Sexually transmitted infections (STIs) are often thought to affect only the genital tract, but these pathogens can impact various systems throughout the body. The gastrointestinal (GI) tract, which manages digestion and nutrient absorption, is one such system susceptible to involvement. Diarrhea is sometimes an unexpected symptom of an infection acquired through sexual contact. This occurs because certain pathogens capable of causing STIs can also be transmitted through sexual activities involving fecal-oral exposure. Recognizing the link between an infection and persistent diarrhea is a significant step toward proper diagnosis and treatment.
Specific Infections That Cause Diarrhea
The most direct causes of diarrhea linked to sexual transmission involve enteric pathogens spread through fecal-oral routes. These infections cause intestinal inflammation, leading to the characteristic symptoms of gastroenteritis. The bacterium Shigella is a common culprit, causing shigellosis, which is marked by severe, prolonged diarrhea often containing blood or mucus. This pathogen is highly infectious, requiring only a tiny amount of fecal matter for transmission during oral-anal contact.
Parasitic organisms also commonly cause sexually transmitted enteric infections resulting in diarrhea. Giardia lamblia causes giardiasis, characterized by chronic, watery diarrhea, bloating, and abdominal cramps. Another protozoan, Entamoeba histolytica, causes amebiasis, which can lead to inflammation of the large intestine and rectum (proctocolitis), resulting in diarrhea. While these parasites can be acquired through contaminated food or water, their transmission is strongly associated with sexual practices allowing fecal-oral spread.
The human immunodeficiency virus (HIV) itself can cause diarrhea, especially during the acute stage of infection. This initial presentation often mimics a flu-like illness as the virus rapidly replicates. Untreated, the virus can directly affect the digestive tract lining, contributing to chronic diarrhea. Additionally, viruses like Hepatitis A, B, and C are transmissible through sexual contact and can cause general GI symptoms, though they rarely cause persistent diarrhea.
How STDs Affect Digestive Function
Diarrhea associated with STIs can arise from direct infection or secondary effects on the digestive system. One significant mechanism is HIV enteropathy, where the virus causes structural and functional changes in the intestinal lining. This involves chronic inflammation that damages intestinal cells and flattens the villi, which are responsible for nutrient absorption. Such damage results in poor absorption of water, electrolytes, and nutrients, causing chronic, unexplained diarrhea.
In advanced, untreated HIV infection, the weakened immune system allows opportunistic infections to cause severe diarrhea. Pathogens easily controlled by a healthy immune system, such as Cryptosporidium, Cytomegalovirus (CMV), and Microsporida, can cause debilitating, chronic diarrheal illness. CMV can cause severe colitis, while Cryptosporidium causes persistent, watery diarrhea. The presence of these opportunistic infections indicates a systemic issue.
GI distress can also be a side effect of medications used to treat the underlying infection, most notably antiretroviral therapy (ART) for HIV. Certain classes of these drugs, particularly older protease inhibitors, can cause diarrhea as a common side effect. This complication must be distinguished from diarrhea caused by the infection itself or an opportunistic pathogen.
When to Seek Testing and Diagnosis
Any persistent or unusual change in bowel habits warrants medical attention. Immediate evaluation is needed if diarrhea is severe, lasts longer than a few days, or is accompanied by blood, pus, or mucus. Systemic symptoms like high fever, unexplained weight loss, night sweats, or signs of dehydration also indicate a more serious underlying condition.
Diagnosis begins with a thorough medical history, requiring an open discussion of any sexual activities that may have involved oral-anal contact. Healthcare providers order a combination of tests to identify the cause. Stool samples check for bacterial or parasitic pathogens like Shigella, Giardia, or Entamoeba histolytica.
Blood tests screen for systemic infections, such as HIV and viral hepatitis. Standard STI panels often do not screen for enteric pathogens, so a specific request for a GI symptom evaluation is necessary. Open communication with the provider ensures the correct diagnostic tests are ordered.
Treatment and Symptom Management
Effective management of diarrhea caused by an STI requires a dual approach: treating the underlying pathogen while providing supportive care for GI symptoms. For bacterial infections like shigellosis, specific antibiotics are prescribed, although careful selection is needed due to increasing resistance. Parasitic infections such as giardiasis and amebiasis are treated with antiparasitic drugs to eradicate the organism.
When diarrhea is linked to HIV, the mainstay of treatment is antiretroviral therapy (ART). Successfully suppressing the viral load with ART allows the immune system to recover, resolving HIV enteropathy and preventing opportunistic infections. If opportunistic infections have taken hold, specific antimicrobial or antiviral medications are used to target those secondary pathogens.
Supportive care is necessary to prevent complications. Maintaining adequate hydration is paramount, often requiring electrolyte replacement solutions to counteract fluid loss. Dietary modifications, such as avoiding foods that worsen symptoms, may be advised, and antidiarrheal agents can manage bowel movement frequency while the underlying infection is treated. Diarrhea typically resolves completely only after the primary infection is effectively treated or, in the case of chronic conditions like HIV, brought under control.