ICD-11 Chapter 01: Certain infectious or parasitic diseases

What is Chapter 01 of ICD-11?

The Chapter 01 of the ICD-11 groups the infectious and parasitic diseases. Note the official name: "Some" infectious diseases — not all. This is because many localized infections (such as pneumococcal pneumonia or a urinary tract infection) are coded in the affected system chapter, not here.

In ICD-10, this material was in the Chapter I (A00–B99). The ICD-11 reorganizes it following a mixed logic: first it groups by clinical syndrome (e.g. infectious gastroenteritis), then transmission mode (e.g. STI), and finally specific agent (e.g. HIV, dengue, tuberculosis).

Important news: The flu was moved from the respiratory chapter to Chapter 01 in ICD-11, due to its impact on multiple systems and its relevance to public health. Also added the COVID-19 (RA01.0, in Chapter 25) and the monkeypox (1E71).

The prion diseases (e.g. Creutzfeldt-Jakob) were moved to Chapter 08 (nervous system), since they are neurological diseases although they can be communicable.

Chapter 01 Blocks

The chapter organizes infections first by clinical syndrome, then by mode of transmission, and finally by agent. Click on each block to see the main codes.

1A00–1A4Z

Gastroenteritis or colitis of infectious origin

›

Diarrheal diseases of infectious origin. One of the most codified blocks globally. Includes cholera, salmonellosis, shigellosis, campylobacter and gastroenteritis without an identified agent.

Code	Diagnosis
1A00	Cholera
1A02	Intestinal infections due to Shigella
1A02	Intestinal infections due to Shigella
1A03	Intestinal infections due to Escherichia coli
1A07	Typhoid fever
1A08	Paratyphoid fever
1A20	Enteritis due to Adenovirus
1A22	Gastroenteritis due to Rotavirus
1A40	Gastroenteritis or colitis without specification of infectious agent

1B10–1B2Z

mycobacterial diseases

›

Groups tuberculosis and leprosy together for the first time in ICD-11, as they share similarities in identification, course and treatment. Tuberculosis is the deadliest bacterial infection in the world.

Code	Diagnosis
1B10	Tuberculosis of the respiratory system
1B11	Tuberculosis of the nervous system
1B12.5	Tuberculosis of the genitourinary system
1B12.40	Tuberculosis of bones or joints
1B14	Latent tuberculosis
1B13.Z	Miliary tuberculosis, unspecified
1B1Z	Tuberculosis, unspecified
1B20	Leprosy

TB coding: Tuberculosis should NOT be accepted as a cause due to other conditions, except HIV disease, malignancies, and conditions that impair the immune system.

1B50–1C4Z

Bacterial diseases

›

It groups together zoonotic bacterial diseases (transmitted from animals) and other systemic bacterial diseases, including those notifiable.

Code	Diagnosis
1B50	Scarlet fever
1B51	Streptococcal pharyngitis
1B97	Anthrax
1B91	Leptospirosis
1B93	Plague
1B95	Brucellosis
1C12	Whooping cough
1C13	Tetanus
1C17	Diphtheria
1C1C	Meningococcal disease

1A60–1A9Z

Sexually transmitted infections (STIs)

›

Infections with a predominantly sexual mode of transmission. Includes syphilis, gonorrhea, chlamydia and other STIs. HIV has its own block (1C60–1C62).

Code	Diagnosis
1A60	Congenital syphilis
1A61	Early syphilis
1A62	Late syphilis
1A70	Gonococcal genitourinary infection
1A80	Chlamydial lymphogranuloma
1A94	Anogenital herpes simplex infection
1A92	Trichomoniasis

1C60–1C62

Human immunodeficiency virus (HIV) disease

›

HIV disease categories distinguish associated tuberculosis, associated malaria and cases without mention of either. More specific subcategories describe clinical stage and manifestations.

Code	Diagnosis
1C60	Human immunodeficiency virus disease associated with tuberculosis
1C61	Human immunodeficiency virus disease associated with malaria
1C62	Human immunodeficiency virus disease without mention of tuberculosis or malaria

Coding instruction: HIV (1C60–1C62) should NOT be accepted as the underlying cause due to other conditions, except conditions requiring blood transfusion (hemophilia, anemia), invasive procedures, or drug abuse.

1D20–1D4Z

Arthropod-borne viral fevers and viral hemorrhagic fevers

›

Viral diseases transmitted mainly by mosquitoes, ticks and other arthropods. It includes dengue, Zika, chikungunya, yellow fever and hemorrhagic fevers such as Ebola.

Code	Diagnosis
1D20	Dengue without warning signs
1D21	Dengue with warning signs
1D22	Severe dengue
1D47	Yellow fever
1D40	Chikungunya virus disease
1D46	West Nile virus infection
1D48	Zika virus disease
1D60.0Y	Other specified Ebola disease
1D60.1Y	Other specified Marburg disease
1D61.2	Lassa fever
1D86	Viral haemorrhagic fever, not elsewhere classified

1E50–1E9Z

Viral infections — hepatitis, skin and mucous membranes

›

It includes viral hepatitis, measles, rubella, chickenpox and other viral infections that predominantly affect the skin and mucous membranes.

Code	Diagnosis
1E50	Acute viral hepatitis
1E51	Chronic viral hepatitis
1E70	Smallpox
1E71	Mpox
1F03	Measles
1F02	Rubella
1D80	Mumps

1E30–1E32

Influenza (flu) — New in Chapter 01

›

In ICD-11, influenza was moved to Chapter 01 from the respiratory chapter (ICD-10: J09–J11), given its impact on multiple systems and its importance to global public health.

Code	Diagnosis
1E30	Influenza due to identified seasonal influenza virus
1E31	Influenza due to identified zoonotic or pandemic influenza virus
1E32	Influenza, virus not identified

Change vs ICD-10: In ICD-10 influenza was in J09–J11 (respiratory chapter). In ICD-11 it is in 1E30–1E32 (infectious chapter). Important for coding causes of death.

1F28.Z–1F2Z

Mycoses (fungal infections)

›

Infections caused by fungi, including superficial infections (ringworm, candidiasis), subcutaneous and invasive systemic infections, especially relevant in immunocompromised patients.

Code	Diagnosis
1F28.Z	Dermatophytosis, unspecified
1F25	Coccidioidomycosis
1F27	Cryptococcosis
1F20.Z	Aspergillosis, unspecified
1F2A.Z	Histoplasmosis, unspecified
1F2Z	Mycoses, unspecified

1F4Z–1H0Z

Parasitic diseases

›

Groups protozoa, helminthiasis and ectoparasitosis. It includes malaria, Chagas disease, leishmaniasis, toxoplasmosis and intestinal helminthiases.

Code	Diagnosis
1F4Z	Malaria, unspecified
1F51	African trypanosomiasis
1F53	Chagas disease
1F54	Leishmaniasis
1F57.Z	Toxoplasmosis, unspecified
1F60	Angiostrongyliasis
1F62	Ascariasis
1G00	Pediculosis
1G04	Scabies

1G80–1G8Z

Sequelae of infectious diseases

›

Codes for the late consequences of infectious diseases, when the active disease is no longer present but its effects persist. Equivalent to ICD-10 block B90–B94.

Code	Diagnosis
1G80	Sequelae of tuberculosis
1G83	Sequelae of poliomyelitis
1G82	Sequelae of leprosy
1G8Z	Sequelae of unspecified infectious diseases

RA01.0

COVID-19 — Special Code (Chapter 25)

›

Although clinically an infectious disease, COVID-19 is coded in the Chapter 25 (Codes for special purposes) due to its nature as a global health emergency.

Code	Diagnosis
RA01.0	COVID-19, virus identified
RA01.0	COVID-19, virus identified
RA01.1	COVID-19, virus not identified
RA02	Post COVID-19 condition

Antimicrobial Resistance (AMR)

The ICD-11 includes a specific system for coding the antimicrobial resistance, designed to support the WHO Global Surveillance System. The AMR codes are located in the Chapter 21 (symptoms and findings) and should be reported always in combination with the infectious disease code of Chapter 01.

Key rule: AMR codes never report themselves. When only one condition can be reported, the infectious disease code is retained, not the ADR code. For tabulation, both must be reported together.

Comparison ICD-10 vs ICD-11 — Chapter 01

Main structural changes according to the official WHO Reference Guide:

ICD-10 block	ICD-11 Equivalent
A00–A09 Intestinal infectious diseases	1A00–1A4Z Gastroenteritis or colitis of infectious origin
A15–A19 Tuberculosis	1B10–1B1Z Mycobacterial diseases (along with leprosy)
A30 Leprosy	1B20 Leprosy (now together with tuberculosis in mycobacteria)
A50–A64 STI	1A60–1A9Z Sexually transmitted infections
B00–B09 Viral infections (skin and mucous membranes)	1E00–1E9Z Viral infections characterized by skin lesions
B15–B19 Viral hepatitis	1E50–1E5Z Viral hepatitis
B20–B24 HIV	1C60–1C62 HIV disease (by clinical stages)
B35–B49 Mycosis	1F23–1F2Z Mycosis
B50–B64 Protozoal diseases	1F50–1G7Z Parasitic diseases
B90–B94 Aftermath	1G80–1G8Z Sequelae of infectious diseases
B95–B98 Infectious agents (as cause)	Now part of Chapter X extension codes
J09–J11 Influenza (respiratory chapter)	1F40–1F4Z Influenza (moved to the infectious ward)
G-series Prion diseases (nervous chapter)	Continued in Chapter 08 (nervous system) — no change

Coding Guidance

Location logic in Chapter 01

According to the WHO Reference Guide, the main rule is:

If the infection is systemic or the agent is clinically relevant → use Chapter 01
If the infection is mainly localized and the agent is unknown or there is a mixed etiology → use the chapter on the affected system (e.g. pneumonia without agent = Chapter 12)
Common infectious agents may appear as categories under localized infections in other chapters

Special instructions for basic causes of death

The anger (1A00) does not accept other conditions as a cause
The tuberculosis (1B10–1B1Z) only accepts HIV, malignant neoplasms, and conditions that impair the immune system as causes
The HIV (1C60–1C62) does not accept other conditions as a cause, except: necessary transfusions, invasive procedures or drug abuse

ℹ️ Source: ICD-11 Reference Guide, February 2023, WHO. Independent information portal. For official clinical coding consult icd.who.int.

Frequently asked questions

What is the ICD-11 code for COVID-19?

COVID-19 is classified under RA01. The subcode RA01.0 means virus identified, and RA01.1 means virus not identified. These subcodes do not distinguish cases with and without pneumonia.

What ICD-11 code does tuberculosis have?

Tuberculosis is grouped into 1B10–1B1Z. Respiratory tuberculosis is 1B10, that of the central nervous system 1B11 and miliary tuberculosis 1B13.Z. In ICD-10 it was A15–A19. A novelty is that in ICD-11 tuberculosis shares a block with leprosy within "Mycobacterial Diseases".

What is the ICD-11 code for HIV/AIDS?

1C60 covers HIV disease associated with tuberculosis, 1C61 HIV disease associated with malaria, and 1C62 HIV disease without mention of tuberculosis or malaria. More specific subcodes distinguish clinical stage and manifestations.

What ICD-11 code does dengue have?

Dengue has three codes according to severity: 1D20 (no warning signs), 1D21 (with warning signs) and 1D22 (severe dengue). In ICD-10 it was A90–A91.

Why is influenza in Chapter 01 and not in respiratory?

The WHO moved influenza from the respiratory chapter (ICD-10: J09–J11) to infectious Chapter 01 in ICD-11 because it affects multiple body systems and is a major global public health concern. Influenza ICD-11 codes are 1E30–1E32.

Where are prion diseases in ICD-11?

Prion diseases (such as Creutzfeldt-Jakob disease) moved to the Chapter 08 (diseases of the nervous system) in ICD-11, because although they can be communicable, they are fundamentally neurological diseases. In the ICD-10 they were in A81.

How is monkeypox (mpox) coded in ICD-11?

Monkeypox (mpox) is coded as 1E71 in ICD-11. Classic smallpox is 1E70. Both are in the block of viral infections characterized by skin lesions.