Risk Factors for Invasive Pneumococcal Disease in Children: A Population-based Case–Control Study in North America

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Abstract
Objective. To identify risk factors for invasive pneumococcal disease, including penicillin-resistant infections, among children 2 to 59 months of age. Design. Case–control study. Participants. Patients with invasive pneumococcal infections identified by population-based surveillance ( n = 187) and controls identified through random-digit telephone dialing ( n = 280). Outcome measures. Invasive pneumococcal disease was defined as isolation of Streptococcus pneumoniae from a normally sterile site. Patients 2 to 59 months of age who were residents of one of four active surveillance areas were included. S pneumoniae isolates were tested by broth microdilution. Isolates with a minimum inhibitory concentration to penicillin ≥2 μg/mL were considered resistant. Results. Invasive pneumococcal disease was strongly associated with underlying disease and with day care attendance in the previous 3 months. Among 2- to 11-month-olds, current breastfeeding was associated with a decreased likelihood of invasive pneumococcal disease (odds ratio, 0.27; 95% confidence interval: 0.08, 0.90). Penicillin-resistant infections were independently associated with day care attendance, at least one course of antibiotics, and at least one ear infection in the previous 3 months. Conclusions. This study shows the association of underlying illnesses, day care attendance, and lack of breastfeeding with risk of invasive pneumococcal disease in children. The association of recent antibiotic use and infection with penicillin-resistant S pneumoniae highlights the need to avoid unnecessary antibiotic use in children.