Disentangling short-term and long-term asthma risk following early childhood lower respiratory tract infections

Ruzsa, Z. Imre and Csiszárik, Adrián and Forrai, Botond István and Árki, Kornél and Laki, Judit (2026) Disentangling short-term and long-term asthma risk following early childhood lower respiratory tract infections. SCIENTIFIC REPORTS, Submit. ISSN 2045-2322

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Abstract

Early childhood lower respiratory tract infections (LRTIs) are consistently associated with subsequent asthma, but the extent to which this association reflects short-term diagnostic effects, reverse causation, or longer-term asthma susceptibility remains unclear. We analysed nationwide Hungarian health insurance claims data of 473,847 children with at least 7 years follow-up. LRTIs and asthma were identified from ICD-10 codes and dispensed medications. Associations were assessed using contingency-table odds ratios (ORs), Kaplan-Meier curves, and a time-varying Cox hazard model. Unlike in many previous studies, exposure (infection) and outcome (asthma onset) windows were explicitly separated to reduce reverse-time overlap between asthma and LRTI occurrence. LRTI before age 3 was associated with increased asthma risk at ages 3–7 (OR 1.84, 95% CI 1.77–1.92), with a stronger relative effect in girls. Asthma risk after first LRTI up to age 5 years showed a marked temporal pattern, peaking shortly after LRTI and declining over time while remaining elevated. Recurrent LRTIs showed a dose-response relationship (two episodes HR 1.19 (1.14–1.24); four or more episodes HR 1.38 (1.29–1.47)). Early-life LRTIs were associated with subsequent asthma through a pronounced temporal risk pattern characterised by a marked short-term increase and a persistent longer-term component. Although diagnostic and surveillance effects likely contribute to the observed association, the persistence of elevated risk after temporal separation of exposure and outcome supports an association not fully explained by short-term diagnostic effects.

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