Low dosage and long treatment duration of beta-lactam: risk factors for carriage of penicillin-resistant Streptococcus pneumoniae.

The spread of drug-resistant Streptococcus pneumoniae in the community is a public health problem in developed and developing nations, but whether antibiotic use is responsible for the increase in drug resistance is not known. To analyze the relationship between penicillin-resistant S pneumoniae (PRSp) pharyngeal carriage and characteristics of beta-lactam use. Observational study of children attending 20 randomly sampled schools. The Loiret, in the center of France. A total of 941 children, 3 to 6 years old. Pharyngeal carriage of S pneumoniae, antibiotic use, and medical events during the preceding 30 days. Pneumococcal penicillin G sodium minimal inhibitory concentrations and serotyping were performed. Medical illnesses and the use of antibiotics were not associated with PRSp carriage. However, oral beta-lactam use was associated with an increased risk of PRSp carriage (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.1-8.3; P=.03). Children treated by low daily doses of an oral beta-lactam (defined as lower than clinical recommendations) had an increased risk of PRSp carriage, as compared with children who did not (OR, 5.9; 95% CI, 2.1-16.7; P=.002). A treatment of long duration (>5 days) with a beta-lactam was associated with an increased risk of PRSp carriage (OR, 3.5; 95% CI, 1.3-9.8; P=.02). Our results suggest that a low daily dose and a long duration of treatment with an oral beta-lactam contribute to the selective pressure in promoting pharyngeal carriage of PRSp.