A woman returning home to China from the US carried coronavirus back with her and sparked an outbreak that ended up infecting at least 71 people, researchers reported Tuesday.
It started with an elevator ride, the researchers report in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases.
The woman returned to Heilongjiang Province from a trip to the US on March 19, about a week after the last coronavirus case was diagnosed in the province. She had no symptoms and tested negative for coronavirus, but was asked for quarantine at home.
No one suspected anything was wrong until a man with no obvious connection to the traveler suffered a stroke. It turns out he had been at a party with relatives of a neighbor living in the same building as the traveler.
When the researchers in China finally put the story together, they determined that the traveler must have somehow contaminated the elevator in her building. Her downstairs neighbor, who used the same elevator, also got infected, and she in turn infected her mother and her mother’s boyfriend. They went to a party and infected the stroke patient and his sons.
The stroke patient and two of his sons went to two hospitals. At least 28 people were infected at the first hospital and 20 more were infected when he was moved to a second facility.
When the Chinese Center for Disease Control and Prevention investigated the genetic makeup of the virus found in this new outbreak, they found it was different from strains previously seen in China. The viruses in the patients were genetically identical or at least very similar, which led them to believe the virus originated overseas.
When investigators learned that a neighbor of one of the cases had recently returned from abroad, they tested her again. She was not currently infected but had antibodies to the virus, indicating a previous infection. They designated her A0, meaning she was the first case. “Therefore, we believe A0 was an asymptomatic carrier and that B1.1 (her neighbor) was infected by contact with the elevator surfaces in the building where they both lived,” they wrote. Other residents in the building all tested negative.
“As of April 22, 2020, A0 was asymptomatic, and a total of 71 SARS-CoV-2 – positive cases had been identified in the cluster,” the researchers wrote.
“Our results illustrate how a single asymptomatic SARS-CoV-2 infection could result in widespread community transmission.”