Maximum Daily Temperature, Precipitation, Ultra-Violet Light and Rates of Transmission of SARS-Cov-2 in the United States

Clin Infect Dis. 2020 May 30;ciaa681. doi: 10.1093/cid/ciaa681. Online ahead of print.

Abstract

Background: Previous reports have suggested that transmission of SARS-CoV-2 is reduced by higher temperatures and higher humidity. We analyzed case-data from the United States to investigate effects of temperature, precipitation, and UV Light on community transmission of SARS-CoV-2.

Methods: Daily reported cases of SARS-CoV-2 across the United States from 01/22/2020 to 04/03/2020 were analyzed. We used negative binomial regression modelling to investigate whether daily maximum temperature, precipitation, UV Index and the incidence 5 days later were related. We performed sensitivity analyses at 3 days, 7 days and 9 days to assess transmission lags.

Results: A maximum temperature greater than 52°F on a given day was associated with a lower rate of new cases at 5 days[IRR: 0.85(0.76,0.96)p=0.009]. Among observations with daily temperatures below 52°F, there was a significant inverse association between the maximum daily temperature and the rate of cases at 5 days [IRR 0.98(0.97,0.99)p=0.001]. The rate of new cases was predicted to be lower for theoretical states that maintained a stable maximum daily temperature above 52°F with a predicted 23-fewer cases per-million per-day by 25 days of the epidemic. A 1-unit higher UV index was associated with a lower rate at 5 days [IRR 0.97(0.95,0.99)p=0.004]. Precipitation was not associated with a greater rate of cases at 5 days [IRR 0.98(0.89,1.08)p=0.65].

Conclusion: The incidence of disease declines with increasing temperature up until 52°F and is lower at warmer versus cooler temperatures. However, the association between temperature and transmission is small and transmission is likely to remain high at warmer temperatures.

Keywords: SARS-CoV-2; Temperature; transmission rates.