It seems incredible that the duration of the Covid transmission period is still surrounded by uncertainties.
At the beginning of the pandemic, the recommendation was that the isolation of patients last two weeks, counted from the first symptoms.
In December 2021, however, the US Centers for Disease Control (CDC) reduced this period to five days. The agency relied on observations that transmission occurred mostly in the two days before symptoms began, up to two or three days after they started.
According to the CDC, the day of onset of symptoms should be considered day zero (the next day would be day one). Thus, if the disease started on a Monday, the patient could already return to normal life on Sunday, with one caveat: as long as he was afebrile for 24 hours and with the other symptoms regressing. From that day on, he should keep wearing a mask for another five days. A little complicated, no?
Since then, this orientation has been questioned by experts, many of whom consider it influenced by political pressures.
The criticism is based on studies that detected the virus in nasal secretions during the second week of illness.
Interviewed by Nature magazine, Amy Barczak, an infectious disease specialist at Massachusetts General Hospital, linked to Harvard University, was emphatic: “There is not enough data to guarantee that it is less than ten days”. Her work, published online on Medrxiv, suggests that about 25% of people infected with the omicron variant reach the eighth day still able to transmit it.
In fact, it is not reasonable to choose a specific day for the person to stop being contagious: the question is statistical, dear reader.
The right question is: when do most people stop transmitting the virus? Is the number of those who continue to transmit over the course of the second week relevant to public health?
The problem is far more complex than the CDC’s rush to ensure a return to work suggests.
Today we are dealing with new variants of the coronavirus, with the immunological stimulus caused by vaccination and with the natural immunity induced by previous Covid. What is the impact of these factors on infection control and the speed of virus elimination?
To complicate matters, in the evaluation of the studies, behavioral factors come into play: the more debilitating the symptoms, the longer the period in which the patient will stay at home, while those who are asymptomatic or with mild symptoms will tend to move earlier, increasing the risk of transmission. .
Another complicating factor is the fact that the PCR test can remain positive even after the person stopped transmitting several days ago.
This positivity is explained by the presence of non-viable RNA fragments that persist even after the complete elimination of the virus.
In the evaluation of these cases, the ideal is to perform the rapid antigen test, since it detects proteins produced only while the virus still maintains replication. If after a week or more the rapid test is positive, isolation should be continued until negative results occur.
What about when the quick test is already negative, but the cough, tiredness and sore throat still haven’t gone away? The persistence of these complaints does not mean that the person still transmits the virus. This symptomatology can be caused by the immune response itself, a phenomenon that eventually persists even after the virus has been eliminated.
To be sure if the patient still transmits it, the ideal would be to collect the virus directly from the nasal secretions, to sow it in culture media, a technique accessible only in specialized laboratories, not routinely available.
The data that emerged from research with this technology showed that it is very rare to find viable SARS-CoV-2 after the tenth day, counted after the appearance of the first symptoms.
Perhaps we can summarize it as follows: on the tenth day, isolation can be suspended without the need to repeat any tests. Before, only after the fifth day, in cases where the rapid test is negative. Patients with immunosuppression can transmit for longer periods.
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