A new research adds to the growing body of evidence that airborne transmission of Covid-19 spreads more quickly in enclosed spaces.
Researchers were able to link a community outbreak of Covid-19 in China to a source patient who likely spread the virus to fellow bus riders through the bus's air conditioning system. "Our study provided epidemiologic evidence of transmission over long distances, which was likely airborne," said study lead author Ye Shen from University of Georgia in the US.
According to the study, published in the journal JAMA Internal Medicine, it was largely believed that close contact through droplets is a major route of transmission for Covid-19.
"However, the widely adopted social distancing and hand washing did not effectively prevent the transmission globally. Instead, the number of new Covid-19 cases increased steadily," said Shen.
The research team worked with epidemiologists from two regional Centers for Disease Control and Prevention in China to trace infections following a large outdoor worship event in Zhejiang province.
Some of the attendees, it turns out, took two buses to the event creating a unique natural experiment for the researchers.
Both buses had closed windows and had air conditioning running, said Changwei Li, study co-author, but one bus carried a patient infected with the virus, and the other did not.
Of the passengers who later got sick, the majority of them rode on the same bus as the source patient.
Even though the two groups later mixed in with the larger crowd at the worship event, the number of new cases attributed to the event were much lower, suggesting that the bus was the major point of transmission.
Further, some of the bus passengers who later showed symptoms of Covid-19, the authors found, were not sitting close to the infected passenger.
These findings highlight scenarios where Covid-19 could be spread through fine aerosol particles being circulated in an enclosed space.
"Understanding the transmission routes of Covid-19 is critical to contain the pandemic, so that effective prevention strategies can be developed targeting all potential transmission routes," said Shen.
"Our findings provide solid support for wearing face covering in enclosed environments with poor ventilation," the study author wrote.
Recently, another study published in the journal Proceedings of the National Academy of Sciences, found that ordinary conversation creates a conical 'jet-like' airflow that quickly carries a spray of tiny droplets from a speaker's mouth across metres of interior space.
