Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that has developed resistance to many common antibiotics, including methicillin and penicillin. This resistance makes MRSA infections more difficult to treat than typical staph infections. Medical classification systems, such as the International Classification of Diseases, 10th Revision (ICD-10), use specific codes to track and report diagnoses for healthcare management and billing. The correct code depends entirely on the location of the infection, whether it is an active disease or merely colonization, and requires strict sequencing rules for accurate reporting.
Identifying the Organism The Secondary Code
The most common way to identify MRSA as the causative agent in a patient with an active infection is through the use of a secondary diagnosis code. This code, B95.62, is titled “Methicillin resistant Staphylococcus aureus infection as the cause of diseases classified elsewhere”. B95.62 is typically never used as the first or primary diagnosis code; its purpose is to provide the microbiological detail that the patient’s primary illness is caused by the drug-resistant MRSA strain.
The secondary code B95.62 is paired with a code that explicitly identifies the infection site and manifestation. For example, if a patient has a bladder infection caused by MRSA, the primary code identifies the urinary tract infection, and B95.62 follows it to specify the organism. This sequencing is necessary because the primary diagnosis code describes the patient’s condition, while the secondary code explains the specific cause. This two-code system alerts healthcare systems to the antibiotic resistance, which impacts treatment decisions and public health surveillance.
Coding for Active Infection Sites
When MRSA causes an active disease, the primary ICD-10 code must identify the location and manifestation of the infection. These primary codes are known as combination codes when they include both the site of the infection and the causative organism. Using a combination code is preferred because it provides the most detail in a single entry and replaces the need for the secondary code B95.62.
For instance, if MRSA enters the bloodstream, the diagnosis is Sepsis due to Methicillin-resistant Staphylococcus aureus, coded A41.02. Similarly, a serious lung infection caused by MRSA is coded J15.212, which denotes Pneumonia due to Methicillin-resistant Staphylococcus aureus. Both A41.02 and J15.212 are single combination codes that fully describe the condition and the agent.
However, not all MRSA infections have a dedicated combination code, such as many skin and soft tissue infections. In these cases, a code identifying the site, such as L03.211 for Cellulitis of face, is sequenced first. This is then followed by the organism code B95.62 to complete the picture of cellulitis caused by MRSA.
Coding for MRSA Colonization Carrier Status
A distinct coding situation arises when a patient carries MRSA without showing signs or symptoms of an active infection. This is known as colonization or carrier status, where the bacteria live on the body without causing disease. For this scenario, the ICD-10 system uses a Z-code, which describes factors influencing health status rather than a current illness.
The specific code for this status is Z22.322, “Carrier or suspected carrier of Methicillin resistant Staphylococcus aureus”. This code is used when the patient is asymptomatic, perhaps identified during screening prior to a surgical procedure. When Z22.322 is used, it often serves as the principal diagnosis because the purpose of the encounter is to manage the carrier status, and the organism code B95.62 is not used since there is no active disease.
Essential Documentation and Sequencing Rules
Accurate ICD-10 coding for MRSA relies heavily on meticulous clinical documentation from the healthcare provider. The physician must clearly state the causal relationship between MRSA and the patient’s illness, using phrases such as “pneumonia due to MRSA” or “wound infection caused by MRSA”. Without this explicit documentation, coders are often restricted to using less specific codes that fail to capture the drug-resistant nature of the infection.
The fundamental rule for sequencing is to prioritize the condition over the organism, unless a combination code exists. For active infections without a combination code, the primary diagnosis identifies the site and nature of the disease (e.g., cellulitis). The secondary diagnosis, B95.62, is then used to specify the MRSA organism. This ordering ensures the patient’s most significant condition is recognized first, followed by the detail of the resistant microbe.