A00-B99

Certain infectious and parasitic diseases

Chapter 1 of the ICD-10-CM (A00-B99) encompasses a wide array of diseases caused by pathogenic microorganisms, including bacteria, viruses, fungi, protozoa, helminths, and prions. This chapter is primarily dedicated to conditions generally recognized as communicable or transmissible. It is structured to include systemic infections and those with specific epidemiological significance, such as tuberculosis, zoonotic bacterial diseases, and infections with a predominantly sexual mode of transmission. It excludes infections that are localized to specific body systems unless the condition is explicitly categorized within this chapter (e.g., most respiratory infections are in Chapter 10, but certain systemic viral and bacterial agents remain here). This chapter also contains essential codes for sequelae of infectious diseases and bacterial/viral agents as causes of diseases classified elsewhere, which are vital for longitudinal patient tracking and public health monitoring.

Clinical Symptoms

  • Fever and rigors (chills)
  • Generalized malaise and fatigue
  • Myalgia and arthralgia
  • Lymphadenopathy (swollen lymph nodes)
  • Nausea, vomiting, and diarrhea
  • Maculopapular or vesicular rashes
  • Persistent or productive cough
  • Unexplained weight loss
  • Night sweats
  • Acute or chronic inflammation
  • Splenomegaly or hepatomegaly

Common Causes

  • Bacterial pathogens (e.g., Mycobacterium tuberculosis, Staphylococcus aureus, Salmonella)
  • Viral agents (e.g., HIV, Hepatitis A/B/C, Herpesviruses)
  • Parasitic protozoa (e.g., Plasmodium species, Giardia)
  • Helminthic infestations (e.g., Schistosoma, Tapeworms)
  • Fungal infections (e.g., Candida, Coccidioides)
  • Prion proteins (e.g., Creutzfeldt-Jakob disease)
  • Vector-borne transmission via mosquitoes, ticks, or fleas
  • Zoonotic transmission from animals to humans
  • Fecal-oral contamination in food and water
  • Direct contact or droplet/aerosol transmission
  • Sexual transmission

Documentation & Coding Tips

Identify and document the specific causal organism and its relationship to the site of infection.

Example: Patient presents with acute pyelonephritis. Laboratory results confirm Escherichia coli. Assessment: Acute pyelonephritis due to E. coli. Billing Focus: Identification of the B96.20 agent to supplement the N10 code. Risk Adjustment: Specificity in organism impacts HCC category 135 for acute renal failure or related complications.

Billing Focus: Inclusion of the causal organism code (B95-B97) as a secondary diagnosis.

Clearly differentiate between HIV disease and asymptomatic HIV status.

Example: Patient with known HIV status presents with pneumocystis jirovecii pneumonia. Assessment: HIV disease (B20) with associated opportunistic infection. Billing Focus: Use B20 for any history of HIV-related illness; do not use Z21 if the patient has ever had an AIDS-defining condition. Risk Adjustment: B20 maps to HCC 1 (HIV/AIDS) which carries a high risk score.

Billing Focus: Transitioning from Z21 to B20 once a patient develops an AIDS-defining illness.

Document sepsis using clinical criteria and link it to the localized infection site.

Example: Patient admitted with altered mental status and hypotension. Blood cultures positive for MRSA. Diagnosis: Sepsis due to Methicillin resistant Staphylococcus aureus (A41.02). Billing Focus: Documenting the specific organism (MRSA) rather than unspecified sepsis. Risk Adjustment: Sepsis is a major complication/comorbidity (MCC) and maps to HCC 2.

Billing Focus: Sepsis specificity (organism, septic shock) determines the DRG assignment.

Specify the acuity and presence of complications in Viral Hepatitis.

Example: Patient with chronic Hepatitis C (B18.2) is evaluated for cirrhosis. Assessment: Chronic viral hepatitis C without hepatic coma. Billing Focus: Differentiating between acute (B17.10) and chronic (B18.2) status. Risk Adjustment: Chronic Hepatitis C maps to HCC 29 and indicates long-term management needs.

Billing Focus: Acuity (Acute vs Chronic) and the presence of hepatic coma.

Utilize Z16 codes to document antimicrobial resistance for all infectious agents.

Example: Patient with recurrent UTI. Culture shows E. coli resistant to fluoroquinolones. Assessment: Cystitis due to E. coli (N30.00, B96.20) with resistance to fluoroquinolones (Z16.22). Billing Focus: Supplemental Z16 codes describe the complexity of the infection. Risk Adjustment: Resistance codes signify higher treatment complexity and potential for treatment failure.

Billing Focus: Adding Z16 codes to describe drug resistance profiles.

Relevant CPT Codes

Related Diagnoses

Hierarchy