Respiratory infections and cold exposure in asthmatic and healthy military conscripts

Abstract The purpose was to study respiratory infections in a cold environment among young Finnish men. The seasonal variation in the occurrence of respiratory tract infections is well-known, but the impact of cold exposure is obscure. The burden of respiratory tract infections is especially apparent during military service, but the possible risk factors for infections are not. A total of 892 young military conscripts, 224 men with physician-diagnosed asthma, from the intake groups of July 2004 and January 2005 in Kainuu Brigade, were recruited for the study. In Kajaani area, the average daily temperature is above 10°C only from June to August and all conscripts serve during the cold season, too. The previous history of respiratory tract symptoms, infections, smoking habits and cold sensations were obtained with a questionnaire. Blood samples were taken for determination of the markers of inflammation and infection and peak expiratory flow, height and weight were measured. Data on respiratory tract infections requiring a physician consultation and results of a 12-min running test were collected. The temperature data was obtained from the nearest meteorological station located ca. 15 km from the garrison. At the beginning of the service, asthmatic men reported to have experienced more respiratory tract symptoms and were in poorer physical condition according to the 12-min running test compared to non-asthmatic men. However, 48% of men with asthma were without medication. After the 180–362 -day service, both men with and without asthma had enhanced their physical fitness as determined with the 12-min running test. At the same time, the levels of high sensitive C-reactive protein as a marker of low-grade inflammation, decreased. Infection episodes requiring physician consultation were more common among men with, rather than without, asthma. Chlamydia pneumoniae infections were mostly mild upper respiratory tract infections, common cold and sinusitis, and were as common in asthmatic as in non-asthmatic men. However, prolonged Chlamydia pneumoniae infections were more common among asthmatic men. Obesity and previous respiratory tract infections were independent risk factors for frequent infections among men with 180-day service. There was a typical seasonal variation in respiratory tract infections among conscripts: most infections occurred in the wintertime. The men with 180-day service had most infections during the first three months of the service, both in the July and January intake groups. Temperature was significantly associated with the occurrence of respiratory infection episodes. The most common temperature for the onset of an episode was in the outdoor temperature range of 0°C to –5°C. Respiratory tract infections were preceded by linearly decreasing outdoor temperature, the coldest day being the day before physician consultation