Epidemiology of pharyngeal colonization of infants with aerobic gram-negative rod bacteria.

By using a selective medium, pharyngeal colonization with gram-negative rod (GNR) bacteria was determined in a cohort of 49 normal infants monitored from birth to 6 months of age. Culture swabs were diluted in 1 ml of saline for quantitation. The prevalence of GNR in the first 72 h of life was 8% and rose to 29% during the first month, 52% at 2.5 months, 67% at 4.5 months, and 62% at 6 to 7 months. Colonization was with substantial numbers of organisms, generally greater than 100 colonies per ml and frequently greater than 1,000 colonies per ml. The most common species were Klebsiella species, Escherichia coli, Enterobacter species, and Acinetobacter anitratus. Fewer infants who were breast fed rather than formula fed at the time of culture harbored GNR (26 versus 45%, P less than 0.05). The point prevalence of pharyngeal GNR colonization in our special care nursery was 12 of 47 (26%), which was found to be similar to that of age-matched normal infants. GNR carriage in normal infants does not appear to be a residual of organisms acquired at birth, and interpretations of GNR carriage in ill or hospitalized infants should be evaluated by comparison with these data in healthy infants.