2027 ICD-10-CM Diagnosis Code A79.9Rickettsiosis, unspecified
ICD-10-CM Codes›A00–B99›A75-A79›A79
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Not Chronic
A79.9 is a billable ICD-10-CM diagnosis code for rickettsiosis, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 867 through 869. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 15 closely related codes. 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
Code Classification
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
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to A79.9: its own notes plus those printed at Chapter 1. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- diseases generally recognized as communicable or transmissible
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Rickettsial infection NOS
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- 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
Add a second code, after this one, to fully describe the condition.
- code to identify resistance to antimicrobial drugs (Z16.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name A79.9, its category, or a range that includes it.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Disease, diseased See Also: Syndrome;
rickettsial NOS A79.9
Rickettsial disease A79.9
Rickettsiosis A79.9
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Rickettsia Infections
infections by the genus rickettsia.
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.
Code HistoryHistory
Questions About A79.9Overview
What is the ICD-10 code for rickettsiosis, unspecified?
The ICD-10-CM code for rickettsiosis, unspecified is A79.9 (sometimes written as A799). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
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, 2026 through September 30, 2027.
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, 869, 868, with relative weights from 0.6784 to 2.1855 depending on complications. Higher weights mean higher Medicare reimbursement.
Is A79.9 a CC or MCC?
CMS lists A79.9 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 15 closely related codes in its exclusion list.
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.
