The most common vacation sickness in Thailand is traveler's diarrhea. You can take some solace in knowing that it is also the most common affliction of the locals. It generally comes from eating contaminated food, be it fruit, veggies, unclean water, or badly prepared or stored foods—really anything. It can also be triggered by a change in diet. Avoid ice unless you know it comes from clean water, uncooked or undercooked foods (particularly seafood, sometimes served raw in salads), and unpasteurized dairy products. Drink only bottled water or water that has been boiled for at least 20 minutes, even when brushing your teeth. The water served in pitchers at small restaurants or in hotel rooms is generally safe, as it is either boiled or from a larger bottle of purified water, though if you have any suspicions about its origins, it's best to go with your gut feeling.
The best way to treat "Bangkok belly" is to wait for it to pass. Take Pepto-Bismol to help ease your discomfort and if you must travel, take Imodium (known generically as loperamide), which will immobilize your lower gut and everything in it. It doesn't cure the problem, but simply postpones it until a more convenient time. Note that if you have a serious stomach sickness, taking Imodium can occasionally intensify the problem, leading to a debilitating fever and sickness. If at any time you get a high fever with stomach sickness, find a doctor.
If you have frequent, watery diarrhea for more than two days, see a doctor for diagnosis and treatment. Days of sickness can leave you seriously dehydrated and weak in the tropics.
In any case, drink plenty of purified water or tea—chamomile, lemongrass, and ginger are good choices. In severe cases, rehydrate yourself with a salt-sugar solution (½ teaspoon salt and 4 tablespoons sugar per quart of water) or rehydration salts, available at any pharmacy.
No vaccinations are required to enter Thailand, but we strongly recommend the hepatitis A vaccination, and you should make sure your tetanus and polio vaccinations are up-to-date, as well as measles, mumps, and rubella.
Malaria and dengue fever are also possible (though remote) risks as you move out of the main tourist areas. There is much debate about whether travelers headed to Thailand should take malarial prophylactics. Though many western doctors recommend that you take antimalarials, many health-care workers in Thailand believe they can do more harm than good: They can have side effects, they are not 100% effective, they can mask the symptoms of the disease if you do contract it, and they can make treatment more complicated. Consult your physician, see what medications your insurance will cover, and do what makes you feel most comfortable.
There are no prophylactics available for dengue fever. The best way to prevent mosquito-borne illness is to protect yourself against mosquitoes as much as possible.
According to the U.S. government's National Centers for Disease Control (CDC) there's also a risk of hepatitis B, rabies, and Japanese encephalitis in rural areas of Thailand, as well as drug-resistant malaria near the Myanmar border and in parts of Cambodia. In most urban or easily accessible areas you need not worry. However, if you plan to visit remote regions or stay for more than six weeks, check with the CDC's International Travelers Hotline.
National Centers for Disease Control & Prevention (800/311–3435 international travelers' health line. www.cdc.gov/travel.)
World Health Organization (www.who.int/en.)
The avian flu crisis that ripped through Southeast Asia at the start of the 21st century had a devastating impact on Thailand. Poultry farmers went out of business, tourists stayed away, and each week brought news of a new species found to be infected (including isolated cases of humans contracting the virus). At this writing, the worry has died down as human cases continue to be exceedingly rare. That doesn't mean it won't flare up again, but note that all cases have occurred in rural areas outside the tourist track, and most infected people dealt with large numbers of dead birds.
Malaria and dengue fever, though more common than bird flu, are still quite rare in well-traveled areas. Malarial mosquitoes generally fly from dusk to dawn, while dengue carriers do the opposite; both are most numerous during the rainy season, as they breed in stagnant water.
The best policy is to avoid being bitten. To that end, wear light-color clothing and some form of insect repellent (preferably containing DEET) on any exposed skin when out and about in the mornings and evenings, especially during the rainy season. Make sure that hotel rooms have air-conditioning, mosquito nets over the bed, good screens over windows, or some combination thereof. You can also use a bug spray (available everywhere) in your room before heading out to dinner, and return to a bug-free room. The ubiquitous bottles of menthol-scented Siang Pure Oil both ward off mosquitoes and stop the incessant itching of bites.
Dengue fever tends to appear with a sudden high fever, sweating, headache, joint and muscle pain (where it got the name "breakbone fever"), and nausea. A rash of red spots on the chest or legs is a telltale sign. Malaria offers a raft of symptoms, including fever, chills, headache, sweating, diarrhea, and abdominal pain. A key sign is the recurrent nature of the symptoms, coming in waves every day or two.
Find a doctor immediately if you think you may have either disease. In Thailand, the test for both is quick and accurate and the doctors are much more accustomed to treating these diseases than are doctors in the United States. Left untreated, both diseases can quickly become serious, possibly fatal. Even when properly treated, dengue has a long recovery period, leaving the victim debilitated for weeks, sometimes months.
Reliable condoms in a variety of brands and styles are available at most 7-Elevens (yes, they have come to Thailand), supermarket, and minimart, usually near the checkout counter. Be aware that a high percentage of sex workers in Thailand are HIV positive, and unprotected sex is extremely risky.
Do not fly within 24 hours of scuba diving, as you may risk decompression sickness, which is caused by tiny bubbles forming in the body if you move from deep water (higher pressure) to the surface (lower pressure) too quickly. The low pressure encountered while flying can trigger the sickness.
Thailand has nearly every drug known to the western world, and many that aren't. All are readily available at pharmacies throughout the country. They are also often cheaper than in the United States and many drugs don't require the prescriptions and doctor visits needed at home. Be wary, however, of fake medications. It's best to visit larger, well-established pharmacies that locals vouch for.