ICD 10 Codes From A70-A74

Medical Codes
January 19, 2026

The International Classification of Diseases, 10th Revision (ICD-10) provides a standardized system for documenting and coding medical diagnoses. Among these classifications, the A70-A74 code range represents a specific category of infections caused by various Chlamydia species.

These infections primarily affect the respiratory system, eyes, and other bodily systems, making accurate coding essential for proper diagnosis, treatment tracking, and insurance reimbursement.

Overview of the A70-A74 Code Range

The A70-A74 code range encompasses infections caused by different species of Chlamydia bacteria that manifest in various parts of the body. Unlike sexually transmitted chlamydial infections (which fall under codes A55-A56), this range focuses on chlamydial diseases transmitted through other means, such as contact with infected birds or environmental exposure.

Detailed Code Breakdown

A70: Chlamydia psittaci Infections (Psittacosis)

Code Definition: A70 designates infections caused by Chlamydia psittaci, commonly known as Psittacosis or “parrot fever.”

Clinical Context: This zoonotic infection is typically contracted through exposure to infected birds, particularly parrots, parakeets, pigeons, and other avian species. Transmission occurs when humans inhale airborne particles from dried bird droppings, respiratory secretions, or feather dust containing the bacteria.

Common Symptoms: Patients with psittacosis may present with flu-like symptoms including fever, chills, headache, muscle aches, and a dry cough. In severe cases, the infection can progress to pneumonia.

Coding Application: Use code A70 when documenting confirmed cases of Chlamydia psittaci infection, regardless of the severity or specific manifestation of the disease.

A71: Trachoma

Code Definition: A71 represents trachoma, a chronic and contagious infection of the conjunctiva caused by Chlamydia trachomatis serovars A, B, Ba, and C.

Clinical Context: Trachoma is the leading infectious cause of blindness worldwide, though it is rare in developed countries. The disease progresses through distinct stages, which is why the A71 category includes specific subdivisions to indicate disease progression.

A71.0: Initial Stage of Trachoma

Code Definition: This code identifies the earliest stage of trachoma infection.

Clinical Presentation: In the initial stage, patients experience mild inflammation of the conjunctiva with minimal follicular development. Symptoms may include slight irritation, tearing, and light sensitivity.

Coding Application: Use A71.0 when documenting newly diagnosed trachoma cases in the early inflammatory phase before significant follicular development occurs.

A71.1: Active Stage of Trachoma (Granular Conjunctivitis)

Code Definition: This code represents the active, infectious stage of trachoma characterized by pronounced follicular conjunctivitis.

Clinical Presentation: The active stage features visible follicles on the upper tarsal conjunctiva, intense inflammation, and discharge. This stage is highly contagious and, if left untreated, can lead to scarring.

Coding Application: Apply code A71.1 when patients present with active inflammatory trachoma showing characteristic follicular changes and inflammatory thickening of the conjunctiva.

A71.9: Trachoma, Unspecified

Code Definition: This code serves as the default designation for trachoma cases when the specific stage cannot be determined or is not documented.

Coding Application: Use A71.9 when trachoma is diagnosed but clinical documentation does not provide sufficient detail to classify the infection into a specific stage (A71.0 or A71.1).

A74: Other Diseases Caused by Chlamydiae

Code Definition: A74 functions as a comprehensive category for chlamydial diseases that do not fit into other specific classifications within the ICD-10 system.

Clinical Context: This “catch-all” category ensures that all chlamydial infections affecting non-genital sites can be properly documented, even when they don’t fall under the more specific A70 or A71 classifications.

A74.0: Chlamydial Conjunctivitis

Code Definition: This code identifies chlamydial conjunctivitis, also known as paratrachoma or inclusion conjunctivitis.

Clinical Context: Unlike trachoma (A71), which is caused by specific serovars of Chlamydia trachomatis, chlamydial conjunctivitis under A74.0 is typically caused by other serovars (D-K) and presents differently. This condition is often associated with genital chlamydial infection and can be transmitted through contact with infected genital secretions.

Clinical Presentation: Patients present with acute or subacute conjunctivitis featuring mucopurulent discharge, follicular reaction, and sometimes preauricular lymphadenopathy. Unlike trachoma, this condition typically does not lead to scarring or blindness.

Coding Application: Use A74.0 for documented cases of chlamydial conjunctivitis that are not classified as trachoma, particularly when associated with genital chlamydial infection.

A74.8: Other Chlamydial Diseases

Code Definition: This subcategory encompasses various chlamydial infections affecting body systems other than the eyes, when not otherwise specified.

A74.81: Chlamydial Peritonitis

Code Definition: This specific code identifies inflammation of the peritoneum (the membrane lining the abdominal cavity) caused by Chlamydia species.

Clinical Context: Chlamydial peritonitis typically occurs as a complication of pelvic inflammatory disease or can result from the spread of chlamydial infection from other sites.

Coding Application: Apply code A74.81 when clinical and laboratory findings confirm peritoneal inflammation caused by Chlamydia species.

Other A74.8 Applications: This category may also include other organ-specific chlamydial infections such as chlamydial pneumonia in adults, chlamydial pharyngitis, or other manifestations not specifically coded elsewhere.

A74.9: Chlamydial Infection, Unspecified

Code Definition: This code serves as the most general classification for chlamydial infections when the specific type, location, or manifestation cannot be determined from available documentation.

Coding Application: Use A74.9 only when chlamydial infection is confirmed but documentation lacks sufficient detail to assign a more specific code. This should be considered a code of last resort when specificity cannot be achieved.

Critical Coding Guidelines and Conventions

1. Exclusion Guidelines

Sexually Transmitted Chlamydial Diseases (A55-A56): The A70-A74 range specifically excludes sexually transmitted chlamydial diseases, which are classified under codes A55-A56. This distinction is crucial for proper coding.

A55 includes: Chlamydial lymphogranuloma (venereum)

A56 includes: Other sexually transmitted chlamydial diseases, including chlamydial infection of the lower and upper genitourinary tract

Practical Application: When encountering chlamydial infections of the cervix, urethra, or other genital organs, coders must use the A55-A56 range rather than A70-A74, even though the causative organism is the same.

2. Neonatal Considerations

Special Coding for Newborns: Chlamydial infections occurring in newborns require specific coding from the perinatal chapter (Chapter 16, codes P00-P96) rather than from the A70-A74 range.

P39.1: Neonatal Chlamydial Conjunctivitis

This code should be used for conjunctivitis caused by Chlamydia in newborns, typically acquired during passage through an infected birth canal.

P23.1: Neonatal Chlamydial Pneumonia

This code designates pneumonia caused by Chlamydia trachomatis in newborns, another common manifestation of perinatal chlamydial transmission.

Rationale: Using perinatal codes for newborns ensures proper categorization of congenital and perinatally acquired infections, which have different epidemiological and clinical implications than infections acquired later in life.

Importance of Coding Specificity

Clinical Documentation

Accurate and detailed clinical documentation is the foundation of proper ICD-10 coding. Physicians and healthcare providers must document:

The specific Chlamydia species when identified through laboratory testing
The anatomical site of infection
The stage or severity of disease (particularly for trachoma)
Any complications or comorbidities
The source or mode of transmission when known

Reimbursement Implications

Proper use of ICD-10 codes directly impacts reimbursement from Medicare, Medicaid, and private insurance carriers. Specificity in coding:

Justifies the medical necessity of diagnostic tests and treatments
Supports appropriate payment levels based on disease complexity
Reduces claim denials and delays
Minimizes audit risk and compliance issues

Public Health Tracking

Accurate coding of chlamydial infections serves important public health functions:

Enables surveillance of disease prevalence and trends
Identifies potential outbreaks (particularly important for psittacosis)
Guides resource allocation for prevention and treatment programs
Supports epidemiological research

Best Practices for Medical Coders

Review Complete Medical Records: Always review laboratory results, imaging studies, and clinical notes to determine the most specific code possible.
Query Providers When Necessary: If documentation is unclear or incomplete, query the treating physician for clarification rather than defaulting to unspecified codes.
Stay Updated on Guidelines: Regularly review updates from the National Center for Health Statistics (NCHS) and Centers for Medicare & Medicaid Services (CMS) regarding coding conventions.
Use Official Coding Resources: Reference the official ICD-10-CM code books and guidelines rather than relying solely on memory or abbreviated coding sheets.
Document Rationale: Maintain clear documentation explaining code selection, particularly when choosing between similar or related codes.

Conclusion

The ICD-10 codes A70-A74 provide essential tools for accurately documenting and tracking chlamydial infections affecting the respiratory system, eyes, and other bodily systems. Understanding the nuances of each code, including the specific clinical contexts in which they apply and the important exclusions and special coding rules, is critical for healthcare professionals involved in clinical documentation and medical coding.

By adhering to established coding guidelines from NCHS and CMS, ensuring maximum specificity in code selection, and maintaining clear documentation, medical professionals can support optimal patient care, facilitate appropriate reimbursement, and contribute to important public health surveillance efforts. As with all medical coding, ongoing education and attention to detail remain paramount to achieving accuracy and compliance in this specialized area of infectious disease classification.