Impact of underweight on pneumonia mortality in children: results from a twelve years national database in Malawi and a systematic review of literature.

Objectives About 1.4 million children die every year from pneumonia, most of them in low and middle-income countries. On the other hand, underweight is highly prevalent in these countries: in 2011, 3.3% of children younger than five years were severely underweight and 17.4% moderately underweight. To explore the association between being underweight and pneumonia mortality, we analysed data on children admitted for pneumonia in a 12-years period in Malawi and we conducted a systematic review and meta-analysis of observational studies. Materials and Methods - Malawian database: we collected all the individual patients’ charts of children younger than five years admitted for pneumonia in 40 Malawian hospitals during the period 2001-2012. Data were inputted in a database and analysed with STATA 12. We calculated the crude Odds Ratio (OR) and 95% confidence interval (95%CI) for death from pneumonia in severe underweight (weight-for-age z-score < –3 standard deviations) and moderate underweight (–3 to –2 standard deviations). We performed a logistic multivariate analysis to calculate the Odds Ratio adjusted for sex and age. - Systematic Review: we searched Medline, Embase, Lilacs, Web of Science, and Global Health Library for published observational studies reporting on the association between underweight and pneumonia mortality in children younger than five years in low and middle-income countries. No date or language filters were applied. Data were meta-analysed using a random-effects model. Results -Malawian database: of the 100,936 cases (6,563 deaths) of pneumonia with complete data (89.0% of the total), 11.0% were severely underweight and 12.6% moderately underweight. Univariate analysis showed an increased odds of death in both severe underweight (OR 4.8; 95% CI 4.5-5.1) and moderate underweight (OR 2.2; CI 95% 2.1-2.4). After adjustment for age and sex the ORs increased to 5.3 (95% CI 5.0-5.7) and 2.5 (95% CI 2.3-2.7), respectively. -Systematic Review: we identified 26 studies from 11 countries, including 18,890 children. The pooled OR for death from pneumonia was 4.3 (95% CI 3.5-5.4) for severe underweight (17 studies) and 2.5 (95% CI 1.9, 3.3) for moderate underweight (16 studies). Substituting the adjusted ORs to the crude ORs in the meta-analysis did not change the results for moderate underweight but increased the pooled OR for severe underweight (OR 5.2; 95%CI 3.8-7.2). Key findings These two different types of data and analysis led to similar results, confirming that underweight remains a major risk factor for pneumonia mortality in children in low and middle-income countries.