BACKGROUND: Secondhand smoke (SHS) exposure is a major public health concern, particularly in LMICs like Pakistan and Bangladesh. This study aimed to address critical gaps in understanding SHS exposure among school-going children in Dhaka and Karachi by combining self-reported data with salivary cotinine measurements, a reliable biomarker of nicotine intake.
METHODS: We analyzed baseline data from the Children Learning About Secondhand Smoke (CLASS-III), a cluster randomized controlled trial conducted in public and private schools. A total of 2,769 grade 5 students, aged 9–12, were enrolled as self-reported non-tobacco users, with assent and parental consent obtained on an opt-out basis. Baseline data included salivary cotinine levels, sociodemographic characteristics, and self-reported SHS exposure within and outside home. Children with cotinine levels ≤12.0 ng/mL were included. Descriptive analyses summarized cotinine levels by country and SHS exposure settings using appropriate statistical measures.
RESULTS: Among the 2,716 children analyzed (1,368 from Bangladesh and 1,348 from Pakistan), the mean age was 11.3 ± 1.0 years, with 54.9% being girls. The median cotinine level was 0.40 ng/mL (IQR: 0.49), higher in Pakistan (0.57 ng/mL, IQR: 0.56) than Bangladesh (0.27 ng/mL, IQR: 0.33). Boys had higher levels (0.47 ng/mL, IQR: 0.55) than girls (0.36 ng/mL, IQR: 0.44). SHS exposure in both venues (home and outside) led to higher cotinine levels (0.64 ng/mL, IQR: 0.70) than exposure at home (0.61 ng/mL, IQR: 0.64) or outside (0.36 ng/mL, IQR: 0.45) alone. Exposure from smokers at home resulted in higher levels (0.68 ng/mL, IQR: 0.70) compared to guest smoking (0.62 ng/mL, IQR: 0.67). Outside exposure was highest near communities (0.44 ng/mL, IQR: 0.57) and during transportation (0.43 ng/mL, IQR: 0.51).
CONCLUSIONS: The findings underscore the urgent need for targeted interventions, including strict enforcement of smoke-free laws in public places and public awareness campaigns to educate people promoting smoke-free homes to reduce SHS exposure among children.