CLINICAL MATTERS
The US Centers for Disease Control recently changed its guidance on isolation for patients who test positive for Covid-19. From Covid-19 focused advice, the CDC is increasingly shifting to a broader respiratory virus guidance given the high rates of vaccination and the availability of effective treatment for SARS-CoV-2 (https://www.cdc.gov/respiratory-viruses/background/index.html).
As Covid-19 becomes just one of the many seasonal respiratory viruses, it is expected that people are less likely test for it. Therefore, it is more important to provide guidance on recommended isolation times for those with respiratory virus infections in general regardless of testing behavior. The societal costs of prolonged isolation in the light of decreasing risk of hospitalization from Covid-19 infection and transmission have dramatically shifted as more people achieve hybrid immunity. An overly restrictive isolation recommendation will just discourage people from testing and potentially increase transmission instead.
Early in the pandemic, the most stringent isolation protocols were used. Only RT-PCRs were available for testing at that time. To aggressively mitigate the risk of rapid spread, anyone who tested positive needed at least two consecutive negative RT-PCR tests before being released. This resulted in prolonged isolation of up to eight weeks—the time it took for RT-PCRs to become negative. This caused hospitals and quarantine facilities to become overcrowded and contributed to the shortage of test kits.
As we began to better understand viral dynamics, the requirement of testing for release from isolation started to be relaxed. In some cases, doctors used a measurement called Ct value which was a surrogate for the amount of virus in a respiratory sample. Ct stands for cycle threshold, which is the number of cycles of PCR it takes before a sample tests positive. An RT-PCR test is considered negative if around 40 cycles of PCR does not result in a detectable RNA result. Above a certain number of cycles (usually 20 to 30), the virus may still be detected but the patient is no longer considered contagious since only residual genetic material is causing the test to become positive. This was an imperfect measure but was better than having to get two negative tests before releasing someone.
After it became apparent that SARS-CoV-2 was no longer transmissible in most patients after seven days from the start of symptoms, the Department of Health started shifting from discontinuing isolation from a test-based approach to a symptom-based approach. Those with mild symptoms could be released after seven days while those with moderate and severe symptoms had to isolate longer since they had higher levels of viral shedding. Those who tested positive but were asymptomatic were required to isolate for seven days from the date of the positive test.
When antigen tests became widely available, aside from being a cheaper test, these were also useful as a surrogate marker of infectivity. While less sensitive than RT-PCR, antigen tests usually tested positive with an equivalent Ct value of about 20 to 30, so it roughly correlated with infectivity of the virus. Coupled with a symptom-based approach, antigen tests gave doctors more confidence in releasing patients from isolation especially among those patients with prolonged residual symptoms.
As more and more people got vaccinated and boosted against Covid-19, the number of hospitalizations began to decouple from the number of cases. This first became apparent during the Omicron spike in January 2022 where, despite causing more than double the number of cases from Delta, resulting deaths were less than half the number from Delta and hospitalizations were much fewer. At that point, the risk to benefit ratio of stringent isolation continued to shift. We advised the Department of Health to further shorten the required isolation days from seven days to five days for both asymptomatic and mild confirmed Covid-19 cases as long as they were fully vaccinated. Vaccinated individuals tend to have shorter duration of symptoms and shed less infective virus. In the case of the case of symptomatic patients, the start date of the count to stopping isolation was the first day of symptoms. So someone who tested positive for Covid-19 and started having symptoms two days ago only needed to isolate for three more days, as long as he or she continued to get better and was no longer febrile. While we recognized that some people could still be infectious beyond five days from symptom onset, the consequences of this residual risk were much less than before. In addition, residual infectivity could be further mitigated by wearing a mask for as long as symptoms were present. At that time, the mask mandate was still in place so this was not a big deal. We felt that the risk of severe disease was low enough as long as people continued to practice good public health standards.
Most recently, the Department of Health has done away with the last of the mask mandates in hospitals and healthcare facilities. It continues to recommend and encourage the use of masks however when taking care of patients, especially among those with respiratory symptoms. Lifting a mask mandate doesn’t mean we don’t use masks. It only means we have a choice whether or not to wear one depending on the risk. Nevertheless, we can now literally breathe easier in most cases, while remaining vigilant and responsible for our own protection.
The latest US CDC guidelines have now decreased the mandatory five-day isolation period for confirmed Covid-19 cases to just 24 hours after the last fever. Updated studies show that the highest risk for transmission is in the first three days of illness followed by a substantial drop in viral shedding afterwards especially among vaccinated and boosted individuals. The subsequent residual shedding of the virus does not represent as much of a threat in a highly vaccinated population with access to effective treatment. They still urge caution and updated vaccination among the most vulnerable populations, however, including the elderly and the immunocompromised.
A syndromic approach to isolation even without testing is a good step for three major reasons. First is that it significantly reduces the burden of isolation of Covid-19 when the risk of severe disease is much lower. Second is that it makes testing less burdensome by giving those with respiratory symptoms an option to just isolate while they have fever without having to spend money on testing. Third – and this is probably the most value added to this policy shift—a syndromic approach to isolation also decreases the transmission of other respiratory viruses other than Covid-19. This also addresses the risk of false negatives and will in the long run result in decreased transmission of all respiratory viruses in general.