- Antibiotic treatment, day-care center (DCC) attendance and young age are associated with penicillin-non-susceptible Streptococcus pneumoniae (PNSSp) carriage. Yet, it is unclear whether each is an independent risk factor for the individual. This cross-sectional surveillance study was designed to answer this question. Nasopharyngeal cultures were obtained from 429 children (< 6 y) during a visit to the pediatrician's office. Two risk rates were calculated: the individual's absolute risk to carry PNSSp [simple odds ratio (ORS)] and the risk of an individual who is already a carrier [conditional odds ratio (ORC)]. Streptococcus pneumoniae was isolated from 52.7% of 401 children. PNSSp was detected in 37.1% of carriers. Independent risk factors were: young age [ORS 2.24, 95% confidence interval (95% CI) 1.2-4.2], DCC attendance (ORS 3.8, 95% CI 1.9-7.5), having young siblings (ORS 2.3, 95% CI 0.95-5.57) and each antibiotic treatment during the previous 3 months (ORS 1.5, 95% CI 1.25-1.85). The only significant risk factor among carriers was prior antibiotic treatment (ORC 2.24, 95% CI 1.64-3.05). Young children, who attended DCC and received 1 antibiotic course (9% of the population) had a risk 12.9 times higher than children without these features.