.

We get regular updates about COVID-19 with lots of data, figures and graphs with some interpretations to see if we are flattening the curve on the number of new cases.

But most of these are based on using only the total or the daily number of confirmed new cases.




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This does not provide enough information about whether the situation is improving, stabilising or getting worse. That is why we also need to consider the number of people tested daily for COVID-19.

For example, in percentage terms there is no actual difference between getting 20 positive cases out of 1,000 tests one day and 100 positive cases out of 5,000 tests the next. Both lead to the conclusion we have 2% reported infected people of those tested.

If we are only given the number of new cases, getting 100 in a day sounds a lot worse than getting 20. The 2% percentage figure here tells us things are pretty much the same over the two days.

Curves and trends

Take Victoria, if we look at the total number of confirmed cases we see it followed an exponential trend for a while – one that was increasingly rising – and then started to divert on April 3.



The Conversation, CC BY-ND

In the daily number of confirmed cases we see high jumps and large fluctuations going back and forth.



The Conversation, CC BY-ND

When the daily number of applied tests is considered, we can calculate the actual percentage of new cases each day. Now we have a way flatter curve (below) with different fluctuations.



The Conversation, CC BY-ND

The peak is now on March 24 when the number of tests is included. If we just look at the daily count, the highest number of confirmed cases was on March 27. When we look at the percentage, it shows a decrease rather than an increase with more than 2,300 tests.

From the daily new cases data it looks like there is a strongly decreasing trend in the number of confirmed cases between April 2 and 6.

But we do not see the same strong downward movement in the percentage data on the number of tests. Although both figures go down, then up slightly, the percentage trend downward is not as strong as the daily trend.

This is a good example of the discrepancy between the inferences from the raw and percentage data. When we consider the number of tested people, we get a different view on the progress of the pandemic.

More tests needed

In using the number of tests to get a more reliable picture of the situation, there is an important point to consider. That’s were the purple error bars in the graph (above) come in.

They show the margin of error where each percentage estimate swings for the daily number of applied tests, so the actual number could be higher or lower but within those purple bars.

When we have a larger number of applied tests, we get a reduced margin of error, and that gives us a clearer picture of what is happening.




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Since the peak on March 24 is backed up by only 500 tests, it has the largest margin of error. The figure on March 28 is based on 8,900 tests with a very small amount of error.

To get a more reliable picture of the situation, the number of applied tests has to be expanded, which it is what is happening in some states. This should reduce the margin of error.

Out in the community

After getting some signals of flattening the curve in Victoria and Australia as well, do we see an exponential increase in just the community transmission?

Community transmission is where someone has caught the virus locally, not an infected traveller who’s returned from a cruise or overseas. At the moment they are the minority of cases and authorities would like it to stay that way to contain the spread of the virus.

Again, we need to consider the number of tests to answer this question clearly. The raw numbers of community transmission in Victoria looked like they were increasing exponentially.



The Conversation, CC BY-ND

But the numbers as a percentage of the number tested tell a different story. Although there is some increase in the rate of community transmissions recently, it still shows a way flatter behaviour far from the exponential curve.



The Conversation, CC BY-ND

That is why it is important to understand the impact of the number of tests on the figures displaying the progress of the pandemic. Understanding this relationship could reassure people about new numbers.The Conversation

Haydar Demirhan, Senior Lecturer in Analytics, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We’re running out of time to use Endgame C to drive coronavirus infections down to zero



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John Daley, Grattan Institute and Jonathan Nolan, Grattan Institute

The New South Wales and Victorian governments showed foresight on Sunday by announcing a shut-down of all non-essential activity. We described this strategy on Saturday as Endgame C – with the goal to drive new infections down to zero.

But after meeting Prime Minister Scott Morrison last night, the two states backtracked and for now will only close pubs, clubs, cinemas, nightclubs, and restaurants. Schools will be closed in Victoria and the ACT, and parents will be encouraged to keep their children home in NSW.

State governments should stick to their guns and move more quickly to shutting down more non-essential businesses and activities.




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Our best hope to limit the long-term economic damage and to save the lives of our friends and families is to do everything we can to reverse the spread of this virus.

Coronavirus is growing exponentially in Australia – with a sufficiently broad shutdown, it should fall exponentially as well. Choosing Endgame C now means that the shut-down will be much shorter than if we wait another week.


Australian COVID-19 cases up to Monday March 23


The goal should be to all but remove coronavirus from the community as soon as possible.

Modelling shows that “flattening the curve” is unlikely to save the health care system, and it definitely won’t save the economy.

Business cannot return to normal while this disease festers. But once infections are very low, tracking and tracing them becomes feasible, particularly if we upgrade existing systems.




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Whatever restrictions are implemented, the challenge for the states will be to set community expectations so there is all but universal compliance.

The most effective public health messages are clear and simple. When people are told that it is too dangerous to go to a café but they are fine to get a haircut, they are right to be confused.

If the messages are contradictory, many people will ignore them, and we will waste our best chance to contain this virus.

Legal enforcement also helps to send the message, and Victorian Premier Daniel Andrews should be commended for announcing that 500 police will be knocking on doors to check that people are following self-isolation rules.

We’ll need control of our borders

The federal government must also step up and take control of our borders. If they cannot track every new entrant to ensure compliance, the borders should be closed to passengers completely, or quarantine should be enforced in airport hotels.

Australians may be complacent about the spread of coronavirus because we so far have had fewer cases than the UK, the US or Italy. But Australia is a smaller country; we need far fewer cases to create a crisis.

We are only just behind the UK when it comes to coronavirus cases per person, and only a couple of days behind France, Germany and the US. We are in a similar position to Italy three weeks ago.

Our biggest advantage is that we are testing more people than these countries, and growth of infections is a little slower, but there are no signs yet that we are changing the trajectory of our infection rates.

Data current as at Monday March 23, 2020. The rate of testing is not equal across countries. Three-day average of new cases used because not all countries report accurately on weekends.
Source: Johns Hopkins University Center for Systems Science and Engineering.

Our best endgame is to do everything we can to reduce infection rates. Over the coming days there will be many ideas about ways we can minimise the chance of this virus spreading. Some countries have been successful without implementing every single measure.

But every country is different – what works in one climate or culture might not be as effective in Australia. The risks of doing too little too late are high. The risks of doing too much are relatively small.




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If Endgame C succeeds, Australians society will be able to slowly return much more closely to normal functioning after eight to twelve weeks.

South Korea, Singapore, and Hubei province in China have successfully implemented Endgame C – and their infection rates have fallen.

Economic life is reappearing, and they now have the benefit of a public health workforce that can focus laser-like attention on any new outbreaks to prevent widespread community spread.

With Endgame C, Australians can have hope for a brighter future.The Conversation

John Daley, Chief Executive Officer, Grattan Institute and Jonathan Nolan, Associate, Grattan Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How to flatten the curve of coronavirus, a mathematician explains



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Andrew Black, University of Adelaide; Dennis Liu, University of Adelaide, and Lewis Mitchell, University of Adelaide

People travelling into Australia will now have to self-isolate for 14 days – one of a range of measures announced at the weekend by Prime Minister Scott Morrison, with the aim of slowing the spread of the coronavirus and easing the stress on hospital beds.

This general concept of slowing the virus’s spread has been termed “flattening the curve” by epidemiologists – experts who study how often diseases occur in different populations, and why. The term has become widespread on social media as the public is encouraged to practise “social distancing”.

But how does social distancing help to flatten the curve? We can explain by referring to what mathematicians call “exponential growth”.

Exponential growth

In the early stages of an epidemic, when most people are susceptible to infection, mathematicians can model a disease’s spread from person to person as essentially a random “branching process”.

This diagram shows the number of cases, over time, in a branching process with exponential growth. Author Provided.

If one infected person infects two others on average, the number of infected people doubles each generation. This compounding is known as exponential growth.

Of course, an infected person is not definitely going to infect others. There are many factors affecting the likelihood of infection. In a pandemic, the growth rate depends on the average number of people one person can infect, and the time it takes for those people to become infectious themselves.




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Research suggests the number of confirmed COVID-19 cases is growing exponentially worldwide with the number doubling about every six days

Exponential growth models closely match reality when starting with a small number of infected individuals in a large population, such as when the virus first emerged in Wuhan, or when it arrived in Italy or Iran.

But it’s not a good model once a large number of people have been infected. This is because the chance of an infected person contacting a susceptible person declines, simply because there are fewer susceptible people around, and a growing fraction of people have recovered and developed some level of immunity.

Eventually, the chances of an infected person contacting a susceptible person becomes low enough that the rate of infection decreases, leading to fewer cases and eventually, the end of the viral spread.

Flatten the curve

Health authorities around the world have been unable to completely prevent COVID-19’s spread. If cases double every six days, then hospitals, and intensive care units (ICUs) in particular, will be quickly overwhelmed, leaving patients without the necessary care.

But the growth rate can be slowed by reducing the average number of cases that a single case gives rise to.

In doing so, the same number of people will probably be infected, and the epidemic will last longer, but the number of severe cases will be spread out. This means that if you plot a graph of the number of cases over time, the rising and falling curve is longer but its peak is lower. By “flattening the curve” in this way, ICUs will be less likely to run out of capacity.

Flattening the curve is another way of saying slowing the spread. The epidemic is lengthened, but we reduce the number of severe cases, causing less burden on public health systems. The Conversation/CC BY ND

As there is currently no vaccine or specific drug for COVID-19, the only ways we can reduce transmission is through good hygiene, isolating suspected cases, and by social distancing measures such as cancelling large events and closing schools.

Avoid “super-spreaders”

Of course, the situation is not quite as straightforward as a simple branching process. Some people interact more than others, and might come into contact with many different groups.




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Mathematicians model these connections as a social network, such as the one below. Infected people are red nodes, and susceptible people are blue. The large node in the middle of the diagram is a super-spreader, a person who connects with many others, and thus has more potential to spread the disease.

This graph shows how an epidemic might spread across a network over time. Blue dots are susceptible individuals, while red dots are infected people. Two dots are connected by a line if they are in contact with each other, and the more contacts a person has, the bigger their dot is on the network. Author provided

Interventions help remove nodes and break connections.

In the diagram above, the large, highly connected central node would be the best one to remove to break connections. This is why it’s a good idea to avoid large public gatherings during the COVID-19 outbreak.

Mathematical simulations of social distancing have shown how breaking the network apart helps flatten the curve of infection.

How maths is helping

How much social distancing is required to flatten the curve enough to stop hospitals being overwhelmed? Is it enough to quarantine people who have been in contact with confirmed cases? Do we need widespread closure of events, schools and workplaces?

Answers to these questions require mathematical modelling.

We are still in the early stages of the COVID-19 outbreak and there is great uncertainty about the characteristics of this virus. To accurately forecast COVID-19’s growth, the underlying dynamics of transmission need to be determined.

These are driven by factors including:

  • How many people on average does an individual infect? (the “reproduction number” which, according to the World Health Organisation, is currently between 1.4–2.5 people)
  • How long until the onset of symptoms? (the “incubation period”, which is estimated to be 5.1 days)
  • What proportion of transmission occurs prior to the onset of symptoms, if any?

As such data is collected and integrated into models over the coming months, we will be better placed to offer accurate predictions about the course of COVID-19.

Until then, it’s better to err on the side of caution and take swift action to slow transmission, rather than risk a spike in cases, and put strain on our health system.The Conversation

Andrew Black, Lecturer in Applied Mathematics, University of Adelaide; Dennis Liu, PhD Candidate, University of Adelaide, and Lewis Mitchell, Senior Lecturer in Applied Mathematics, University of Adelaide

This article is republished from The Conversation under a Creative Commons license. Read the original article.

What is a virus? How do they spread? How do they make us sick?



NIAID Rocky Mountain Laboratories (RML), U.S. NIH, CC BY-SA

Lotti Tajouri, Bond University

Viruses are the most common biological entities on Earth. Experts estimate there are around 10,000,000,000,000,000,000,000,000,000,000 of them, and if they were all lined up they would stretch from one side of the galaxy to the other.

You can think of them as nature’s own nanotechnology: molecular machines with sizes on the nanometre scale, equipped to invade the cells of other organisms and hijack them to reproduce themselves. While the great majority are harmless to humans, some can make you sick and some can even be deadly.

Are viruses alive?

Viruses rely on the cells of other organisms to survive and reproduce, because they can’t capture or store energy themselves. In other words they cannot function outside a host organism, which is why they are often regarded as non-living.

Outside a cell, a virus it wraps itself up into an independent particle called a virion. The virion can “survive” in the environment for a certain period of time, which means it remains structurally intact and is capable of infecting a suitable organism if one comes into contact.

When a virion attaches to a suitable host cell – this depends on the protein molecules on the surfaces of the virion and the cell – it is able to penetrate the cell. Once inside, the virus “hacks” the cell to produce more virions. The virions make their way out of the cell, usually destroying it in the process, and then head off to infect more cells.

Does this “life cycle” make viruses alive? It’s a philosophical question, but we can agree that either way they can have a huge impact on living things.

This illustration shows the shape of a coronavirus particle.
CDC / Alissa Eckert, MS; Dan Higgins, MAM, CC BY

What are viruses made of?

At the core of a virus particle is the genome, the long molecule made of DNA or RNA that contains the genetic instructions for reproducing the virus. This is wrapped up in a coat made of protein molecules called a capsid, which protects the genetic material.

Some viruses also have an outer envelope made of lipids, which are fatty organic molecules. The coronavirus that causes COVID-19 is one of these these “enveloped” viruses. Soap can dissolve this fatty envelope, leading to the destruction of the whole virus particle. That’s one reason washing your hands with soap is so effective!

What do viruses attack?

Viruses are like predators with a specific prey they can recognise and attack. Viruses that do not recognise our cells will be harmless, and some others will infect us but will have no consequences for our health.

Many animal and plant species have their own viruses. Cats have the feline immunodeficiency virus or FIV, a cat version of HIV, which causes AIDS in humans. Bats host many different kinds of coronavirus, one of which is believed to be the source of the novel coronavirus that causes COVID-19.

Bacteria also have unique viruses called bacteriophages, which in some cases can be used to fight bacterial infections.

Viruses can mutate and combine with one another. Sometimes, as in the case of COVID-19, that means they can switch species.

Why are some viruses so deadly?

The most important ones to humans are the ones that infect us. Some families of viruses, such as herpes viruses, can stay dormant in the body for long periods of time without causing negative effects.

How much harm a virus or other pathogen can do is often described as its virulence. This depends not only on how much harm it does to an infected person, but also on how well the virus can avoid the body’s defences, replicate itself and spread to other carriers.

In evolutionary terms, there is often a trade-off for a virus between replicating and doing harm to the host. A virus that replicates like crazy and kills its host very quickly may not have an opportunity to spread to a new host. On the other hand, a virus that replicates slowly and causes little harm may have plenty of time to spread.

What’s the difference between COVID-19 and the flu?

How do viruses spread?

Once a person is infected with a virus, their body becomes a reservoir of virus particles which can be released in bodily fluids – such as by coughing and sneezing – or by shedding skin or in some cases even touching surfaces.

The virus particles may then either end up on a new potential host or an inanimate object. These contaminated objects are known as fomites, and can play an important role in the spread of disease.

The novel coronavirus that causes COVID-19 (yellow) emerging from the surface of cells (blue/pink) cultured in the lab.
NIAID Rocky Mountain Laboratories (RML), U.S. NIH, CC BY

What is a coronavirus?

The coronavirus COVID-19 is a member of the virus family coronaviridae, or coronaviruses. The name comes from the appearance of the virus particles under a microscope: tiny protein protrusions on their surfaces mean they appear surrounded by a halo-like corona.

Other coronaviruses were responsible for deadly outbreaks of Serious Acute Respiratory Syndrome (SARS) in China in 2003 and Middle East Respiratory Syndrome (MERS) from 2012. These viruses mutate relatively often in ways that allow them to be transmitted to humans.The Conversation

Lotti Tajouri, Associate Professor, Biomedical Sciences, Bond University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

There’s no evidence the new coronavirus spreads through the air – but it’s still possible


Ian M. Mackay, The University of Queensland and Katherine Arden, The University of Queensland

A recent announcement by a Chinese health official suggested the new coronavirus might spread more easily than we thought, via an “airborne route”. The virus is now known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), while the name of the disease it causes is now called COVID-19.

The Chinese Center for Disease Control and Prevention almost immediately corrected the announcement, noting SARS-CoV-2 was not known to be an airborne virus.

The centre confirmed the virus appears to spread via droplets, direct contact and by coming into contact with contaminated surfaces and objects. The World Health Organisation agrees.

So far no infectious virus has been recovered from captured air samples. This would need to occur to demonstrate the virus was airborne.




Read more:
How does the Wuhan coronavirus cause severe illness?


What’s the difference between airborne and droplet spread?

When we sneeze, cough or talk, we expel particles in a range of sizes.

The bigger, wet droplets larger than 5-10 millionths of a meter (µm or micrometre) fall to the ground within seconds or land on another surface.

These wet droplets are currently considered to be the highest risk routes for the SARS-CoV-2.

But smaller particles aren’t implicated in the spread of SARS-CoV-2.

Smaller particles remain suspended in the air and evaporate very quickly (at less than one-tenth of a second in dry air). They leave behind gel-like particles made of proteins, salts and other things, including viruses.

These leftovers are called “droplet nuclei” and can be inhaled. They may remain aloft for hours, riding the air currents through a hospital corridor, shopping centre or office block. This is what we mean when we talk about something being airborne.




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But there’s more to airborne spread. To infect humans, the droplet nuclei need to contain infectious virus. The virus must be able to land on our mucous membranes – the soft lining of our ears, nose, conjunctiva (eyelid), throat and digestive tract and it must be able to enter our cells and replicate.

There also needs to be enough virus to overcome our early immune responses to the invader and start an infection.

So a few stars have to align for airborne infection to result.

When we cough, sneeze or talk, we expel particles in a range of sizes.
Shutterstock

But airborne transmission wouldn’t be a shock

We already know the measles virus can remain aloft in a room for up to 30 minutes after an infected person leaves it.

Likewise, the MERS coronavirus has been captured in infectious form from hospital air samples and found to be infectious.

So there is some precedent.

Other viruses that can be infectious via an airborne route include rhinoviruses (the main causes of the common cold) and flu viruses.

The ability for common respiratory viruses to spread via airborne particles means it wouldn’t be a shock to find SARS-CoV-2 also had this capability.

But there is no evidence this is currently occurring.




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Why would airborne spread be such a problem?

Airborne spread would mean the virus could travel further. It could spread through unfiltered air conditioning ducting and reach people further away from the infected person, despite them not being in their direct line of sight.

It would also affect how far away from the patient hard surfaces need cleaning and whether airborne personal protective equipment (PPE) precautions – such as P2 respirator masks – would need to be more widely used.

Our definition of “sufficient contact” for someone to be a possible new infection may broaden, which would mean more people need to be monitored, tested and possibly quarantined for each known patient.

But even if an airborne route is found in the future, it’s unlikely to be the major route of transmission.

People who are ill and show symptoms such as coughing and sneezing usually produce and expel viruses in greater amounts than those who show fewer symptoms. These sicker people are more likely to spread the virus via bigger wet droplets, physical contact and contamination of surfaces and objects.

Do I need to worry?

No. SARS-CoV-2 has been spreading the whole time, regardless of our understanding of how. That spread doesn’t look to be changing.

Currently, relatively few people infected with SARS-CoV-2 are outside of mainland China. Only 15 cases have been identified in Australia. Those found are isolated quickly and are well cared for.




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How contagious is the Wuhan coronavirus and can you spread it before symptoms start?


The chances of catching SARS-CoV-2 outside of mainland China are, at the moment, remote (provided you aren’t on a certain cruise ship).

If the situation changes because infected travellers arrive in greater numbers than we can contain, then our best tools to mitigate spread remain the ones we already know:

  • distancing ourselves from obviously ill people
  • hand-washing
  • cleaning surfaces
  • good cough etiquette (coughing into a tissue or your elbow and washing your hands)
  • keeping our hands away from our face.

And if you are at risk, stay home and seek medical advice by phone.The Conversation

Ian M. Mackay, Adjunct assistant professor, The University of Queensland and Katherine Arden, Virologist, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How contagious is the Wuhan coronavirus and can you spread it before symptoms start?


C Raina MacIntyre, UNSW

Cases of the Wuhan coronavirus have increased dramatically over the past week, prompting concerns about how contagious the virus is and how it spreads.

According to the World Health Organisation, 16-21% of people with the virus in China became severely ill and 2-3% of those infected have died.




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A key factor that influences transmission is whether the virus can spread in the absence of symptoms – either during the incubation period (the days before people become visibly ill) or in people who never get sick.

On Sunday, Chinese officials said transmission had occurred during the incubation period.

So what does the evidence tell us so far?

Can you transmit it before you get symptoms?

Influenza is the classic example of a virus that can spread when people have no symptoms at all.

In contrast, people with SARS (severe acute respiratory syndrome) only spread the virus when they had symptoms.

No published scientific data are available to support China’s claim transmission of the Wuhan coronavirus occurred during the incubation period.

However, one study published in the Lancet medical journal showed children may be shedding (or transmitting) the virus while asymptomatic. The researchers found one child in an infected family had no symptoms but a chest CT scan revealed he had pneumonia and his test for the virus came back positive.

This is different to transmission in the incubation period, as the child never got ill, but it suggests it’s possible for children and young people to be infectious without having any symptoms.

This is a concern because if someone gets sick, you want to be able to identify them and track their contacts. If someone transmits the virus but never gets sick, they may not be on the radar at all.

It also makes airport screening less useful because people who are infectious but don’t have symptoms would not be detected.

How infectious is it?

The Wuhan coronavirus epidemic began when people exposed to an unknown source at a seafood market in Wuhan began falling ill in early December.

Cases remained below 50 to 60 in total until around January 20, when numbers surged. There have now been more than 4,500 cases – mostly in China – and 106 deaths.




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Researchers and public health officials determine how contagious a virus is by calculating a reproduction number, or R0. The R0 is the average number of other people that one infected person will infect, in a completely non-immune population.

Different experts have estimated the R0 of the Wuhan coronavirus is anywhere from 1.4 to over five, however the World Health Organisation believes the RO is between 1.4 and 2.5.

Here’s how a virus with a R0 of two spreads:



The Conversation, CC BY-ND

If the R0 was higher than 2-3, we should have seen more cases globally by mid January, given Wuhan is a travel and trade hub of 11 million people.

How is it transmitted?

Of the person-to-person modes of transmission, we fear respiratory transmission the most, because infections spread most rapidly this way.

Two kinds of respiratory transmission are through large droplets, which is thought to be short-range, and airborne transmission on much smaller particles over longer distances. Airborne transmission is the most difficult to control.

SARS was considered to be transmitted by contact and over short distances by droplets but can also be transmitted through smaller aerosols over long distances. In Hong Kong, infection was transmitted from one floor of a building to the next.




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Initially, most cases of the Wuhan coronavirus were assumed to be from an animal source, localised to the seafood market in Wuhan.

We now know it can spread from person to person in some cases. The Chinese government announced it can be spread by touching and contact. We don’t know how much transmission is person to person, but we have some clues.

Coronaviruses are respiratory viruses, so they can be found in the nose, throat and lungs.

The amount of Wuhan coronavirus appears to be higher in the lungs than in the nose or throat. If the virus in the lungs is expelled, it could possibly be spread via fine, airborne particles, which are inhaled into the lungs of the recipient.

How did the virus spread so rapidly?

The continuing surge of cases in China since January 18 – despite the lockdowns, extended holidays, travel bans and banning of the wildlife trade – could be explained by several factors, or a combination of:

  1. increased travel for New Year, resulting in the spread of cases around China and globally. Travel is a major factor in the spread of infections

  2. asymptomatic transmissions through children and young people. Such transmissions would not be detected by contact tracing because health authorities can only identify contacts of people who are visibly ill

  3. increased detection, testing and reporting of cases. There has been increased capacity for this by doctors and nurses coming in from all over China to help with the response in Wuhan

  4. substantial person-to-person transmission

  5. continued environmental or animal exposure to a source of infection.




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However, with an incubation period as short as one to two days, if the Wuhan coronavirus was highly contagious, we would expect to already have seen widespread transmission or outbreaks in other countries.

Rather, the increase in transmission is likely due to a combination of the factors above, to different degrees. The situation is changing daily, and we need to analyse the transmission data as it becomes available.The Conversation

C Raina MacIntyre, Professor of Global Biosecurity, NHMRC Principal Research Fellow, Head, Biosecurity Program, Kirby Institute, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Hand sanitisers in public won’t wipe out the flu but they might help reduce its spread



It’s quicker to use hand sanitiser than soap and water, which means people might be more likely to use it.
Shutterstock

Trent Yarwood, The University of Queensland

This year’s flu season is off to an early start, with 144,000 confirmed cases so far in 2019. That’s more than twice as many confirmed cases of the flu than for all of 2018 (58,000), and almost as many as the 2017 horror flu season (251,000).

The number of cases so far this year, including more than 231 deaths nationwide, led the NSW opposition health spokesperson to call for hand sanitisers in public spaces to help slow the spread.




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Influenza spreads via droplets from coughing and sneezing, which is why it’s a good idea to catch your cough. But coughing into your hand can leave flu virus on your hands, which is why we recommend coughing into your elbow or sleeve and washing your hands afterwards.

Along with getting vaccinated and staying home if you’re sick, washing your hands is the best defence against getting the flu.

If the government can make this easier by providing hand sanitisers in public places, it may be worth the investment. It won’t solve our flu problem but it might be an important tool in the toolbox of measures to reduce its spread.

What does the research say?

The scientific literature on hand sanitisers isn’t so clear-cut.

A 2019 study in university colleges showed the use of hand hygiene and face masks didn’t protect against flu any better than mask use alone. But unlike some other countries, Australia doesn’t have a strong habit of mask use when people are unwell, so this may not be very helpful to us.

A 2014 study in New Zealand schools showed that providing sanitiser didn’t reduce the rate of absenteeism from school either.

While these studies make it sound like hand sanitiser is not very effective, that’s not the end of the story.

Other studies show a positive effect – a 16% reduction in respiratory illness in one and a 21% reduction in another. For some infections, the evidence is even stronger – for example, gastroenteritis, most of which is also viral.

However, few of these studies showing the benefits of hand sanitisers were done during a large disease outbreak, which means the potential benefit may be even greater.

Not all influenza-like illness is caused by the flu – it can be other viruses as well, so the estimates are a bit rubbery at best. Hand sanitiser trials which look at influenza-like illness or respiratory infections generally are more likely to show benefits than those that just look for influenza – meaning good hand hygiene prevents other infections as well.

If you have the flu, the best place to be is at home.
Tero Vesalainen/Shutterstock

Lessons from hospitals

Although preventing infection in hospitals is not the same as doing it in the community, there are two important lessons from hospital infection control.

First, in hospital hand-hygiene programs, hand sanitiser is more effective than soap-and-water hand-washing, provided your hands aren’t visibly dirty.

This is partly because of the rapid effect of the alcohol, but mostly because it’s much quicker and therefore more likely that staff will use it.




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The second important point from hand hygiene and other areas of hospital infection control is that introducing a “bundle” of strategies usually reduces healthcare-associated infection rates – even when the individual parts of these bundles don’t show benefits alone.

This could be because the individual effect sizes are too small, or that change in practice highlights a “safety culture”.

Sanitisers can be one of many strategies

Installing hand rub in public areas won’t solve this year’s flu outbreak by itself. But it can be part of a bundle of strategies – as long as the dispensers are kept topped up.

And it’s certainly a safe intervention – despite some desperate hysteria about the safety of hand gels, or the risk of people drinking them, there is little evidence this actually occurs in reality.

Hand sanitiser is also likely to be easier to implement than fixing the much larger social problem of Australians going to work when they’re sick. This may be because of inadequate sick leave, concerns about “letting the team down”, or other logistical problems such as child-care.

Get your flu vaccine – even now it’s still not too late – and get it for your kids as well, for their sake as well as your own.

Remember to stay home if you’re unwell, and always to cough into your sleeve. And don’t forget to clean your hands – even if the government doesn’t end up making it easier for you.




Read more:
The 2019 flu shot isn’t perfect – but it’s still our best defence against influenza


The Conversation


Trent Yarwood, Infectious Diseases Physician, Senior Lecturer, James Cook University and, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.