A woman returning from China from the U.S. carried the coronavirus with her and caused an epidemic that eventually infected at least 71 people, researchers reported on Tuesday.
It all started with an elevator ride, the researchers reported in the journal Emerging Infectious Diseases, the Centers for Disease Control and Prevention.
The woman returned to Heilongjiang Province from a trip to the United States on March 19, about a week after the last case of coronavirus was diagnosed in that province. She had no symptoms and was tested negative for coronavirus, but was sought for quarantine at home.
No one suspected anything was wrong until a man who had no obvious connection to the passenger suffered a stroke. It turned out that he was at a party with a neighbor’s relative who lives in the same building as the passenger.
When researchers in China finally put together a story, they determined that the passenger must have polluted the elevator in her building. Her neighbor in the neighborhood, who used the same elevator, also became infected, and she infected her mother and her mother’s boyfriend. They went to a party and infected a stroke patient and his sons.
The stroke patient and his two sons went to two hospitals. At least 28 people were infected at the first hospital, and another 20 were infected when he was transferred to another facility.
When the Chinese Centers for Disease Control and Prevention investigated the genetic patterns of the virus found in the new epidemic, they found that it differed from the strains previously seen in China. The viruses in the patients were genetically identical or at least very similar, which is why they believed the virus originated abroad.
When investigators learned that the neighbor of one of the cases had recently returned from abroad, they tested her again. She is not currently infected, but she had antibodies to the virus, which indicates a previous infection. They assigned her A0, which means the first case. “Therefore, we believe that A0 was an asymptomatic carrier and that B1.1 (her neighbor) was infected by contact with surfaces in the elevator in the building in which they both lived,” they wrote. Other tenants in the building tested everything negatively.
“As of April 22, 2020, A0 remained asymptomatic, and a total of 71 SARS-CoV-2-positive cases were identified in the cluster,” the researchers wrote.
“Our results illustrate how a single asymptomatic SARS-CoV-2 infection can result in widespread transmission in the community.”