Urinary Cotinine Levels as a Biomarker of Secondhand Smoke Exposure Among Children in Maiduguri, Borno State

Secondhand tobacco smoke exposure poses a serious physiological hazard, particularly for children whose respiratory and neurological systems are still developing. This study assessed urinary cotinine levels as a biomarker of passive smoke exposure among children aged 5 to 12 years in Maiduguri, Borno State, North East Nigeria. A cross-sectional design was employed, recruiting 100 children from households with at least one adult smoker and 50 children from non-smoking households as controls. Spot urine samples were collected and analysed for cotinine concentration using enzyme-linked immunosorbent assay. Household information including number of smokers, daily cigarette consumption, and indoor smoking behaviour was documented through parental interviews. Mann-Whitney U test was used to compare groups. Results showed that children from smoking households had significantly elevated urinary cotinine levels compared to controls, confirming active passive exposure. Higher cotinine was associated with more smokers per household and indoor smoking. Children with raised cotinine levels also reported higher frequencies of cough and wheeze. The study concludes that children in Maiduguri are exposed to significant levels of secondhand smoke, warranting urgent public health intervention. Smoke-free household policies, community sensitisation, and targeted smoking cessation support for parents are recommended. Keywords: cotinine, secondhand smoke, passive exposure, children, Borno State.