Respiratory infections in coal miners exposed to nitrogen oxides

Coal miners working underground may be exposed chronically to low levels of nitric oxide and nitrogen dioxide from diesel engine emissions and from the use of explosives for blasting. The aims of this study were to establish whether long-term exposures to low concentrations of these gases at nine British coal mines had been associated with increased susceptibility to respiratory infections and, if so, to estimate the relative risks for different levels of exposure. The nine mines concerned had been involved, since 1954, in a prospective epidemiological study of coal miners' health. Median levels of nitrogen oxides in 4,933 pairs of full-shift samples, taken at the mines during the years 1976 through 1982 were 0.2 ppm nitric oxide and 0.03 ppm nitrogen dioxide; 10 percent of the concentrations exceeded 1.1 ppm nitric oxide and 0.08 ppm nitrogen dioxide. Multiple regression estimates of concentrations associated with different underground locations, types of work, and mining conditions at each mine were combined with detailed records of miners' attendance at work at similar locations in earlier years. These retrospective estimates of individuals' underground exposures to nitrogen oxides referred to between five- and 16-year periods of exposure. Also available for study were records of the men's exposures to respirable mine dusts and information from five-yearly medical surveys about their smoking habits, respiratory symptoms, and questionnaire-elicited reports of sickness absences attributed, among other things, to respiratory infections. The reliability of the latter reports was examined in a sample of 471 of the men by comparing the answers to the questionnaire with physicians' diagnoses on certified sickness absence records. Miners' references to bronchitis, influenza, or colds as the cause of prolonged sickness absence during the three years preceding the surveys did, in general, reflect real spells of absence from work, lasting at least seven days, that had been diagnosed by doctors as due to respiratory infections. But only about 20 percent of the men whose colliery records indicated that there had been such an absence acknowledged them in the survey as due to a "chest illness". Most of the under-reporting was of absence certified as due to influenza, colds, or "upper respiratory tract infection", and this under-reporting was not related to the men's ages or smoking habits. The main analyses referred to 5,408 reports of colds, influenza, or bronchitis at a total of 40,071 interviews involving nearly 20,000 miners.(ABSTRACT TRUNCATED AT 400 WORDS)