Wisconsin State Laboratory of Hygiene (WSLH) Updates Carbapenemase Testing
This bulletin is being sent to local health officers, Tribal health directors, public health nurses, local public health department staff, and infection preventionists.
Testing updates at WSLH
As of August 24, 2026, WSLH has discontinued testing carbapenem-resistant Acinetobacter baumannii (CRAB) isolates for OXA-23-like, OXA-24/40-like, and OXA-58-like carbapenemase genes. These genes are unique to CRAB and are not included on carbapenemase testing panels used for other carbapenem-resistant species testing at WSLH. CRAB isolates should still be submitted to WSLH for characterization. WSLH will still be testing for the presence of rare carbapenemases (KPC, NDM, OXA-48-like, VIM, and IMP) found in CRAB isolates.
Due to this change, clinical labs who submit a CRAB isolate for testing will likely receive a report indicating that the CRAB isolate is negative for all carbapenemases tested. This is because testing no longer includes the commonly identified OXA-23, OXA 24/40, and OXA-58 genes. A negative result indicates that the isolate tested is negative for the less common carbapenemases (KPC, NDM, OXA-48-like, VIM, and IMP). It’s important to note that the CRAB isolate is still likely carbapenemase-producing, even if it doesn’t test positive for one of the tested carbapenemase types.
Rationale for the change
Data from the past five years shows that approximately 90% of CRAB isolates tested have a carbapenemase gene, such as OXA-23, OXA-24/40, and OXA-58. Due to the common occurrence of these genes, the CDC (Centers for Disease Control and Prevention) has revised the Antimicrobial Resistance (AR) Lab Network carbapenemase testing guidance. The updated guidance discontinues routine testing for OXA-23, OXA 24/40, and OXA-58 in CRAB isolates because it can be presumed, without testing, that CRAB isolates have one of these genes.
Changes in response and reporting
CDC recommends that jurisdictional public health departments should treat CRAB as a carbapenemase-producing organism (CPO). The Wisconsin Department of Health Services (DHS), HAI Prevention Program is working to update the Communicable Disease Case Reporting and Investigation Protocol (EpiNet) (PDF) for CPOs to reflect the updated testing guidance. In the meantime, the HAI Prevention Program will continue to respond to CRAB cases as if they are a CPO. This may include recommendations for colonization screening at health care facilities.
Impact on infection prevention
The HAI Prevention Program advises all Wisconsin health care facilities to remain diligent in their infection prevention and control of CRAB regardless of this change in testing. This includes the following:
- Follow appropriate precautions and ensure personal protective equipment (PPE) is used properly.
- Increase the frequency of environmental cleaning and disinfection, especially for frequently touched surfaces, using an effective disinfectant (PDF).
- Practice consistent hand hygiene with alcohol-based hand rub (ABHR) or soap and water.
- Communicate the patient’s or resident’s CRAB status upon transfer to another health care facility so that proper precautions may be taken upon their arrival. To keep communication consistent, facilities are encouraged to use a tool such as the DHS Health Care Facility Transfer Form (PDF).
Questions?
For more information on MDROs, visit the HAI Prevention Program MDRO webpage.
Contact the HAI Prevention Program at DHSWIHAIPreventionProgram@dhs.wisconsin.gov for further assistance.
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