Why air-con could be aiding spread of Covid-19

Two studies in China suggest the virus that causes Covid-19 can be transmitted through air conditioners, ventilators and poor air quality.

The first study conducted by Guangzhou Centre for Disease Control suggested that the virus, apart from just being transmitted from person to person, also has the ability to move far with the help of air currents caused by ventilation systems.

“During January 26–February 10, 2020, an outbreak of 2019 novel coronavirus disease in an air-conditioned restaurant in Guangzhou, China, involved three family clusters. The airflow direction was consistent with droplet transmission,” wrote the researchers in the research letter.

The study has been published as an early release by Centers for Disease Control and Prevention (CDC). It followed up 10 infected people from three families who ate from a restaurant in Guangzhou during the period in the study; the restaurant had air-conditioning.

The report noted, “One of the families had just travelled from Wuhan, Hubei Province, China. We performed a detailed investigation that linked these ten cases together.” The research pointed out that one of the families travelled from Wuhan and arrived in Guangzhou on January 23. One of the family members had a meal with three other members of the same family at the restaurant marked X.

“Two other families, B and C, sat at neighbouring tables at the same restaurant. Later that day, patient A1 experienced onset of fever and cough and went to the hospital. By February 5, a total of 9 others (4 members of family A, 3 members of family B, and 2 members of family C) had become ill with Covid-19,” the researchers wrote.

They found out that the patient from Wuhan was the only known contact of the two families marked as B and C.

“We determined that virus had been transmitted to >1 member of family B and >1 member of family C at the restaurant and that further infections in families B and C resulted from within-family transmission,” reads the report.

However, more intriguing was the hypothesised nature of transmission. The restaurant where they ate was a five-storey building without windows, with the third floor area occupying 145 square metres and each floor having its own air conditioner. The distance between tables was one metre.

The research therefore concluded that the mode of transmission was largely through droplets aided by close proximity of the persons infected. It pointed out that the first patient from Wuhan was asymptomatic. In the second study by the University of Hong Kong, the researchers suggest that air conditioning and quality most likely played a key role in the spread of the virus. They built on the fact that some of the infected people were 4.5 metres away from the index patient.

The second team of researchers carefully examined the ventilation system, used mannequins and tracer gas in simulation to study the flow of air as it could have been during the January 24 lunch.

Their conclusion was that the density of the crowd as well as poor ventilation were the culprits for the outbreak.