Extremely low birthweight (ELBW) infants are the highest risk group for neonatal nosocomial infections, but specific risk factors which can predict which ELBW infants will subsequently develop bacteremia have not been elucidated. We reviewed the clinical records of 62 infants with birthweight<1000 grams born in one calendar year at the University of Maryland, of whom 36 developed nosocomial bacteremia after the first week of life. The following potential risk factors were analyzed: birthweight, gestational age, gender, race, presence and duration of intravascular central line utilization, duration and type of antibiotic therapy prior to the onset of bacteremia, duration of ventilator therapy, maternal pre-treatment with steroids or antibiotics, presence and duration of PROM, use of intralipids, and low absolute neutrophil count prior to the bacteremic episode. Control ELBW infants without infection were matched to infants with bacteremia, and the above risk factors were catalogued for a period of time equal in days to the time prior to the onset of bacteremia in the cases.

Sixty percent of the bacteremias were caused by coagulase negative staphylococci; an additional 22% were the result of infection with E. faecalis. Mothers of infants with nosocomial bacteremia were significantly more likely to have received prenatal antibiotic therapy than mothers of control infants (71% vs 42%; p<.05). Lower gestational age, even in this sharply defined population, was another predictor of nosocomial bacteremia(26.3 ± 0.3 (S.E.) wks in bacteremic infants vs. 27.3 ± 0.4 wks in controls; p<.05). The need for umbilical venous and arterial catheters also significantly correlated with later bacteremia. No significant association was noted between nosocomial bacteremia and duration of prior antibiotic therapy (12.4 ± 2.0 days in cases; 11.5 ± 1.2 days for controls). There was no correlation between the other risk factors studied and nosocomial bacteremia.

We speculate that maternal pre-treatment with antibiotics may alter the microbial flora colonizing ELBW infants and may thus predispose these infants to the later development of nosocomial infection.