Infection control response to an outbreak of OXA-23 carbapenemase-producing carbapenem-resistant Acinetobacter baumannii in a skilled nursing facility in Utah

Clinical impact of active screening cultures for carbapenem-resistant Acinetobacter baumannii: A systematic review and meta-analysis

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a significant health care-associated infection carrying substantial mortality. We assessed the clinical impact of active screening cultures for CRAB.

METHODS

A systematic review and meta-analysis, aiming to answer 2 questions: (1) Does screening versus no screening improve clinical outcomes? (2) Does positive screening ("CRAB carrier") predict CRAB infections? We searched the literature until January 2024 for comparative studies reporting clinical outcomes (mortality, invasive CRAB infections).

RESULTS

Of 5,407 screened publications, 9 studies (10,865 individuals) were included. Invasive CRAB infection rate was significantly higher among CRAB carriers (OR 11.14, 95% CI 4.95-25.05, with substantial heterogeneity stemming from size rather than direction of the effect). Negative predictive value of noncarriage for invasive infection was 97%. CRAB bloodstream infection rate was significantly higher among carriers (odds ratio 16.23, 95% confidence interval 2.9-110.08). No difference was demonstrated between the groups for CRAB ventilator-associated pneumonia, length of stay, and mortality. Only 1 study reported outcomes for study question #1.

CONCLUSIONS

Data to support active CRAB screening are scarce regarding its clinical benefit for patients. Positively screened patients are at significantly higher risk for invasive CRAB infections, with high negative predictive value for noncarriage. This did not translate to reduced mortality.

Pathogenesis of Gram-Negative Bacteremia

Gram-negative bacteremia is a devastating public health threat, with high mortality in vulnerable populations and significant costs to the global economy. Concerningly, rates of both Gram-negative bacteremia and antimicrobial resistance in the causative species are increasing. Gram-negative bacteremia develops in three phases. First, bacteria invade or colonize initial sites of infection. Second, bacteria overcome host barriers, such as immune responses, and disseminate from initial body sites to the bloodstream. Third, bacteria adapt to survive in the blood and blood-filtering organs. To develop new therapies, it is critical to define species-specific and multispecies fitness factors required for bacteremia in model systems that are relevant to human infection. A small subset of species is responsible for the majority of Gram-negative bacteremia cases, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii The few bacteremia fitness factors identified in these prominent Gram-negative species demonstrate shared and unique pathogenic mechanisms at each phase of bacteremia progression. Capsule production, adhesins, and metabolic flexibility are common mediators, whereas only some species utilize toxins. This review provides an overview of Gram-negative bacteremia, compares animal models for bacteremia, and discusses prevalent Gram-negative bacteremia species.