Acinetobacter Species

Health Care–Associated Infections

Health care–associated infections represent the most substantial public health impact of Acinetobacter, given the rapid spread of strains resistant to all first-line antimicrobials. The application of molecular typing methods has revealed that a limited number of widespread clonal lineages of A. baumannii are responsible for hospital outbreaks worldwide. Although increasing globally, the prevalence of carbapenem-resistant A. baumannii is decreasing over time in developed countries, suggesting that patients presenting for care after travel from areas with higher endemic rates should be considered for screening. A. baumannii causes the bulk of health care–associated infections due to Acinetobacter, but a variety of species, including A. pittii, A. nosocomialis, A. lwoffii, and Acinetobacter ursingii, are emerging as nosocomial pathogens, especially in immunocompromised hosts. Ventilator-associated pneumonia is the most frequent health care–associated A. baumannii infection, implicated in 3% to 7% of cases. Among patients requiring mechanical ventilation for more than 5 days, the frequency of Acinetobacter increases dramatically, accounting for 26% of respiratory infections in one series. Other nosocomial manifestations of Acinetobacter include bloodstream infections associated with intravascular catheters, surgical site infections, urinary tract infections, meningitis after neurosurgery, and soft tissue infections after burns.

The factors that promote the emergence and transmission of A. baumannii in health care settings include hospitalization of patients at high risk for colonization, such as long-term care residents; breaches in environmental cleaning and disinfection; and antibiotic utilization, especially third-generation cephalosporins, fluoroquinolones, or carbapenems. The ability of Acinetobacter species to survive for weeks on surfaces within the hospital environment leads to prolonged outbreaks, and patient movement between health care facilities without the intervention of adequate communication results in regional spread. Essentially any surface within a patient care area can become contaminated with Acinetobacter and serve as a reservoir for ongoing transmission; these include sinks, faucets, humidifiers, hydrotherapy pools, curtains, pillows, and bedrails, as well as equipment such as supply carts, infusion pumps, and equipment control touch pads. Patients with either recent or remote history of infection can remain colonized and able to contaminate their surrounding environment.

Transmission of Acinetobacter within the health care setting occurs after lapses in proper hand hygiene, and failure to disinfect mobile medical equipment and surfaces within patient care areas. Units with multiple-bedded rooms and susceptible patients, such as neonatal intensive care units (ICUs), are at high risk for outbreaks. Procedures that result in a spray of contaminated fluids, such as pulsatile lavage of wounds or bronchoscopy, may also lead to heavy environmental contamination and transmission. In addition to contaminated surfaces, airborne particles are believed to play a role in transmission of Acinetobacter, either by spread through open units with multiple beds or through contamination of internal air filters of medical equipment. An increase in health care–associated Acinetobacter infections during warmer, more humid months has been reported, potentially due to contamination of air handling systems.

The integration of whole-genome sequencing with epidemiologic data such as patient movement and health care environment exposures is needed to determine transmission routes in an outbreak, and should become the standard. In order to appropriately utilize whole-genome sequencing in an outbreak, an understanding of the endemic strains within a facility is needed.

Community-Associated Infections

Acinetobacter pneumonia is a rare but serious cause of community-acquired pneumonia in tropical regions during the summer months, and often presents with respiratory failure and shock. Community-onset bacteremia is typically associated with respiratory infections, and is also associated with a worse outcome compared with hospital-onset infections. Community-acquired Acinetobacter meningitis in patients without underlying medical compromise has been rarely reported; outcomes in those who received prompt therapy were favorable. A. baumannii skin colonization and invasive soft tissue infections have been associated with warfare, natural disasters, and societal disruptions. The environmental source of these community infections, which typically present in tropical or warm regions, is unknown. In addition to soil, there is an increasing appreciation for the potential role of contaminated food, infected head and body lice, colonized pets or other animals, and hospital wastewater as environmental reservoirs of Acinetobacter.