A new case report has pieced together how air conditioning in a restaurant may have helped to infect at least nine people with Covid-19. While there are important limitations and drawbacks to the non-peer reviewed research, it’s one of the first case reports to suggest air conditioning could play a role in the transmission of Covid-19
At lunchtime on January 24, 2020, at least 83 people sat down to eat at a windowless restaurant on the third floor of a multistory building in the Chinese city of Guangzhou. Among them were a family of four people (known as family A) who had returned from Wuhan, the city where the viral outbreak is thought to have originated, the previous day.
Later that afternoon, one of the people who had returned from Wuhan (person A1) started to feel sick with a sudden onset of fever and cough, and went to the hospital. By February 5, a total of 9 others who were eating at the restaurant that afternoon – including 4 members of family A, as well as five members of two other families who sat at neighboring tables (called family B and C) – had all become ill with Covid-19.
Researchers suggest the isolated outbreak can be connected to the airflow of an air-conditioning (AC) unit that blew respiratory droplets around the unventilated restaurant.
The research, carried out by the Guangzhou Center for Disease Control and Prevention, was reported in an early release letter in the journal Emerging Infectious Diseases, a publication by the CDC. This means the research – set to be officially released in July – is not considered a final copy and has not been peer-reviewed. However, it’s been released early by the CDC due to the timely nature and importance of the findings.
The study tracked the customers who had attended the restaurant during lunchtime hours, noting where they sat and the path of airplay from the restaurant's AC units. As you can see in the diagram, it became clear that those who became infected with Covid-19 all sat in the same path of airflow as infected patient A1. Those that didn’t sit in this path of airflow, on the other hand, were not infected.
“We conclude that in this outbreak, droplet transmission was prompted by air-conditioned ventilation. The key factor for infection was the direction of the airflow,” the researchers write.
However, there are few big caveats to the research that need to be taken on board. Firstly, they could not exclude the possibility the infection spread to one family member at the restaurant and from there went on to infect other members of the family after dinner.
Furthermore, there is no definitive scientific consensus that Covid-19 can be spread through the airborne transmission of aerosolized particles. Although we know the coronavirus can travel distances in the air, it’s not clear how stable, viable, and infectious it remains in this airborne state. Additionally, the study points out that samples from the AC unit did not test positive for SARS-Cov-2, saying “the smear samples from the air conditioner were all nucleotide negative. This finding is less consistent with aerosol transmission.”
With that in mind, it’s known that indoor air circulation can spread some airborne pathogens. Whether or not air conditioning can spread Covid-19, however, needs further research before it is treated as gospel.