Lately, I’ve been seeing an increase in patients coming to the clinic complaining of diarrhea and stomach upset. This may be due to the recent floods, which can increase the risk of food and water contamination. The term acute gastroenteritis (AGE) is used to lump together any number of infectious illnesses that cause diarrhea and/or vomiting. While most bouts of AGE are self-limited and don’t require treatment, some forms may require antibiotics or even hospitalization. When evaluating potential causes of diarrhea, doctors do a thorough history and physical examination to pinpoint the most likely culprit.

Most instances of infectious diarrhea are caused by viruses or bacteria that are inadvertently ingested with our food or drink. These organisms can survive the highly acidic environment of the stomach and start to proliferate when they make it to the intestines. The typical AGE course is mild and will resolve in one to three days. Supportive care and proper rest are important for a quick recovery. The most important intervention is to replace the lost fluids and electrolytes by drinking enough water, minerals, and salts. You can drink water and salty food, or use commercial oral rehydration fluids for convenience. If you cannot replace the lost fluids fast enough, you may need to be admitted to the hospital for hydration. Mild AGE does not typically need treatment with antibiotics. While it may be tempting to reach for antimotility agents like loperamide, it is usually not necessary if the fluid losses can be adequately replaced. Most bouts of mild diarrhea will stop on their own (with exceptions), and it is probably best to get the viral and bacterial toxins out of your system.

Danger signs that doctors look out for in AGE, which may need more urgent care, include bloody diarrhea, pain with bowel movement, high fever, and if the diarrhea is of large volume and intractable.

Bloody diarrhea is usually caused by invasive bacteria (Campylobacter, Shigella, Salmonella, etc.) or amoebae (Entamoeba histolytica). The presence of blood in the stool means that microorganisms are invading the intestinal lining and are destroying the tissue underneath. This is problematic because it can lead to sepsis and overwhelming infection. In addition, severe bleeding can drop blood levels to the point that oxygen delivery to the rest of the body is impaired, causing shortness of breath, easy fatiguability, and severe weakness. Patients with bloody diarrhea need to be seen by a doctor. While some instances can be treated on an outpatient basis, some may need IV antibiotics, IV hydration, and occasionally endoscopy or surgery to stop the bleeding.

Painful diarrhea, especially if there is also blood in the stool, suggests some sort of blockage or injury to the gastrointestinal tract. If the diarrhea stops abruptly but the pain continues, there may be a complete blockage. This may herald a rupture of the intestine if not treated quickly, leading to a surgical emergency. The intestinal tract is very sensitive, and an infection can cause it to become dysfunctional or paralyzed. If this happens, doctors usually admit the patient to the hospital for observation and hydration. Electrolytes are checked since these can affect the mobility of the intestinal tract, and patients may need to be put on NPO (nothing by mouth). Once the pain improves, the diet can be slowly restarted and advanced as tolerated.

Fever may signal the invasion of bacteria deeper into the body and into the bloodstream. This may also be accompanied by bloody diarrhea. Invasive bacteria like Salmonella typhi, which causes typhoid fever, can cross into the circulation and be seeded throughout the body. The fever in typhoid fever is very high, 39 to 40°C and can take a while to resolve even with antibiotic treatment. Invasive amoebae like Entamoeba histolytica can transfer from the intestines to the liver and create a large abscess, which may need to be drained.

Intractable diarrhea is seen with certain organisms like cholera (Vibrio cholera) and some strains of toxin-producing E. coli. One clue that you may be infected with one of these bacteria is that even if you stop eating and drinking, the diarrhea keeps going at a large volume. This is because the toxin these organisms produce induces the intestinal lining to dump large amounts of fluid. If not treated with antibiotics and rapid hydration, a person can die from severe dehydration and electrolyte deficiency.

Most cases of mild AGE do not need any laboratory evaluation. For moderate cases and for those with bloody diarrhea, doctors will usually request a complete blood count (CBC) and a fecalysis (stool examination under the microscope). For suspected bacterial infection, the doctor can prescribe antibiotics and send a stool culture. For patients with low blood pressure, severe dehydration, or signs of sepsis, admission to the hospital for further workup and treatment is warranted.

If the diarrhea does not resolve despite treatment and it lasts more than two weeks, a more extensive workup may need to be done. There are PCR-based gastrointestinal panels that can test the stool for more than 20 different organisms, including bacteria, viruses, and parasites, all at the same time in about one hour. However, these are quite expensive and are only used for diagnostic dilemmas. Imaging studies like ultrasound and CT scan may be helpful, especially when looking for intrabdominal abscesses, masses, and other abnormalities. A colonoscopy may also be indicated to visualize what the inside of the gastrointestinal tract looks like, and specimens can be obtained for additional studies. A lot of people with chronic diarrhea have tuberculosis of the gut, and the best way to diagnose this is through endoscopy.

Not all diarrhea is caused by infectious causes. Other potential causes include malabsorption syndromes, gut obstruction (which can end up infectious), and food allergies. Changes in bowel movements, especially for older people, may be a sign of colon or rectal cancer. Everyone above 50 years of age should consider a colonoscopy for early detection. In this case, diarrhea may actually be calling your attention to something more serious and may save your life.