2027 ICD-10-CM Diagnosis Code A77.0Spotted fever due to Rickettsia rickettsii

ICD-10-CM Codes›A00–B99›A75-A79›A77

ICD-10-CM A77.0
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

A77.0 is a billable ICD-10-CM diagnosis code for spotted fever due to Rickettsia rickettsii. 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 56 closely related codes. Coders also document this condition as Eastern Rocky Mountain spotted fever. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Parasitic, other specified and unspecified infections.

Code Identity

ICD-10-CM Code
A77.0
Billable Status
Yes — Valid for Submission
Code Describes
Spotted fever due to Rickettsia rickettsii
Short Description
Spotted fever due to Rickettsia rickettsii
Same as the full description in the CMS dataset.
Parent Code
A77
Spotted fever [tick-borne rickettsioses]

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA75-A79Rickettsioses
CategoryA77Spotted fever [tick-borne rickettsioses]
This CodeA77.0Spotted fever due to Rickettsia rickettsii

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Eastern Rocky Mountain spotted fever
  • Rocky Mountain spotted fever
  • Western Rocky Mountain spotted fever

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to A77.0: 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.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • 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.

  • Rocky Mountain spotted fever
  • Sao Paulo fever

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.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • 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.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 A77.0 to ICD-9-CMHistory

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

ICD-9-CM
082.0 Spotted fevers
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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About A77.0Overview

What is the ICD-10 code for spotted fever due to Rickettsia rickettsii?

The ICD-10-CM code for spotted fever due to Rickettsia rickettsii is A77.0 (sometimes written as A770). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is A77.0 (Spotted fever [tick-borne rickettsioses]) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report spotted fever due to Rickettsia rickettsii on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does A77.0 group to?

When spotted fever due to Rickettsia rickettsii 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 A77.0 a CC or MCC?

CMS lists A77.0 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 56 closely related codes in its exclusion list.

What is the ICD-9 equivalent of A77.0?

Under the General Equivalence Mappings, spotted fever due to Rickettsia rickettsii converts to ICD-9-CM 082.0 (spotted fevers). The mapping is approximate, so confirm the match fits the documentation.