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Travelers should be current on all routine immunizations, including COVID-19. Some countries require specific vaccinations (see table Vaccines for International Travel). The Centers for Disease Control and Prevention (CDC) website provides general travel and up-to-date immunization information, travel information related to COVID-19, and malaria chemoprophylaxis requirements (also available from the CDC's malaria hotline: 855-856-4713).

The COVID-19 pandemic has necessitated limitation of travel to and from various countries. Entry requirements (eg, testing, vaccination, quarantine) change frequently, and patients should be advised to check the website of their nation's health agency (eg, CDC in the US) as well as the destination countries for current recommendations.

Dengue fever is a mosquito-borne viral infection endemic to the tropical regions of the world in latitudes from about 35° north to 35° south. Outbreaks are most prevalent in Southeast Asia but also occur in the Caribbean, including Puerto Rico and the US Virgin Islands, Oceania, and the Indian subcontinent; more recently, dengue incidence has increased in Central and South America.

A vaccine for dengue is approved in several countries outside the US, but efficacy is only moderate and varies by dengue immune status, serotype, and patient age; studies are ongoing.

People traveling to endemic areas should try to prevent mosquito bites. Effective personal protection measures include applying DEET or picaridin to exposed skin, applying permethrin to clothing, and sleeping under a permethrin-treated mosquito net if sleeping quarters are not air conditioned (see CDC: Prevent Mosquito Bites). These measures also offer protection from other insect-transmitted diseases including Zika and chikungunya.

Influenza is common in international travelers; hence annual influenza vaccines are indicated for all travelers.

Malaria is endemic in much of Africa, Asia, Latin America, and other regions. The CDC provides information about specific countries where malaria is transmitted (see Yellow Fever and Malaria Information, by Country), types of malaria, and resistance patterns.

Travelers to endemic regions should take preventive measures for malaria, including chemoprophylaxis. Although the RTS,S/AS01 (RTS,S) malaria vaccine is recommended for children living in regions with moderate to high Plasmodium falciparum malaria transmission, this vaccine is not recommended for travelers to those regions.

Schistosomiasis is common and is caused by exposure to contaminated freshwater in Africa, Southeast Asia, China, and eastern South America. Risk of schistosomiasis can be reduced by avoiding freshwater activities in areas where schistosomiasis is common. Asymptomatic travelers with freshwater exposure in endemic regions should be screened by serologic testing for antibody to the adult worm at 6 to 8 weeks following their most recent exposure. Alternately, travelers may elect to presumptively treat a potential exposure with praziquantel, at 6 to 8 weeks after the most recent potential exposure: 20 mg/kg orally twice per day for one day (Schistosoma mansoni, S. haematobium, S. intercalatum) or 20 mg/kg 3 times per day for one day (S. japonicum, S. mekongi).

Traveler’s diarrhea (TD) is the most common health problem among international travelers. TD is usually self-limited, typically resolving in 5 days; however, 3 to 10% of travelers with TD may have symptoms lasting > 2 weeks, and up to 3% of travelers have TD lasting > 30 days. TD lasting < 1 week requires no testing. For persistent TD, laboratory testing is done.

Self-initiated treatment is indicated for moderate to severe symptoms, especially if vomiting, fever, abdominal cramps, or blood in the stool are present. Treatment of traveler's diarrhea is with an appropriate antibiotic (eg, azithromycin, 500 mg or one gram once, or 500 mg once a day for 1 to 3 days). Additional measures include loperamide (except in patients with fever, bloody stools, or abdominal pain and in children < 2 years); replacement of fluids; and, in older people and small children, electrolytes (eg, oral rehydration solution).

Measures that may decrease the risk of TD include

• Drinking and brushing teeth with bottled, filtered, boiled, or chlorinated water

• Avoiding ice

• Eating freshly prepared foods only if they have been heated to steaming temperatures

• Eating only fruits and vegetables that travelers peel or shell themselves

• Avoiding food from street vendors

• Washing hands frequently

• Avoiding all foods likely to have been exposed to flies

Prophylactic antibiotics are effective in preventing diarrhea, but because of concerns about adverse effects and development of resistance, they should probably be reserved for immunocompromised patients. One option is rifaximin, 200 mg once or twice a day.

Road traffic crashes are the most frequent cause of death of international travelers, with the exception of older adults. Travelers should at all times use a seat belt in vehicles and a helmet when cycling. Travelers should avoid motorcycles and mopeds and avoid riding on bus roofs or in open truck beds.

Drowning is another common cause of death while abroad. Travelers should avoid beaches with turbulent surf and avoid swimming after drinking alcoholic beverages.

The most common medical problem after travel is

• Persistent traveler's diarrhea

The most common potentially serious diseases are

• Malaria

• Hepatitis A and B

• Typhoid fever

• Sexually transmitted infections, including HIV infection

• Amebiasis

• Meningitis

People can also acquire lice and scabies after being in crowded living conditions or places where hygienic measures are poor.

Some diseases become evident months after a traveler has returned home; a travel history with exposure risks is a useful diagnostic clue when patients present with a puzzling illness. The International Society of Travel Medicine (www.istm.org) has lists of travel clinics. Many of these clinics specialize in assisting travelers who are ill after their return home. For health care practitioners, the Centers for Disease Control provides assistance and information to help patients returning from travel abroad.