ICD-10-CM Code for Presumed Infectious Diarrhea
The ICD-10-CM code for presumed infectious diarrhea is A09, which represents "Infectious gastroenteritis and colitis, unspecified."
Code Selection Rationale
A09 is the appropriate code when infectious diarrhea is clinically suspected but no specific pathogen has been identified through laboratory testing. This code encompasses both gastroenteritis and colitis of presumed infectious origin.
This code applies when clinical presentation suggests an infectious etiology—such as acute onset diarrhea with or without fever, nausea, vomiting, or abdominal cramping—but stool studies have either not been performed or have not yet identified a specific organism. 1
When to Use A09
Use A09 for patients presenting with acute diarrhea (≤13 days duration) when the clinical picture suggests infection but diagnostic testing is pending or not indicated. 1
This code is appropriate for self-limited diarrheal illness in immunocompetent adults where stool testing is not warranted, such as uncomplicated traveler's diarrhea or community-acquired gastroenteritis without fever, bloody stools, or severe symptoms. 2, 3
A09 applies when norovirus or other viral gastroenteritis is clinically suspected based on presentation (violent vomiting, nonbloody diarrhea lasting 2-3 days, associated headache and body aches) but viral testing is not performed, as it rarely changes management. 3, 4
When More Specific Codes Apply
If a specific pathogen is identified through stool culture, molecular testing, or other diagnostic methods, use the organism-specific ICD-10-CM code instead of A09. For example, use A02.0 for Salmonella enteritis, A03.9 for Shigella infection unspecified, or A04.5 for Campylobacter enteritis. 1
For Clostridioides difficile infection confirmed by toxin detection or nucleic acid amplification testing, use A04.7 rather than A09. 1
When Shiga toxin-producing E. coli (STEC) is identified, use A04.3 for enterohemorrhagic E. coli infection rather than the nonspecific code. 1
Clinical Context for Code Assignment
The decision to assign A09 versus pursuing specific pathogen identification depends on clinical severity markers: fever documented in a medical setting, bloody or mucoid stools, severe abdominal cramping, signs of sepsis, immunocompromised status, or symptoms persisting ≥8 days all warrant stool testing and may lead to more specific coding once results return. 1, 2
In outbreak settings where multiple individuals share a common exposure, public health authorities may require specific pathogen identification, which would then necessitate a more specific ICD-10-CM code than A09. 1
For persistent diarrhea (14-29 days) or chronic diarrhea (≥30 days) where infectious etiology remains suspected but unconfirmed, A09 may still be appropriate, though noninfectious causes including inflammatory bowel disease and irritable bowel syndrome should be considered. 1, 2