Nonmalignant Respiratory Disease Mortality in Styrene-Exposed Workers

Abstract

To the Editor: Collins and colleagues1 focus on cancer risk in their study of more than 15,000 workers at 30 US reinforced-plastic facilities. Yet their demonstration of excess mortality from nonmalignant respiratory disease warrants further discussion. For this cohort of styrene workers, the standardized mortality ratio (SMR) for “bronchitis, emphysema, and asthma” was elevated at 1.35 (95% confidence interval [CI] = 1.17–1.56). The authors attribute this excess of deaths to smoking. Certainly, smoking is a recognized contributor to obstructive lung diseases. Furthermore, the observed inverse relationship with employment duration may appear to be inconsistent with an occupational cause of disease. However, previous studies have demonstrated excess mortality from nonmalignant respiratory disease in short-term styrene workers. An earlier examination of this same cohort found excess mortality (SMR = 1.40 [95% CI = 1.04–1.84]) from “other nonmalignant respiratory diseases,” with the highest risk (SMR 1.79) in those with less than 1 year of styrene exposure.2 Similarly, among US fiberglass boat builders employed between 1959 to 1978 and followed to 1998, those with high styrene exposures had elevated mortality (SMR = 2.54 [95% CI = 1.31–4.44]) from “pneumoconioses and other respiratory diseases”; the excess mortality was associated with short (<1 year) employment duration.3 How could occupational styrene exposure be responsible for an excess of mortality from obstructive lung disease among mostly short-term workers? A recent report of obliterative bronchiolitis in styrene-exposed workers is informative.4 Obliterative bronchiolitis is a disabling lung disease that follows, with short latency, certain inhalational exposures. Obliterative bronchiolitis is likely under-recognized and confused with other obstructive lung diseases. Hence the excess mortality due to “bronchitis, emphysema, and asthma” described by Collins et al may represent not a consequence of smoking but a burden of misdiagnosed obliterative bronchiolitis in workers who were disabled by styrene exposure early in their tenure and thus left employment. The authors note a lack of trend between cumulative or peak styrene exposures and nonmalignant respiratory disease. Analytic approaches designed for cancer mortality may be poorly suited, however, to mortality from disease with short latency from exposure to disability. In a study of European reinforced-plastics workers, associations between short duration of exposure and nonmalignant respiratory mortality may have been obscured by an assumption that longer exposures pose greater risk.5 In future studies of styrene-exposed workers, consideration of obliterative bronchiolitis and its mechanism, so distinct from carcinogenesis, is warranted. Kristin J. Cummings Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV, [email protected] Anna-Binney McCague Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV Kathleen Kreiss Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV