Five of 17 infected cases with a recorded smoking status smoked while 18 of 50 uninfected cases did so.
Smoking was quantified (number of cigarettes and years smoked), and smoking status was classified into current or nonsmokers.
Our fully-adjusted model included participants' age, sex, educational status, occupational exposure to vapour, dusts and fumes, active smoking status, smoked pack-years, alcohol consumption, consumption of raw vegetables, citrus fruits and other fruits, PM10 exposure and body mass index.
Because age, sex, and smoking may be related to both lead exposure and ALS, all models included age at interview (as a log-transformed continuous variable), sex, and a dichotomous variable for ever having smoked; considering smoking status (never, former, current) at the time of the interview gave similar results.
When analyses were adjusted for pack-years smoked instead of smoking status, results did not change (data not shown).
If pregnancy occurred within the time a woman reported having smoked, we recorded smoking status as affirmative.
In this analysis, we reclassified participants in each 2-year follow-up cycle by smoking status, cigarettes smoked per day among current smokers, time since quitting among past smokers, and age at start of smoking among ever smokers.
Age-adjusted associations were attenuated after adjustment for age at starting to smoke regularly and smoking status but did not change appreciably after additional inclusion of the other covariates.
Population risk factors extracted were sex, smoking status (ever smoked against never smoked), and longitudinal records of age, BMI, total cholesterol, serum creatinine, diastolic blood pressure (DBP), HbA1c, HDL cholesterol (HDL-c), systolic blood pressure (SBP) and triglycerides.
In multivariable modelling, adjustments were made for age (40 50, 51 60, 61 70 and 71 79), sex, education level (<9, 10 12 and >12 years), tobacco-smoking status (ever smoked and never smoked), physical activity (<30 min at least once weekly and >30 min once weekly) and comorbidity (yes and no).
We categorized smoking status as never smoked, former smoker, and current smoker based on responses to the following two questions: "Have you smoked at least 100 cigarettes in your entire life?" and "Do you now smoke cigarettes every day, some days, or not at all?" A never smoker was an individual who answered no to the first question.
