A09Infectious gastroenteritis and colitis, unspecified

A09 is the ICD-10-CM diagnosis code for infectious gastroenteritis and colitis, unspecified. It belongs to block A00-A09 (intestinal infectious diseases) and chapter 1 (certain infectious and parasitic diseases). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Don't report A09 together with the conditions in its Excludes1 note: colitis NOS (K52.9), diarrhea NOS (R19.7), enteritis NOS (K52.9), gastroenteritis NOS (K52.9) and 1 more.

As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 391 (Esophagitis, Gastroenteritis and Miscellaneous Digestive Disorders with MCC, relative weight 1.2392) and DRG 392 (Esophagitis, Gastroenteritis and Miscellaneous Digestive Disorders without MCC, relative weight 0.7645), in MDC 06 (Diseases and Disorders of the Digestive System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 009.0 (infectious colitis, enteritis, and gastroenteritis).