Between 30% and 70% of international travelers to developing countries get traveler's diarrhea. That range is wide because your risk depends almost entirely on where you go, what you eat, and how your immune system responds to pathogens it has never encountered. South Asia sits at the top of the risk scale. Latin America and Southeast Asia fall in the middle. Eastern Europe and the Caribbean carry lower but non-trivial risk.
Enterotoxigenic E. coli (ETEC) causes 30-40% of all cases. The rest comes from a rotating cast of bacteria (Campylobacter, Salmonella, Shigella), viruses (norovirus, rotavirus), and parasites (Giardia, Cryptosporidium). Knowing the dominant pathogen by region helps you decide whether to pack bismuth tablets or prescription antibiotics.
How bad is the risk by region?
South Asia carries the highest attack rates. Studies of travelers to India, Nepal, and Bangladesh show incidence rates of 50-70% over a 2-week trip. ETEC and Campylobacter dominate, but enteric viruses contribute significantly during monsoon season. Tap water in most South Asian cities is not potable, and ice in restaurants is frequently made from unfiltered municipal supply.
Southeast Asia runs slightly lower at 20-50%. Thailand, Vietnam, and Cambodia present moderate risk, with street food culture making exposure nearly unavoidable. However, the high cooking temperatures used in wok-based cuisine provide some protection compared to raw preparations. The Philippines and Indonesia carry higher risk than mainland Southeast Asia, partly due to water infrastructure gaps outside major cities.
Latin America and the Caribbean range from 15-40%. Mexico has long been associated with "Montezuma's revenge," though urban areas like Mexico City now have better water treatment than many travelers expect. Central America, Peru, and Bolivia carry higher risk. Brazil varies enormously by region. Southern Brazilian cities have relatively safe water; the Amazon basin does not.
Africa sits at 30-60%, comparable to South Asia. Sub-Saharan Africa presents the widest pathogen diversity, including parasitic causes that are less common elsewhere. Cholera adds a dimension of risk in countries with active outbreaks, particularly in East and Southern Africa.
What is the "boil it, cook it, peel it, or forget it" rule?
Six words that prevent most cases. If food has been cooked to high temperature and served hot, it's almost certainly safe. If you can peel it yourself, the interior is protected from contamination. Everything else is a gamble.
Raw leafy salads are the single riskiest food category for travelers. Washing lettuce in local tap water doesn't remove pathogens; it adds them. Even "washed in purified water" claims at restaurants are unreliable. Skip the salad. Eat cooked vegetables instead.
Fruit you peel yourself is safe. Bananas, oranges, mangoes, papayas. Fruit that's been pre-cut and sitting on a vendor's tray is not safe. Pre-sliced watermelon in tropical heat is a bacterial incubator.
Drink sealed bottled water, hot tea, hot coffee, or carbonated beverages. Avoid ice unless you made it yourself from purified water. Wipe the rim of bottles and cans before drinking. Brush your teeth with bottled water in high-risk destinations. Yes, this actually matters.
Should you take prophylaxis?
Bismuth subsalicylate (Pepto-Bismol) reduces traveler's diarrhea incidence by about 65% when taken as prophylaxis: 2 tablets four times daily. That's 8 tablets a day, which is a lot. Side effects include black tongue, black stool, and constipation. It's reasonable for short trips of 1-2 weeks to high-risk destinations where getting sick would ruin a once-in-a-lifetime trip. Not practical for longer stays.
Antibiotic prophylaxis is not recommended for most travelers. The risk of side effects, drug interactions, and contributing to antibiotic resistance outweighs the benefit of preventing what is usually a self-limited illness lasting 3-5 days. Exceptions exist: immunocompromised travelers, those with inflammatory bowel disease, and people on critical business trips where any illness would have serious consequences. In these cases, a doctor may prescribe rifaximin 200mg three times daily.
Probiotics have been studied extensively. The evidence is weak. A 2018 Cochrane review found that Saccharomyces boulardii might provide modest protection, but the data wasn't strong enough to recommend routine use. Save your money or spend it on bottled water instead.
When do you need antibiotics for treatment?
Most traveler's diarrhea resolves in 3-5 days without antibiotics. Oral rehydration is the priority. You lose water and electrolytes rapidly. WHO oral rehydration salts (ORS) are available at pharmacies throughout the developing world for pennies. Pack a few sachets before you travel.
Antibiotics shorten illness duration from about 3 days to roughly 1 day. They're appropriate when symptoms are moderate to severe: more than 3 unformed stools in 8 hours, fever, blood in stool, or illness that's preventing you from functioning.
Azithromycin (single 1000mg dose or 500mg daily for 3 days) is the first-line treatment in most regions. It covers the major bacterial causes including Campylobacter, which is especially important in Southeast Asia where fluoroquinolone-resistant Campylobacter rates exceed 80%.
Rifaximin (200mg three times daily for 3 days) works well for uncomplicated watery diarrhea caused by ETEC, the most common culprit. It stays in the gut and isn't absorbed systemically, which means fewer side effects. But it doesn't work against invasive pathogens like Shigella or Campylobacter, so it's not the right choice if you have fever or bloody stool.
Fluoroquinolones (ciprofloxacin, levofloxacin) were once the standard recommendation. Resistance rates have climbed so high in South and Southeast Asia that they're no longer reliable first-line options for those regions. They remain effective for travelers to Africa and Latin America, but azithromycin has largely replaced them as the default carry-along antibiotic.
Loperamide (Imodium) stops diarrhea symptoms but doesn't treat the infection. It's useful for long bus rides or flights when you simply cannot afford to keep running to the bathroom. Do not use it if you have bloody diarrhea or fever. Combine it with an antibiotic when you need both symptom control and treatment.
When should you see a doctor?
Four red flags mean you need medical care, not self-treatment.
Bloody diarrhea. Blood in your stool suggests an invasive pathogen like Shigella, Salmonella, or Entamoeba histolytica. These can cause serious complications without proper treatment. Self-treating with loperamide alone when you have dysentery is dangerous.
Fever above 38.5°C (101.3°F). High fever with diarrhea suggests a systemic infection, not just a gut upset. In malaria-endemic regions, fever with GI symptoms could also be malaria. Get tested.
Symptoms lasting more than 3 days without improvement. Bacterial diarrhea should start improving within 24-48 hours of antibiotic treatment. If it doesn't, you may have a parasitic infection (Giardia, Cryptosporidium, amoeba) that requires different medication entirely.
Signs of severe dehydration. Dark urine, dizziness when standing, rapid heartbeat, inability to keep fluids down. Children and elderly travelers can become dangerously dehydrated within hours. Oral rehydration works for mild to moderate cases. Severe dehydration needs IV fluids.
Pack a basic traveler's medical kit: ORS sachets, azithromycin (get a prescription before you leave), loperamide, bismuth tablets, and a thermometer. Knowing what you're carrying and when to use each item is the difference between losing a day and losing a week of your trip.