ICD-10 Code A70: Chlamydia psittaci infections (psittacosis)

Key Takeaways

ICD-10 Code A70 is the billable, specific code for Chlamydia psittaci infections, including psittacosis, ornithosis, and parrot fever.

Transmission occurs via inhalation of dust-borne particles from infected bird droppings, feathers, or secretions; high-risk groups include veterinarians, poultry workers, and pet shop staff.

When antimicrobial resistance is clinically relevant, add code Z16.- alongside A70 per ICD-10-CM instructional notation.

Pabau’s claims management software supports accurate diagnostic code entry and claim submission for rare zoonotic infections like psittacosis.

ICD-10 Code A70 (Chlamydia psittaci infections) is a billable, specific ICD-10-CM diagnosis code covering psittacosis, ornithosis, and parrot fever. It classifies infections caused by Chlamydia psittaci (previously reclassified as Chlamydophila psittaci), a bacterial pathogen transmitted from birds to humans. The code is valid for the 2025 and 2026 code years with no pending changes.

Integrative medicine practices and occupational health practices see these cases, particularly when patients work with birds professionally

A70 sits within ICD-10-CM section A70-A74 (Other diseases caused by chlamydiae), which falls under chapter A00-B99 (Certain infectious and parasitic diseases). The CMS ICD-10-CM code set confirms A70 carries no subclassifications – the code stands alone as a single-level, fully specified entry

Inclusion terms and clinical description for ICD-10 Code A70

Three inclusion terms appear under A70 in the official ICD-10-CM tabular list. All three describe the same underlying infection and are coded identically.

• Psittacosis – the most common clinical term; used when the patient reports bird exposure and presents with atypical pneumonia
• Ornithosis – a broader synonym covering infections from any bird species, not limited to parrots or psittacine birds
• Parrot fever – a colloquial term historically associated with parrot-to-human transmission; still a valid index entry in ICD-10-CM

The pathogen is Chlamydia psittaci, a gram-negative obligate intracellular bacterium. Humans acquire infection by inhaling dust-borne particles contaminated with infected bird nasal secretions, droppings, or feather dust. Person-to-person spread is rare but documented in healthcare settings.

Clinically, psittacosis presents as a febrile illness with prominent respiratory symptoms. The onset is typically abrupt, with fever, severe headache, and myalgia preceding cough by several days. Radiographic findings show patchy or lobar infiltrates consistent with atypical pneumonia, though respiratory symptoms may be milder than the systemic presentation suggests.

Transmission, risk factors, and high-risk occupations

Occupational exposure drives most psittacosis cases in the United States. Knowing the at-risk populations helps clinicians maintain a higher index of suspicion when the history fits.

Psittacosis is a nationally notifiable disease in the United States, and reporting requirements vary by state jurisdiction. Clinicians should check their state public health department’s requirements before assuming federal-level reporting alone is sufficient.

Some coders add Z57.5 (Occupational exposure to toxic agents in other industries) when documenting work-related bird exposure. Apply this with caution: Z57.5 describes exposure to toxic agents, not biological or infectious agents, so it is an imperfect fit for a zoonotic infection and is never required for an A70 encounter. Confirm your payer accepts it in this context before assigning it.

ICD-10 Code A70 documentation requirements

Coding A70 correctly starts with the physician’s documented diagnosis. Coders cannot assign a specific infectious disease code based on symptoms or lab results alone – the clinician must name the condition in the medical record.

The following elements strengthen the A70 claim and reduce the risk of denial or audit scrutiny. Use digital intake and clinical forms to capture this information at the point of care rather than reconstructing it after the visit.

• Confirmed diagnosis statement: The physician must explicitly document psittacosis, ornithosis, parrot fever, or Chlamydia psittaci infection in the assessment section of the note
• Exposure history: Species, duration, and nature of bird contact (professional or household)
• Clinical presentation: Fever onset date, respiratory symptoms, headache, myalgia, and any neurological involvement
• Diagnostic testing: Serology (complement fixation or microimmunofluorescence), PCR from respiratory specimen, or culture results supporting the diagnosis
• Treatment initiated: Antibiotic class and duration; doxycycline is the standard first-line agent for psittacosis

Maintaining thorough patient record documentation for zoonotic infections protects providers during payer audits. Psittacosis is rare enough that an undocumented exposure history can prompt a payer to question whether the atypical workup was medically necessary.

For HIPAA-compliant medical documentation, ensure all records related to the diagnosis, treatment, and any public health reporting are stored securely and accessible only to authorized personnel. Structured clinical documentation software makes it easier to capture exposure history and testing details consistently.

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Pabau's claims management tools help practices document rare infections like psittacosis accurately, reducing denials and keeping billing workflows on track from first visit to paid claim.

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Coding guidelines and instructional notations for ICD-10 Code A70

The ICD-10-CM tabular list carries one instructional notation at A70: use an additional code from Z16.- to identify resistance to antimicrobial drugs when this is clinically relevant and documented.

Z16.- antimicrobial resistance add-on code

Z16.- is an additional code, not a sequencing requirement for every A70 claim. Assign it only when the medical record documents confirmed or suspected antimicrobial resistance affecting treatment decisions. Routine psittacosis cases treated successfully with doxycycline do not require a Z16.- code.

Psittacosis is typically sensitive to tetracyclines and macrolides. However, treatment failures have been reported, and resistance documentation may arise in immunocompromised patients or cases involving unusual strains. When resistance is documented, the Z16.- code supports accurate epidemiological tracking and may affect authorization for alternative antibiotic regimens.

Sequencing: principal vs. secondary diagnosis

When psittacosis is the confirmed reason for the outpatient visit or inpatient admission, A70 is the principal diagnosis. Assign respiratory complications (such as pneumonia with respiratory failure) as secondary codes if they meet the criteria for additional diagnosis reporting under UHDDS guidelines.

If the patient presents with pneumonia that is later confirmed as psittacosis during the admission, A70 becomes the principal diagnosis at discharge, superseding a provisional pneumonia code assigned at admission.

ICD-10-CM vs. WHO ICD-10

The US ICD-10-CM code A70 aligns with the WHO ICD-10 browser classification, but practices outside the United States should verify code applicability under their national version. ICD-10-CM is the US-specific clinical modification maintained by CMS and NCHS. International practices may use country-specific ICD-10 adaptations that differ in structure or descriptor language.

Differential diagnosis and related ICD-10 codes near A70

Psittacosis presents as atypical pneumonia, which overlaps clinically with several other infectious conditions. Getting the code right depends on documented diagnostic confirmation, not just symptom pattern. Miscoding an atypical pneumonia carries audit risk, particularly when the pathogen workup is incomplete.

These are the most common differential codes for clinicians and coders to distinguish from A70. For a closely related atypical pneumonia example, see the coding guidance for pneumonia due to Streptococcus pneumoniae (J13), and make sure your practice management system supports structured code entry alongside encounter notes.

• A78 – Q fever: Caused by Coxiella burnetii; transmitted from cattle, sheep, and goats, not birds. Serological confirmation distinguishes Q fever from psittacosis. Q fever pneumonia may be indistinguishable clinically without testing.
• A48.1 – Legionellosis (Legionnaires’ disease): Water-source transmission from cooling towers or hospital plumbing; no bird exposure history. Urinary antigen test is the primary rapid diagnostic for Legionella.
• J15.7 – Pneumonia due to Mycoplasma pneumoniae: Common atypical pneumonia with gradual onset; no animal exposure. Cold agglutinins and Mycoplasma serology differentiate from psittacosis.
• A74.9 – Chlamydial infection, unspecified: Use only when chlamydial infection is confirmed but the specific organism (psittaci vs. other Chlamydia species) is not identified in the record. Do not default to A74.9 when the history and testing support A70.
• A71 – Trachoma: A different chlamydial disease (Chlamydia trachomatis affecting the conjunctiva); unrelated to respiratory psittacosis but within the same ICD-10-CM section A70-A74.

For reference, the legacy ICD-9 code for psittacosis was 073. When converting older records or crosswalking for payer reporting, A70 is the direct equivalent. For a related chlamydial infection, see ICD-10 code A55 (chlamydial lymphogranuloma).

Billing and claims usage for ICD-10 Code A70: Chlamydia psittaci infections (psittacosis)

A70 is a standalone, fully specified code. No additional ICD-10-CM subcode exists under it. Coders can assign A70 directly without needing a 5th or 6th character extension.

Common claim submission scenarios

Psittacosis encounters typically fall into two billing contexts: outpatient evaluation and management visits (usually with a CPT E/M code reflecting moderate to high complexity given the infectious disease workup) and inpatient admissions when the patient requires hospitalization for pneumonia management.

Pair A70 with the appropriate E/M CPT code at the appropriate complexity level. The atypical pneumonia workup – including serology, chest imaging, and antibiotic initiation – generally supports medical decision-making complexity documentation at the moderate or high level.

Using Pabau’s claims management software for A70 submissions

Rare zoonotic codes like A70 are where billing workflows either hold together or fall apart. A practice relying on manual code entry or disconnected systems faces higher denial risk simply because coders have fewer reference checks in the workflow. If your team is refining its end-to-end process, this overview of how medical billing works is a useful reference.

Pabau’s claims management software supports structured ICD-10-CM code entry linked directly to the clinical record, reducing transcription errors between the physician’s documented diagnosis and the submitted claim. The platform also supports additional code tracking, so Z16.- entries are captured when resistance documentation exists in the encounter note rather than being overlooked at billing time.

For practices concerned about practice software HIPAA requirements when handling notifiable disease records, Pabau’s architecture supports HIPAA-compliant data handling across diagnostic documentation and claims workflows. Also relevant for occupational health practices is Pabau’s AI-powered clinical documentation capability, which supports faster, more accurate note generation for complex infectious disease presentations.

For additional coding tools, the AAPC Codify ICD-10-CM lookup provides a searchable reference that coders can use to verify A70 alongside adjacent chlamydial and atypical pneumonia codes before submission.

Protecting patient diagnostic records for rare notifiable infections requires both clinical documentation accuracy and secure data handling practices throughout the claims lifecycle.

Conclusion

Rare zoonotic infections like psittacosis test the limits of a billing team’s code familiarity. A70 is billable, specific, and supported by a clear set of inclusion terms – but it requires solid occupational exposure documentation, careful differential coding, and an understanding of when to add Z16.- for resistance notation.

Pabau’s claims management software keeps ICD-10-CM code entry connected to the clinical record, so the path from documented psittacosis diagnosis to accurate, submitted claim is shorter and less error-prone. To see how Pabau handles diagnostic coding workflows for complex and rare infection encounters, book a demo.

Continue your research

Need to review other ICD-10 diagnostic code references? ICD-10 code A55 (chlamydial lymphogranuloma) covers the coding structure, documentation requirements, and clinical criteria for a related chlamydial infection.

Looking for guidance on structuring clinical notes for unusual presentations? Safer clinical notes walks through best practices for documenting complex and rare diagnoses in a way that withstands payer review.

Want to understand how practice software should handle HIPAA-sensitive records? Patient data security tools explains the key features that protect diagnostic data across the full clinical and billing workflow.

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