Travelers' diarrhea is the most common travel-related ailment. The cornerstone of prevention is food and water precautions, as outlined below. All travelers should bring along an antibiotic and an antidiarrheal drug to be started promptly if significant diarrhea occurs, defined as three or more loose stools in an 8-hour period or five or more loose stools in a 24-hour period, especially if associated with nausea, vomiting, cramps, fever or blood in the stool. A recent study indicated that, due to the frequency of quinolone-resistant Campylobacter in Thailand, the most effective antibiotic is azithromycin (Zithromax), given either as a single dose of 1 g or a three-day course of 500 mg/day (Clinical Infectious Diseases 2007; 44:338-46). Alternative regimens include a three day course of rifaximin (Xifaxan) 200 mg three times daily or a quinolone antibiotic: either ciprofloxacin (Cipro)(PDF) 500 mg twice daily or levofloxacin (Levaquin) (PDF) 500 mg once daily for a total of three days. Quinolones are generally well-tolerated, but occasionally cause sun sensitivity and should not be given to children, pregnant women, or anyone with a history of quinolone allergy. Rifaximin should not be used by those with fever or bloody stools and is not approved for pregnant women or those under age 12. Azithromycin should be avoided in those allergic to erythromycin or related antibiotics. An antidiarrheal drug such as diphenoxylate (Lomotil) (PDF) or loperamide (Imodium) should be taken as needed to slow the frequency of stools, but not enough to stop the bowel movements completely. Diphenoxylate (Lomotil) and loperamide (Imodium) should not be given to children under age two.

Most cases of travelers' diarrhea are mild and do not require either antibiotics or antidiarrheal drugs. Adequate fluid intake is essential.

If diarrhea is severe or bloody, or if fever occurs with shaking chills, or if abdominal pain becomes marked, or if diarrhea persists for more than 72 hours, medical attention should be sought.

Though effective, antibiotics are not recommended prophylactically (i.e. to prevent diarrhea before it occurs) because of the risk of adverse effects, though this approach may be warranted in special situations, such as immunocompromised travelers.

Malaria in Thailand: prophylaxis is recommended for rural areas bordering Cambodia, Laos, and Myanmar, including Mae Hong Son. The malaria risk in Phang Nga and Phuket is very limited; therefore, prophylaxis is not recommended for these two areas. There is no malaria risk in Bangkok, Chiang Mai, Chiang Rai, Pattaya, Ko Samui, and Ko Phangan.

For the areas near Cambodia and Laos, either atovaquone/proguanil (Malarone)(PDF) or doxycycline may be given. Atovaquone/proguanil (Malarone) is a recently approved combination pill taken once daily with food starting two days before arrival and continuing through the trip and for seven days after departure. Side-effects, which are typically mild, may include abdominal pain, nausea, vomiting, headache, diarrhea, or dizziness. Serious adverse reactions are rare. Doxycycline is effective, but may cause an exaggerated sunburn reaction, which limits its usefulness in the tropics. The recommended dosage is 100 mg daily, starting one-to-two days before arrival and continuing for four weeks after departure from the malarious area.

For travel to rural areas near the border with Myanmar (but not Cambodia or Laos), either Malarone, doxycycline, or mefloquine (Lariam) may be given. Mefloquine is taken once weekly in a dosage of 250 mg, starting one-to-two weeks before arrival and continuing through the trip and for four weeks after departure. Mefloquine may cause mild neuropsychiatric symptoms, including nausea, vomiting, dizziness, insomnia, and nightmares. Rarely, severe reactions occur, including depression, anxiety, psychosis, hallucinations, and seizures. Mefloquine should not be given to anyone with a history of seizures, psychiatric illness, cardiac conduction disorders, or allergy to quinine or quinidine. Those taking mefloquine (Lariam) should read the Lariam Medication Guide (PDF).

Insect protection measures are essential.

Long-term travelers who will be visiting malarious areas and may not have access to medical care should bring along medications for emergency self-treatment should they develop symptoms suggestive of malaria, such as fever, chills, headaches, and muscle aches, and cannot obtain medical care within 24 hours. See malaria for details. Symptoms of malaria sometimes do not occur for months or even years after exposure.

Cases of malaria are sometimes reported from the southern part of the country (see "Recent outbreaks"). Because the risk appears to be extremely low, malaria prophylaxis is not generally recommended for travel to the south. However, travelers should be aware that the risk, though small, does exist, and should immediately seek medical attention if they develop fever or other malaria symptoms.

For further information concerning malaria in Thailand, go to the World Health Organization - South-East Asia Region.

Hepatitis A vaccine is recommended for all travelers over one year of age. It should be given at least two weeks (preferably four weeks or more) before departure. A booster should be given 6-12 months later to confer long-term immunity. Two vaccines are currently available in the United States: VAQTA (Merck and Co., Inc.) (PDF) and Havrix (GlaxoSmithKline) (PDF). Both are well-tolerated. Side-effects, which are generally mild, may include soreness at the injection site, headache, and malaise.

Older adults, immunocompromised persons, and those with chronic liver disease or other chronic medical conditions who have less than two weeks before departure should receive a single intramuscular dose of immune globulin (0.02 mL/kg) at a separate anatomic injection site in addition to the initial dose of vaccine. Travelers who are less than one year of age or allergic to a vaccine component should receive a single intramuscular dose of immune globulin (see hepatitis A for dosage) in the place of vaccine.

Typhoid vaccine is recommended for all travelers, with the exception of short-term visitors who restrict their meals to major restaurants and hotels, such as business travelers. It is generally given in an oral form (Vivotif Berna) consisting of four capsules taken on alternate days until completed. The capsules should be kept refrigerated and taken with cool liquid. Side-effects are uncommon and may include abdominal discomfort, nausea, rash or hives. The alternative is an injectable polysaccharide vaccine (Typhim Vi; Aventis Pasteur Inc.) (PDF), given as a single dose. Adverse reactions, which are uncommon, may include discomfort at the injection site, fever and headache. The oral vaccine is approved for travelers at least six years old, whereas the injectable vaccine is approved for those over age two. There are no data concerning the safety of typhoid vaccine during pregnancy. The injectable vaccine (Typhim Vi) is probably preferable to the oral vaccine in pregnant and immunocompromised travelers.

Japanese encephalitis vaccine is recommended only for long-term (1 month) travelers to rural areas or travelers who may engage in extensive unprotected outdoor activities in rural areas, especially in the evening, during shorter trips. Japanese encephalitis is transmitted by mosquitoes and occurs from May through October in Thailand. The disease is highly prevalent in the north and occurs sporadically in the south. Annual outbreaks have been reported in the Chiang Mai Valley. Sporadic cases have been described in the Bangkok suburbs.

The vaccine (JE-VAX; Aventis Pasteur Inc.) (PDF) is given as a series of three injections on days 0, 7 and 30. Mild side effects including fever, headache, muscle aches, malaise and soreness at the injection site occur in about 20% of those vaccinated. Serious allergic reactions including urticaria, angioedema, respiratory distress and anaphylaxis occur in approximately 0.6% of vaccinees and may occur as long as one week after vaccination. Any person who receives the vaccine should be observed in the doctor's office for at least 30 minutes following the injection and should complete the full series at least 10 days before departure. There are no data concerning the safety of Japanese encephalitis vaccine during pregnancy. In addition to vaccination, strict attention to insect protection measures is essential for anyone at risk.

Hepatitis B vaccine is recommended for travelers who will have intimate contact with local residents or potentially need blood transfusions or injections while abroad, especially if visiting for more than six months. It is also recommended for all health care personnel. Two vaccines are currently licensed in the United States: Recombivax HB (Merck and Co., Inc.) (PDF) and Engerix-B (GlaxoSmithKline) (PDF). A full series consists of three intramuscular doses given at 0, 1 and 6 months. Engerix-B is also approved for administration at 0, 1, 2, and 12 months, which may be appropriate for travelers departing in less than 6 months. Side-effects are generally mild and may include discomfort at the injection site and low-grade fever. Severe allergic reactions (anaphylaxis) occur rarely.

Rabies vaccine is recommended only for those at high risk for animal bites, such as veterinarians and animal handlers, and for long-term travelers who may have contact with animals and may not have access to medical care. In Thailand, the chief risk is from dog bites. A complete preexposure series consists of three doses of vaccine injected into the deltoid muscle on days 0, 7, and 21 or 28. Side-effects may include pain at the injection site, headache, nausea, abdominal pain, muscle aches, dizziness, or allergic reactions.

Any animal bite or scratch should be thoroughly cleaned with large amounts of soap and water and local health authorities should be contacted immediately for possible post-exposure treatment, whether or not the person has been immunized against rabies.

Tetanus-diphtheria vaccine is recommended for all travelers who have not received a tetanus-diphtheria immunization within the last 10 years.

Measles-mumps-rubella vaccine: two doses are recommended (if not previously given) for all travelers born after 1956, unless blood tests show immunity. Many adults born after 1956 and before 1970 received only one vaccination against measles, mumps, and rubella as children and should be given a second dose before travel. MMR vaccine should not be given to pregnant or severely immunocompromised individuals.

Polio vaccine is not generally recommended for adult travelers who completed the recommended childhood immunizations, since polio has not been reported from Thailand for several years. A one-time booster of inactivated polio vaccine may be considered for extended travel to rural areas.

Cholera vaccine is not generally recommended, though cholera is reported, because most travelers are at low risk for infection. Two oral vaccines have recently been developed: Orochol (Mutacol), licensed in Canada and Australia, and Dukoral, licensed in Canada, Australia, and the European Union. These vaccines, where available, are recommended only for high-risk individuals, such as relief workers, health professionals, and those traveling to remote areas where cholera epidemics are occurring and there is limited access to medical care. The only cholera vaccine approved for use in the United States is no longer manufactured or sold, due to low efficacy and frequent side-effects.

Yellow fever vaccine is required for all travelers greater than one year of age arriving from a yellow-fever-infected country in Africa or the Americas or from a country in the endemic zones, but is not recommended or required otherwise. Yellow fever vaccine (YF-VAX; Aventis Pasteur Inc.) (PDF) must be administered at an approved yellow fever vaccination center, which will give each vaccinee a fully validated International Certificate of Vaccination. Yellow fever vaccine should not in general be given to those who are younger than nine months of age, pregnant, immunocompromised, or allergic to eggs. It should also not be given to those with a history of thymus disease or thymectomy.

Dengue fever, a flu-like illness sometimes complicated by hemorrhage or shock, is highly prevalent in Thailand. The number of cases usually peaks during the rainy season (ranging from May through November), when mosquitoes proliferate. More than 10,000 cases, including 12 deaths, were reported during the first four months of 2008, a marked increase compared to the same time period in 2007. For the first nine months of 2007, more than 40,000 dengue cases were reported nationwide, including 47 deaths. The number of dengue cases appeared to rise earlier than usual in 2007, due to early, heavy rains. A dengue outbreak was reported from Phuket in August 2007, resulting in 110 cases and at least two deaths by November. In May 2007, an outbreak was reported from Trat province, 400 km southeast of Bangkok on the Cambodian border, and in the southernmost provinces along the Malaysian border. In August 2006, the provinces of Kamphaeng Phet, Nakhon Sawan, Phichit and Uthai Thani were declared dengue "alert zones" by the Ministry of Public Health because of a large number of cases (more than a thousand) being reported from these provinces (see Thailand Ministry of Public Health). A dengue outbreak was reported from Surin Province in July 2006 and from Ampur Mae Sareang in June 2006. Earlier in the year, a dengue outbreak was reported from Chaiyaphum Province. In April 2002, a unusually large number of cases was reported among travelers to southern Thailand, especially the island of Koh Pha Ngan. Dengue is transmitted by Aedes mosquitoes, which bite primarily in the daytime and favor densely populated areas, though they also inhabit rural environments. No vaccine is available at this time. Insect protection measures are strongly advised, as outlined below.

An increased number of cholera cases has been reported from the northeastern part of Thailand, due to the consumption of raw cockles, poorly prepared som tam, and fast food. A cholera outbreak was reported in June 2007 among Burmese migrant workers and in a Burmese refugee camp in Tak province, which shares a long border with Burma (see ProMED-mail,August 4 and 10 and October 30, 2007). As above, cholera vaccine is not recommended for most travelers.

Four cases of Legionnaires' disease were reported in December 2006 among guests who had stayed at a hotel in Patong Beach, Phuket, Thailand. See Eurosurveillance for further information. Legionnaires' disease is a bacterial infection which typically causes pneumonia but may also involve other organ systems. The disease is usually transmitted by airborne droplets from contaminated water sources, such as cooling towers, air conditioners, whirlpools, and showers. Legionnaires' disease is not transmitted from person-to-person.

A total of 25 human cases of H5N1 avian influenza ("bird flu"), 17 of them fatal, have been reported from Thailand. The first twelve cases were reported in January-February 2004, at the time of the initial avian influenza outbreaks in Thailand and other Asian countries. New poultry outbreaks were reported in July 2004, followed by five additional human cases in September-October, 2004. Five more human cases were reported between October and December, 2005. No human or avian cases were reported in the first half of 2006, but fresh poultry outbreaks and three additional human cases were reported between July and September 2006. The most recent poultry outbreaks were reported from the northern province of Phichit in September 2007 and again in January 2008, and from Nakhon Sawan province, also in January 2008.

Most travelers are at extremely low risk for avian influenza, since almost all human cases have occurred in those who have had direct contact with live, infected poultry, or sustained, intimate contact with family members suffering from the disease. The Centers for Disease Control does not advise against travel to Thailand, but recommends that travelers should avoid exposure to live poultry, including visits to poultry farms and open markets with live birds; should not touch any surfaces that might be contaminated with feces from poultry or other animals; and should make sure all poultry and egg products are thoroughly cooked. A vaccine for avian influenza was recently approved by the U.S. Food and Drug Administration (FDA), but produces adequate antibody levels in fewer than half of recipients and is not commercially available. The vaccines for human influenza do not protect against avian influenza. Anyone who develops fever and flu-like symptoms after travel to Thailand should seek immediate medical attention, which may include testing for avian influenza. For further information, go to the World Health Organization, the Centers for Disease Control, and ProMED-mail.

An outbreak of leptospirosis was reported in September 2006 from Nan province in the northern part of the country, related to recent floods (see ProMED-mail; September 12, 2006). Leptospirosis is acquired by exposure to water contaminated by the urine of infected animals. In Thailand, the animal reservoir includes rats and dogs. Outbreaks often occur in between August and November, which is the rainy season, and at times of flooding. Most cases occur in the north and northeast regions of the country (see Emerging Infectious Diseases). Symptoms may include fever, chills, headache, muscle aches, conjunctivitis (pink eye), photophobia (light sensitivity), and rash. Most cases resolve uneventfully, but a small number may be complicated by meningitis, kidney failure, liver failure, or hemorrhage. Those who may be exposed to contaminated fresh water, such as those on adventure trips, may consider taking a prophylactic 200 mg dose of doxycycline, either once weekly or as a one-time dose. A previous outbreak occurred in September-October 1999 in the Khumuang subdistrict, Buriram province, in the northeastern part of the country.

An outbreak of hand, foot, and mouth disease was reported from Thailand in September 2006. The cause has not been determined, but most other outbreaks have been caused by enteroviruses (see ProMED-mail; September 7, 2006). Most cases of hand, foot and mouth disease occur in infants and young children, though adults may also be affected. The illness is characterized by fever, oral blisters, and a rash or blisters on the palms and soles. Most cases resolve uneventfully, but a small percentage are complicated by encephalitis (inflammation of the brain), myocarditis (inflammation of the heart muscle), or pulmonary edema (fluid in the lungs). Enterovirus is transmitted by exposure to fecal material from infected individuals. The key to prevention is good personal hygiene and scrupulous hand-washing, especially after defecation and before handling food.

An outbreak of botulism was reported in March 2006 among people who had eaten home-preserved bamboo shoots at a local village Buddhist festival in Baan Luang District, Nan Province. A total of 163 people were affected. Symptoms included dry mouth, dysphagia, dysarthria, ptosis, diplopia, abdominal discomfort, and muscle weakness. Forty people required intubation, but there were no fatalities. For further information, go to the World Health Organization and the Centers for Disease Control. Another botulism outbreak was reported in June 2006, affecting more than 50 people in the northern province of Phayao who had eaten raw deer meat. See Global Health for details.

Three cases of malaria were reported in late 2005 and early 2006 among travelers to Koh Phangan in the southern part of the country, where malaria is thought to be highly uncommon. See ProMED-mail (May 20, 2006) and Eurosurveillance for further information. In 2002, two cases were reported in German travelers who had visited Khao Sok national park, also in the southern part of the country (see Eurosurveillance). Because the risk appears to be extremely low, malaria prophylaxis is not generally recommended for travel to the southern peninsula. However, travelers should be aware that the risk, though small, does exist, and should immediately seek medical attention if they develop fever or other symptoms suggestive of malaria.

Three cases of melioidosis were reported in January 2005 among Finnish tourists who had survived the tsunami in December 2004. The tourists had been visiting Khao Lak on the southwest coast of Thailand when the tsunami struck. Melioidosis is caused by a soil bacterium known as Burkholderia pseudomallei, which gains entrance to the body through cuts or other breaks in the skin, leading to pneumonia or wound infections. The infection may progress to septicemia and may be life-threatening, especially in those with compromised immune systems. In Thailand, most cases are reported from the northeastern part of the country, usually in rice farmers during the rainy season. To prevent melioidosis, travelers are advised to wear waterproof gloves and shoes or boots whenever coming into direct contact with soil, especially during the rainy season.

Toxic jellyfish stings were reported to have killed two tourists swimming off the coast of Koh Phangan in August 2002. Three years before that, a fatal jellyfish sting was reported off Koh Samui in the Gulf of Siam. In general, the time of highest risk for jellyfish stings is the evening, when they come to the surface.

HIV disease has reached epidemic levels in Thailand. Most cases result from heterosexual transmission. HIV infection is common in prostitutes of both sexes.

• Gnathostomiasis (acquired by eating raw or undercooked freshwater fish; chief symptom is intermittent, migratory swellings under the skin, sometimes associated with joint pains, muscle pains, or gastrointestinal symptoms; symptoms may not begin until months after exposure)
• Vibrio parahemolyticus (intestinal infection similar to cholera; numbers increasing rapidly over the last several years)
• Scrub typhus (deforested areas; transmitted by chigger bites; marked by thick black scab at the site of the initial bite and rash which starts on the trunk; also causes fever, headache, sweating, pink-eye, swollen glands)
• Spotted fever rickettsioses (reported from Sangkhlaburi District on the Myanmar border; trasnmitted by ticks)
• Schistosomiasis (acquired by exposure to contaminated water; incidence declining)
• Hepatitis E (transmitted by contaminated food or water; particularly dangerous for pregnant women)
• Eosinophilic meningitis (caused by roundworm; acquired by eating contaminated food; chief symptoms are headache, neck stiffness, numbness and tingling)
• Chikungunya fever (transmitted by mosquitoes; causes fever and incapacitating joint pains; rarely fatal but may be complicated by protracted fatigue and malaise)

A recent study of febrile illnesses along the Thai-Myanmar border showed that the most frequent documented causes were malaria and leptospirosis. Other common diagnoses included rickettsial infections, dengue fever, and typhoid. For further information, go to the American Journal of Tropical Medicine and Hygiene (74(1), 2006, pp. 108-113).

For a guide to physicians and other hospitals in Thailand, go to the Welcome to Thailand document (Appendix K) on the U.S. Embassy website. Many doctors and hospitals will expect payment in cash, regardless of whether you have travel health insurance. Life-threatening medical problems may require air evacuation to a country with state-of-the-art medical facilities.

All children should be up-to-date on routine childhood immunizations, as recommended by the American Academy of Pediatrics. Children who are 12 months or older should receive a total of 2 doses of MMR (measles-mumps-rubella) vaccine, separated by at least 28 days, before international travel. Children between the ages of 6 and 11 months should be given a single dose of measles vaccine. MMR vaccine may be given if measles vaccine is not available, though immunization against mumps and rubella is not necessary before age one unless visiting a country where an outbreak is in progress. Children less than one year of age may also need to receive other immunizations ahead of schedule (see the accelerated immunization schedule).

The recommendations for malaria prophylaxis are the same for young children as for adults, except that (1) dosages are lower; (2) Malarone is not recommended for children weighing less than 25 pounds; and (3) doxycycline should be avoided. DEET-containing insect repellents are not advised for children under age two, so it's especially important to keep children in this age group well-covered to protect them from mosquito bites.

When traveling with young children, be particularly careful about what you allow them to eat and drink (see food and water precautions), because diarrhea can be especially dangerous in this age group and because the vaccines for hepatitis A and typhoid fever, which are transmitted by contaminated food and water, are not approved for children under age two. Baby foods and cows' milk may not be available in developing nations. Only commercially bottled milk with a printed expiration date should be used. Young children should be kept well-hydrated and protected from the sun at all times.

Be sure to pack a medical kit when traveling with children. In addition to the items listed for adults, bring along plenty of disposable diapers, cream for diaper rash, oral replacement salts, and appropriate antibiotics for common childhood infections, such as middle ear infections.

As a rule, pregnant women should avoid visiting areas where malaria occurs. Malaria may cause life-threatening illness in both the mother and the unborn child. None of the currently available prophylactic medications is 100% effective. Mefloquine (Lariam) is the drug of choice for malaria prophylaxis during pregnancy, but should not be given if possible in the first trimester. If travel to malarious areas is unavoidable, insect protection measures must be strictly followed at all times. The recommendations for DEET-containing insect repellents are the same for pregnant women as for other adults.

Strict attention to food and water precautions is especially important for the pregnant traveler because some infections, such as listeriosis, have grave consequences for the developing fetus. Additionally, many of the medications used to treat travelers' diarrhea may not be given during pregnancy. Quinolone antibiotics, such as ciprofloxacin (Cipro) and levofloxacin (Levaquin), should not be given because of concern they might interfere with fetal joint development. Data are limited concerning trimethoprim-sulfamethoxazole, but the drug should probably be avoided during pregnancy, especially the first trimester. Options for treating travelers' diarrhea in pregnant women include azithromycin and third-generation cephalosporins. For symptomatic relief, the combination of kaolin and pectin (Kaopectate; Donnagel) appears to be safe, but loperamide (Imodium) should be used only when necessary. Adequate fluid intake is essential.

Americans living in or visiting Thailand are encouraged to register, either online, or in person at the Consular Section of the U.S. Embassy in Bangkok or the U.S. Consulate General in Chiang Mai. At both locations, updated information on travel and security in Thailand is available. The Consular Section of the U.S. Embassy is located at 95 Wireless Road in Bangkok; the U.S. mailing address is APO AP 96546-0001. The central switchboard number is (66-2) 205-4000; the American Citizen Services Unit number is (66-2) 205-4049; and the fax number is (66-2) 205-4103. The web site for the U.S. Embassy is http://bangkok.usembassy.gov. American citizens can register online via the web site. Questions regarding American Citizens Services can be submitted by E-mail to acsbkk@state.gov. The U.S. Consulate General in Chiang Mai is located at 387 Wichayanond Road; the U.S. mailing address is Box, C, APO AP 96546. The telephone number is (66-53) 252-629, and the fax number is (66-53) 252-633.

For information on safety and security, go to the U.S. Department of State, United Kingdom Foreign and Commonwealth Office, Foreign Affairs Canada, and the Australian Department of Foreign Affairs and Trade.