During the first wave of the coronavirus disease 2019 (COVID-19) pandemic, public health authorities recommended that those exposed to the causative pathogen – severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – should isolate themselves for 14 days.

In a new study, published on the pre-print medRxiv* server, researchers at the Instituto de Medicina Tropical, Faculdade de Medicina da Universidade de São Paulo, Brazil reported that mild COVID-19 patients can still be infectious at day 10 from the illness onset, even in the absence of symptoms.

Quarantine and isolation guidelines

The primary recommendation of 14 days isolation or quarantine for COVID-19 patients was based on the description that people with moderate or severe disease could remain reverse transcription-polymerase chain reaction (RT-PCR) positive until day 12 to 14.

The U.S. Centers for Disease Control and Prevention (CDC) reported that data indicates that the vast majority with mild to moderate COVID-19 remain infectious no longer than 10 days after symptom onset. Meanwhile, most with more severe illness remain infectious no more than 20 days after symptom onset.

The health agency recommends that for most individuals with COVID-19, isolation and precautions can be discontinued 10 days after the onset of symptoms and resolution of fever for at least 24 hours, without fever-reducing drugs and with the improvement of symptoms.

For asymptomatic patients, they are also recommended to stop isolation, quarantine, and precautions at 10 days after the date of their first positive RT-PCR test for SARS-CoV-2.

Detecting SARS-CoV-2 RNA in RT-PCR test in respiratory samples from COVID-19 patients is not a direct indication of the presence of viable viruses. However, isolation of SARS-CoV-2 in cell culture systems can act as a surrogate marker of infectiousness.

In hospitalized patients with moderate or severe COVID-19, cell-culture based studies suggested that no replication-competent virus is found after nine days of symptom onset. Hence, health experts recommend that after 10 days of isolation, the patient can be discharged.

The study

The study, which was part of an umbrella project developed in Araraquara, São Paulo, Brazil, aimed to determine if it is safe to discharge COVID-19 patients 10 days after symptom onset, even if their symptoms have already resolved.

The study involved 53 patients with confirmed mild COVID-19, who provided nasopharyngeal samples on day 10 of illness. The team used reverse transcription-polymerase chain reaction (RT-PCR) to detect the presence of SARS-CoV-2 RNA.

The team found 40 from the 53 patients (or 79 percent) were SARS-CoV-2 positive at day 10. Further, the researchers cultured the cells of 29 SARS-CoV-2 RT-PCR positive samples on the 10^th day after the illness in Vero E6 cells.

After two cell-passages, eight samples presented cytopathic effect, but only seven filled the criteria. In terms of the symptoms, three of the seven patients presented symptoms on day 10, but they noted that the symptoms were milder than those experienced during the acute phase of the infection.

We report here that mild COVID-19 patients can still be contagious at day 10 from the illness onset even in the absence of symptoms. Positivity in cell culture was also strongly associated with cycle thresholds lower than 21 in S gene at the nasopharyngeal samples,” the team concluded in the study.

Despite the fact that that available data on SARS-CoV-2 culture is limited, the studies have shown that persons with mild or moderate COVID-19 can remain infections no longer than 9 days after the symptom onset. However, the findings from the current study suggests that some patients may still be contagious on the 10^th day.

Infection control measures to prevent transmission that are focused mainly on the absence or presence of symptoms and PCR results to determine isolation time may not be enough to prevent transmission. The current study highlights the need for further research on the ideal isolation time for COVID-19 patients. This is a crucial dynamic of pandemic management that needs clarification as cases rise in many parts of the world and faster-spreading variants continue to emerge.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.