What to expect, the first year: Infant bacterial colonization and resistance

Background: Newborns have sterile nasopharyngeal (NP) and GI tracts, yet young children are frequent antibiotic consumers and important reservoirs of antibiotic-resistant organisms. This creates an opportunity to study colonization and resistance from a microbiological tabula rasa. Objectives: To characterize longitudinal colonization with bacterial pathogens and associated antibiotic resistance from birth over the first 12 months of life, and their relationship with antibiotic and daycare exposure. Methods: In this ongoing study, 35 newborns enrolled, with interviews and NP, anterior nasal, and rectal swabs at 3-month intervals for 12 months, and cultured for S pneumoniae, S aureus, and extended spectrum beta lactamase (ESBL)-resistant gram negatives, respectively. Exposures are infant and household antibiotics and daycare. Outcomes are S pneumoniae and S aureus colonization and antibiotic resistance and ESBL. Results: We screened 35 infants' nursery and 19 3-month visits. 14/35 had perinatal or nursery antibiotic exposure. In the nursery, 0/35 infants were colonized with S pneumonia, 2 with S aureus (1 intermediate, 1 full erythromycin-resistance). By 3 months, 9/19 had antibiotic exposure, 11 personal or household exposure. 1 was colonized with S. pnemoniae (serotype 19A, penicillin, amoxicillin, azithromycin, clindamycin-resistant, intermediate cefotaxime-resistance) and 2 with S. aureus (erythromycin-resistant); both had household but not personal antibiotic exposure. The infant with S pneumoniae had perinatal antibiotic exposure and daycare. Those with S. aureus had perinatal antibiotics, not daycare. No ESBLs were identified. Conclusions: This pilot study quantifies antibiotic exposure and longitudinal resistance. Further follow-up and a larger sample could identify key areas for potential intervention to foster judicious antibiotic prescribing in infants.