At Risk for Acinetobacter Baumannii: Factors That Increase Colonization in Patients

There are a variety of microorganisms that cause health care-associated infections and ultimately, put patients at risk on a daily basis. Some of these organisms are prolific in the environment, in soil or water, but can become opportunistic and infect patients if they have a weakened immune system. One of these microorganisms is a bacteria called Acinetobacter.

The most common to cause infections is Acinetobacter baumannii, which causes infections in the blood, urinary tract, wounds, or even in the lungs. Moreover, Acinetobacter baumannii can commonly colonize in the human body without causing infection.

Since this organism is so prolific and can easily colonize patients, investigators have worked to understand the risk factors that make it endemic, and therefore assess the it as a public health and health care threat. From an infection prevention perspective, the nature of Acinetobacter baumannii makes it an organism on the radar for prevention efforts against health care-associated infections.

The ease at which it colonizes patients can also make it problematic as patients might transmit or become infected when the immune system is stressed. Understanding the endemic nature of colonization though, can help guide prevention efforts against both infection and transmission. Over the course of 17 months, investigators at the Detroit Medical Center (DMC), which holds over 2000 beds, studied eligible patients who were admitted as inpatients and had an incident positive culture for Acinetobacter baumannii during the course of hospitalization.

The authors note that “The isolates were part of a larger surveillance study for common nosocomial agents (ESKAPE pathogens) within the DMC. Isolates were collected from a variety of specimens: blood, urine, sputum or other respiratory, wound, skin, and eye exudates. Isolates were included from both patients who were asymptomatic (colonized but not infected) and those with symptomatic infection. If a patient had multiple positive isolates, 1 was randomly selected for study.”

A patient was considered a case if they were infected or colonized with Acinetobacter baumannii and then broken into 2 groups—those with the most common genotype (REP-1) and those with the remaining endemic strains (REP-2 through REP-5). The study team then reviewed medical records to review several components: demographics, risk factor, and outcome data of interest.

These included factors like 3-month mortality, 3-month prior hospitalization, intensive care unit days before index culture, prior antibiotic usage within the last 3 months, comorbidities (19 listed), and a Schmid score (a fall risk assessment tool for hospitalized patients) were also used to assess risk regarding mobility. Researchers also assessed for the patients had an invasive medical device, like tracheostomy, central venous catheter, Foley catheter, and percutaneous endogastric tube.

After assessing 290 isolates, they found that 169 were endemic (96 of REP-1) and the most common site for isolation was the respiratory tract. In total, 109 patients (37%) had only Acinetobacter baumannii isolated, while some had up to 5 other organisms also identified.

In those colonized, 69 were REP-1, and 64 with REP-2-5, the research team found that for those patients with REP-1, there was a 70% increase in carriage per increase in Schmid score (statistically significant), and a 50% increase in REP-2-5. Interestingly, prior colonization, longer lengths of stay, and immunosuppression did now have a statistically significant relationship with Acinetobacter baumannii colonization.

Ultimately, the investigators emphasized that antibiotic stewardship and hand hygiene are critical in reducing Acinetobacter baumannii bioburden in the health care environment. Since antibiotic exposure has a well-documented history as a risk factor for drug-resistant Acinetobacter baumannii colonization, the widespread presence of the organism and those risk factors should be indicators of how abundant it is in health care, which in turn, presents the need for antimicrobial stewardship.