Logistic regression analyses revealed that septic appearance on admission (odds ratio [OR] 8.95, 95% confidence interval [CI] 1.5–54.1), acute otitis media (OR 4.5, 95% CI 2.1–9.4), a longer oxygen therapy (OR 1.40; 95% CI 1.13–1.74) and a higher C-reactive protein (CRP) (OR 1.7, 95% CI 1.5–2.0) were significantly associated with antibiotic use in both groups, but not age or pneumonia. The gene discussed is CRP; the disease is susceptibility to pneumonia measurement.