Evaluation of Chronic Diarrhea in Men Who Have Sex with Men (MSM) Engaging in Oral-Anal Contact
In a man with chronic diarrhea who engages in fecal-oral sexual activity, you must test for HIV, perform comprehensive stool testing for sexually transmitted enteric infections (particularly Shigella, Campylobacter, and Giardia), and conduct standard chronic diarrhea workup including celiac disease screening and inflammatory markers.
Critical First Steps: HIV and Sexual History
The sexual history fundamentally changes your diagnostic approach. Men engaging in oral-anal contact are at high risk for sexually transmitted enteric infections (STEIs), and chronic diarrhea is a common presenting symptom in newly diagnosed HIV 1. HIV testing is mandatory as immunodeficiency dramatically alters the differential diagnosis and enables detection of opportunistic infections like cryptosporidia or norovirus 1.
Document specific sexual practices including:
- Frequency of oral-anal contact
- Number and gender of sexual partners
- Use of barrier protection
- Partner symptoms or recent illness
- HIV status and PrEP use
Pathogen-Specific Testing Algorithm
Mandatory Stool Testing
Test for Giardia using antigen detection or PCR (sensitivity and specificity >95%) 2. This is a strong recommendation for all chronic diarrhea patients, but particularly critical in MSM given sexual transmission through oral-anal contact 3.
Obtain stool cultures specifically for Shigella and Campylobacter, as these are the most commonly sexually transmitted bacterial enteric pathogens in MSM 4, 5, 3. Shigella has a particularly low infectious dose making sexual transmission highly efficient, and extensively drug-resistant strains are emerging in MSM populations 5. Campylobacter, despite requiring a higher infectious dose, is also frequently transmitted sexually 3.
Do NOT routinely test for other ova and parasites unless there is travel history to high-risk areas 2. This is a conditional recommendation that saves resources while maintaining diagnostic yield.
Standard Chronic Diarrhea Workup
Regardless of sexual history, perform:
Celiac disease screening with IgA tissue transglutaminase (tTG) plus total IgA level 2. If IgA deficient, use IgG-tTG or IgG deaminated gliadin peptides. This has >90% sensitivity and specificity in appropriate populations.
Fecal calprotectin or lactoferrin to screen for inflammatory bowel disease 2. This helps stratify patients into inflammatory versus non-inflammatory categories, directing further evaluation.
Complete blood count, ferritin, thyroid function tests 1 as part of initial screening.
Clostridium difficile testing using the two-stage approach: first, glutamate dehydrogenase EIA or PCR to detect organism presence; second, toxin EIA to demonstrate active toxin production 1. This is particularly relevant as C. difficile can cause persistent or relapsing diarrhea.
Critical Pitfalls to Avoid
Do not assume all chronic diarrhea in MSM is infectious. While STEIs are important, celiac disease prevalence in chronic diarrhea patients ranges from 3-10% 1, and standard causes still apply.
Do not rely on traditional "three stool ova and parasite" examination for Giardia—it has only 60-90% sensitivity 1. Modern antigen or PCR testing is superior 2.
Do not overlook asymptomatic carriage. Patients may be asymptomatic carriers of enteric pathogens and still transmit through sexual activity 4. If a partner has diarrhea, recommend avoiding sexual contact during active illness and for 1-2 weeks after symptom resolution, with oral-anal contact avoided for 4-6 weeks 4.
Do not miss amoebiasis if there is any travel history or immigration from endemic areas. While routine ova/parasite testing is not recommended without travel history 2, Entamoeba histolytica can cause chronic infection and requires specific consideration in the appropriate epidemiologic context 1.
If Initial Testing is Negative
Once immunodeficiency and infectious causes are excluded:
Consider bile acid diarrhea testing if available (48-hour fecal bile acid collection or serum FGF-19) 2, or empiric trial of bile acid binder
Proceed to colonoscopy with biopsies to evaluate for microscopic colitis, IBD, or other structural abnormalities
Consider duodenal biopsy even with negative celiac serology if clinical suspicion remains high, as antibody-negative celiac disease accounts for 6-7% of cases 1
Prevention Counseling
Provide harm reduction strategies:
- Minimize oral-anal contact during sexual activity
- Use dental dams or other barriers
- Clean sex toys between uses
- Maintain good hand hygiene
- Avoid sexual contact if partner has diarrhea 4
This integrated approach addresses both the unique infectious risks associated with oral-anal sexual contact while ensuring standard chronic diarrhea etiologies are not overlooked.