Health maintenance recommendations are based not only on the traveler's destination but also on assessment of risk, which is determined by such variables as health status, specific itinerary, purpose of travel, season, and lifestyle during travel. Detailed information regarding country-specific risks and recommendations may be obtained from the Centers for Disease Control and Prevention (CDC) publication Health Information for International Travel (available at wwwnc.cdc.gov/travel/).
Fitness for travel is an issue of growing concern in view of the increased numbers of elderly and chronically ill individuals journeying to exotic destinations (see "Travel and Special Hosts," below). Since most commercial aircraft are pressurized to 2500 m (8000 ft) above sea level (corresponding to a Pao2 of ∼55 mmHg), individuals with serious cardiopulmonary problems or anemia should be evaluated before travel. In addition, those who have recently had surgery, a myocardial infarction, a cerebrovascular accident, or a deep vein thrombosis may be at high risk for adverse events during flight. A summary of current recommendations regarding fitness to fly has been published by the Aerospace Medical Association Air Transport Medicine Committee (www.asma.org/publications/). A pretravel health assessment may be advisable for individuals considering particularly adventurous recreational activities, such as mountain climbing and scuba diving.
Immunizations for travel fall into three broad categories: routine (childhood/adult boosters that are necessary regardless of travel), required (immunizations that are mandated by international regulations for entry into certain areas or for border crossings), and recommended (immunizations that are desirable because of travel-related risks). Required and recommended vaccines commonly given to travelers are listed in Table 123-1.
Table 123–1. Vaccines Commonly Used for Travel |Favorite Table|Download (.pdf)
Table 123–1. Vaccines Commonly Used for Travel
|Vaccine||Primary Series||Booster Interval|
|Cholera, live oral (CVD 103 - HgR)||1 dose||6 months|
|Hepatitis A (Havrix), 1440 enzyme immunoassay U/mL||2 doses, 6–12 months apart, IM||None required|
|Hepatitis A (VAQTA, AVAXIM, EPAXAL)||2 doses, 6–12 months apart, IM||None required|
|Hepatitis A/B combined (Twinrix)||3 doses at 0, 1, and 6–12 months or 0, 7, and 21 days plus booster at 1 year, IM||None required except 12 months (once only, for accelerated schedule)|
|Hepatitis B (Engerix B): accelerated schedule||3 doses at 0, 1, and 2 months or 0, 7, and 21 days plus booster at 1 year, IM||12 months, once only|
|Hepatitis B (Engerix B or Recombivax): standard schedule||3 doses at 0, 1, and 6 months, IM||None required|
|Immune globulin (hepatitis A prevention)||1 dose IM||Intervals of 3–5 months, depending on initial dose|
|Japanese encephalitis (JE-VAX)||3 doses, 1 week apart, SC||12–18 months (first booster), then 4 years|
|Japanese encephalitis (Ixiaro)||2 doses, 1 month apart, SC||Optimal booster schedule not yet determined|
|Meningococcus, quadrivalent [Menimmune
(polysaccharide), Menactra, Menveo (conjugate)]||1 dose SC||>3 years (optimal booster schedule not yet determined)|
|Rabies (HDCV), rabies vaccine absorbed (RVA), or purified chick embryo cell vaccine (PCEC)||3 doses at 0, 7, and 21 or 28 days, IM||None required except with exposure|
|Typhoid Ty21a, oral live attenuated (Vivotif)||1 capsule every other day × 4 doses||5 years|
|Typhoid Vi capsular polysaccharide, injectable (Typhim Vi)||1 dose IM||2 years|
|Yellow fever||1 dose SC||10 years|
Diphtheria, Tetanus, and Polio
Diphtheria (Chap. 138) continues to be a problem worldwide. Large outbreaks have occurred in countries that have reduced their public vaccination programs. Serologic surveys show that tetanus (Chap. 140) antitoxin is lacking in many North Americans, especially in women over the age of 50. The risk of polio (Chap. 191) to the international traveler is extremely low, and wild-type poliovirus has been eradicated from the Western Hemisphere and Europe. However, studies in the United States suggest that 12% of adult travelers are unprotected against at least one poliovirus serogroup. Foreign travel offers an ideal opportunity to have these immunizations updated. With the recent increase in pertussis among adults, the diphtheria–tetanus–acellular pertussis (Tdap) combination is now recommended for adults as a once-only replacement for the 10-year Td booster.
Measles (rubeola) continues to be a major cause of morbidity and death in the developing world (Chap. 192). Several outbreaks of measles in the United States have been linked to imported cases. The group at highest risk consists of persons born after 1956 and vaccinated before 1980, in many of whom primary vaccination failed.
Influenza—possibly the most common vaccine-preventable infection in travelers—occurs year-round in the tropics and during the summer months in the Southern Hemisphere (coinciding with the winter months in the Northern Hemisphere). One prospective study showed that influenza developed in 1% of travelers to Southeast Asia per month of stay. Vaccination should be considered for all travelers to these regions, particularly those who are elderly or chronically ill. Travel-related influenza continues to occur during summer months in Alaska and the Northwest Territories of Canada among cruise-ship passengers and staff (Chap. 187). The speed of global spread of the pandemic H1N1 virus once again illustrates why influenza immunization is so important for travelers.
Regardless of travel, pneumococcal vaccine should be administered routinely to the elderly and to persons at high risk of serious infection, including those with chronic heart, lung, or kidney disease and those who have been splenectomized or have sickle cell disease (Chap. 134).
Documentation of vaccination against yellow fever (Chap. 196) may be required as a condition of entry into or passage through countries of sub-Saharan Africa and equatorial South America, where the disease is endemic or epidemic, or for entry into countries at risk of having the infection introduced. This vaccine is given only by state-authorized yellow fever centers, and its administration must be documented on an official International Certificate of Vaccination. A registry of U.S. clinics that provide the vaccine is available from the CDC (wwwnc.cdc.gov/travel/). Recent data suggest that fewer than 50% of travelers entering areas endemic for yellow fever are immunized. Severe adverse events associated with this vaccine have recently increased in incidence. First-time vaccine recipients may present with a syndrome characterized as either neurotropic (1 case per 125,000 doses) or viscerotropic (1 case per 250,000 doses; among persons 60–69 years of age, 1 case per 100,000 doses; and among persons ≥70 years of age, 1 case per 40,000 doses). Immunosuppression and thymic disease increase the risk of these adverse events (www.cdc.gov/vaccines/pubs/vis/downloads/vis-yf.pdf).
Protection against meningitis (using one of the quadrivalent vaccines) is required for entry into Saudi Arabia during the Hajj (Chap. 143).
Both seasonal and pandemic H1N1 vaccines (the latter, where available) were required for entry into Saudi Arabia during the Hajj in 2009.
Hepatitis A (Chap. 304) is one of the most common vaccine-preventable infections of travelers. The risk is six times greater for travelers who stray from the usual tourist routes. The mortality rate for hepatitis A increases with age, reaching almost 3% among individuals over age 50. Of the four hepatitis A vaccines currently available in North America (two in the United States), all are interchangeable and have an efficacy rate of >95%.
Long-stay overseas workers appear to be at considerable risk for hepatitis B infection (Chap. 304). The recommendation that all travelers be immunized against hepatitis B before departure is supported by two studies showing that 17% of the assessed travelers who received health care abroad had some type of injection; according to the World Health Organization, nonsterile equipment is used for up to 75% of all injections given in the developing world. A 3-week accelerated schedule of the combined hepatitis A and B vaccine has been approved in the United States. Virtually all travelers to less developed countries should be immunized against hepatitis A and B.
The attack rate for typhoid fever (Chap. 153) is 1 case per 30,000 travelers per month of travel to the developing world. However, the attack rates in India, Senegal, and North Africa are tenfold higher and are especially high among travelers to relatively remote destinations and among VFRs (immigrants and their families returning to their homelands to visit friends or relatives). Between 1999 and 2006 in the United States, 66% of imported cases involved the latter group. Both of the available vaccines—one oral (live) and the other injectable (polysaccharide)—have efficacy rates of ∼70%. In some countries, a combined hepatitis A/typhoid vaccine is available.
Although the risk of meningococcal disease among travelers has not been quantified, it is likely to be higher among travelers who live with poor indigenous populations in overcrowded conditions (Chap. 143). Because of its enhanced ability to prevent nasal carriage (compared with the older polysaccharide vaccine), a quadrivalent conjugate vaccine is the product of choice for immunization of persons traveling to sub-Saharan Africa during the dry season or to areas of the world where there are epidemics. The vaccine, which protects against serogroups A, C, Y, and W-135, has an efficacy rate of >90%.
The risk of Japanese encephalitis (Chap. 196), an infection transmitted by mosquitoes in rural Asia and Southeast Asia, is ∼1 case per 5000 travelers per month of stay in an endemic area. Most symptomatic infections among U.S. residents have involved military personnel or their families. The vaccineefficacy rate is >90%. The vaccine is recommended for persons staying>1 month in rural endemic areas or for shorter periods if their activities (e.g., camping, bicycling, hiking) in these areas will increase exposure risk. A new Vero cell vaccine is now available in the United States.
The risk of cholera (Chap. 156) is extremely low, with ∼1 case per 500,000 journeys to endemic areas. Cholera vaccine, no longer available in the United States, was rarely recommended but was considered for aid and health care workers in refugee camps or in disaster-stricken/war-torn areas. A more effective oral cholera vaccine is available in other countries.
Domestic animals, primarily dogs, are the major transmitters of rabies in developing countries (Chap. 195). Several studies have shown that the risk of rabies posed by a dog bite in an endemic area translates into 1–3.6 cases per 1000 travelers per month of stay. Countries where canine rabies is highly endemic include Mexico, the Philippines, Sri Lanka, India, Thailand, and Vietnam. The three vaccines available in the United States provide >90% protection. Rabies vaccine is recommended for long-stay travelers, particularly children, and persons who may be occupationally exposed to rabies in endemic areas; however, in a large-scale study, almost 50% of potential exposures occurred within the first month of travel. Even after receipt of a preexposure rabies vaccine series, two postexposure doses are required. Travelers who have had the preexposure series do not require rabies immune globulin (which is often unavailable in developing countries) if they are exposed to the disease.
Prevention of Malaria and Otherinsect-Borne Diseases
It is estimated that more than 30,000 American and European travelers develop malaria each year (Chap. 210). The risk to travelers is highest in Oceania and sub-Saharan Africa (estimated at 1:5 and 1:50 per month of stay, respectively, among persons not using chemoprophylaxis); intermediate in malarious areas on the Indian subcontinent and in Southeast Asia (1:250–1:1000 per month); and low in South and Central America (1:2500–1:10,000 per month). Of the more than 1000 cases of malaria reported annually in the United States, 90% of those due to Plasmodium falciparum occur in travelers returning or immigrating from Africa and Oceania. VFRs are at the highest risk of acquiring malaria. With the worldwide increase in chloroquine- and multidrug-resistant falciparum malaria, decisions about chemoprophylaxis have become more difficult. In addition, the spread of malaria due to primaquine- and chloroquine-resistant strains of Plasmodium vivax has added to the complexity of treatment, as has the recently described "monkey malaria" of humans, which is caused by P. knowlesi. The case-fatality rate of falciparum malaria in the United States is 4%; however, in only one-third of patients who die is the diagnosis of malaria considered before death.
Several studies indicate that fewer than 50% of travelers adhere to basic recommendations for malaria prevention. Keys to the prevention of malaria include both personal protection measures against mosquito bites (especially between dusk and dawn) and malaria chemoprophylaxis. The former measures include the use of DEET-containing insect repellents, permethrin-impregnated bed-nets and clothing, screened sleeping accommodations, and protective clothing. Thus, in regions where infections such as malaria are transmitted, DEET products (25–50%) are recommended, even for children and infants at birth. Studies suggest that concentrations of DEET above ∼50% do not offer a marked increase in protection time against mosquitoes. The CDC also recommends picaridin (icaridin), oil of lemon eucalyptus (PMD, para-menthane-3,8-diol), and IR3535 (ethyl butylacetylaminopropionate). In general, higher concentrations of active ingredient provide longer duration of protection, regardless of the active ingredient. Personal protection measures also help prevent other insect-transmitted illnesses, such as dengue fever (Chap. 196). Over the past decade, the incidence of dengue has increased, particularly in the Caribbean region, Latin America, and Southeast Asia. Both dengue and chikungunya viruses are transmitted by an urban-dwelling mosquito that bites primarily at dawn and dusk.
Table 123-2 lists the currently recommended drugs of choice for prophylaxis of malaria, by destination.
Table 123–2. Malaria Chemosuppressive Regimens, According to Geographic Areaa |Favorite Table|Download (.pdf)
Table 123–2. Malaria Chemosuppressive Regimens, According to Geographic Areaa
|Geographic Area||Drug of Choice||Alternatives|
|Central America (north of Panama), Iraq, Turkey, northern Argentina, and Paraguay||Chloroquine|
Primaquine (except Honduras)
|South America, including Haiti, Dominican Republic, and Panama but not northern Argentina or Paraguay; Asia, including Southeast Asia; Africa; and Oceania|
|Thai-Myanmar and Thai-Cambodian borders and central Vietnam|
Prevention of Gastrointestinal Illness
Diarrhea, the leading cause of illness in travelers (Chap. 128), is usually a short-lived, self-limited condition; however, 40% of affected individuals need to alter their scheduled activities, and another 20% are confined to bed. The most important determinant of risk is the destination. Incidence rates per 2-week stay have been reported to be as low as 8% in industrialized countries and as high as 55% in parts of Africa, Central and South America, and Southeast Asia. Infants and young adults are at particularly high risk. Recent reviews suggested that there is little correlation between dietary indiscretions and the occurrence of travelers' diarrhea. Earlier studies of U.S. students in Mexico showed that eating meals in restaurants and cafeterias or consuming food from street vendors was associated with increased risk.
(See also Table 128-3) The most frequently identified pathogens causing travelers' diarrhea are toxigenic Escherichia coli and enteroaggregative E. coli (Chap. 149), although in some parts of the world (notably northern Africa and Southeast Asia) Campylobacter infections (Chap. 155) appear to predominate. Other common causative organisms include Salmonella (Chap. 153), Shigella (Chap. 154), rotavirus (Chap. 190), and norovirus (Chap. 190). The latter virus has caused numerous outbreaks on cruise ships. Except for giardiasis (Chap. 215), parasitic infections are uncommon causes of travelers' diarrhea. A growing problem for travelers is the development of antibiotic resistance among many bacterial pathogens. Examples include strains of Campylobacter resistant to quinolones and strains of E. coli, Shigella, and Salmonella resistant to trimethoprim-sulfamethoxazole.
General food and water precautions include eating foods piping hot; avoiding foods that are raw, poorly cooked, or sold by street vendors; and drinking only boiled or commercially bottled beverages, particularly those that are carbonated. Heating kills diarrhea-causing organisms, whereas freezing does not; therefore, ice cubes made from unpurified water should be avoided. In spite of these recommendations, the literature has repeatedly documented dietary indiscretions by 98% of travelers within the first 72 h after arrival at their destination. The maxim "Boil it, cook it, peel it, or forget it!" is easy to remember but apparently difficult to follow.
(See also Table 128-5) As travelers' diarrhea often occurs despite rigorous food and water precautions, travelers should carry medications for self-treatment. An antibiotic is useful in reducing the frequency of bowel movements and duration of illness in moderate to severe diarrhea. The standard regimen is a 3-day course of a quinolone taken twice daily (or, in the case of some newer formulations, once daily). However, studies have shown that a single double dose of a quinolone may be equally effective. For diarrhea acquired in areas such as Thailand, where >90% of Campylobacter infections are quinolone resistant, azithromycin may be a better alternative. Rifaximin, a poorly absorbed rifampin derivative, is highly effective against noninvasive bacterial pathogens such as toxigenic and enteroaggregative E. coli. The current approach to self-treatment of travelers' diarrhea is for the traveler to carry three once-daily doses of an antibiotic and to use as many doses as necessary to resolve the illness. If neither high fever nor blood in the stool accompanies the diarrhea, loperamide should be taken in combination with the antibiotic; studies have shown that this combination is more effective than an antibiotic alone.
Prophylaxis of travelers' diarrhea with bismuth subsalicylate is widely used but only ∼60% effective. For certain individuals (e.g., athletes, persons with a repeated history of travelers' diarrhea, and persons with chronic diseases), a single daily dose of a quinolone, azithromycin, or rifaximin during travel of <1 month's duration is 75–90% efficacious in preventing travelers' diarrhea. Probiotics have been only ∼20% effective as prophylaxis. In Europe and Canada, an oral subunit cholera vaccine that cross-protects against enterotoxigenic E. coli has been shown to provide 30–50% protection against travelers' diarrhea.
Although extremely common, acute travelers' diarrhea is usually self-limited or amenable to antibiotic therapy. Persistent bowel problems after the traveler returns home have a less well-defined etiology and may require medical attention from a specialist. Infectious agents (e.g., Giardia lamblia, Cyclospora cayetanensis, Entamoeba histolytica) appear to be responsible for only a small proportion of cases with persistent bowel symptoms. By far the most common causes of persistent diarrhea after travel are postinfectious sequelae such as lactose intolerance or irritable bowel syndrome. A meta-analysis showed that postinfectious irritable bowel syndrome lasting months to years may occur in as many as 4–13% of cases. When no infectious etiology can be identified, a trial of metronidazole therapy for presumed giardiasis, a strict lactose-free diet for 1 week, or a several-week trial of high-dose hydrophilic mucilloid (plus an osmotic laxative such as lactulose or PEG 3350 for persons with alternating diarrhea and constipation) relieves the symptoms of many patients.
Prevention of Other Travel-Related Problems
Travelers are at high risk for sexually transmitted diseases (Chap. 130). Surveys have shown that large numbers engage in casual sex, and there is a reluctance to use condoms consistently. An increasing number of travelers are being diagnosed with schistosomiasis (Chap. 219). Travelers should be cautioned to avoid bathing, swimming, or wading in freshwater lakes, streams, or rivers in parts of northeastern South America, the Caribbean, Africa, and Southeast Asia. Prevention of travel-associated injury depends mostly on common-sense precautions. Riding on motorcycles (especially without helmets) and in overcrowded public vehicles is not recommended; in developing countries, individuals should not travel by road in rural areas after dark. In addition to its association with motor vehicle accidents, excessive alcohol use has been a significant factor in drownings, assaults, and injuries. Travelers are cautioned to avoid walking barefoot because of the risk of hookworm and Strongyloides infections (Chap. 217) and snakebites (Chap. 396).
The Traveler's Medical Kit
A traveler's medical kit is strongly advisable. The contents may vary widely, depending on the itinerary, duration of stay, style of travel, and local medical facilities. While many medications are available abroad (often over the counter), directions for their use may be nonexistent or in a foreign language, or a product may be outdated or counterfeit. For example, a multicountry study in Southeast Asia showed that a mean of 53% (range, 21–92%) of antimalarial products were counterfeit or contained inadequate amounts of active drug. In the medical kit, the short-term traveler should consider carrying an analgesic; an antidiarrheal agent and an antibiotic for self-treatment of travelers' diarrhea; antihistamines; a laxative; oral rehydration salts; a sunscreen with a skin-protection factor of at least 30; a DEET-containing or equivalent insect repellent for the skin; an insecticide for clothing (permethrin); and, if necessary, an antimalarial drug. To these medications, the long-stay traveler might add a broad-spectrum general-purpose antibiotic (levofloxacin or azithromycin), an antibacterial eye and skin ointment, and a topical antifungal cream. Regardless of the duration of travel, a first-aid kit containing such items as scissors, tweezers, and bandages should be considered. A practical approach to self-treatment of infections in the long-stay traveler who carries a once-daily dose of antibiotics (e.g., levofloxacin) is to use 3 tablets "below the waist" (bowel and bladder infections) and 6 tablets "above the waist" (skin and respiratory infections).