Meta‐Analysis of COVID‐19 Cluster Events Suggestive of Long‐Distance Airborne Transmission/Inhalation

ABSTRACT SARS‐CoV‐2 spreads through both contact and airborne routes, the latter encompassing airborne transmission/inhalation as well as the direct deposition of infectious respiratory particles. During the early phase of the COVID‐19 pandemic, numerous cluster events were suspected to involve long‐distance airborne transmission/inhalation. We conducted a comparative analysis of these cluster events to characterize outbreak settings and associated clinical parameters. Thirteen cluster events from 2020 attributed to the original SARS‐CoV‐2 strain were examined, including choral activities, indoor sports, and bus tours. Incubation periods and infection–hospitalization rates (IHRs) were compared across settings and against estimates from large‐scale cohort studies that predominantly reflect transmission via direct deposition. Statistical analyses were performed using the Mann–Whitney U test, Student's t ‐test, and Fisher's exact test ( p  < 0.05). The mean incubation period in suspected long‐distance airborne transmission/inhalation cases was 6.1 ± 3.9 days (median: 5 days; N = 176), with indoor sports and choral events showing significantly shorter incubation periods ( p  = 0.034). The average IHR was 6.7 ± 12.5%, with significantly higher rates in choral clusters ( p  = 0.013). Age‐adjusted IHRs were lower in long‐distance airborne transmission/inhalation‐related clusters than those reported from contact‐tracing datasets. This analysis provides an integrated evaluation of long‐distance airborne transmission/inhalation settings and their associated clinical characteristics. Activities involving vigorous respiration may contribute to shorter incubation periods and higher disease severity, potentially reflecting increased viral inoculum at exposure.