Individuals with mild symptoms of Covid-19 may test positive for SARS-CoV-2 for a prolonged period of time

8% of the patients assessed tested positive for more than 70 days. This phenomenon had only been observed before in immunosuppressed persons or those with comorbidities

A study by Scientific Platform Pasteur USP (SPPU), Brazil, showed that 8% of the patients with a slight case of Covid-19, who are healthy and have mild symptoms, could experience episodes of prolonged positivity, and the coronavirus continues to be detected in the body, even after the symptoms are gone. According to Marielton dos Passos Cunha, a SPPU doctoral fellow and the first author of the article, the results raise the question if there is a need to perform tests after a 14-day quarantine of the infected individual, to confirm whether or not the virus has, in fact, been eliminated. However, more studies must be carried out, in order to assess the ability to transmit the virus in cases of prolonged infection.

The study is part of a SARS-CoV-2 monitoring project in the metropolitan area of São Paulo, where samples were collected between March and November 2020. It is funded by the São Paulo Research Foundation (FAPESP), by the Institut Pasteur, and by the French Consulate in São Paulo, under the coordination of the franco-brazilian scientist, Paola Minóprio. Thirty-eight patients who tested positive and had mild symptoms were selected to participate in the study. “We collected test samples every week from those patients. Three were classified as atypical, since they remained positive for longer periods of time,” Mr. Cunha explains. One of the patients is HIV-positive and tested SARS-CoV-2-positive for 232 days; the other two tested positive for 71 and 81 days, respectively. However, in general, the individuals were asymptomatic most of the time.

The researchers stress that the HIV patient had the disease under control during the coranavirus infection, with a normal immune cell counts. Therefore, the data suggest that he was as able of reacting to SARS-Cov-2 as the other two, non-HIV, patients. “We would need to study a larger cohort of HIV patients who were infected by Covid-19, to assess whether or not HIV interferes with the immune response against the coronavirus,” they point out.

Despite the long extent of the infection, the researchers managed to follow its entire duration – that is, until the patients were definitively tested negative. "This means that the immune system itself, despite having some initial difficulty, managed to eliminate the virus."

Why this happens – Up to that time, other studies on prolonged positivity had shown patients with immunosuppression associated with a disease or a transplant, which explains the difficulty in controlling the infection. “Our research deals with healthy patients, without any other comorbidity, who present natural defenses against the virus. Some host factors may be linked to this prolonged positivity, such as the nutritional or immune status, and age,” Cunha says.

Prolonged infection can also be associated with the virus itself, which develops survival mechanisms to perpetuate itself. “For example, the virus can modulate some of the host genes to help replication, thus, evading immune system strategies. Therefore, the viral mutations accumulated throughout the infection period may be related to the prolonged positivity.”

The next step is to understand the epidemiological impact of this phenomenon: whether or not the viruses that remain in the body are capable of establishing a new infection in another host. In addition to these studies, the group is sequencing samples from new patients who have similar health conditions, to verify if, for instance, there are some mutations associated with a more prolonged SARS-VoV-2 infection.