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Background There is some evidence that dampness, mould and cockroaches can increase the risk of respiratory infections in children but few studies exist from China on this topic. Aim To study associations between domestic early life exposure to biological indoor factors (dampness, mould, cats, dogs, rats, cockroaches), cleaning habits and common cold among pre-school children across China. Methods Children aged 3–6 years (n = 39,782) were recruited from randomly selected day care centres in seven cities in China. Data on common cold and prenatal and postnatal exposure to dampness, mould, windowpane condensation in wintertime (WPC), cats, dogs, cockroaches and rats were assessed by a parentally administered questionnaire. Data on annual ambient temperature and PM 10 was assessed on city level. Associations between high frequency (> 5 colds per year) and long duration (≥ 2 weeks) of common colds in the past year and exposure were calculated by multilevel logistic regression. Results A total of 9.2% had a high frequency and 11.9% had long duration of common cold. Exposure to mould (OR = 1.38, 95% CI 1.24–1.53) and WPC (OR 1.23, 95%CI 1.13–1.33) at birth was associated with frequent common cold. Exposure to dogs at birth was associated with long duration of common cold. (OR = 1.22, 95% CI 1.06–1.41). Exposure to mould (OR = 1.36, 95% CI 1.22–1.54), WPC (OR = 1.27, 95%CI 1.17–1.39) and water leakage (OR 1.34, 95% CI 1.20–1.49) in the current home was associated with frequent common cold. Presence of cockroaches were positively (OR = 1.12, 95% CI 1.02–1.24) and presence of rats (OR = 0.86, 95% CI 0.77–0.96) negatively associated with high frequency of common cold. Daily cleaning was negatively associated with frequent common cold (OR = 0.89, 95% CI 0.81–0.97). Similar associations for mould, WPC, cockroaches and rats were found for long duration. Ambient PM 10 (OR = 1.21, 95% CI 1.21–1.35 per 10 μg/m 3 ) and temperature (OR = 1.13, 95% CI 1.06–1.35 °C) on city level were associated with high frequency of common cold. Associations between cat keeping and high frequency of common cold were found only in southern China. Associations with cockroaches were stronger in northern China. Associations with dampness and mould were the same in the north and south. Conclusions Indoor mould, water damage, windowpane condensation, cockroaches and keeping cats or dogs as pets can be risk factors for common cold while daily cleaning can be protective factor. PM 10 and a warmer climate zone can be other risk factors for common cold. [ABSTRACT FROM AUTHOR]

We studied indoor sources of indoor particulate matter (PM), outdoor air pollution and antibiotic use in relation to asthma, rhinitis and eczema among pre-school children and investigated synergistic effects between PM and antibiotics use. Children (3-6y) from randomly selected day care centres in seven cities across China were included (n = 39,782). Data on ambient temperature and air pollution were collected from local monitoring stations. Data on indoor PM sources (ETS, burning of incense or mosquito coils and biomass for cooking), antibiotics use and health (doctor diagnosed asthma and rhinitis, lifetime eczema, current wheeze and current rhinitis) were assessed by a parental questionnaire. Associations were calculated by multilevel logistic regression. Asthma diagnosis was associated with outdoor temperature, NO 2 and burning mosquito coils. Rhinitis diagnosis was associated with NO 2 , ETS, gas cooking and burning biomass for cooking. Lifetime eczema was associated with temperature, PM 10, NO 2 , ETS, biomass cooking and burning mosquito coils. Burning incense was associated with current wheeze and current rhinitis. Children using antibiotics had more asthma, wheeze, rhinitis, and eczema. Excluding children with respiratory infections did not change associations with antibiotics use. Antibiotics use enhanced the effects of ETS and PM 10 (a synergistic effect). In conclusion, a warmer climate, outdoor NO 2 and PM 10, ETS, gas cooking and burning biomass, incense and mosquito coils can increase the risk of asthma, wheeze, rhinitis and eczema among pre-school children in China. Antibiotics use is a risk factor for childhood asthma, wheeze, rhinitis and eczema and ETS and outdoor PM 10 can enhance the effect., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)