Respiratory effects of fire smoke exposure in firefighters and the general population

Abstract

The main aim of this thesis was to investigate associations between smoke exposure of accidental fires and the occurrence of respiratory effects in first responders and the general population. Respiratory effects among 138 subjects exposed to smoke in the aftermath of a chemical waste depot fire were explored. Subjects with persistent respiratory symptoms were suspected as having Reactive Airways Dysfunction Syndrome (RADS). Bronchial responsiveness was expressed as bronchial hyperresponsiveness (BHR) and as a dose-response slope (DRS). Suspected RADS cases were more frequently exposed than controls [OR=6.5 (2.4–18.0)]. Suspected cases had a higher DRS than controls. High exposure was associated with a higher DRS (p=0.06). These differences were significant when restricted to non-smokers (p=0.03) and males (p=0.02). A study among firefighters comprised 3 subsequent stages. First, firefighters filled in a questionnaire. Second, a randomly chosen subset underwent spirometry and methacholine provocation, and blood samples were taken to assess atopy and serum pneumoproteins. Third, subjects were re-examined after a week following exposure to fire smoke. Additional blood samples were taken 24 hours and 3 months post-exposure. Furthermore, sputum was induced within 5 days following exposure. In serum cytokines were assessed. First, in 1330 firefighters general respiratory symptoms were associated with the number of fires fought in the last 12 months with odds ratios between 1.2 (CI 95% 1.0-1.4) and 1.4 (CI 95% 1.2-1.7) per 25 fires. Adjustments for potential confounders did not change any of the associations. Atopics showed elevated odds ratios. Comparison with the Dutch general population (ELON) showed an elevated prevalence of firefighters who had ever had asthma [OR=1.5 (CI95% 1.1-2.0)]. Second, in 402 firefighters DRS was positively associated with the number of fires fought in the last 12 months (?=0.157, p=0.02) with and without adjustments for potential confounders. Among atopics this association was stronger (?=0.311, p=0.04) and PD20 was also associated [OR=4.9 (1.4, 16.6)], indicating that atopics are at higher risk of developing BHR as a result of smoke exposure. Clara cell protein (CC16) levels were negatively associated with the number of fires fought in the last 12 months in current non-smokers. Third, no changes were observed following smoke exposure in BHR and serum pneumoprotein levels. Nevertheless, in a sizable proportion of the firefighters (44%) elevated sputum neutrophil levels (?60%) were found. Serum IL-8 concentrations were higher 24 hours post-exposure compared to pre-exposure. Elevated neutrophil levels in sputum were associated with elevated serum IL-8 (?=0.010, p=0.004) levels within 24 hours post-exposure and IL-8 elevation lasted up to 3 months. To summarize, in firefighters and the general population positive associations were found between exposure to fire smoke and asthma-like outcomes. Although, irritant-induced asthma following exposure to very high concentrations of airway irritants are known, in this thesis it was found that multiple exposures to relatively low concentrations of fire smoke can invoke similar health effects. This suggests that the risk of health consequences of exposure to fire smoke is underestimated in public and occupational health. Therefore, it is recommended to reduce exposure airway irritants such as fire smoke.