Chapter 1

A00–B99: Certain Infectious and Parasitic Diseases

Certain Infectious and Parasitic Diseases diagnostic classification updated for 2026.

Chapter Instructions

Includes

diseases generally recognized as communicable or transmissible

Excludes1(Not coded here. Use a different code.)

certain localized infections - see body system-related chapters

Excludes2(Not included here. Code separately if applicable.)

carrier or suspected carrier of infectious disease (Z22.-)
infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
infectious and parasitic diseases specific to the perinatal period (P35-P39)
influenza and other acute respiratory infections (J00-J22)

Use Additional Code

code to identify resistance to antimicrobial drugs (Z16.-)

All Codes Billable Only

Internal Codes

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A41.02|
Sepsis due to Methicillin resistant Staphylococcus aureus
A41.1|
Sepsis due to other specified staphylococcus
A41.2|
Sepsis due to unspecified staphylococcus
A41.3|
Sepsis due to Hemophilus influenzae
A41.4|
Sepsis due to anaerobes
A41.5|
Sepsis due to other Gram-negative organisms
A41.50|
Gram-negative sepsis, unspecified
A41.51|
Sepsis due to Escherichia coli [E. coli]
A41.52|
Sepsis due to Pseudomonas
A41.53|
Sepsis due to Serratia
A41.54|
Sepsis due to Acinetobacter baumannii
A41.59|
Other Gram-negative sepsis
A41.8|
Other specified sepsis
A41.81|
Sepsis due to Enterococcus
A41.89|
Other specified sepsis
A41.9|
Sepsis, unspecified organism
A42|
Actinomycosis
A42.0|
Pulmonary actinomycosis
A42.1|
Abdominal actinomycosis
A42.2|
Cervicofacial actinomycosis
A42.7|
Actinomycotic sepsis
A42.8|
Other forms of actinomycosis
A42.81|
Actinomycotic meningitis
A42.82|
Actinomycotic encephalitis
A42.89|
Other forms of actinomycosis
A42.9|
Actinomycosis, unspecified
A43|
Nocardiosis
A43.0|
Pulmonary nocardiosis
A43.1|
Cutaneous nocardiosis
A43.8|
Other forms of nocardiosis
A43.9|
Nocardiosis, unspecified
A44|
Bartonellosis
A44.0|
Systemic bartonellosis
A44.1|
Cutaneous and mucocutaneous bartonellosis
A44.8|
Other forms of bartonellosis
A44.9|
Bartonellosis, unspecified
A46|
Erysipelas
A48|
Other bacterial diseases, not elsewhere classified
A48.0|
Gas gangrene
A48.1|
Legionnaires' disease
A48.2|
Nonpneumonic Legionnaires' disease [Pontiac fever]
A48.3|
Toxic shock syndrome
A48.4|
Brazilian purpuric fever
A48.5|
Other specified botulism
A48.51|
Infant botulism
A48.52|
Wound botulism
A48.8|
Other specified bacterial diseases
A49|
Bacterial infection of unspecified site
A49.0|
Staphylococcal infection, unspecified site
A49.01|
Methicillin susceptible Staphylococcus aureus infection, unspecified site

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