Chronic bronchitis incidence in the extended cohort of Mayak workers first employed during 1948-1982

Objectives: This paper describes findings from the study of chronic bronchitis (CB) incidence after occupational exposure to ionising radiation among workers employed at Russian Mayak Production Association (PA) during 1948 and 1982 and followed up until 2008 based on 'Mayak Worker Dosimetry System 2008'. Methods Analyses were based on 2135 verified cases among 21 417 workers. Rate ratios (RR) were estimated by categorical analysis for non-radiation and radiation factors. Excess rate ratios per Gy (ERR/Gy) of external or internal exposures with adjustments via stratification on other factors were calculated. Results The interesting finding in relation to nonradiation factors was a sharp increase in the RR for CB incidence before 1960, which could be caused by a number of factors. Analyses restricted to the follow-up after 1960 revealed statistically significant associations of the CB incidence and external γ-ray radiation, ERR/Gy=0.14 (95% CI 0.02 to 0.28) having adjusted for sex, attained age, calendar period, plant, smoking status and lung α-particle dose, and internal α-particle radiation, ERR/Gy=1.14 (95% CI 0.41 to 2.18) having adjusted for sex, attained age, calendar period, plant, smoking status and lung γ-ray dose and ERR/Gy=1.19 (95% CI 0.32 to 2.53) having additionally adjusted for pre-employment occupational hazards and smoking index instead of smoking status. Conclusions Analyses of CB incidence in the study cohort identified positive significant association with occupational exposure to radiation: however, there are no similar studies of CB incidence in relation to radiation in other cohorts to date with which a meaningful comparison of the results could be made.