key: cord-0871753-sjw2ifmj
authors: Razani, Nooshin; Malekinejad, Mohsen; Rutherford, George W
title: Clarification regarding Outdoor Transmission of SARS-CoV-2 and Other Respiratory Viruses, a Systematic Review
date: 2021-06-04
journal: J Infect Dis
DOI: 10.1093/infdis/jiab298
sha: 0caa19886c12635a249864741159d561314f265d
doc_id: 871753
cord_uid: sjw2ifmj

nan

A c c e p t e d M a n u s c r i p t On April 24, 2021, the Centers for Disease Control and Prevention (CDC) issued new guidance on outdoor activities [1] . In subsequent testimony before the United States Senate, a number reported in our article, "Outdoor Transmission of SARS-CoV-2 and Other Respiratory Viruses: A Systematic Review," was cited that the proportion of SARS-CoV-2 transmission occurring in outside settings is less than 10% [2].

We are writing to clarify how we arrived at the less than ten percent summary number. Our abstract and results sections state that "five identified studies found a low proportion of reported global SARS-CoV-2 infections occurred outdoors (<10%)." Because of the small number of heterogeneous studies we reviewed, as well as their methodological limitations, we could not provide a meta-analytically pooled estimate of the exact proportion of SARS-CoV-2 transmissions that have occurred outdoors or the associated risk. Nishiura et al 2020 (odds of indoor transmission 18-times higher than outdoors, no raw data available) (6), and Szablewski 2020, which described an outbreak of SARS-CV-2 during a summer camp (7) . Given the paucity and limitations of identified data and timing of study (i.e., still early in pandemic), we reported 10% --the highest upper confidence interval in any M a n u s c r i p t of the studies we reviewed --to signify a small risk when compared to indoor settings, but not so negligible that it should be ignored pending further studies that could help clarify the risk more accurately.

As we discussed, our review has several limitations. The reports we found may have Given the growing body of evidence pertaining to the risk of outdoor transmission and policy implication of our findings, we are in the process of updating our systematic review.

Additional relevant studies found to date range in study design and quality but augment our findings that the risk of respiratory virus transmission outdoors is much lower than indoors (8, 9, 10).

Among these is a study that examined low secondary transmission rates of SARS-CoV-2 infection among contacts of construction laborers in India: 496 close contacts of 18 SARS-CoV-2 infected construction laborers were assessed for infection and exposure time, both A c c e p t e d M a n u s c r i p t outdoors and indoors, at work as well as at home. The study reports a low secondary attack rate (1.4%) among contacts of construction laborers at locations with free air flow compared to a 30-fold higher rate of transmission among households. Their primary data may help further delineate the incidence rate ratio of outdoor versus indoor infectionsa number which may be more useful than proportions in explaining the relative risk of infections outdoors by accounting for person-time of exposure (8).

These updates support our initial conclusion that the risk of SARS-CoV-2 transmission is much lower outdoors than indoors. The proportion of infections happening outdoors is likely much lower than 10%, and most of the studies that we have reviewed thus far suggest that it is likely less than 1%.

Work-related COVID-19 transmission in six Asian countries/areas: a follow-up study

Indoor transmission of SARS-CoV-2

Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19). medRxiv [Preprint

What settings have been linked to SARS-CoV-2 transmission clusters?

SARS-CoV-2 Transmission and Infection Among Attendees of an Overnight Camp -Georgia