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Introduction: The association between ambient air pollution and length of hospital stay (LOS) for children with lower-respiratory infection is unclear., Materials and Methods: The association was examined using admission data for 75,432 children in Hanoi, aged 0-5 years, hospitalized with acute lower-respiratory infection (ALRI) and daily air pollutant levels in Hanoi between 2007 and 2016. We estimated the odds ratio of being discharged for an interquartile range (IQR) increment (IQR) of ambient pollutants during one to four days prior to admission date. We used pooled logistic regression models including a B-spline function of calendar time and terms describing the baseline odds, adjusting for meteorological factors, age, gender, residential location, week-day of admission, discharge on weekends or holidays, and number of respiratory hospitalizations one day prior to the discharge date., Results: An IQR increase in O 3 concentrations (85.8 μg/m 3 ) was associated with a 5% (95%CI: 2%-8%) decrease in the odds of discharge from hospital among children with ALRI. Results were similar for PM 10 , but only for children aged 2-5 years. For the other pollutants, corresponding associations were close to null or in the opposite direction. For example, increase in CO was associated with shorter LOS., Conclusions: Our study provides the first investigation of the associations between lengths of hospital stays and air pollutant levels prior to hospitalization in Asian children. Increased levels of O 3 prior to admission predicted prolonged hospitalizations. The inconsistencies in the findings for other pollutants call for further investigations., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Ambient air pollution has been associated with respiratory diseases in children. However, its effects on pediatric pneumonia have not been meta-analyzed. We conducted a systematic review and meta-analysis of the short-term association between ambient air pollution and hospitalization of children due to pneumonia. We searched the Web of Science and PubMed for indexed publications up to January 2017. Pollutant-specific excess risk percentage (ER%) and confidence intervals (CI) were estimated using random effect models for particulate matter (PM) with diameter ≤ 10 (PM 10 ) and ≤2.5 μm (PM 2.5 ), sulfur dioxide (SO 2 ), ozone (O 3 ), nitrogen dioxide (NO 2 ), and carbon monoxide (CO). Results were further stratified by subgroups (children under five, emergency visits versus hospital admissions, income level of study location, and exposure period). Seventeen studies were included in the meta-analysis. The ER% per 10 μg/m 3 increase of pollutants was 1.5% (95% CI: 0.6%-2.4%) for PM 10 and 1.8% (95% CI: 0.5%-3.1%) for PM 2.5 . The corresponding values per 10 ppb increment of gaseous pollutants were 2.9% (95% CI: 0.4%-5.3%) for SO 2 , 1.7% (95% CI: 0.5%-2.8%) for O 3 , and 1.4% (95% CI: 0.4%-2.4%) for NO 2 . ER% per 1000 ppb increment of CO was 0.9% (95% CI: 0.0%-1.9%). Associations were not substantially different between subgroups. This meta-analysis shows a positive association between daily levels of ambient air pollution markers and hospitalization of children due to pneumonia. However, lack of studies from low-and middle-income countries limits the quantitative generalizability given that susceptibilities to the adverse effects of air pollution may be different in those populations. The meta-regression in our analysis further demonstrated a strong effect of country income level on heterogeneity., (Copyright © 2017 Elsevier Ltd. All rights reserved.)