An asymptomatic coronavirus carrier infected an apartment neighbor without sharing the same space. A study blames the building's elevator buttons.

• An asymptomatic coronavirus carrier traveled from the US to China in March. Even though she didn't interact with anyone face-to-face, her downstairs neighbor was infected.
• According to a new study, transmission likely occurred in the elevator, when the neighbor touched the same buttons that the quarantined traveler had.
• The neighbor was later linked to 70 other coronavirus infections in the local community.
• Coronavirus particles can live on surfaces like plastic and stainless steel, which are common in elevators, for up to seven days.

New research reveals that an elevator can be a coronavirus transmission hotspot, even if an infected person doesn't have symptoms and doesn't ride with anyone else.

A woman traveled from the US back to her home in China's Heilongjiang province on March 19. Although she did not have any symptoms, she quarantined in her apartment following her arrival, avoiding any close contact with other apartment-building residents. An antibody test would later reveal she was an asymptomatic coronavirus carrier.

Three weeks later, her downstairs neighbor (and four of the neighbor's close contacts) tested positive.

The two apartment-building neighbors had not crossed paths. But they had used the same elevator at different times.

According to a new CDC study, the downstairs neighbor "likely became infected by using the elevator in the building" after the asymptomatic carrier had ridden it, the study authors wrote. They think transmission likely occurred when the neighbor touched surfaces and buttons in the elevator.

No other residents in the building tested positive, but contact tracing later revealed the neighbor was patient zero of a 71-person cluster in the local community.

Elevators could be coronavirus-transmission hotspots

The primary concern when it comes to coronavirus and elevators is that nearly all lifts are small, enclosed indoor spaces. Those are the ideal conditions for the coronavirus' spread, since it's expelled in droplets when an infected person coughs, sneezes, or speaks.

Elevators also tend to lack strong airflow, which mean people who have COVID-19 (no matter whether they're presymptomatic, asymptomatic, or feeling ill) could leave some virus behind.

Although it's not common, a person can get the coronavirus if they touch a surface or object that has viral particles on it and then touch their mouth, nose, or eyes.

The virus' lifespan on different surfaces depends on the surrounding temperature, humidity, type of surface, and other factors. But two studies found that it lasts longest — up to seven days — on stainless steel and plastic, which are commonly found in elevators. That means elevator buttons and doors could harbor viral particles for days.

Indeed, a May study found the coronavirus' genetic material on elevator buttons in a hospital in Wuhan, China.

CDC guidelines stipulate that commonly touched surfaces, including those in public elevators, should be frequently cleaned and disinfected.

Even so, it's important to "punch the buttons with something other than your fingers," Linsey Marr, an aerosol scientist at Virginia Tech, previously told Business Insider.

A 71-person cluster

The downstairs neighbor's infection jump-started a chain reaction in the local community.

A week after the asymptomatic traveler returned home, the neighbor hosted her mother and her mother's boyfriend for an overnight stay. Three days later (on March 29), the mother and boyfriend attended a party, interacting with another gentleman. By April 10, all six people had tested positive.

The man from the party had a stroke before testing positive for COVID-19. He went to the hospital on April 2, where his sons cared for him. The sons later tested positive, too. The three of them interacted with hospital staff and other patients, unknowingly passing the virus on to them as well: A total of 28 people were infected. Then the man moved to a second hospital, catalyzing another series of infections.

By mid-April, 70 people were infected who could be traced back to the neighbor's case.

Scientists from the Chinese Center for Disease Control and Prevention sequenced the genome of virus samples from across the 71-person cluster. They determined that the samples were nearly identical, and that the virus genome differed from any other samples previously found circulating in China. That indicated the virus originated abroad.

That's how they figured out that the asymptomatic traveler was likely "the origin of infection for this cluster."

"Our results illustrate how a single asymptomatic SARS-CoV-2 infection could result in widespread community transmission," the study authors concluded.