Abstract
Both temperature and humidity may independently or jointly contribute to the risk of human rhinovirus (HRV) infections, either through altered survival and spread of viruses in the environment or due to changes in host susceptibility. This study examined the relationship between short-term variations in temperature and humidity and the risk of HRV infections in a subarctic climate. We conducted a case-crossover study among conscripts (n = 892) seeking medical attention due to respiratory symptoms during their military training and identified 147 HRV cases by real-time PCR. An average temperature, a decline in daily ambient temperature and absolute humidity (AH) during the three preceding days of the onset (hazard period) and two reference periods (a week prior and after the onset) were obtained. The average daily temperature preceding HRV infections was −9.9 ± 4.9 °C and the average AH was 2.2 ± 0.9 g/m3. An average (odds ratios (OR) 1.07 (95% confidence interval (CI) 1.00–1.15)) and maximal (OR 1.08 (1.01–1.17)) change in temperature increased the risk of HRV infections by 8% per 1 °C decrease. An average (OR 1.20 (CI 1.03–1.40)) and maximal decrease (OR 1.13 (CI 0.96–1.34)) in AH increased the risk of HRV infection by 13% and 20% per 0.5 g/m3 decrease. A higher average temperature during the three preceding days was positively associated with HRV infections (OR 1.07 (CI 1.00–1.15)). A decrease rather than low temperature and humidity per se during the preceding few days increases the risk of HRV infections in a cold climate. The information is applicable to populations residing in cold climates for appropriate personal protection and prevention of adverse health effects.
Highlights
Human rhinovirus (HRV) infections have a dominant role as causative agents in upper respiratory tract infections (RTIs) [1,2]
Our results show that a decrease in temperature and absolute humidity (AH) is associated with the increased occurrence of HRV infections
The risk of HRV infections is reduced at subfreezing temperatures and higher AH
Summary
Human rhinovirus (HRV) infections have a dominant role as causative agents in upper respiratory tract infections (RTIs) [1,2]. RTIs are the most common infections worldwide, and pose a significant public health burden in terms of absenteeism at schools and at work, increased costs related to lower work productivity, and overload of health care services. Substantial evidence exists on the seasonal variation of respiratory morbidity and mortality with the increased use of health services and hospital admissions during the winter season [4,5,6]. Environmental factors, in particular ambient air temperature and humidity, may contribute to the observed seasonal variation of respiratory viruses and the resulting RTIs [6,7,8]. The reasons for the seasonal variation of HRV infections are not clear and their association with meteorological parameters, if any, has remained largely unknown. Experimental [7,9] and epidemiological [10,11]
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