In the first 2 years or more of the COVID-19 pandemic, the risk of infection was higher in open-space offices, long-distance trains, convenience stores, taxis, airplanes, and nightclubs and during take-away food delivery, carpooling with relatives, and attending concerts, suggests a case-control study of various work, leisure, and other spaces in France.
A team led by Institut Pasteur researchers in Paris matched 175,688 adults who had a recent COVID-19 infection with 43,922 uninfected controls during nine periods from October 2020 to October 2022, a range spanning the wild-type to Omicron-variant eras. Participants completed an online questionnaire about sociodemographic information, health status, household, and recent exposures during the 10 days before symptom onset or diagnosis.
The results were published this week in BMC Public Health.
"As the impact of the pandemic recedes in most countries, knowledge on the settings of transmission can help guide improvement in air quality and individual protection approaches, particularly for elderly or immunocompromised people," the researchers wrote.
Open-space offices, long-distance trains
Spaces associated with an increased risk of COVID-19 infection were open-space offices (odds ratio [OR] range across the nine periods, 1.12 to 1.57) and long-distance trains (OR range, 1.25 to 1.88) and during most of the study period for convenience stores (OR range in periods of increased risk, 1.15 to 1.44), taxis (OR range, 1.08 to 1.89), airplanes (OR range, 1.20 to 1.78), and nightclubs (OR range, 1.45 to 2.95).
"The contrast we found between short- and long-distance shared transport supports the importance of the duration spent onboard," the researchers wrote. "Long-distance bus travels were inconsistently at increased risk, which might result from better air renewal during the mandatory driving breaks compared to other shared transport."
A higher likelihood of infection was also observed during take-away delivery (OR range, 1.07 to 1.28), carpools with family members (OR range, 1.09 to 1.68), and concerts (OR range, 1.31 to 2.09).
Importance of air renewal, filtration
The researchers found no increased risk during short-distance shared transport or carpooling booked over platforms or in venues such as markets, supermarkets, malls, hairdressers, museums, movie theaters, outdoor sports events, or swimming pools.
All settings associated with an increased risk of infection in our study are characterized by varying degrees of common characteristics: mostly indoor settings with little air renewal, where contacts are close, numerous, often maskless, sometimes including singing or shouting, and usually last more than a mere few minutes.
"The absence of increased risk for retail facilities, as well as hairdressers and beauty salons, also reported by others, suggests that these facilities had low enough density and stringent enough measures to effectively limit transmission," the authors wrote.
After an initial period of increased risk (OR, 1.97), bars and restaurants were no longer tied to an increased risk of transmission after reopening in 2021, except in bar patrons younger than 40 years.
"All settings associated with an increased risk of infection in our study are characterized by varying degrees of common characteristics: mostly indoor settings with little air renewal, where contacts are close, numerous, often maskless, sometimes including singing or shouting, and usually last more than a mere few minutes," the researchers wrote.
In settings such as these, the researchers recommended improving air renewal or filtration to enhance air quality and lower COVID-19 transmission risk: "These investments are costly but have potential long-term benefits on population health and should be properly evaluated for their feasibility and effectiveness."
