Enterococcal colonization of infants in a neonatal intensive care unit: associated predictors, risk factors and seasonal patterns

Abstract

Background: During and shortly after birth, newborn infants are colonized with enterococci. This study analyzes predictors for early enterococcal colonization of infants in a neonatal intensive care unit and describes risk factors associated with multidrugresistant enterococci colonization and its seasonal patterns.

Methods: Over a 12-month period, we performed a prospective epidemiological study in 274 infants admitted to a neonatal intensive care unit. On the first day of life, we compared infants with enterococcal isolates detected in meconium or body cultures to those without. We then tested the association of enterococcal colonization with peripartal predictors/risk factors by using bivariate and multivariate statistical methods.

Results: Twenty-three percent of the infants were colonized with enterococci. The three most common enterococcal species were E. faecium (48% of isolates), E. casseliflavus (25%) and E. faecalis (13%). Fifty-seven percent of the enterococci found were resistant to three of five antibiotic classes, but no vancomycin-resistant isolates were observed. During winter/spring months, the number of enterococci and multidrug-resistant enterococci were higher than in summer/fall months (p = 0.002 and p < 0.0001, respectively). With respect to enterococcal colonization on the first day of life, predictors were prematurity (p = 0.043) and low birth weight (p = 0.011). With respect to colonization with multidrug-resistant enterococci, risk factors were prematurity (p = 0.0006), low birth weight (p < 0.0001) and prepartal antibiotic treatment (p = 0.019). Using logistic regression, we determined that gestational age was the only parameter significantly correlated with multidrug-resistant enterococci colonization. No infection with enterococci or multidrugresistant enterococci in the infants was detected. The outcome of infants with and without enterococcal colonization was the same with respect to death, necrotizing enterocolitis, intracerebral hemorrhage and bronchopulmonary dysplasia.

Conclusion: In neonatal intensive care units, an infant's susceptibility to early colonization with enterococci in general, and his or her risk for colonization with multidrug-resistant enterococci in particular, is increased in preterm newborns, especially during the winter/spring months. The prepartal use of antibiotics with no known activity against enterococci appears to increase the risk for colonization with multidrug-resistant enterococci.

Figure 1

Distribution of different enterococcal species detected in meconium or surveillance cultures of infants (white bars). The black bars represent the number of multidrug-resistant enterococci for each enterococcus species.

Figure 2

Distribution of isolates of enterococci and multidrug-resistant enterococci (in % of samples taken per month) in meconium and surveillance cultures from colonized infants stratified by month of the year. There is a statistically significant association for a higher colonization rate with enterococci (p = 0.002, Chi-square test) and multidrug-resistant enterococci (p < 0.0001, Chi-square test) during the winter/spring months as compared to summer/fall months.

Figure 3

Comparison of gestational age of infants either colonized or not colonized with (A) enterococci and (B) multidrug-resistant enterococci in meconium or surveillance cultures. Boxes extend from the 25th to the 75th percentile, with a line at the median (50th percentile) and whiskers show the highest and the lowest gestational ages. The p values refer to the comparison of the median values using the Mann Whitney test.

Figure 4

Comparison of birth weights of infants either colonized or not colonized with (A) enterococci and (B) multidrug-resistant enterococci in meconium or surveillance cultures. Boxes extend from the 25th to the 75th percentile, with a line at the median (50th percentile) and whiskers show the highest and the lowest birth weights. The p values refer to the comparison of the median values using the Mann Whitney test.