Failure to report mild symptoms combined with highly contagious nature of disease raises fears existing figures are ‘tip of the iceberg’

Global health experts have warned that “hidden” infections make containment of the coronavirus unlikely and raised fears that the rapidly rising caseload of 25,000 people could be the “tip of the iceberg”.

“Hidden” cases – where people with mild symptoms do not seek medical help and so remain untested and unrecorded – combined with the highly contagious nature of the disease mean there could be “vastly more cases” than previously thought, according to Tom Frieden, a former director at the US Centers for Disease Control and Prevention.

“It’s becoming increasingly clear that containment is very unlikely,” said Frieden, who now heads Resolve to Save Lives, an NGO focusing largely on preparedness for infectious diseases.

“It probably isn’t worth giving up, but trying to contain Wuhan coronavirus like Sars and Mers is very unlikely, just because of the number of cases and the number of [Chinese] provinces and the ease with which it is ease spreading in families.

“It’s a fog of war reality, which is what makes me suspect that what are seeing is the tip of the iceberg.”

Frieden added that while such confusion is common in every outbreak, what marks this one as different is the very large number of cases and how contagious the virus appears to be, although he added that the relative death rate was likely to diminish as more mild cases were identified.

Quick guide What are coronavirus symptoms and should I go to a doctor? Show Hide What is Covid-19? Covid-19 is caused by a member of the coronavirus family that has never been encountered before. Like other coronaviruses, it has come from animals. The World Health Organization (WHO) has declared it a pandemic. What are the symptoms this coronavirus causes? According to the WHO, the most common symptoms of Covid-19 are fever, tiredness and a dry cough. Some patients may also have a runny nose, sore throat, nasal congestion and aches and pains or diarrhoea. Some people report losing their sense of taste and/or smell. About 80% of people who get Covid-19 experience a mild case – about as serious as a regular cold – and recover without needing any special treatment. About one in six people, the WHO says, become seriously ill. The elderly and people with underlying medical problems like high blood pressure, heart problems or diabetes, or chronic respiratory conditions, are at a greater risk of serious illness from Covid-19. In the UK, the National health Service (NHS) has identified the specific symptoms to look for as experiencing either: a high temperature - you feel hot to touch on your chest or back

a new continuous cough - this means you’ve started coughing repeatedly As this is viral pneumonia, antibiotics are of no use. The antiviral drugs we have against flu will not work, and there is currently no vaccine. Recovery depends on the strength of the immune system. Should I go to the doctor if I have a cough? Medical advice varies around the world - with many countries imposing travel bans and lockdowns to try and prevent the spread of the virus. In many place people are being told to stay at home rather than visit a doctor of hospital in person. Check with your local authorities. In the UK, NHS advice is that anyone with symptoms should stay at home for at least 7 days. If you live with other people, they should stay at home for at least 14 days, to avoid spreading the infection outside the home.

Researchers have identified a time lag of reporting infections of one to two weeks, while estimating a doubling in the number of infections roughly every six days, making the real figure at least 75,000.

Dr Nathalie MacDermott, a clinical lecturer at King’s College London, said: “The mortality rate is literally the number of people dying as a proportion of cases of the disease. It is currently likely to be an overestimate, based on milder cases of the disease not being identified. But it is not accurate. What’s missing is the number of people with a milder form.”

For example, if 400 deaths and 20,000 cases are reported, the mortality rate is 2%, she said. “But if you divide the deaths by 75,000, you would get a rate of 0.5%.”

Mild cases have the potential for making containment more difficult, she said.

Asked if measures taken in China to contain the virus were effective, she said it was too early to tell, particularly because of the time lag, which also might change.

“We are not clearly seeing an impact at the moment. We would need to monitor for a month or so.”

Exponential spread of the virus in other cities outside China was unlikely, added MacDermott. “We haven’t so far seen a significant spread in cities outside China. In cases outside China we are still watching. So we could get a shock. But we probably won’t see a Wuhan situation in other countries. We could see a surge in other Chinese cities, particularly as there is a 14-day incubation period, so there might be a time lag in identifying all cases.”

Professor David Heymann, who led the World Health Organization’s infectious disease unit at the time of the Sars outbreak, urged caution, saying it was too soon to accurately predict the spread of the virus.

“What’s important is the cases outside of China,” said Heymann. “Inside China there is a lot of disorder in the health system, because it is overstretched. Patient management has to come first. But with a victim outside China, you can follow that case and see how others are being infected, by observing the reproduction rate and the spectrum of disease.

“It’s a 26 country laboratory, where there is a chance of much better understanding of the dynamics of the outbreak and the spectrum of the disease in people who are infected.

“What helps in an outbreak is to know what you don’t know,” he added.

“The evidence will come, as the rate of transmission and reproductive rates are estimates, not models. Models are only as good as the information in them.”

The number of people that each infected person will go on to infect has been estimated at between 2.6 and 2.68.

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Heymann, now professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine, said: “The risk factors include the transmission ability, reflected in the reproductive number, but also how it is infected, ie body secretions, not washing your hands, or face to face, like sneezing.”

As late as last week, Chinese officials were only looking at severe cases of the virus. Now, attention is turning to less severe cases and what that means, Heymann said. “Each gives a different picture,” he said. “As more and more information becomes available, the models will be refined.”

Some experts have predicted outbreak epicentres elsewhere. Gabriel Leung and colleagues from the University of Hong Kong published the results of their model in the Lancet a few days ago, estimating 75,000 cases at the end of January.

Like others, they identified a time lag of about one to two weeks while estimating a doubling in number of infections every six days or so.

Leung warned that other “large cities overseas with close transport links to China could also become outbreak epicentres, unless substantial public health interventions at both the population and personal levels are implemented immediately.”