On Wednesday, the US Centers for Disease Control and Prevention (CDC) updated its guidelines for ending isolation and precautions for Covid-19 patients. With these new guidelines, the CDC is now focussing on a “symptom-based” strategy for ending isolation rather than a test-based strategy.
What are the new recommendations?
The CDC now says that for most persons with Covid-19, isolation and precautions can be discontinued after a period of 10 days from symptom onset and resolution of fever for at least 24 hours, without the use of fever-reducing medications.
Exceptions to this include those patients that have severe illness due to which they may produce replication-competent virus even after 10 days. For such patients, the duration of isolation and the period for taking precautions may be extended to 20 days after symptom onset.
For asymptomatic patients too, isolation and other precautions can be discontinued after a period of 10 days from the date of their first positive RT-PCR test.
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What does this mean?
CDC now recommends a test-based strategy for ending isolation for exceptional cases only, such as those that are immunocompromised or have developed severe illness from Covid-19. For all other kinds of patients, the CDC recommends discontinuing tests for ending isolation.
What are these recommendations based on?
The changes come after considering findings that those with mild to moderate illness remain infectious for no longer than 10 days and those with severe illness remain infectious for no longer than 20 days after symptom onset. “The majority of those with severe disease, more than 88 per cent, were no longer infectious after 10 days. Ninety-five per cent were no longer infectious after 20 days,” CDC said.
Can a person be reinfected?
The CDC in its revised guidelines has said that to date there has not been any definitively confirmed case of reinfection with SARS-CoV-2 in any recovered person. “If, and if so when, persons can be reinfected with SARS-CoV-2 remains unknown and is a subject of investigation,” it said, adding that persons infected with related endemic human betacoronavirus appear to become susceptible again at around 90 days after the onset of infection. Thus, for persons recovered from SARS-CoV-2 infection, a positive PCR during the 90 days after illness onset more likely represents persistent shedding of viral RNA than reinfection. It is also important to note that these recommendations are based on findings until July and are of an evolving pandemic, and could be revised.
The changes in the guidelines are based on the following findings:
Concentrations of SARS-CoV-2 measures in the upper respiratory tract declines after symptom onset
The likelihood of recovering replication-competent virus also declines after onset of symptoms. For patients with mild to moderate COVID-19, replication-competent virus has not been recovered after 10 days following symptom onset
A large contact tracing study demonstrated that high-risk household and hospital contacts did not develop infection if their exposure to a case patient started 6 days or more after the case patient’s illness onset
Although replication-competent virus was not isolated three weeks after symptom onset, recovered patients can continue to have SARS-CoV-2 RNA detected in their upper respiratory specimens for up to 12 weeks. But “persistent positivity” of a recovered patient does not necessarily mean that the patient can still spread the disease to others.
Specimens from patients who recovered from an initial Covid-19 illness and subsequently developed new symptoms and retested positive by RT-PCR did not have replication-competent virus detected. Limited evidence also points out that those who have contracted COVID-19 may be immune from re-infection for an intial period of three months.
Currently, over six months after the emergence of SARS-CoV-2, there have been no confirmed cases of SARS-CoV-2 reinfection. However, the number of areas where sustained infection pressure has been maintained, and therefore reinfections would be most likely observed, remains limited.
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