October 29, 2020

Coronavirus sufferers symptom-free for five days on average – study

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The 5.1-day average incubation period is similar to that seen in Sars and Mers. Coronaviruses that cause common colds typically have a three-day symptom-free period after infection.


Powered by Guardian.co.ukThis article titled “Coronavirus sufferers symptom-free for five days on average – study” was written by Hannah Devlin Science correspondent, for The Guardian on Monday 9th March 2020 21.00 UTC

People infected with coronavirus are symptom-free for an average of five days, according to a study that reinforces the need for strict quarantine measures.

The analysis found that 5.1 days was the median length of time before people started showing signs of illness, although there was a wide range of incubation periods, with a tiny minority of people taking up to two weeks.

What is Covid-19 – the illness that started in Wuhan?

It is caused by a member of the coronavirus family that has never been encountered before. Like other coronaviruses, it has come from animals.

What are the symptoms this coronavirus causes?

The virus can cause pneumonia. Those who have fallen ill are reported to suffer coughs, fever and breathing difficulties. In severe cases there can be organ failure. As this is viral pneumonia, antibiotics are of no use. The antiviral drugs we have against flu will not work. Recovery depends on the strength of the immune system. Many of those who have died were already in poor health.

Should I go to the doctor if I have a cough?

In the UK, the medical advice is that if you have recently travelled from areas affected by coronavirus, you should:

  • stay indoors and avoid contact with other people as you would with the flu
  • call NHS 111 to inform them of your recent travel to the area

More NHS advice on what to do if you think you have been exposed to the virus can be found here, and the full travel advice to UK nationals is available here.

Is the virus being transmitted from one person to another?

China’s national health commission confirmed human-to-human transmission in January, and there have been such transmissions elsewhere.

How many people have been affected?

As of 9 March, more than 110,000 people have been infected in more than 80 countries, according to the Johns Hopkins University Center for Systems Science and Engineering.

There have over 3,800 deaths globally. Just over 3,000 of those deaths have occurred in mainland China. 62,000 people have recovered from the coronavirus.

Why is this worse than normal influenza, and how worried are the experts?

We don’t yet know how dangerous the new coronavirus is, and we won’t know until more data comes in. Seasonal flu typically has a mortality rate below 1% and is thought to cause about 400,000 deaths each year globally. Sars had a death rate of more than 10%.

Another key unknown is how contagious the coronavirus is. A crucial difference is that unlike flu, there is no vaccine for the new coronavirus, which means it is more difficult for vulnerable members of the population – elderly people or those with existing respiratory or immune problems – to protect themselves. Hand-washing and avoiding other people if you feel unwell are important. One sensible step is to get the flu vaccine, which will reduce the burden on health services if the outbreak turns into a wider epidemic.

Have there been other coronaviruses?

Severe acute respiratory syndrome (Sars) and Middle Eastern respiratory syndrome (Mers) are both caused by coronaviruses that came from animals. In 2002, Sars spread virtually unchecked to 37 countries, causing global panic, infecting more than 8,000 people and killing more than 750. Mers appears to be less easily passed from human to human, but has greater lethality, killing 35% of about 2,500 people who have been infected.

Sarah BoseleyHannah Devlin and Martin Belam

Justin Lessler, of the Johns Hopkins Bloomberg School of Public Health and senior author of the report, said: “Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although with that period some cases would be missed over the long term.”

The findings did not reveal the extent to which people can transmit the illness during this symptom-free period, but preliminary evidence suggests there is at least a short window before people start feeling ill when they can pass on the virus to others.

Lessler and colleagues found that about 98% of people who develop symptoms of Covid-19 will do so within 11.5 days of exposure. For every 10,000 individuals quarantined for 14 days, only about 101 would develop symptoms after being released from quarantine, the analysis estimated.

The study, published in the journal Annals of Internal Medicine, looked at 181 cases from China and other countries that were detected before 24 February, reported in the media, and included likely dates of exposure and symptom onset. Most of the cases involved travel to or from Wuhan, the Chinese city where the epidemic began, or exposure to other people who had been there.

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The 5.1-day average incubation period is similar to that seen in Sars and Mers. Coronaviruses that cause common colds typically have a three-day symptom-free period after infection.

The NHS and other public health authorities around the world have been using a 14-day quarantine or active-monitoring period for individuals who are known to be at high risk of infection due to contact with known cases or travel to a heavily affected area.

The latest findings suggest this strikes a good balance between minimising chances of transmission and not causing unnecessary disruption – particularly as health workers are among those being quarantined.

“It’s very reassuring that by 14 days, while it might not be 100%, it will be close,” said Graham Cooke, professor of infectious diseases at Imperial College London.

Cooke added that people should not interpret the findings as a clear bill of health if they have not shown any signs of illness within five days of a potential exposure. “That’s absolutely the wrong interpretation,” he said. “At five days, half of people won’t yet have developed symptoms.”

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