Thread by @jeffgilchrist

COVID-19: Test yourself before leaving isolation

Multiple studies have shown people on average are still infectious for more than 5 days and is even worse with Omicron ( nejm.org/doi/full/10.10… ). 🧵1/

It seems common now in Canada and the USA to have public health implement 5-day isolation policies when infected with COVID-19 despite the evidence showing that most people remain infectious at 5 days. 2/

The study looking specifically at Omicron BA.1 found that the median time for cultures to be negative for infectious virus after symptom onset or positive test was 8 days! That means half the people they tested were still infectious at 8 days, regardless of vaccine status. 3/

The researchers found the duration of being infectious was:
75% of people > 5 days
50% of people > 8 days
24% of people > 10 days

4/

It is critical for people to test themselves before leaving isolation because you are likely still infectious even when public health says you can go back to work/school/shopping/visiting. 5/

Rapid antigen tests (RATs) are a quick and effective way to see if your viral load has gone down enough to no longer test positive and thus unlikely to be infectious. 6/

In Ontario you can get rapid tests free of charge from many pharmacies and grocery stores (service desk) until at least Dec. 31, 2022 ( covid-19.ontario.ca/rapid-test-loc… ). 7/

Dr. Michael Mina discusses in the video how to best test yourself for COVID-19 and why some people become symptomatic so early before the virus has a chance to replicate to high levels so you might test negative when you first start having symptoms (

https://twitter.com/michaelmina_lab/status/1542350636234055682

). 8/

Especially during times of high transmission like now, if you are experiencing symptoms, assuming you are infected and air on the side of caution. 9/

If you test negative with a RAT, the virus may not have had enough time to replicate to be detected yet so test again the following day, and if negative, test again on day 3. 10/

People's immune systems who have been vaccinated or previously infected can sometimes detect the virus quickly enough that they start to feel immune reaction symptoms early before the virus has replicated significantly to test positive. 11/

RATs will help you know if you are infected with COVID-19 *and* infectious. Rapid tests do not work with spike protein so COVID-19 vaccines will not interfere with the tests. 12/

The rapid tests still work very well with Omicron as they look for a part of the virus (nucleocapsid protein) that has changed much less with the Omicron variants than the spike protein (

https://twitter.com/michaelmina_lab/status/1472024457640394756

). 13/

Rapid tests do not amplify the sample so they can only detect when someone has a relatively high viral load which through multiple studies has been found to test positive when people are shedding infectious virus. 14/

If a RAT test has a faint line, that does not mean you are close to having 0 viral load, you are closer to the bottom end of the medium/high viral load that RATs are able to detect, so likely still infectious. 15/

If a RAT tests negative it could mean you are infected but viral load isn't high enough to detect, you did not swab properly, or you are not infected. 16/

"The Ontario Science Advisory Table says you should swab the insides of your cheeks, then your tongue or the back of your throat, and then your nostrils to make the tests more accurate." - CBC News ( cbc.ca/news/canada/to… ). 17/

The whole point of self-isolation is to prevent transmission to others so they do not get infected and go on to infect even more people, causing additional suffering, death, virus mutations and burden on the healthcare system. 18/

Allowing people to exit self-isolation when the majority are still infectious is completely a political and business decision, not one to minimize the amount of transmission in the community. 19/

With the amount of evidence available, self-isolation should be longer and backed up with paid sick days for those who don't have them so people can actually afford to self-isolate for the time needed to stop being infectious. 20/

This thread has some additional details and pointers to previous studies along with exit strategies (

https://twitter.com/Billius27/status/1544685306544357378

). 21/