Changing epidemiology of bacteremia in infants aged 1 week to 3 months.

Background: Bacteremia in young infants has remained an important ongoing concern for decades. Despite changes in prenatal screening and infant immunizations, the current epidemiology of this problem has received little attention.

Methods: We conducted a retrospective analysis of all blood cultures collected at Kaiser Permanente Northern California on full-term, previously healthy infants presenting for care between 1 week to 3 months of age for whom a blood culture was drawn from January 1, 2005, through December 31, 2009.

Results: During the study period, 4255 blood cultures were collected from 160 818 full-term infants. Only 2% of all blood cultures were positive for pathogens (93/4255), whereas 247 positive cultures were due to contaminants. The incidence rate of true bacteremia was 0.57 in 1000 full-term births. The most common pathogen was Escherichia coli (56%). Ninety-eight percent of infants with E coli bacteremia had a urinary tract infection. Group B Streptococcus and Staphylococcus aureus were the second and third most common pathogens, respectively. There were no cases of Listeria monocytogenes bacteremia or meningococcemia and only 1 case of enterococcal bacteremia. Ampicillin resistant pathogens accounted for 36% of organisms.

Conclusions: Our study indicates bacteremia in young infants occurs infrequently and in only 2.2% of those who had a blood culture drawn. On the basis of the epidemiology of pathogens found in this large cohort, these data suggest a change in currently recommended presumptive antibiotic coverage in 1-week to 3-month-old infants with suspected bacteremia.