Mildly symptomatic COVID-19 patients may be contagious for longer than previously thought

Researchers in Brazil have reported two cases of people with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) shedding infectious virus for a significantly longer period than has previously been reported.

The patients, who developed mild but prolonged symptoms of coronavirus disease 2019 (COVID-19), were still shedding replicating SARS-CoV-2 up to 37 days (in case 1) and 24 days (in case 2) after symptom onset.

“It has been estimated that individuals with COVID-19 can shed replication-competent virus up to a maximum of twenty days after initiation of symptoms,” says the team from the University of São Paulo and the University of São Caetano do Sul.

“To the best of our knowledge, there are no previous reports of replication-competent virus being isolated three weeks after symptom onset,” they write.

The researchers say the findings suggest that individuals with mild symptoms can remain infectious for prolonged periods, highlighting the need for them to take appropriate precautions to avoid spreading the virus to others.

A pre-print version of the paper is available on the medRxiv* server, while the article undergoes peer review.

Electron microscopy of Vero cells inoculated with nasopharyngeal samples from women infected with SARS-CoV-2. Panel A, B, C, D are representative thin section electronmicrographs of the detection of SARS-CoV-2.  Long blue arrows indicate elongated and spheroid viral particles, respectively, attached to the cell border membrane in panels A and B. In panel B small arrow points to a virus spike. In panel C small arrows indicate petite and longer virus spikes. Panel D contains several viral particles inside a cytoplasmic vacuole.
Electron microscopy of Vero cells inoculated with nasopharyngeal samples from women infected with SARS-CoV-2. Panel A, B, C, D are representative thin section electronmicrographs of the detection of SARS-CoV-2. Long blue arrows indicate elongated and spheroid viral particles, respectively, attached to the cell border membrane in panels A and B. In panel B small arrow points to a virus spike. In panel C small arrows indicate petite and longer virus spikes. Panel D contains several viral particles inside a cytoplasmic vacuole.

What have studies shown so far?

Since the COVID-19 outbreak first began in Wuhan, China, late last year ((2019), research has indicated that SARS-CoV-2 can be detected among infected individuals 1 to 3 days before developing symptoms.  

Viral load then peaks during the first week of symptom onset before gradually declining over time.

Studies have estimated that replication-competent virus is no longer present in COVID-19 patients 20 days following symptom onset

However, this estimate has come from studies that have mostly involved hospitalized individuals and those with severe disease, says Antonio Sesso (University of São Paulo) and the team.

“Studies to address the possible presence of SARS-CoV-2 during the different phases of COVID-19 disease in mildly infected individuals, and utilization of viral culture techniques to identify replication-competent viruses, have been limited,” they write.

What did the current study involve?

Now, Sesso and colleagues have shown that in two SARS-CoV-2-infected women with mild disease, the virus was shown to be replication-competent for longer than has previously been reported.

The women had participated in the Corona São Caetano Program, an initiative offering primary care for COVID-19 to all residents of São Caetano do Sul.

All people living in the municipality were encouraged to complete a questionnaire if they developed symptoms consistent with COVID-19. People who met the criteria for suspected COVID-19 were contacted and asked to complete a risk assessment. Individuals who met the triage criteria for mild disease were offered a home visit where they could provide a nasopharyngeal swab for analysis.

The two clinical cases

The first case (case 1) is a woman in her 50s who reported in mid-April that she had first experienced a dry cough, headache, loss of strength, joint pain, and muscle pain, but no fever, 20 days previously.

Twenty-two days following symptom onset, the woman had a nasopharyngeal swab taken that tested positive for SARS-CoV-2.

The woman then developed nausea, vomiting, and a loss of taste and smell.

Significant symptoms persisted, and 37 days following symptom onset, a second nasopharyngeal swab tested positive for the virus.

Although the woman was still reporting a mild headache and loss of strength in mid-May, most symptoms gradually resolved.

The second woman (case 2), also in her 50s, reported experiencing fever, headache, sore throat, cough, loss of strength, joint pain, muscle pain, discharge of nasal fluids, and nausea at the beginning of May.

A nasopharyngeal swab test taken five days following symptom onset tested positive for SARS-CoV-2. After symptoms continued to persist, a second nasopharyngeal swab was taken 24 days following symptom onset, which showed that the woman was still infected. Case 2 remained symptomatic for around 35 days following onset.  

Testing the replicative capacity of SARS-CoV-2

“Due to the persistence of symptoms and a prolonged positive RT-PCR result, it was decided to investigate the replicative capacity of their SARS-CoV-2 virus,” said Sesso and colleagues.

The samples obtained from case 1 on day 37 and from case 2 on day 24 were inoculated into Vero CCL81 cells, and diagnostic tests were performed on the supernatant.

In both cases, cytopathic effects were observed in the cell culture supernatants and the presence of replicating SARS-CoV-2 was confirmed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR).

According to the World Health Organization (WHO) recommendations regarding the criteria for discharging SARS-CoV-2-positive individuals from isolation, patients must be clinically recovered and symptom-free, say the researchers.

“Our data reinforce that even mildly symptomatic individuals are potentially contagious,” they write.

The team says further clarification of the frequency of presumed prolonged infectivity will be defined by prospective follow-up studies involving a more significant number of individuals.

“Nevertheless, this report highlights that individuals with prolonged but mild symptoms can remain positive for the replication-competent virus, highlighting the need for such individuals to exercise appropriate precautions to avoid potential transmission of SARS-CoV-2 in their community,” the researchers conclude.

*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.

Journal reference:
Sally Robertson

Written by

Sally Robertson

Sally first developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Central (BMC), after having graduated with a degree in biomedical science from Greenwich University.

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