Multidrug resistance

The latest edition of ICD-10 includes new codes for antibiotic resistance.


For the 2020 ICD-10-CM, new codes were created to capture antibiotic resistance in clinical settings. The intent is to identify antibiotic resistance in the U.S. for our health care databases collected by the Healthcare Cost and Utilization Project under the stewardship of the Agency for Healthcare Research and Quality.

Multidrug-resistant (MDR) infections are associated with increased mortality, length of stay, and hospital costs. MDR is defined as organisms with resistance to one or more antibiotics in three or more antibiotic/antimicrobial drug classes. To identify multidrug resistance, clinicians should have a working knowledge of the drug class of commonly used antibiotics and antimicrobials reported on culture sensitivity testing (Table 1).

Image by Getty Images
Image by Getty Images

Methicillin-resistant Staphylococcus aureus (MRSA) is by far the most frequently encountered MDR organism, accounting for up to 80% of bacterial MDR infections. Other commonly encountered MDR bacteria are vancomycin-resistant enterococci (VRE), Acinetobacter, Klebsiella, Pseudomonas, and coliforms, particularly E. coli and Clostridioides (formerly Clostridium) difficile.

The incidence of MDR tuberculosis infection is rapidly increasing and particularly worrisome because many strains are resistant to all known antitubercular drugs. MDR Candida species are also becoming problematic. Parasites and many viral pathogens are also becoming MDR.

Circumstances that put patients at high risk for multidrug resistance are shown in Table 2. Commonly encountered and particularly important ones include immunosuppression from any cause, history of an MDR infection, known colonization by an MDR organism, and exposure to an MDR-infected person, especially at home. Structural lung disease, as occurs in cystic fibrosis and bronchiectasis, is typically associated with Pseudomonas colonization and pneumonia, often with multidrug resistance.

The three most common inpatient situations associated with multidrug resistance are ventilator-associated pneumonia (VAP), catheter-related bloodstream infection (CRBSI), and catheter-associated urinary tract infection (CAUTI).

The new drug resistance codes (category Z16) identify the antibiotics to which the infectious organism is resistant (Table 3). One of the codes (Z16.24) identifies “multidrug resistance.” If individual or multiple drugs to which an organism is resistant are documented by the clinician, a code is assigned for each of the drugs identified. This means that resistance to even a single antibiotic may be documented and assigned one of the codes. These drug resistance codes are classified as comorbidity/complications (CCs) so may change the diagnosis-related group and have a significant impact on quality metrics and reimbursement.

The clinician must specifically document the term “resistance” or “resistant” in describing the circumstances. When the clinician documents resistance to a particular drug, it is the coder's responsibility to assign a code for the correct drug class, making clinical pharmacology knowledge essential. For example, if the clinician documents tobramycin resistance, the coder must know that the aminoglycoside code (Z16.29) should be used. Coding software should lead the coder from a specific antibiotic to the correct drug-class code.

The type of infection is coded first, followed by a code for the organism—unless the infection code itself describes the organism (e.g. code J13, pneumococcal pneumonia)—and then the drug resistance code. In the case of MRSA, a drug resistance code is not assigned because the infection code identifies the antibiotic. In contrast, codes for specific infections caused by other drug-resistant organisms, such as VRE, do not count as identifying the presence of drug resistance for coding purposes.

In summary, be alert to single- or multiple-drug resistance identified by culture sensitivity testing and document the type of drug resistance exhibited by the organism. The coding sequence is type of infection first, followed by codes for the organism (unless incorporated by the infection code) and then for the antibiotic(s) to which it is resistant.