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 quinolone antibiotic is usually prescribed: 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. Alternative regimens include a three day course of rifaximin (Xifaxan) 200 mg three times daily or azithromycin (Zithromax) 500 mg once daily. 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 loperamide (Imodium) or diphenoxylate (Lomotil) 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 prophylaxis is recommended for the Demilitarized Zone and for rural areas in the northern parts of Kyunggi and Kangwon Provinces (see Emerging Infectious Diseases). The drug of choice is chloroquine, taken once weekly in a dosage of 500 mg, starting one-to-two weeks before arrival and continuing through the trip and for four weeks after departure. Chloroquine may cause mild adverse reactions, including gastrointestinal disturbance, headache, dizziness, blurred vision, and itching, but severe reactions are uncommon. Insect protection measures are advised. For further information on malaria in South Korea, go to the World Health Organization - Western Pacific Region.

The following are the recommended vaccinations for South Korea:

Measles vaccine is recommended for any traveler born after 1956 who does not have either a history of two documented measles immunizations or a blood test showing immunity. Many adults who had only one vaccination show immunity when tested and do not need the second vaccination. Measles vaccine should not be given to pregnant or severely immunocompromised individuals. A measles outbreak affecting almost 40,000 people, resulting in six deaths, was reported in the year 2000.

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 and cruise passengers. 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 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. The incidence of Japanese encephalitis has fallen markedly in recent decades due to universal vaccination, in conjunction with improved living conditions, agricultural modernization, and mosquito control programs. The risk is greatest in North and South Cholla provinces in the southwestern part of the country. Cases are also reported from Kyonggi and Cheju provinces. (See the recent article by Dr. Young Mo Sohn in Emerging Infectious Diseases for further information.)

The vaccine (JE-VAX; Aventis Pasteur Inc.) (PDF) is given as a series of three injections on days 0, 7 and 30. If time is short, the third dose may be given on day 14. 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.

Hepatitis B vaccine is recommended for all travelers if not previously vaccinated. 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, for long-term travelers living in areas with a high risk of exposure, and for travelers involved in any activities that might bring them into direct contact with bats. 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.

All travelers should be up-to-date on routine immunizations, including

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

• Varicella (chickenpox) vaccine (recommended for any international traveler over one year of age who does not have either a history of documented chickenpox or a blood test showing immunity. Many people who believe they never had chickenpox show immunity when tested and do not need the vaccine. Varicella vaccine should not be given to pregnant or immunocompromised individuals.)

Polio vaccine is not recommended for any adult traveler who completed the recommended childhood immunizations. In October 2000, the World Health Organization certified that polio had been eradicated from the Western Pacific region.

Cholera vaccine is not recommended, even though cholera is reported from South Korea, 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.

Outbreaks of H5N1 avian influenza ("bird flu") have been reported periodically from poultry farms since December 2003. A series of outbreaks were reported in November and December 2006 from poultry farms in the provinces of North Jeolla, Jeollabuk-do, and South Chungchong. The most recent outbreaks were reported in April 2008 from North Jeolla, South Jeolla, Gyeonggi, Chungcheong, and Gyeongsang. By May, the outbreaks had spread to Seoul and all poultry in the city were destroyed. No human cases have been reported to date.

Most travelers are at extremely low risk for avian influenza, since almost all human cases in other countries 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 and the World Health Organization do not advise against travel to countries affected by avian influenza, but recommend 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 South Korea should seek immediate medical attention, which may include testing for avian influenza. For further information, go to the World Health Organization, Health Canada, the Centers for Disease Control, and ProMED-mail.

• Vibrio vulnificus (acquired by eating raw fish or shellfish; also through cuts in the skin; frequent outbreaks from June to October, usually in waters off the south and west coasts; isolated from oysters collected in waters off South Cholla Province; see ProMED-mail)
• Hemorrhagic fever with renal syndrome (transmitted by inhalation of aerosols from rodent excreta)
• Tick-borne encephalitis (rural and forested areas in spring and summer)
• Leptospirosis (rodents are the chief animal reservoir)
• Brucellosis (the most common animal source is infected cattle)
• Scrub typhus (rural areas; transmitted by chigger bites)
• Murine typhus (rare)
• Lung fluke (paragonimiasis)
• Oriental liver fluke (clonorchiasis) (acquired by eating raw fresh water fish)
• Fish tapeworm (diphyllobothriasis)
• Enterovirus 71 (causes small skin and mouth blisters, known as hand, foot and mouth disease, or a mild form of meningitis)

HIV (human immunodeficiency virus) infection is reported, but travelers are not at risk unless they have unprotected sexual contacts or receive injections or blood transfusions.

Tap water is generally safe to drink in major cities, but water quality is variable in rural areas. If in doubt, do not drink tap water unless it has been boiled, filtered, or chemically disinfected. Do not drink unbottled beverages or drinks with ice. Do not eat fruits or vegetables unless they have been peeled or cooked. Avoid cooked foods that are no longer piping hot. Cooked foods that have been left at room temperature are particularly hazardous. Avoid unpasteurized milk and any products that might have been made from unpasteurized milk, such as ice cream. Avoid food and beverages obtained from street vendors. Do not eat raw or undercooked meat or fish. Some types of fish may contain poisonous biotoxins even when cooked. Barracuda in particular should never be eaten. Other fish that may contain toxins include red snapper, grouper, amberjack, sea bass, and a large number of tropical reef fish.

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 accompanied by nausea, vomiting, cramps, fever or blood in the stool. Antibiotics which have been shown to be effective include ciprofloxacin (Cipro), levofloxacin (Levaquin), rifaximin (Xifaxan), or azithromycin (Zithromax). Either loperamide (Imodium) or diphenoxylate (Lomotil) should be taken in addition to the antibiotic to reduce diarrhea and prevent dehydration.

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.

Wear long sleeves, long pants, hats and shoes (rather than sandals). To prevent tick bites, boots are preferable, with pants tucked in. Apply insect repellents containing 25-50% DEET (N,N-diethyl-3-methylbenzamide) or 20% picaridin (Bayrepel) to exposed skin (but not to the eyes, mouth, or open wounds). DEET may also be applied to clothing. Products with a lower concentration of either repellent need to be repplied more frequently. Products with a higher concentration of DEET carry an increased risk of neurologic toxicity, especially in children, without any additional benefit. Do not use either DEET or picaridin on children less than two years of age. For additional protection, apply permethrin-containing compounds to clothing, shoes, and bed nets. Permethrin-treated clothing appears to have little toxicity. Don't sleep with the window open unless there is a screen. If sleeping outdoors or in an accomodation that allows entry of mosquitoes, use a bed net, preferably impregnated with insect repellent, with edges tucked in under the mattress. The mesh size should be less than 1.5 mm. If the sleeping area is not otherwise protected, use a mosquito coil, which fills the room with insecticide through the night. Perform a thorough tick check at the end of each day with the assistance of a friend or a full-length mirror. Ticks should be removed with tweezers, grasping the tick by the head. Many tick-borne illnesses can be prevented by prompt tick removal.

Bring adequate supplies of all medications in their original containers, clearly labeled. Carry a signed, dated letter from the primary physician describing all medical conditions and listing all medications, including generic names. If carrying syringes or needles, be sure to carry a physician's letter documenting their medical necessity.Pack all medications in hand luggage. Carry a duplicate supply in the checked luggage. If you wear glasses or contacts, bring an extra pair. If you have significant allergies or chronic medical problems, wear a medical alert bracelet.

Make sure your health insurance covers you for medical expenses abroad. If not, supplemental insurance for overseas coverage, including possible evacuation, should be seriously considered. If illness occurs while abroad, medical expenses including evacuation may run to tens of thousands of dollars. For a list of travel insurance and air ambulance companies, go to Medical Information for Americans Traveling Abroad on the U.S. State Department website. Bring your insurance card, claim forms, and any other relevant insurance documents. Before departure, determine whether your insurance plan will make payments directly to providers or reimburse you later for overseas health expenditures. The Medicare and Medicaid programs do not pay for medical services outside the United States.

Pack a personal medical kit, customized for your trip (see description). Take appropriate measures to prevent motion sickness and jet lag, discussed elsewhere. On long flights, be sure to walk around the cabin, contract your leg muscles periodically, and drink plenty of fluids to prevent blood clots in the legs. For those at high risk for blood clots, consider wearing compression stockings.

Avoid contact with stray dogs and other animals. If an animal bites or scratches you, clean the wound with large amounts of soap and water and contact local health authorities immediately. Wear sun block regularly when needed. Use condoms for all sexual encounters. Ride only in motor vehicles with seat belts. Do not ride on motorcycles.

For an ambulance in South Korea, call the fire department at 119. Ambulances will usually respond quickly, but will not have the same level of equipment or staffing as an ambulance in the United States.

High quality medical care is available in Seoul, Pusan, Daegu, and a few other large cities, but may be difficult to locate in rural areas. In Seoul, many expatriates use the Samsung Medical Center (#50, Ilwon-dong, Kangnam-ku, Seoul; tel. 02-3410-2114, 3410-3114; emergency tel. 02-3410-2060, 3410-2061; website http://www.samsunghospital.com/), which includes an International Health Services unit dedicated to the care of foreign residents (registration tel. 82 (2) 3410-0200, 0226; emergency tel. 010-9933-0200, 0226, 0223), Asan Medical Center (388-1, Pung Nap-dong, Song Pa-ku, Seoul; tel. 02-1688-7575; emergency tel. 02-3010-3333; International Clinic 02-3010-5001; website http://www.amc.seoul.kr/eng/index.jsp), which is associated with Harvard Medical International, or Severance Hospital (134 Sinchon-dong, Seodaemun-gu, Seoul 120-752; tel. 82-2-2228-0114, 82-2-2228-0114; website http://www.severance.or.kr), which is a member of the international networks of the Massachusetts General Hospital and the New York-Presbyterian Hospital, two of the finest hospitals in the United States.

For an online list of English-speaking physicians and dentists in South Korea, as well as other major hospitals with English-speaking staff, go to 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.

Pharmacies are well-supplied, though not all psychiatric medications may be available. Travelers carrying psychiatric or controlled medications should bring them in their original containers, clearly labelled, as well as a copy of the prescription for Korean customs clearance at the airport.

Before you leave, make sure you have the names and contact information for physicians, clinics, and hospitals where you can obtain emergency medical care if needed (see the U.S. Embassy website).

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 the dosages are lower. 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.

International travel should be avoided by pregnant women with underlying medical conditions, such as diabetes or high blood pressure, or a history of complications during previous pregnancies, such as miscarriage or premature labor. For pregnant women in good health, the second trimester (18–24 weeks) is probably the safest time to go abroad and the third trimester the least safe, since it's far better not to have to deliver in a foreign country.

Before departure, make sure you have the names and contact information for physicians, clinics, and hospitals where you can obtain emergency obstetric care if necessary (see the U.S. Embassy website). In general, pregnant women should avoid traveling to countries which do not have modern facilities for the management of premature labor and other complications of pregnancy.

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. If travel to malarious areas is unavoidable, chloroquine must be taken once a week and 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.

Helpful maps are available in the University of Texas Perry-Castaneda Map Collection and the United Nations map library. If you have the name of the town or city you'll be visiting and need to know which state or province it's in, you might find your answer in the Getty Thesaurus of Geographic Names.

Americans living in or visiting the Republic of Korea are encouraged to register on the Internet at http://seoul.usembassy.gov or http://www.asktheconsul.org/, by fax (011-82-02)-397-4101, or in person at the Consular Section of the U.S. Embassy in Seoul and obtain updated information on travel and security within the Republic of Korea. American citizens may also sign up for warden messages and monthly newsletters by providing their e-mail address at http://www.asktheconsul.org or by sending an e-mail to join-seoulacs@mh.databack.com. The U.S. Embassy is located at 82 Sejong-Ro Chongro-Ku, Seoul, telephone (82-2) 397-4114 fax (82-2) 738-8845. The U.S. Embassy's web page can be found at http://seoul.usembassy.gov.

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.