BACKGROUND AND PURPOSE:

• Sehra et al. (Clinical Infectious Diseases, 2020) investigated the effects of temperature, precipitation, and UV Light on community transmission of SARS-CoV-2

METHODS:

• Observational analysis of case data
• Data analyzed (January 22 to April 3, 2020)
  • Daily reported cases of SARS-CoV-2 and daily weather patterns across the US
• Analysis
  • Null hypothesis: There is no association between daily temperatures and COVID-19 spread
  • Modeling techniques were used to investigate whether daily maximum temperature, precipitation, UV Index and the SARS-CoV-2 incidence 5 days later were related
  • Sensitivity analyses to assess transmission lags were performed at 3 days, 7 days and 9 days

RESULTS:

• 974 daily observations
• Max temperature of >52°F associated with a lower rate of new cases at 5 days
  • Incidence rate ratio (IRR) 0.85 (95% CI 0.76 to 0.96; p = 0.009)

Temperature

• Temperature <52°F was inversely associated with case rate at 5 days
  • IRR 0.98 (95% CI 0.97 to 0.99; p = 0.001)
• Modeling results: Rate of new cases was lower for theoretical states where daily temperature remained >52°F
  • At this temperature threshold, modeling predicted that there would be 23-fewer cases per-million per-day by 25 days of the epidemic

UV Index

• A 1-unit higher UV index associated with a lower rate at 5 days
  • IRR 0.97(95% CI 0.95 to 0.99; p = 0.004)

Precipitation

• Precipitation was not associated with a greater rate of cases at 5 days
  • IRR 0.98 (95% CI 0.89 to 1.08; p = 0.65)

CONCLUSION:

• COVID-19 incidence was lower at warmer vs cooler temperatures
  • Incidence declined with increasing temperature until 52°F
• The authors state that while statistically significant, the actual association is small and therefore

…unlikely to provide significant effect beyond current strategies for mitigation

…although there is an association between daily temperature and subsequent case volume the disease may continue to spread in the United States even in periods of warmer weather

Learn More – Primary Sources:

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

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