Cigarette smoking and risk of infection-related mortality: A cohort study.

BACKGROUND Cigarette smoking is a leading cause of death worldwide and is associated with various diseases. However, studies addressing its impact on infection-related deaths are limited. This study examined the relationship between smoking and infection-related mortality. METHODS A cohort of 583,034 South Korean adults who underwent annual or biennial health examinations were followed-up for infection-related deaths using national records. Cox proportional hazards regression assessed hazard ratios (HRs) and 95% confidence intervals (CIs) for infection-related mortality. RESULTS The median follow-up was 9.1 years (maximum 18 years), and 335 infection-related deaths were identified. Current smoking, but not former smoking, was positively associated with an increased risk of infection-related mortality. After adjusting for possible confounders, the multivariable-adjusted HRs ( 95% CIs) for infection-related mortality comparing former and current smokers with never smokers were 0.94 (0.68-1.30) and 1.45 (1.05-2.02), respectively; and those for infection-related mortality by number of pack-years comparing 10-19.9 and ≥20 pack-years to <10 pack-years were 1.26 (0.81-1.96) and 1.47 (1.03-2.09), respectively, while those comparing 10-19 and ≥20 cigarettes/day to <10 cigarettes/day were 1.35 (0.86-2.11) and 1.54 (1.13-2.11), respectively (p for trend <0.05). Individuals with ≥20 pack-years had a 2.06 times greater risk of infection-related mortality when changes in smoking status and confounders during follow-up were updated in the analysis as time-varying covariates. CONCLUSION Current smoking status, intensity and pack-years were associated with an increased risk of infection-related death, with the highest risk of infection-related mortality found consistently in individuals with ≥20 pack-years. IMPLICATIONS In this large-scale cohort study of relatively young and middle-aged South Korean adults, current smoking, smoking intensity, and pack-years were associated with an increased risk of death due to infections; in particular, a significantly increased risk of infection-related mortality was consistently found in individuals with ≥20 pack-years. When appropriate, infection-related mortality should be included in smoking-attributable mortality burdens, and effective smoking control measures should be considered to improve infection-related mortality.