Invasive Bacterial Infections in Infants: Changing Etiologies and Resistance

William T. Basco, Jr., MD, MS


January 07, 2019

What Is Causing Invasive Bacterial Infections in Infants?

The etiology of invasive bacterial infections in infants has changed over the past few decades, partly as a result of prenatal screening for group B Streptococcus infection. To describe the present-day etiologies of invasive bacterial infections and changing antibiotic sensitivity patterns, the researchers examined data from a recent cohort of young infants.

The study examined information collected from infants ≤ 60 days old who were seen in the emergency department (ED) at 11 children's hospitals from 2011 to 2016. By searching the electronic laboratory data at the participating hospitals, the authors identified blood cultures or cerebrospinal fluid (CSF) cultures that were positive at the time of the collection in the ED. When a pathogen was identified, the authors completed a medical record review to gather further information and make sure the child was appropriate to include in the analysis. They eliminated isolates that were felt to be contaminants by the respective treating team. The authors extracted demographic variables, past medical history, as well as clinical variables such as temperature, clinical appearance, examination findings, and laboratory and culture findings from the health records. The analysis ultimately included 442 infants with at least one bacterial infection.

Approximately 2.5% of the febrile infants included in this study had either bacteremia (2.0%) or bacterial meningitis (0.7%). The majority of that group, 79.9%, had bacteremia and no meningitis. An additional 14.5% had both bacterial meningitis and bacteremia. A much smaller percentage, 5.7%, of the infants had bacterial meningitis only.

The researchers also reported on differences between the group of infants < 28 days of life and those 29-60 days of life. The infants who were found to have a bacterial infection were approximately evenly divided between the two age groups, with 52.9% of all infections occurring in infants ≤ 28 days. Similarly, bacteremia without meningitis was almost equally distributed between the two age groups.

However, fully two thirds of the meningitis cases without bacteremia occurred in the younger infants. The greatest number of those cases occurred during the second week of life; the overwhelming majority of these infants (82.4%) were febrile at the time of presentation to the ED. Approximately one third of the infants were ill-appearing on exam, with 7.9% having a clinically apparent infection on examination.

Among the babies with bacteremia or meningitis, just under a third (29.4%) also had a positive urinary tract infection. Group B Streptococcus was the most prevalent organism, present in approximately a third (36.7%) of the infants with invasive bacterial infection. Escherichia coli was a close second, present in just under a third of cases (30.7%).

Group B Streptococcus was the predominant causative organism in the infants with bacterial meningitis, found in 50.8% of infants ≤ 28 days and 60% of infants 29-60 days.

Among all infants, resistance to ampicillin occurred in approximately 29% of isolates. Virtually all (96%) of infants with bacteremia without meningitis had pathogens susceptible to a combination of ampicillin plus either gentamicin or a third-generation cephalosporin. However, across sites, the median proportion of infants with a pathogen resistant to a third-generation cephalosporin alone was 13.3%. The most frequent resistant isolates were Enterococcus species.

The authors concluded that for most infants ≤ 60 days old, a combination treatment of ampicillin plus gentamicin or a third-generation cephalosporin would provide sufficient coverage, but treatment with cephalosporins alone would be insufficient for as many as 1 in 10 infants.


It is always helpful to know what is out there to better inform our clinical decisions. Probably the most important take-home point of this study is the fact that, potentially, 11% of the infants would not have been well served by treating empirically with only a third-generation cephalosporin. If practitioners can remember only one thing from this study, that is probably the most important thing. The individual contributions of each bacterial type are both harder to remember and less helpful in everyday clinical practice.

The other important take-home point is that while knowing what you're treating is always a great idea, adjusting medications as needed once isolates and their sensitivities are finalized may be even more important. Given high contributions of E coli and Enterococcus species and their associated greater resistance frequencies, this is more important than ever in this current era of increasing antimicrobial resistance. Good antimicrobial stewardship is always a good idea, and that is true for even the youngest infants.

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