In the past year or so, I’ve read about a number of outbreaks of carbapenem-resistant Acinetobacter baumanii (commonly abbreviated to CRAB) that highlight the threat from this particular antibiotic resistant pathogen. Before describing those in more detail, a little about CRAB. 

Like bacteria in the Enterobacteriaceae family, A. baumannii is a gram-negative bacterium that can also develop resistance to carbapenem antibiotics. It is part of the Moraxellaceae family and is the most important species causing human infections within that family. The most common resistance genes found in A. baumannii include those that code for New Delhi metallo-beta-lactamase (NDM) and oxacillinase (OXA) enzymes, both of which chemically degrade carbapenem antibiotics. The high levels of resistance mean that the infections caused by CRAB in the bloodstream, lungs, wounds, and urinary tract increasingly require the use of last-line antibiotics such as colistin, polymyxin B and tigecycline. 

The first reports of CRAB infections appeared in the early 1990’s but reports have increased steadily since then. Around 800 articles have been published since 1999, and outbreaks have been reported globally.

The serious global threat of CRAB

In the CDC’s first Antibiotic Resistance Threats report issued in 2013, multi-drug resistant A. baumanii is listed as a “Serious Threat.”1 Carbapenem resistance is not specifically mentioned. In the 2019 report, CRAB is specifically listed as an “Urgent Threat,” the highest threat level.2 This report estimates that in 2017, there were 8,500 cases in the U.S., resulting in 700 deaths and a significant cost to the health system of $281 million. The one piece of good news is that rates have declined by 25% since 2011. That said, WHO’s June 2021 Global Antimicrobial Resistance and Use Surveillance System (GLASS) report “depicts a dire scenario” noting that a median of 66% of A. baumannii causing bloodstream infections are carbapenem-resistant.3

The challenges of controlling and preventing and controlling CRAB infections

In the first half of 2020, New Jersey, an outbreak at a hospital in New Jersey highlighted the importance of consistently implementing comprehensive infection prevention and control (IPC) measures, especially if patients are intubated and ventilated.4 In the outbreak, 34 patients were infected or colonized with meropenem-resistant A. baumanii infections, 80% of which occurred during the facility’s surge in COVID-19. Of these patients, 25 were intubated and mechanically ventilated and ultimately, 20 with infections were identified. Due to personnel and equipment shortages, space constraints and the high number of critically ill patients admitted during the COVID-19 surge, this hospital understandably had to adopt alternative mitigation measures. As a result, intentional and unintentional changes in IPC measures may have contributed to the outbreak.

A regional outbreak that occurred in May 2021 in California highlights how the infection can rapidly spread between facilities.5 Of 52 NDM-CRAB cases, 43 cases were reported in a single county across multiple facilities including acute care hospitals, two skilled nursing facilities, and a long-term acute care hospital. A further 17 probable NDM-CRAB cases were epidemiologically linked to these cases or facilities. Genome sequencing of 17 isolates pointed to a common source of exposure. This outbreak emphasizes the need for active surveillance including screening new patients being transferred from facilities experiencing outbreaks and placing them on contact precautions while awaiting results.

Finally, an outbreak at a hospital in Israel shows how A. baumanii can persist in the environment.6 Three wards were terminally cleaned with bleach and UV before becoming wards for COVID-19 patients only. Two weeks after reopening, five cases of CRAB infection or colonization were identified, all belonging to the same meropenem-resistant clonal lineage. Three were acquired in a single ward, which prior to COVID-19 had been used to cohort CRAB patients. Epidemiological investigation revealed that the ward’s medication room had not been terminally cleaned and was identified as the source of CRAB. The hospital implemented several measures which stopped the outbreak. The ward in question was closed to new admissions, terminal cleaning repeated, and the medication room closed permanently. CRAB patients were cohorted in a single unit and staff were not permitted to care for CRAB-negative patients until they had left the cohort area and removed all PPE (which included a disposable gown over COVID-19 PPE coveralls. 

Preventing transmission of CRAB and other multi-drug resistant organisms

These three outbreak reports paint a picture of the seriousness of CRAB and why the CDC has declared it an “Urgent Threat.” Although in the U.S., cases were steadily decreasing prior to the pandemic, we won’t know how the pandemic has impacted CRAB and other MDRO rates until more data is analyzed and released. In the meantime, these five actions can help to help prevent transmission of CRAB and other MDROs:

  • Conduct active surveillance and screen new patients from outbreak facilities
  • Test for CRAB and MRDOs through public health labs or the CDC’s AR Lab Network AR Lab Network
  • Implement contact precautions along with standard environmental and personal infection control measures
  • Communicate a patient’s MDRO status to receiving facilities
  • Report carbapenem-resistant organisms and other MDROs to local and state health departments

One final point to note is that if a disinfectant has an EPA-approved claim against A. baumanii, it will most likely not be carbapenem-resistant strain. However, these disinfectants should still be effective against CRAB as drug resistance is not expected to change a bacterium’s susceptibility to disinfectants. 

1. Antibiotic Resistance Threats in the United States, 2013.  U.S. Centers for Disease Control and Prevention.  Accessed July 19, 2021
2. Antibiotic Resistance Threats in the United States, 2019.  U.S. Centers for Disease Control and Prevention.  Accessed July 19, 2021
3. Global antimicrobial resistance and use surveillance system (GLASS) report 2021. Geneva: World Health Organization; 2021. License: CC BY-NC-SA 3.0 IGO.
4. Perez S et al.  Increase in Hospital-Acquired Carbapenem-Resistant Acinetobacter baumannii Infection and Colonization in an Acute Care Hospital During a Surge in COVID-19 Admissions — New Jersey, February–July 2020.  MMWR / December 4, 2020 / Vol. 69 / No. 48
5. Regional Outbreak of Highly Drug-resistant Carbapenemase-producing Acinetobacter baumannii May 2021.  California Department of Public Health. Accessed July 19, 2021
6. Gottesman T et al. An outbreak of carbapenem-resistant Acinetobacter baumannii in a COVID-19 dedicated hospital.  Infection Prevention in Practice. 2021 Mar; 3(1): 100113.