Descriptive and molecular epidemiology of Gram-negative bacilli infections in the neonatal intensive care unit

The critically ill neonate is particularly prone to life threatening bacterial infections compared with other patient populations. Current patterns of neonatal sepsis caused by Gram-negative bacilli are reviewed to enable the clinician to better anticipate and effectively respond to neonatal infection by these serious pathogens.

With increasing use of intrapartum antibiotics for prophylaxis against early-onset group B streptococcal infection, there is growing concern that the incidence of neonatal sepsis by Gram-negative pathogens may rise. Although several surveys indicate no such increase to date, studies in selected neonatal intensive care unit populations have suggested a recent elevation in newborn infection caused by Escherichia coli and other bacillary pathogens. Most recent investigations reveal growing antibiotic resistance in those Gram-negative bacilli causing neonatal infection. Modern molecular genotyping methods have been applied to Gram-negative bacilli in the neonatal intensive care unit in order to understand their epidemiology in greater detail. In most instances these techniques have been used to identify the sources and prevalence of an outbreak strain, and to devise rational interventions to control the epidemic. Studies utilizing molecular genotyping during non-outbreak periods indicate that Gram-negative bacilli, even those expressing antibiotic resistance, may be acquired very early in the intensive care unit course, and that different clones are introduced and lost in the infants' indigenous flora throughout their stay. These studies further indicate that cross-transmission of bacillary pathogens occurs regularly even in the absence of a recognized epidemic.

Gram-negative bacilli are prominent causes of infection in the neonatal intensive care unit. Their incidence, antibiotic susceptibility pattern, and modes of acquisition continue to evolve in the modern intensive care unit setting.