Although a week of isolation is approved here, a latest CDC (Centre for Disease Control and Prevention) advisory in the US recommends that people with a weakened immune system isolate for up to 20 days and says the Omicron-infected can still shed virus after their symptoms wane. With more and more people returning to workspaces and a fresh spiral being reported, there are anxieties.
In fact, The New York Times earlier this week quoted a pair of recent studies, which are awaiting a peer review, suggesting “that some people with Omicron infections shed infectious virus — capable of replicating in a ‘cell culture,’ or a dish of live cells in the laboratory — for more than a week. In the other study, which enrolled vaccinated students and staff at Boston University, researchers found that while most participants no longer had positive viral cultures six days after their symptoms began, a small number had viable virus as late as Day 12.”
Reacting to these new reports, virologist Gagandeep Kang, Professor at Christian Medical College, Vellore, said, “This is a situation where knowing the CT value of the PCR test has relevance. Although all tests are different and the CT (Number of cycles where a signal is detected or critical threshold) across tests does not mean the same thing, in general, a CT value of more than 30 means that the likelihood of infectiousness is very low, a CT value of under 25 means that a lot of the virus is being shed and it may be infectious.”
Another option, she says, is to “retest with a rapid test instead of PCR at the end of isolation. Rapid tests are generally good for low CT values (infectiousness). If the rapid test is positive then go for preventive isolation, otherwise go ahead.”
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Her advice is dependent on the amount of risk that is tolerable. So, consider the following: “Isolate for seven days and do not test at the end of isolation if no contact sports is involved. A small proportion of people may be infectious at this time, so if they are playing sports that require close contact, consider either extending the period of isolation to 10 days or two weeks or retesting at the end of isolation and extending the isolation if the test continues to be positive.”
Dr Chandrakant Lahariya, specialist on infectious diseases and epidemiology, believes, “The duration of isolation after testing COVID-19 positive does not vary by the sub-lineages of the Omicron variant. It has been documented that some people may continue to test RT PCR positive, for up to 90 days. This is true for all variants and sub lineages. However, a majority of those tested positive turn non-infectious (cannot pass on the virus) after 5-7 days. There is no evidence that this situation has changed with sub-variants. Therefore, there is limited value of repeat testing. One can come out of isolation as per standard period, without being worried which sub-lineage of Omicron it is.”
Ruling out the need for an immediate revision of norms, Dr Lahariya said, “We need to remember that in public health guidelines, context— such as level of natural infection, average population age, the vaccine coverage, type of vaccines etc— matters a lot. Then, operational factors determine the policy formulation. It is in this backdrop that what is applicable and a policy in the US,
is not applicable for India.”
What about an immunocompromised host, where, according to US studies, the virus can survive for a longer time? “In immunocompetent host, normally with the Delta strain, it was found that the infectivity could be of 10 days, beyond which it was a dead virus. With Omicron beyond seven days, the virus usually dies. Hence the isolation period was reduced accordingly. Beyond this, patients were asked to wear mask for three days while meeting an immunocompromised person,” says Dr Suranjit Chatterjee, Senior Consultant, Internal Medicine, Indraprastha Apollo Hospital, Delhi.
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