Cigarette smoking as a risk factor for influenza-associated mortality: evidence from an elderly cohort.
BACKGROUND
The effects of individual lifestyle factors on the mortality risk after influenza infection have not been explored.


OBJECTIVE
In this study, we assessed the modifying effects of cigarette smoking on mortality risks associated with influenza in a cohort of Hong Kong elders with a follow-up period of 1998-2009.


METHODS
We used the Cox proportional hazards model with time-dependent covariates of weekly proportions of specimens positive for influenza (termed as influenza virus activity), to calculate the hazard ratio of mortality associated with a 10% increase in influenza virus activity for never, ex- and current smokers. Other individual lifestyle and socioeconomic factors as well as seasonal confounders were also added into the models.


RESULTS
The overall hazard ratio associated with influenza was 1·028 (95% confidence interval, 1·006, 1·051) for all natural cause mortality and 1·035 (1·003, 1·068) for cardiovascular and respiratory mortality. We found that influenza-associated hazard ratio was greater in current and ex-smokers than in never smokers for mortality of all natural causes, cardiovascular and respiratory diseases.


CONCLUSIONS
The findings suggest that smoking might increase influenza-associated mortality risks among elders.
School of Public Health, The University of Hong Kong, Hong Kong, China.
Chit M
CM
Wong
Lin
L
Yang
King P
KP
Chan
Wai M
WM
Chan
Liang
L
Song
Hak K
HK
Lai
Thuan Q
TQ
Thach
Lai M
LM
Ho
Kwok H
KH
Chan
Tai H
TH
Lam
Joseph S M
JS
Peiris
D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006723:Hong Kong; D006801:Humans; D007251:Influenza, Human / Q000401:mortality*; D008297:Male; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D016019:Survival Analysis