Can SARS-CoV-2 still be transmissible once symptoms have subsided?

Researchers based at the University of Missouri, in partnership with U.S. government science facilities in Maryland, have reported that individuals severely infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may be able to continue shedding infectious viral RNA for over three weeks after the symptomatic infection has passed.

A pre-print version of the research paper is available to read in full on the medRxiv*server.

How does COVID-19 spread?

SARS-CoV-2 is the underlying causative pathogen of the coronavirus disease 2019 (COVID-19) pandemic. Since it was first identified in Wuhan, China, in late 2019, the respiratory virus has spread rapidly across the world. The virus is primarily transmitted through respiratory droplets and salivary contact, and has led to millions being hospitalized with symptoms of fever, fatigue, and difficulty breathing.

Hospitalized patients who recover typically stay for between 10 to 13 days, but in some, the virus may continue replicating even once symptoms have resolved. As a result, these patients will still test positive for the virus, and so are kept hospitalized for longer. It is not known, however, if these asymptomatic, recovered patients are still infectious and pose a threat to the general public.

The research team set out to test the post-recovery infectivity of a male Caucasian patient admitted to hospital with SARS-CoV2. Determining whether these asymptomatic patients pose a risk of transmitting COVID-19 is of great importance, as it may allow for pressure to be taken away from clinicians to withhold positive-testing recovered patients, thus providing more hospital space for future admissions.

What did the scientists do?

The researchers had just one individual in their sample, who they described as a “Caucasian male in his 60s presenting to Urgent Care … diagnosed SARS-CoV-2 positive after three days of disease onset”. Their observations began once he was admitted to the hospital, one week after disease onset. The man was admitted to the Intensive Care Unit on the second day, where he suffered from secondary bacterial pneumonia, eosinophilic bronchiolitis, and oral candidiasis. He eventually recovered and was discharged from the hospital 63 days after admission.

The researchers recorded the patient’s clinical readings at least twice a day and took multiple nasopharyngeal swabs and plasma samples. These samples were tested for viral loads and antibodies. The virus RNA was sequenced and found to belong to the D614G/Q57H/T265I subclade, currently widely prevalent in the U.S.

What did they find?

Current hospital guidelines suggest that patients with improved symptoms, either 20 days post-initial disease onset or 24 hours after any feverish display, may be excused from transmission-based precautions.

The study found, however, that viral shedding can continue much longer this period, for 24 days after symptom onset, implying much longer viral infectivity than previously suspected possible. Additionally, the patient presented with fluctuating viral loads, possibly experiencing a recurrent infection, 54 days after initial virus exposure.

These results are consistent with previous findings, one study concluding that viral shedding may still continue for three months after infection. This therefore indicates that current guidelines are inadequate in preventing the transmission of the virus once symptoms have subsided, and that extended hospital stays “may be necessary.”

The paper is currently in pre-print form and yet to be published, but the authors encourage studies encompassing wider sample sizes to be carried out. Especially so because this study only reported the data of a single patient. The researchers note that the patient suffered from complications during the infection period, and was also on steroid treatment prior to hospitalization, so his results may not be generally applicable to wider populations.

*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

Michael Burgess

Michael graduated with a first-class degree in Zoology from the University of Hull, and later received a Masters degree in Palaeobiology from the University of Bristol.