2026 ICD-10-CM Diagnosis Code A79.9Rickettsiosis, unspecified

ICD-10-CM Codes›A00–B99›A75-A79›A79

ICD-10-CM A79.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A79.9 is a billable ICD-10-CM diagnosis code for rickettsiosis, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 867 through 869. Coders also document this condition as disease caused by Rickettsia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Parasitic, other specified and unspecified infections.

Code Identity

ICD-10-CM Code
A79.9
Billable Status
Yes — Valid for Submission
Code Describes
Rickettsiosis, unspecified
Short Description
Rickettsiosis, unspecified
Same as the full description in the CMS dataset.
Parent Code
A79
Other rickettsioses

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA75-A79Rickettsioses
CategoryA79Other rickettsioses
This CodeA79.9Rickettsiosis, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Disease caused by Rickettsia
  • Disease caused by rickettsiae
  • Disease caused by Rickettsiales
  • Encephalitis caused by rickettsia
  • Myocarditis caused by Rickettsia
  • Rickettsial endocarditis
  • Rickettsial pneumonia

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Rickettsial infection NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Disease, diseased
      • rickettsial NOS
    • Infection, infected, infective(opportunistic)
      • rickettsial NOS
    • Rickettsial disease
    • Rickettsiosis

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF009
Parasitic, other specified and unspecified infections
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Bacterial Infections

Bacteria are tiny organisms (living things) that have only one cell. Under a microscope, they look like balls, rods, or spirals. They can be found almost everywhere on Earth. There are lots of bacteria in and on your body. In fact, your body has about 10 times more bacteria cells than human cells.

The full article covers:

  • What are bacteria?
  • How do bacterial infections spread?
  • What are the treatments for bacterial infections?
  • Can bacterial infections be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert A79.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
083.9 Rickettsiosis NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A79.9Overview

Is A79.9 (Other rickettsioses) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report rickettsiosis, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A79.9 group to?

When rickettsiosis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 868, 869, with relative weights from 0.7297 to 2.0932 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A79.9?

Under the General Equivalence Mappings, rickettsiosis, unspecified converts to ICD-9-CM 083.9 (rickettsiosis NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.