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Carbapenem-resistant Acinetobacter baumanii

Orange County Health Care Agency Recommendations for Response to Carapenem-Resistant Acinetobacter baumanii in Health Care Settings

  • Carbapenem-resistant Acinetobacter baumanii (CRAB) is a bacteria that is resistant to most commonly-used antibiotics.
  • The Centers for Disease Control and Prevention (CDC) Antibiotic Resistance (AR) Threats report includes CRAB as an urgent global public health threat.
  • Patients with chronic medical conditions are at the highest risk for CRAB infection.
  • OCHCA uses a coordinated approach between public health and healthcare facilities to contain CRAB. The following guidance outlines the standard public health recommendations for responding to CRAB cases in health care settings.


Carbapanems (such as meropenem, imipenem, and doripenem) are antibiotics that have a broad spectrum of activity against many types of bacteria. In particular, they can be used to treat serious infections caused by gram-negative bacteria such as E. Coli, Klebsiella, Enterobacter, Pseudomonas aeruginosa and Acinetobacter species. Carbapenems are often effective against organisms that are resistant to commonly-used antibiotic groups such as penicillins and cephalosporins; they are thought of as an antibiotic “last line of defense”.

Bacteria can become resistant to carbapenems due to several different mechanisms. Some bacteria develop the ability to prevent the antibiotic from entering the bacteria’s outer membrane or have efflux pumps that eject the antibiotic. Some bacteria are carbapenem-resistant due to having carbapenemase enzymes. Carbapenemases are enzymes that render the antibiotic inactive. They are often produced by bacteria plasmids, which are distinct gene pieces or sequences that can be shared between bacteria of the same or different species and have been responsible for quickly spreading carbapenem resistance in healthcare facilities and communities. Carbapenemase enzymes include KPC, NDM, OXA23, VIM, and IMP.

Carbapenem-resistant bacteria are usually resistant to other antibiotic types as well and will occasionally be identified as pan-nonsusceptible to all tested antimicrobial drugs. Infections caused by CRAB have high mortality rates, due to the severity of these infection (such as blood infection causing sepsis), the patient’s frequent serious underlying medical conditions, and the difficulty of finding an effective antibiotic.

Carbapenem-resistant bacteria have been present in Orange County for over a decade; several, such as carbapenem-resistant E coli, Klebsiella, Enterobacter, and Pseudomonas aeruginosa, are endemic in Southern California, including Orange County. Once a bacteria type becomes endemic in a community, many patients will be unknowingly colonized, making a targeted public response to the known colonized cases less effective. To make the best use of limited public health resources, OCHCA’s particular focus is responding to organisms such as CRAB that are newly emerging in the county before they become endemic.

CRAB infections and outbreaks are most often identified in healthcare settings, including acute care hospitals, long-term acute care hospitals, and skilled nursing facilities. CRAB can be found in the healthcare environment (e.g., water, environmental surfaces, medical devices) and on a person’s skin. It can be transmitted from the environment to individuals or from person-to-person in healthcare settings.

Over 90% of CRAB isolates tested in Orange County in 2021 produce OXA-23 carbapenemase. Thus, any CRAB organism should be presumed to be carbapenemase-producing if no carbapenemase testing is performed. In addition, carbapenemase testing may need to be performed by a referral lab, leading to delays in reporting of results; these cases should be treated as CP-CRAB pending the results of testing.

Recommendations for Routine CRAB Surveillance in Healthcare Settings

Any Acinetobacter baumannii specimen that is resistant to carbapenem antibiotics (such as imipenem, doripenem, or ertapenem) by routine laboratory susceptibility testing should be tested to identify whether a carbapenemase enzyme is present. Clinical laboratories in Orange County should establish carbapenemase testing capacity through either internal or external laboratory resources. While the vast majority of CRAB isolates currently have OXA-23 carbapenemase, it is important to monitor for changes in carbapenemase surveillance over time that may have both treatment and infection control implications.

Testing for a carbapenemase must occur when positive cultures are identified as part of an outbreak. Specimens should also be submitted to OCHCA (if still available) for potential additional evaluation such as whole genome sequencing. OCHCA can arrange for testing for additional carbapenemases in response to outbreaks through the Antibiotic Laboratory Response Network.

Testing for carbapenemases is also particularly recommended for isolates that are:

  • Pan-nonsusceptible to all antimicrobial drugs tested
  • Isolated from a patient that is a resident of a long term care facility

Clinical laboratories must immediately notify clinicians and infection prevention staff when a case of CRAB is identified.

Healthcare facilities must report all CRAB cases to OCHCA according to California State Title 17 guidance, which mandates reporting of occurrence of any unusual disease to public health. New cases identified in licensed healthcare facilities should also be reported to CDPH Licensing & Certification per All Facilities Letters 19-18.15,16. Providers should call the OCHCA Communicable Disease Control Division at 714-834-8180 with any questions or to report a CRAB case.

Screen (or access screening resources) for CRAB and implement preemptive Contact precautions for individuals at risk for CRAB, including those with the following risk factors:

  • Was a roommate of a case, if case was not placed in appropriate precautions
  • Shared a bathroom with a case, if case was not placed in appropriate precautions
  • All residents on a ward or facility where a cluster of cases occurs. An outbreak is defined as 3 or more identified within 2 weeks, with the cases identified to have infection 72 hours or more after admission
  • Patients with a history of receiving healthcare outside the United States during the past 12 months should be screened for CRAB
  • Admitted from facilities known to have ongoing CRAB transmission as designated by OCHCA

Specimens to be obtained for culture for surveillance screening:

  • Axilla and groin combined specimens for all patients


  • Respiratory culture if the patient population includes many who are chronically ventilated and/or have a tracheostomy
  • Urine culture for any patients who are catheterized

Laboratory surveillance in outbreak situations:

  • If one or more additional patients are identified with CRAB, conduct serial point prevalence surveys (PPS) of all potentially affected residents at 2- week intervals until 2 consecutive PPS are completely negative.
  • If a cluster of cases is identified in a facility, conduct retrospective surveillance of culture results to identify additional cases during the previous 6 months.

Infection Control Recommendations

Patients admitted from long-term acute care hospitals (LTACH) or ventilator-equipped skilled nursing facilities (vSNF) can be considered to be potentially colonized with either and/or a carbapenem-producing organism such as CRAB or other multi-drug resistant organism such as C. auris. Because surveillance screening results are frequently delayed, if the admission will be for a shorter period, the patient may simply be placed in empiric Contact precautions during the stay. If the admission is anticipated to be for an extended period of time, the patient may have surveillance screening performed and placed in Contact precautions pending the result.

Patients infected or colonized with CRAB should be placed in a single-bed room when possible, particularly in ACH and LTACH settings

In skilled nursing facility (SNF) settings, patients colonized with CRAB should be placed in a single room when possible. Because in many instances a single room is not available, CRAB-colonized patients should be placed with a roommate who is CRAB-colonized (see Cohorting guidance below), or with a low-risk roommate, who is not immunocompromised, not chronically ventilated, and does not have an indwelling device.

If multiple CRAB-infected or colonized patients are present in a healthcare facility, the following processes should be adhered to whenever possible:

  • Place them in rooms in the same geographic area of the facility.
  • Dedicate primary health care providers (HCP) to care only for the colonized patient (or for multiple patients who are colonized with the same organism).
  • HCP who cannot be dedicated to CRAB patients should care for them after caring for other patients.

In facilities with multi-bed rooms: place patients with CRAB in the same room whenever possible. Also consider other concurrent communicable disease status (e.g., COVID-19, Clostridium difficile, etc.) when determining room placements.

In multi-bed rooms: each bed space should be treated as a separate room, and change gown and gloves and perform hand hygiene between contact with patients in the same room.

Note: While these cohorting processes should be practiced whenever possible, the lack of this capacity should not be considered grounds for transfer or refusal to admit a patient.

  • Dedicate daily care equipment as much as possible

  • Use single-use, disposable, non- critical devices or equipment as much as possible

Proper hand hygiene is critical to preventing the spread of any MDROs. Follow and audit standard hand hygiene practices, including the use of alcohol-based hand sanitizer as the preferred method for cleaning hands if not visibly soiled. If hands are visibly soiled, wash with soap and water.

  • Contact precautions consist of health care providers donning gowns and gloves upon entry to the patient room; patients may only leave room when medically necessary.

  • Continue Contact precautions for the duration of admission in acute care hospitals, including LTACH.

  • In SNFs, once there is no longer evidence of transmission (e.g., two consecutive negative PPS and no new clinical cases), continue Contact precautions, or transition to Enhanced standard precautions for residents with risk factors for transmission.19    Enhanced Standard Precautions for Skilled Nursing Facilities (SNF), 2019

Once a patient is found to be colonized, repeat surveillance screening for CRAB is not generally recommended to demonstrate “clearance” for the purposes of discontinuing transmission-based precautions. CRAB may be shed intermittently and patients generally remain colonized for months, and possibly indefinitely.

Regularly clean and disinfect non-dedicated equipment after use, and high-touch surfaces with an Environmental Protection Agency (EPA)- approved healthcare grade disinfectant effective against A. baumanii as identified on the product label. Examples can be found at US EPA, Pesticide Product Label,  US EPA, Pesticide Product Label, SANI-CLOTH GERMICIDAL DISPOSABLE CLOTH,11/10/2020

  • Clinical laboratories should immediately notify clinicians and infection prevention staff when CRAB is identified.

  • When transferring a CRAB-infected or colonized patient to another healthcare facility, the transferring facility must communicate the patient’s CRAB (and other MDRO) status and other relevant information to determine necessary infection control measures to the receiving facility at time of transfer.

  • When receiving transferred patients, facilities should actively inquire about MDRO status.

  • Facilities with ongoing outbreaks of any MDRO including CRAB should inform facilities to which they transfer patients. Receiving facilities may laboratory-screen such patients and place them in preemptive Contact precautions and single-bed rooms pending the culture result.

  • If patient has had previous healthcare exposure and date of collection is within 3 days of admission, notify the previous facility of CP-CRAB status. The previous facility may also consider conducting a contact investigation.

  • Flag the medical record of patients with CRAB to ensure infection control precautions are implemented upon readmission.

Public Health Response to CRAB

During its investigation OCHCA will routinely ask the facility to provide:

  • Name and date of birth of patient
  • Name and address of facility where patient resides, as well as wing and room number
  • Whether patient was in appropriate infection control precautions during stay
    • If in contact precautions throughout stay, no need for additional workup
  • Previous and subsequent healthcare facilities if not previously known to be positive
  • Date of admission and discharge
  • Indwelling devices and procedures
  • Specimen collection dates, sources and results
  • If novel (non-OXA23) carbapenemase: Healthcare exposures outside Southern California in the previous 12 months.

When a cluster of cases is identified (generally 3 or more cases acquired at a healthcare facility within a 2-week period), the OCHCA HAI team will generally conduct an expanded investigation with an onsite assessment. OCHCA staff will explore whether there are any shared staff, equipment, or sites that are potential sources, and explore whether this source(s) could be minimized or discontinued.