China Superspreader Gave COVID-19 to 71 People in a Single Elevator Trip

A woman in China passed COVID-19 to an estimated 71 people through a single elevator journey, a report published by the U.S. Centers for Disease Control and Prevention has said.

The woman had no direct contact with any of the other people and the only shared space was an elevator in the apartment block where she lived. Researchers say this superspreader case shows how a single case of the disease can result in "widespread community transmission" and the challenges of containment via self isolation.

The 25-year-old woman returned to Heilongjiang Province, China, from the U.S. on March 19. Prior to her arrival, there had been no cases of COVID-19 in the region since March 11. She had no symptoms and was asked to quarantine at home. The only indirect contact she had with anyone else in her building was through a shared elevator. Tests for antibodies for SARS-CoV-2, the virus that causes COVID-19, came back negative on March 31 and April 3.

On March 26, the woman's downstairs neighbor had his mother and her partner stay overnight. Three days later, the mother and her boyfriend went to a party. On April 2, one of the people at the party had a stroke and was admitted to hospitals, accompanied by his sons. On April 7, the mother's boyfriend started showing COVID-19 symptoms.

"He tested positive for SARS-CoV-2 on April 9, the first confirmed case in this cluster," the research letter published in the journal Emerging Infectious Diseases said. Several of his contacts also then tested positive, including the neighbor of the woman who had been traveling in the U.S..

While the stroke patient was in hospital, 28 other people were infected with coronavirus on the ward. Five nurses, one doctor and one member of staff at the hospital were also infected. In the second hospital he was treated, another 20 people became infected.

After investigators learned of the original woman's international travel, they tested her again. Results showed she had antibodies, suggesting previous infection with SARS-CoV-2. Researchers conclude the woman was an asymptomatic carrier who infected her neighbor via surfaces in the elevator. Other residents in the building tested negative for the disease, they said.

The Chinese Center for Disease Control and Prevention carried out tests on the genomes of 21 samples of the virus from patients in the cluster. Their findings showed the genomes were identical in most cases, with just three having small differences. This suggests the cluster was the result of a single point of origin.

The authors of the research letter wrote: "The viral genome sequences from the cluster were distinct from the viral genomes previously circulating in China, indicating the virus originated abroad and suggesting [the woman] was the origin of infection for this cluster."

Concluding, they said: "Our results illustrate how a single asymptomatic SARS-CoV-2 infection could result in widespread community transmission. This report also highlights the resources required for case investigation and challenges associated with containment of SARS-CoV-2. Continued measures to protect, screen, and isolate infected persons are essential to mitigating and containing the COVID-19 pandemic."

The spread of SARS-CoV-2 via surfaces has been well established since the first cases of the virus were identified in Wuhan, China, last year. According to the National Institutes of Health, it can survive on copper for around four hours, on cardboard for about 24 hours, and on plastic and stainless steel for between two to three days. Research published in mSphere also suggests asymptomatic people can spread SARS-CoV-2 via contact with surfaces.

There is also increasing evidence the virus is airborne, with the World Health Organization recently acknowledging this possibility. This followed an open letter from 239 scientists calling on the agency to officially recognize the risk.

On Sunday, one of the U.K.'s leading scientists also said the virus could survive in the air for up to an our. Appearing on the BBC's Andrew Marr Show, Wendy Barclay, from the scientific advisory group SAGE, said: "The virus that causes COVID can remain viable, can remain infectious, in these very small droplets. So that raises the possibility and indeed the likelihood that [COVID-19] can be transmitted through these small particles that can trace through the air.

"Laboratory studies where the virus has been purposefully put into the air tell us that the virus can remain there for more than an hour in its infectious form."