Association between meteorological factors and COVID-19 transmission in low- and middle-income countries: A time-stratified case-crossover study.

BACKGROUND: Evidence is limited regarding the association between meteorological factors and COVID-19 transmission in low- and middle-income countries (LMICs). OBJECTIVE: To investigate the independent and interactive effects of temperature, relative humidity (RH), and ultraviolet (UV) radiation on the spread of COVID-19 in LMICs. METHODS: We collected daily data on COVID-19 confirmed cases, meteorological factors and non-pharmaceutical interventions (NPIs) in 2143 city- and district-level sites from 6 LMICs during 2020. We applied a time-stratified case-crossover design with distributed lag nonlinear model to evaluate the independent and interactive effects of meteorological factors on COVID-19 transmission after controlling NPIs. We generated an overall estimate through pooling site-specific relative risks (RR) using a multivariate meta-regression model. RESULTS: There was a positive, non-linear, association between temperature and COVID-19 confirmed cases in all study sites, while RH and UV showed negative non-linear associations. RR of the 90th percentile temperature (28.1 °C) was 1.14 [95% confidence interval (CI): 1.02, 1.28] compared with the 50th percentile temperature (24.4 °C). RR of the10th percentile UV was 1.41 (95% CI: 1.29, 1.54). High temperature and high RH were associated with increased risks in temperate climate but decreased risks in tropical climate, while UV exhibited a consistent, negative association across climate zones. Temperature, RH, and UV interacted to affect COVID-19 transmission. Temperature and RH also showed higher risks in low NPIs sites. CONCLUSION: Temperature, RH, and UV appeared to independently and interactively affect the transmission of COVID-19 in LMICs but such associations varied with climate zones. Our results suggest that more attention should be paid to meteorological variation when the transmission of COVID-19 is still rampant in LMICs.

Independent and Interactive Effects of Environmental Conditions on Aerosolized Surrogate SARS-CoV-2 - Beijing, China, June to September 2020.

What is already known about this topic?: Environmental factors such as temperature and humidity play important roles in the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via droplets/aerosols. What is added by this report?: Higher relative humidity (61%-80%), longer spreading time (120 min), and greater dispersal distance (1 m) significantly reduced SARS-CoV-2 pseudovirus loads. There was an interaction effect between relative humidity and spreading time. What are the implications for public health practice?: The findings contribute to our understanding of the impact of environmental factors on the transmission of SARS-CoV-2 via airborne droplets/aerosols.

Wearing time and respiratory volume affect the filtration efficiency of masks against aerosols at different sizes.

Face masks are critical in preventing the spread of respiratory infections including coronavirus disease 2019 (COVID-19). Different types of masks have distinct filtration efficiencies (FEs) with differential costs and supplies. Here we reported the impact of breathing volume and wearing time on the inward and outward FEs of four different mask types (N95, surgical, single-use, and cloth masks) against various sizes of aerosols. Specifically, 1) Mask type was an important factor affecting the FEs. The FEs of N95 and surgical mask were better than those of single-use mask and cloth mask; 2) As particle size decreased, the FEs tended to reduce. The trend was significantly observed in FEs of aerosols with particle size < 1 µ m ; 3) After wearing N95 and surgical masks for 0, 2, 4, and 8 h, their FEs (%) maintained from 95.75 ± 0.09 to 100 ± 0 range. While a significant decrease in FEs were noticed for single-use masks worn for 8 h and cloth masks worn >2 h under deep breathing (30 L/min); 4) Both inward and outward FEs of N95 and surgical masks were similar, while the outward FEs of single-use and cloth masks were higher than their inward FEs; 5) The FEs under deep breathing was significantly lower than normal breathing with aerosol particle size <1 µ m. In conclusion, our results revealed that masks have a critical role in preventing the spread of aerosol particles by filtering inhalation, and FEs significantly decreased with the increasing of respiratory volume and wearing time. Deep breathing may cause increasing humidity and hence decrease FEs by increasing the airflow pressure. With the increase of wearing time, the adsorption capacity of the filter material tends to be saturated, which may reduce FEs. Findings may be used to provide information for policies regarding the proper use of masks for general public in current and future pandemics.