A new study from four Chinese scientists currently awaiting peer review suggests that the coronavirus could be much more likely to spread indoors than outdoors. The proctors reviewed more than 1,000 COVID-19 cases in China, classified groups of cases into “clusters” and “outbreaks,” and summarized their findings as such:
Emphasis mine. As the researchers note, the fact that most coronavirus clusters and outbreaks occurred indoors is not particularly surprising given the Chinese government’s enactment of stay-at-home orders. But while the study “does not rule out outdoor transmission of the virus,” it notes that “among our 7,324 identified cases in China with sufficient descriptions, only one outdoor outbreak involving two cases occurred.”
One potential contributing factor to the virus’s potency indoors is the poor air quality that characterizes some urban buildings, which can facilitate the spread of COVID:
Many existing buildings are crowded, poorly ventilated, and unhygienic. A comprehensive review of ventilation conditions in Chinese indoor environments by Ye et al. showed that the CO2 concentration can reach 3,500 ppm in some buildings. The design and operation of buildings have also been under pressure to reduce energy use and increase human productivity.
This study, if true, could raise important questions about the wisdom of closing public parks in urban areas, particularly those urban areas in which large groups of people live in substandard buildings.