Analysis of two choir outbreaks acting in concert to characterize long- range transmission risks through SARS-CoV-2, Berlin, Germany, 2020

Abstract

Background Superspreading events are important drivers of the SARS-CoV-2 pandemic and long-range (LR) transmission is believed to play a major role. We investigated two choir outbreaks with different attack rates (AR) to analyze the contribution of LR transmission and highlight important measures for prevention. Methods We conducted two retrospective cohort studies and obtained demographic, clinical, laboratory and contact data, performed SARS-CoV-2 serology, whole genome sequencing (WGS), calculated LR transmission probabilities, measured particle emissions of selected choir members, and calculated particle air concentrations and inhalation doses. Results We included 65 (84%) and 42 (100%) members of choirs 1 and 2, respectively, of whom 58 (89%) and 10 (24%) became cases. WGS confirmed strain identity in both choirs. Both primary cases transmitted presymptomatically. Particle emission rate when singing was 7 times higher compared to talking. In choir 1, the median concentration of primary cases’ emitted particles in the room was estimated to be 8 times higher, exposure at least 30 minutes longer and room volume smaller than in choir 2, resulting in markedly different estimated probabilities for LR transmission (mode: 90% vs. 16%, 95% CI: 80–95% vs. 6–36%). According to a risk model, the first transmission in choir 1 occurred likely after 8 minutes of singing. Conclusions The attack rate of the two choirs differed significantly reflecting the differences in LR transmission risks. The pooled proportion of cases due to LR transmission was substantial (81%; 55/68 cases) and was facilitated by likely highly infectious primary cases, high particle emission rates, and indoor rehearsing for an extended time. Even in large rooms, singing of an infectious person may lead to secondary infections through LR exposure within minutes. In the context of indoor gatherings without mask-wearing and waning or insufficient immunity, these results highlight the ongoing importance of non-pharmaceutical interventions wherever aerosols can accumulate.

Infectivity of exhaled SARS-CoV-2 aerosols is sufficient to transmit covid-19 within minutes

“…Their calculated ID 50 (notated N 0 ) was in the range of 300–2000. Reichert et al measured particle emission rates from two index cases in choir superspreader events and calculated an ID 50 of 12 virions 26 , which is similar to what was found in the human challenge study. They also predicted that one person would have inhaled one infectious dose within 8 min.…”

“…Our study includes the first model calculations based on measured source emission rates of exhaled viruses. However, previous studies have modelled well-documented superspreading events and estimated emission rates based on the number of people that became infected, by assuming aerosols as the only route of transmission 26 , 27 . Prentiss et al analyzed six superspreading events with attack rates between 15 and 87% for which they assumed emission rates in the range 7.2 × 10 4 to 1.1 × 10 6 virions/h.…”

Field Epidemiology: Fit for the future

“…Field epidemiologists working in public health agencies and/or as members of government advisory bodies were usually not in a position to voice their personal opinion, even though they were well informed about what was needed to protect public health. Field epidemiology investigations were conducted in specific situations [26][27][28] but the rapid and multimodal spread of SARS-CoV-2, along with underlying risks such as inequality, poverty, ethnicity and age structure, meant that studying the main transmission settings and contexts was challenging and often not a priority. The increased day-to-day workload also meant that immediate publication of results in journals and as pre-prints was deprioritised.…”

Probable Evidence of Aerosol Transmission of SARS-COV-2 in a COVID-19 Outbreak of a High-Rise Building

“…2,3 Long-range aerosol transmission, which was overlooked in the early months of the pandemic, 4 has been recognized as an important route of transmission. [5][6][7][8] In many densely populated cities worldwide, high-rise buildings are a common form of residential accommodation. However, they pose a significant risk for COVID-19 transmission, potentially due to low mask-wearing rates in residences and workplaces, inadequate ventilation in bathrooms, and close proximity with family members or colleagues.…”