Understanding the New Enemy of Carbapenem-Resistant Acinetobacter Baumannii: Public Health Watch

Investigators from the Centers for Disease Control and Prevention have determined the incidence of carbapenem-resistant Acinetobacter baumannii and "the basic epidemiology” of infections caused by these isolates in 8 metro areas.

Chinese warrior and strategist Sun Tzu wrote in his seminal text The Art of War: “If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.”

When it comes to the ongoing battle against antimicrobial-resistant pathogens, the folks at the Centers for Disease Control and Prevention (CDC) have taken Sun Tzu’s advice to heart. And, in their latest assessment of the threat posed by these pathogens—the enemy, if you will—we are starting to get a clearer picture of just what they are and, hopefully, how best to defeat them.

In a study published in the March 14th issue of the journal Emerging Infectious Diseases (EID), researchers from the CDC and their colleagues from several regional departments of public health and health care institutions across the country performed population-based surveillance in multiple metropolitan areas in Colorado, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, and Tennessee from 2012 to 2015 to determine “the incidence of carbapenem-nonsusceptible Acinetobacter baumannii cultured from urine or normally sterile sites and to describe the demographic and clinical characteristics of patients and cases.” The authors cited an earlier CDC report, which noted that multidrug-resistant Acinetobacter causes approximately 7000 infections and 500 deaths in the United States each year.

“Carbapenem-resistant Acinetobacter is a well-known antibiotic-resistant threat in some areas,” study co-author Alexander Kallen, MD, MPH, Branch Chief, CDC Prevention and Research Branch, Division of Healthcare Quality Promotion told Contagion®. “These organisms have some of the highest percentages of isolates that are resistant to many important antibiotics, including carbapenem antimicrobials.”

According to Dr. Kallen, the CDC has been tracking Acinetobacter strains resistant to carbapenem antimicrobials for years using data submitted to the National Healthcare Safety Network (NHSN). However, he added, what hadn’t been known prior to the EID study was the incidence of carbapenem-resistant Acinetobacter baumannii and “the basic epidemiology” of infections caused by these isolates. Hence, the project chronicled in the EID article sought to address this important knowledge gap, as part of the CDC’s Emerging Infections Program.

In all, Dr. Kallen and his co-authors identified 621 cases of carbapenem-resistant Acinetobacter baumannii in 537 patients. Over the 4-year period analyzed, the region in Georgia had the highest number of total cases, with 300, while the area in Oregon had the fewest, with 4. Within the 8 metropolitan areas assessed, crude annual incidence was 1.2 cases per 100,000 persons.

“Rates were slightly lower than expected but were comparable to other emerging antimicrobial resistant threats,” Dr. Kallen explained. “Of note, the incidence varied between surveillance sites; these geographic differences have been seen with other resistant pathogens, reflecting the fact that these pathogens are not evenly distributed across the whole United States.”

Overall, for the 598 cases for which complete data were available, 590 (98.7%) were reported in patients that had been admitted to a hospital for an overnight stay during the preceding year. And, 506 (84.6%) patients had an “indwelling device,” such as a urinary catheter and/or central venous catheter. Although the incidence of carbapenem-resistant Acinetobacter baumannii was lower in these 8 areas than that of other well-known health care-associated pathogens, such as carbapenem-resistant Enterobacteriaceae (CRE), the cases identified in the EID study were associated with substantial rates of illness and death. In fact, the crude mortality rate for carbapenem-resistant Acinetobacter baumannii in the EID study was 17.9%, nearly twice that for CRE in the same 8 regions.

“These pathogens are another antimicrobial resistance threat that is still relatively uncommon in the United States but has the potential to become more common,” Dr. Kallen said. “These pathogens appear to be primarily acquired in health care settings, and concerted efforts to control transmission in these settings have the potential to keep these organisms in check.”

In other words, given that the rise in these resistant pathogens can likely be traced to improper (read: excessive) prescribing of antimicrobials, we know the enemy, and it is us. And thankfully, we’re starting to fight back.

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous health care-related publications. He is the former editor of Infectious Disease Special Edition.