Peripheral immune profiles associated with an operational atopy-related phenotype in young infants with pertussis: a single-center retrospective study

Background Host immune responses to pertussis may vary among young infants, but the relevance of concurrently recorded atopy-related features is uncertain. Methods This single-center retrospective study included 120 infants aged 1–3 months with pertussis (75 PCR-confirmed and 45 clinically diagnosed with documented epidemiological contact) and 50 pertussis-PCR-negative pneumonia disease controls. A prespecified operational atopy-related phenotype (OAP) required total IgE >15 IU/mL plus eosinophilia, eczema, or parental allergic history. Primary pertussis-only models compared 45 OAP + with 75 OAP− infants after adjustment for chronological age, sex, PCR status, cough duration before sampling, and admission year; false-discovery-rate adjustment was applied within lymphocyte and cytokine outcome families. Results OAP + status was associated with a higher CD4 + percentage (adjusted mean difference 5.25 percentage points, 95% CI 2.92–7.57), lower CD8 + percentage (−2.36, −4.38 to −0.34), and higher CD4/CD8 ratio (0.44, 0.21–0.68). OAP + infants had lower IFN- γ (adjusted geometric mean ratio 0.72, 0.58–0.90), higher IL-6 (2.07, 1.65–2.59), lower IL-2 (0.70, 0.52–0.94), and a lower IFN- γ /IL-6 ratio (0.35, 0.25–0.48); all corresponding q values were <0.05. Core findings persisted under a stricter phenotype definition and in PCR-confirmed cases. In an exploratory negative-binomial model, OAP + status was associated with longer hospitalization (adjusted incidence rate ratio 1.33, 1.14–1.55), whereas the continuous cytokine ratio was not (0.98 per doubling, 0.92–1.03). Conclusion A locally defined atopy-related phenotype was associated with selected peripheral immune differences and longer hospital stay in young infants with pertussis. These hypothesis-generating associations do not establish an atopy diagnosis, a pertussis-specific mechanism, or prognostic utility.