Paper Information

Participants with influenza had greater risk of developing pneumonia in the 30 days following onset compared to those without influenza (matched odds ratio [mOR]: 2.7, 95% CI: 1.9, 3.9). Odds of developing pneumonia were highest for participants following A(H1N1)pdm09 illness (mOR: 3.7, 95% CI: 2.0, 6.9), followed by influenza B, and A(H3N2). Participants' odds of pneumonia following influenza were not constant, showing distinct peaks 0-6 days (mOR: 8.3, 95% CI: 4.8, 14.5) and 14-20 (mOR: 2.5, 95% CI: 1.1, 5.5) days post influenza infection.

We conducted a matched case-control study and a prospective cohort study among Nicaraguan children aged 0-14 years from 2011-2018. Physicians diagnosed pneumonia cases based on Integrated Management for Childhood Illness (IMCI) guidelines. Cases were matched with up to 4 controls on age (months) and study week. We fit conditional logistic regression models to assess the association between influenza subtype and subsequent pneumonia development, and a Bayesian non-linear survival model to estimate pneumonia hazard following influenza.

Influenza is a significant driver of both primary and secondary pneumonia among children. Distinct periods of elevated pneumonia risk in the 30 days following influenza supports multiple etiological pathways.

Pneumonia is a leading cause of mortality worldwide. Influenza may result in primary pneumonia or be associated with secondary bacterial pneumonia. While the association with secondary pneumonia has been established ecologically, individual-level evidence remains sparse and the risk period for pneumonia following influenza poorly defined.