How Do You Treat Traveler’s Diarrhea in Koh Samui?

Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Doctor Samui. Last reviewed: August 2026

You felt fine at the beach club in Chaweng last night. By 3 a.m. you are making your fifth trip to the bathroom, wondering whether it was the papaya salad or the ice. It was probably the heat plus something you ate, and this is the most common reason people call us for a hotel visit. Most cases are manageable if you treat them correctly from the start.

The mistake most people make is reaching for whatever the pharmacy hands them, which is usually ciprofloxacin. In Thailand, that antibiotic frequently does not work. The bacteria most commonly behind traveler’s diarrhea here have developed strong resistance to it. This article explains what actually causes it on Koh Samui, what to take, when to call a doctor, and what to do when a child is sick too.

What Causes Traveler’s Diarrhea in Koh Samui

The most common culprit in Thailand is Campylobacter jejuni, a bacteria found in undercooked chicken, contaminated water, and raw produce. Enterotoxigenic E. coli, known as ETEC, comes second. Less often, Salmonella or Norovirus, a viral illness that spreads easily between people, is responsible.

Ice is a source people underestimate. Busy resort beach clubs use purified block ice. Smaller local restaurants sometimes do not. Pre-cut fruit sitting in the sun at a beach market is another common source. If you ate somewhere with low turnover or had a salad washed in tap water, that is also a likely candidate.

Viral causes like Norovirus do not respond to antibiotics at all. This is one reason a proper assessment matters before you start any medication.

Why Ciprofloxacin Often Fails Here

This is the thing that matters most before anyone self-medicates. Campylobacter, the dominant pathogen in Thai traveler’s diarrhea, shows fluoroquinolone resistance above 85% in studies from Thailand. Ciprofloxacin is a fluoroquinolone. Taking it for diarrhea picked up here is, in most cases, using the wrong tool entirely.

Azithromycin is the first-line antibiotic for bacterial diarrhea acquired in Thailand. It works well against both Campylobacter and ETEC. The dose and duration depend on how unwell you are.

Do not buy an antibiotic from a pharmacy without knowing what you actually have. If your symptoms are mild and you are keeping fluids down, you may not need one at all.

Traveler’s Diarrhea Treatment Options

Start with oral rehydration salts, called ORS. These are sachets you mix with bottled water. They replace the electrolytes your body is losing. Plain water alone is not enough when diarrhea is significant. ORS sachets are sold at every 7-Eleven on the island. Grab two or three boxes and start early.

Loperamide, sold as Imodium, slows gut contractions and gives short-term relief if you need to travel or board a flight. It is not a treatment. Do not use it if you have a fever or blood in your stool, because it can trap the infection and make things worse.

Ondansetron is an anti-nausea medication that helps when vomiting stops you drinking fluids. It is not available over the counter here and requires a prescription. We prescribe it regularly during hotel visits when a patient cannot keep ORS down.

Probiotics have limited but growing evidence for shortening diarrhea duration. They are safe alongside other treatment and may help restore gut balance faster. They will not replace ORS or antibiotics when antibiotics are genuinely needed.

Dehydration in Koh Samui Happens Faster Than You Expect

Samui’s heat and humidity accelerate dehydration far faster than at home. If you were snorkeling at Ang Thong in the morning and spent the afternoon sweating before the diarrhea started, you may already be running low on fluids before the first episode.

Signs of significant dehydration include dark urine, no urination for more than six hours, dizziness when standing, a dry mouth, and feeling very weak. If you reach that point and cannot keep fluids down, oral rehydration is no longer enough and you need IV fluids.

This threshold arrives faster in children and older travelers. Do not wait it out hoping it improves on its own.

Traveler’s Diarrhea in Children on Family Holidays

Children under age two dehydrate faster than adults, and in Koh Samui’s heat that window closes quickly. ORS is still the first priority. Use a pediatric formula, given in small sips frequently rather than large amounts at once.

Do not give loperamide to young children. It is not safe for them. When a bacterial cause is confirmed or strongly suspected, azithromycin is first-line for children too, not fluoroquinolones.

If your child has a fever above 38.5°C, blood in the stool, or cannot keep any fluid down, do not wait until morning. Doctor Samui can come to your hotel or villa at any hour. Travelling to a clinic at 2 a.m. with a sick child is hard. Having a doctor arrive at your room is not.

When to Stop Managing It Yourself

Most mild cases settle within 24 to 48 hours with ORS and rest. These are the signs that mean you should call a doctor rather than wait.

Blood or mucus in the stool means a bacterial infection is likely and needs treatment. A fever above 38.5°C alongside diarrhea points to a more serious infection. Diarrhea that has not improved after 48 to 72 hours, or is getting worse, needs proper assessment. Vomiting that prevents you keeping any fluids down needs treatment you cannot take by mouth. Dizziness, weakness, or very dark urine means dehydration is already significant.

One more thing. Occasionally, after a bad episode of gastroenteritis, the gut stays sensitive for weeks. If your symptoms settle but digestion stays disrupted for more than two to three weeks after you get home, see a doctor. It is treatable.

How Doctor Samui Treats Traveler’s Diarrhea

At our Chaweng clinic, we assess what kind of infection is likely based on your symptoms, how long it has been going on, and what you have already tried. If the picture is unclear, a stool test identifies the pathogen and tells us whether an antibiotic is needed and which one. You can read more about how we approach diarrhea treatment in Koh Samui on our clinic page.

For patients who cannot get to the clinic, our 24/7 hotel and villa service covers the whole island, from Chaweng and Lamai to Maenam, Bophut, and Choeng Mon. A doctor arrives with the equipment to assess you properly, prescribe the right medication, and set up an IV drip if needed. Most patients feel meaningfully better within a few hours of IV rehydration combined with appropriate treatment.

If you need documentation for travel insurance, we provide a medical certificate and itemized receipt at the time of your visit. Most insurers covering international travel will reimburse clinic fees for acute illness, but they need the paperwork, so ask for it.

Food and Water Safety on Koh Samui

Drink bottled water. Do not drink tap water and do not use it to brush your teeth at smaller guesthouses. Ice in resorts and beach clubs is almost always safe. Ice in small local restaurants is a reasonable risk to avoid.

Street food is not the enemy. Stalls with high turnover and food cooked hot in front of you carry low risk. The problem is food cooked hours earlier and left sitting warm. Pre-cut mango and watermelon at beach markets that has been sitting in the heat for unknown hours is a source we see come up repeatedly.

Wash your hands before eating. Hand sanitizer in your bag is the simplest thing you can do to protect yourself and your children throughout the trip.