Decline in temperature and humidity increases the occurrence of influenza in cold climate

Abstract

BackgroundBoth temperature and humidity may independently or jointly contribute to the risk of influenza infections. We examined the relations between the level and decrease of temperature, humidity and the risk of influenza A and B virus infections in a subarctic climate.MethodsWe conducted a case-crossover study among military conscripts (n = 892) seeking medical attention due to respiratory symptoms during their military training period and identified 66 influenza A and B cases by PCR or serology. Meteorological data such as measures of average and decline in ambient temperature and absolute humidity (AH) during the three preceding days of the onset (hazard period) and two reference periods, prior and after the onset were obtained.ResultsThe average temperature preceding the influenza onset was −6.8 ± 5.6°C and AH 3.1 ± 1.3 g/m3. A decrease in both temperature and AH during the hazard period increased the occurrence of influenza so that a 1°C decrease in temperature and 0.5 g decrease per m3 in AH increased the estimated risk by 11% [OR 1.11 (1.03 to 1.20)] and 58% [OR 1.58 (1.28 to 1.96)], respectively. The occurrence of influenza infections was positively associated with both the average temperature [OR 1.10 per 1°C (95% confidence interval 1.02 to 1.19)] and AH [OR 1.25 per g/m3 (1.05 to 1.49)] during the hazard period prior to onset.ConclusionOur results demonstrate that a decrease rather than low temperature and humidity per se during the preceding three days increase the risk of influenza episodes in a cold climate.

The effects of meteorological factors on influenza among children in Guangzhou, China

“…Our study indicated that influenza cases increased significantly with a low temperature below 20°C, which is consistent with many previous studies . For example, a study using a guinea pig model found the most efficient transmission of influenza virus was at 5°C and the most inefficient transmission at 30°C .…”

The short-term association between asthma hospitalisations, ambient temperature, other meteorological factors and air pollutants in Hong Kong: a time-series study

“…Together with low temperatures, low humidity, which can induce bronchoconstriction and dry the mucosal membrane along the airway, also increases the risk of asthma exacerbations. Cold and dry air decreases the humidity of the mucosal membrane and hence increases susceptibility to airway bacterial and viral infections and irritation by allergens and other irritants 41 42. Low temperatures and low levels of humidity also favour the survival of viruses like influenza and respiratory syncytial virus43 which will also increase the risk of infection-induced triggers.…”

Update of the scientific evidence for specifying lower limit relative humidity levels for comfort, health, and indoor environmental quality in occupied spaces (RP-1630)

“…The virus literature featured a combination of laboratory testing (Akers et al, 1966;Lowen et al, 2007;McDevitt et al, 2010;Noti et al, 2013;de la Noue et al, 2014), epidemiology (Shaman and Kohn, 2009;Shaman et al, 2010;Barreca and Shimshack, 2012;van Noort et al, 2012;Jaakkola et al, 2014), modeling (Shaman and Kohn, 2009;Yang and Marr, 2011), and review papers (Morawska, 2006;Brankston et al, 2007;Weber and Stilianakis, 2008;Tang, 2009;Memarzadeh, 2012;; test conditions are shown in Figure 4. The review paper by Weber and Stilianakis (2008) identified three methods of transmission: droplet (sneezing or coughing), airborne, and contact; the review paper by Brankston et al (2007) also discussed influenza survival and transmission.…”

“…Smedje et al, 1997a surveyed Swedish teenagers (13-14 years old) and took measurements in public school classrooms. Jaakkola et al, 2014 andMakinen et al, 2009 studied Finnish military conscripts, aged 17-29. No studies conducted in controlled, environmental chambers considered the effects of low RH on children or adolescents.…”