A case-crossover analysis of the impact of weather on primary cases of Middle East respiratory syndrome

Abstract

BackgroundMiddle East respiratory syndrome coronavirus (MERS-CoV) is endemic in dromedary camels in the Arabian Peninsula, and zoonotic transmission to people is a sporadic event. In the absence of epidemiological data on the reservoir species, patterns of zoonotic transmission have largely been approximated from primary human cases. This study aimed to identify meteorological factors that may increase the risk of primary MERS infections in humans.MethodsA case-crossover design was used to identify associations between primary MERS cases and preceding weather conditions within the 2-week incubation period in Saudi Arabia using univariable conditional logistic regression. Cases with symptom onset between January 2015 – December 2017 were obtained from a publicly available line list of human MERS cases maintained by the World Health Organization. The complete case dataset (N = 1191) was reduced to approximate the cases most likely to represent spillover transmission from camels (N = 446). Data from meteorological stations closest to the largest city in each province were used to calculate the daily mean, minimum, and maximum temperature (οC), relative humidity (%), wind speed (m/s), and visibility (m). Weather variables were categorized according to strata; temperature and humidity into tertiles, and visibility and wind speed into halves.ResultsLowest temperature (Odds Ratio = 1.27; 95% Confidence Interval = 1.04–1.56) and humidity (OR = 1.35; 95% CI = 1.10–1.65) were associated with increased cases 8–10 days later. High visibility was associated with an increased number of cases 7 days later (OR = 1.26; 95% CI = 1.01–1.57), while wind speed also showed statistically significant associations with cases 5–6 days later.ConclusionsResults suggest that primary MERS human cases in Saudi Arabia are more likely to occur when conditions are relatively cold and dry. This is similar to seasonal patterns that have been described for other respiratory diseases in temperate climates. It was hypothesized that low visibility would be positively associated with primary cases of MERS, however the opposite relationship was seen. This may reflect behavioural changes in different weather conditions. This analysis provides key initial evidence of an environmental component contributing to the development of primary MERS-CoV infections.

Climate factors and incidence of Middle East respiratory syndrome coronavirus

“…A one • C increase in monthly average temperature correlated with increasing the monthly incidence of MERS-CoV infection by 5.4%. This finding contradicts the Gardner et al study, where they reported low temperatures associated with high risk in primary MERS-CoV infections [9]. However, our report was in agreement with the Alghamdi et al study where they found that high temperatures enhance the spread of MERS-CoV in the population [11].…”

“…Gardner et al have recently reported an association between climate factors and the appearance of virus in primary MERS-CoV cases [9]. The findings of this study may represent primary MERS-CoV cases.…”

“…However, our study tends to report the correlation between climate variables (as quantitative) and the occurrence of all laboratory-confirmed MERS-CoV cases. The study also assesses the effects of five climate factors: temperature, rela- tive humidity, ultraviolet index, cloud, and wind speed, which have been reported to be mostly associated with viral activity in primary cases [9]. The monthly variations in MERS-CoV frequencies [10] should be further investigated by exploring the role of climate factors on the incidence of MERS-CoV infection.…”

A systematic review of MERS-CoV seroprevalence and RNA prevalence in dromedary camels: Implications for animal vaccination

“…As well as seasonal calving, environmental factors have also been hypothesised to be associated with zoonotic transmission (measured as the incidence of primary human cases). Lower temperatures and humidity were found to be associated with higher numbers of reported primary human MERS cases in KSA (Gardner et al, 2019). Further investigation of potential seasonality has been highlighted as a priority by the FAO-OIE-WHO MERS-CoV Technical Working Group (FAO-OIE-WHO MERS-CoV Technical Working Group, 2018).…”

MERS-CoV as an emerging respiratory illness: A review of prevention methods

“…Factors that facilitate community transmission include lack of knowledge on transmission mechanisms, poor general hygiene practices and exposure to camels. Primary MERS-CoV human cases are also more likely to occur when conditions are relatively cold and dry [79].…”