Determinants of acquisition and carriage of Staphylococcus aureus in infancy

Abstract

Nasal carriage of Staphylococcus aureus is a major risk factor for invasive S. aureus disease. The aim of this study was to define factors associated with carriage. We conducted a prospective, longitudinal community-based study of infants and their mothers for a period of 6 months following delivery. The epidemiology of carriage was examined for 100 infant-mother pairs. Infant carriage varied significantly with age, falling from 40 to 50% during the first 8 weeks to 21% by 6 months. Determinants of infant S. aureus carriage included maternal carriage, breastfeeding, and number of siblings. Bacterial typing of S. aureus was performed by pulsed-field gel electrophoresis and multilocus sequence typing. The majority of individuals carried a single strain of S. aureus over time, and the mother was the usual source for colonizing isolates in infants. The effect of other components of the normal nasal flora on the development of S. aureus carriage was examined in 157 consecutive infants. Negative associations (putative bacterial interference) between S. aureus and other species occurred early in infancy but were not sustained. An increasing antistaphylococcal effect observed over time was not attributable to bacterial interference. S. aureus carriage in infants is likely to be determined by a combination of host, environmental, and bacterial factors, but bacterial interference does not appear to be an ultimate determinant of carrier status.

FIG. 1.

Breastfeeding and nasal carriage of S. aureus by mothers and their infants over a period of 6 months following delivery. Data are shown as percentages (standard errors [SE]) of individuals carrying S. aureus at each time point sampled.

FIG. 2.

The number of swabs positive (of a possible total of 9 swabs taken) from 96 infants over a period of 6 months following delivery.

FIG. 3.

Graphical representation of S. aureus multilocus STs distributed between mother and infant isolate groups. Each ST is represented by a unique color so that the relative proportions in each group can be seen.

FIG. 4.

Graphical representation of the number of S. aureus STs carried over time by infants according to number of positive swabs over 6 months.

FIG. 5.

(A) Percentage of infants colonized with each species or genus at three time points; (B) antagonism between S. aureus and the other bacterial groups. Antagonism is represented by the OR for not being colonized with S. aureus if positive for a particular bacterial group, derived by multivariate logistic regression analysis. Error bars represent 95% CIs in all cases.