CROs are gram-negative bacteria that are resistant to one or more of the carbapenem class of antibiotics. These include the carbapenem-resistant Enterobacterales (CRE), such as Escherichia coli and Klebsiella pneumoniae, Pseudomonas aeruginosa (CRPA), and Acinetobacter baumannii (CRAB). CROs can cause infections in healthcare settings, including urinary tract infections, pneumonia, bloodstream infections, wound or surgical site infections, and meningitis. CROs are considered a threat to patient safety because carbapenem antibiotics often are the last line of defense against gram-negative infections that are resistant to other antibiotics.

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Certain CPOs confer resistance by producing enzymes called carbapenemases. Carbapenemases allow bacteria to become resistant to carbapenems and other β-lactam antibiotics. The main classes of carbapenemases include Klebsiella pneumoniae carbapenemase (KPC), New Delhi metallo-β-lactamase (NDM), Verona integron-encoded metallo-β-lactamase (VIM), Oxacillinase (OXA), and Imipenemase (IMP) metallo-β-lactamase. The genes that encode carbapenemases are typically found on mobile gene elements called plasmids, which means they can be easily transferred between different types of bacteria. This ability to spread makes CPOs a concern for DPH. Some of these carbapenemase-producing organisms (CPOs) are considered targeted organisms by DPH (see below). People who are infected or colonized with a CPO need a high level of adherence to infection control to prevent the spread of CPOs.

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Candida auris (C. auris) is an emerging fungus that has caused several healthcare facility outbreaks in the United States and abroad. C. auris is a particular health concern because it: can cause severe, antibiotic-resistant infections; is difficult to identify using traditional yeast identification methods; can survive on healthcare setting surfaces for long periods; and can spread easily to patients in healthcare settings. On May 7, 2019, LAC DPH released a LAHAN describing the first cases of C. auris in Southern California. C. auris is now found in all areas of Los Angeles County, so all healthcare facilities should be prepared to admit and care for patients who are positive for C. auris.

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Local and national surveillance has identified novel and targeted forms of MDROs that are difficult to treat, have been associated with international travel, and have the potential to spread rapidly. These need to be detected and contained before they spread further. LACDPH has categorized MDROs into tiers to guide the public health and healthcare facility containment response.

Healthcare facilities and laboratories should contact the Acute Communicable Disease Control Program within one business day when any of the Tier 1 organisms are detected.

¹Resistant (R) to all drugs tested at public health laboratories (including CDC)
²Including echinocandin- or pan-resistant C. auris
³Inclding NDM-, IMP-, VIM-, and KPC-producing Acinetobacter spp.
⁴Including IMP-, VIM-, and OXA-like producing Enterobacterales
⁵Including VIM-, IMP-, NDM-, KPC-, and OXA-like producing Pseudomonas spp.

Key Resources:

• CDC Containment Strategy Responding to Emerging AR Threats
• Interim Tier 2 screening algorithm