Carbapenem-Resistant Organisms (CROs)

Carbapenem-Resistant Organisms (CROs)

CROs Factsheet ThumbnailCarbapenem-resistant organisms, or CROs, are a type of multidrug-resistant (MDRO) organism that can cause both infection and colonization in healthcare settings. CROs include carbapenem-resistant Acinetobacter baumannii (CRAB) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) both of which have been identified in Alameda County. When Enterobacterales, a group of Gram-negative, non-spore forming bacteria, develop resistance to carbapenems, they are referred to as carbapenem-resistant Enterobacterales (CRE). In 2017 there were an estimated 13,100 hospitalizations and 1,100 deaths due to CREs in the U.S.

The 2019 CDC Antibiotic Resistance Threats Report lists CROs as Urgent Threats, which is the highest level of concern. Since the COVID-19 pandemic, the threat of antimicrobial resistance has only become more dire, with hospital-acquired antibiotic-resistant infections increasing by at least 15% in the first year of the pandemic. There are many reasons for this increase in antibiotic resistance including changed healthcare-seeking behaviors allowing undiagnosed and untreated infections to spread, increasing chances of developing resistance; from March to October of 2020, more than 80% of patients hospitalized with COVID-19 received unnecessary antibiotic therapy due to difficulty of distinguishing COVID-19 pneumonia from community-acquired pneumonia, increasing ability of bacteria to develop resistance.

CROs can be classified by their mechanism of resistance, non-carbapenemase producing organisms (non-CP), and carbapenemase-producing organisms (CPO). Carbapenemases are enzymes that break down antibiotics and render them ineffective. These enzymes are categorized into Class A, B, and D. Some common carbapenemases are Klebsiella pneumoniae carbapenemase (KPC), imipenamase (IMP), Verona integron-encoded metallo-β-lactamase (VIM), New Delhi metallo-β-lactamase (NDM), and oxacillinase (OXA). CPOs are of special public health concern because of their ability to easily spread resistance between many species of bacteria in healthcare settings.

Risk factors for CRO colonization or infection include prolonged inpatient stays, severe illness and/or comorbid conditions, invasive medical devices (such as catheters, endotracheal tubes, and feeding tubes), and treatment with certain antibiotics. Because patient populations in long-term care facilities (LTCF) and skilled nursing facilities (SNF) tend to have many of these risk factors, healthcare teams in these facilities should be especially cognizant of CROs.

The spread of CROs is mediated by patient transfer between facilities and inconsistently applied infection control measures. This highlights the importance of using the Infection Control Transfer Form and ensuring your facility is prepared for a patient with CRO, such as implementing appropriate infection control practices and environmental cleaning. In addition, California Department of Public Health (CDPH) advocates that all residents of SNFs be on Enhanced Standard Precautions which is a resident-centered activity-based approach to help limit the spread of resistant organisms.

In 2017, the Alameda County Public Health Department (ACPHD) issued a Health Officer Order for reporting CRE and submitting CRE isolates to the Alameda County Public Health Laboratory. CDPH began to require laboratory reporting of CPOs as of September 2022. Of note, the CDPH requirement does not supercede the local Health Officer Order. Cases and outbreaks of CPOs have been increasingly recognized in California including Alameda County. From mid-2019 to mid-2021 there were 452 CRO cases reported to Alameda County;107 (24%) were identified as CPOs. In 2022, there were 380 cases of CROs in Alameda County and 122 (32%) of those cases were confirmed as CPOs. In 2022 the most commonly isolated organism was Pseudomonas aeruginosa, and the most commonly identified carbapenemase gene was KPC.

ACPHD takes CRO infection control and prevention very seriously. We have provided links to resources below. Further questions can be directed to

If you have a CRO outbreak

Important documents


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