Thursday, 7 May 2020

How long should you self-isolate with COVID?

Isolation is the key to managing any pandemic, so the length of isolation is critical to our attempts to control COVID19. The importance of getting this right will magnify once the lockdown is lifted.

So, if you get symptoms, what should you do?

Public Health England's advice on self isolation once you develop symptoms is clear:

"If you have been symptomatic, then you may end your self-isolation after 7 days and return to your normal routine if you feel better and no longer have a high temperature. If you still have a high temperature, keep self-isolating until your temperature returns to normal. After 7 days you do not need to self-isolate if you just have a cough as a cough can last for several weeks once the infection has gone. The 7-day period starts from the day when you first became ill."

So that's crystal clear! Or it is?

Across the pond Americans are advised to isolate for 10 days from the onset of symptoms. In South Korea for two weeks.

For me it seems unlikely the virus would have been cleared by day 7. The way to tell would be do perform serial tests on those with symptoms and see how long they take to become negative. Not rocket science indeed.

It has been done:

1113 tests were performed on 301 patients with COVID19 in China. The results are sobering:

"This large-scale investigation with 1113 RT-PCR test results from 301 COVID-19 patients showed that the average contagious period of SARS-CoV-2 infected patients was 20 days. Longer observation period and more than 2 series of negative viral test are necessary for patients ≥65 years."

Or, for those who like results displayed graphically:

The only caveat is that these patients were hospitalised, so strictly speaking the data  applies to that group of more severely affected patients. 

Yet the headline (and would be a good headline) is that seven days after the onset of symptoms over 90% of patients will have positive nasal swabs and still be shedding viruses.

Symptoms are frequently evident at and beyond a week from onset. If you still have symptoms it is reasonable to assume you are still shedding viruses. 

I cannot find similar community based studies, though I am sure (fingers crossed) that they are on their way.

In Italy it is reported that the time from the onset of symptoms to 100% negative nasal swabs was 36 days, similar to the results displayed above.

So, what to do? Following PHE's advice will mean that you get go back to work early, and resume normal life one week after the onset of symptoms. It also means you are at risk of infecting those with whom you come into contact.

A more science based approach might be to suggest isolation for one week after symptoms have cleared up for those under 65, and two weeks in the over 65's. Perhaps our short period of self isolation might have something to do with the slow rate of decline seen in the UK?

Contacts of those with infections are advised here and in the US to self-isolate for 14 days from the time of contact. Provided that is, if there are no symptoms. There does seem to be contradictions. If you have contact with a case, and develop symptoms on day 2, (for example) isolating for 7 days thereafter will mean your time in isolation will be shorter than those with no signs of infection at all. I'm left scratching my head! 

Once lockdown is released, this advice will become far more critical with the pressure on to get back to work and see missed loved ones and friends risking further waves of the pandemic.

Right now, I strongly suspect too many cases are being generated by viral shedders and I fear more waves might be the consequence. 

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