The tampon after 14 days? It’s useless

The WHO has experienced the consequences of Covid on its skin knows it very well: once the worst has been avoided, convalescence seems a true limbo marked by the repetition of tampons. Exam after exam, the bewildering wait for the second consecutive negative result, which certifies the definitive elimination of the virus from the body, can last weeks, to pass strictly in isolation.

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Now a large population study conducted by researchers from Reggio Emilia Irccs Ausl, and published in the British Medical Journal Open, quantifies the time required for the swab to become negative and suggests that repeating the test 14 days after diagnosis will produce a positive result in most cases. “Half of symptomatic people need 36 days from the onset of the first symptoms and 30 days from diagnosis to eliminate the virus from the body,” explains epidemiologist Francesco Venturelli, one of the study authors.

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I study
The researchers monitored the infection trend in 4,480 residents in the province of Reggio Emilia who tested positive during the peak of the pandemic, between February 26 and April 22, 2020. During this interval, 1,259 people achieved viral clearance, that is, elimination of the virus from the body, defined by at least one negative swab after the initial positive test. The median time to clearance for this group was 31 days from the first positive swab. The researchers then examined the viral shedding rate in 1,162 of the 4,480 initial subjects for whom sufficient time had elapsed since the first positive swab (at least 30 days). An average of three samples were each taken: approximately 15 days after the first positive swab, 14 days after the second, and 9 days after the third. “To understand if and which population groups responded differently, we detailed the analyzes based on gender, age and severity of illness. In the elderly we observe somewhat longer times, but the differences do not suggest the need for different protocols ”, explains Venturelli. Viral clearance was achieved in 704 people (60.5%) and confirmed in just under 79% of those who were retested after the first negative swab. In other words, after a first negative result, one in five people test positive again on the next test.

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False negatives
The study also shows that the false negative rate remains relatively high for up to 3 weeks from a positive swab. The mean time of elimination, that is, the time required for half of the infected subjects to become negative, was 30 days from the first positive sample and 36 days from the appearance of symptoms. Ultimately, the Emilian researchers suggest that repeating the test 14 days after a positive swab will produce the same result in most cases. The results of the study can be useful to optimize resources and at the same time reduce the probability of spreading the virus, re-evaluating the moment at which to propose control swabs to infected people. To date, contagion during convalescence remains uncertain. Furthermore, the current epidemiological evidence of transmission has inevitably been influenced by the way quarantine has been managed. “A precise evaluation of the time is fundamental to reduce the isolation period of the patients who no longer present symptoms and, at the same time, to reduce the risk of spreading the virus”, concludes the epidemiologist.