Acute hepatitis caused by hepatitis A virus (HAV) may be a serious, even fatal illness that presents with fever, malaise, myalgia and anorexia, followed by jaundice in < 10% of children and approximately 80% of adults. Children are usually minimally symptomatic while adults become ill enough to miss an average of 27 days of work. Moderate- to high-risk regions for hepatitis A include all areas of the world except Canada, Western Europe, Japan, Australia, and New Zealand. HAV is shed in the stool and the predominant mode of spread is through fecal-oral routes, including contaminated foods, water, and person-to-person contact. HAV is the most common vaccine preventable infection of overseas travelers who are non-immune with an attack rate of 2000 cases per 1,000,000 non-immune travelers per month. This rate is higher for campers and hikers. The risk for HAV is increased even among travelers who report that they observe measures to protect themselves against enteric infection or who only stay in urban areas or luxury hotels. Although the overall mortality of HAV is 0.3%, it is over 2% in those over the age of 50. Travelers should minimize their exposure to HAV and other enteric pathogens by avoiding drinking water (or beverages with ice) of unknown purity and avoiding eating uncooked shellfish/fruits or vegetables they did not peel or prepare.
Who is most likely to have immunity to HAV? The overall prevalence of antibody to hepatitis A virus in the general US population has been shown to be 38% based on a national survey. This prevalence increases progressively with age, ranging from 11% in persons < 5 years of age to 74% in persons ³ 50 years old.
Passive immunity with an intramuscular injection of serum immune globulin (SIG) is effective in preventing severe HAV. SIG is a sterile preparation of concentrated immunoglobulins made from pooled human plasma. SIG provides protection against HAV through passive transfer of antibody. Preexposure prophylaxis with SIG confers protection for 3-5 months depending on the dosage administered. Serious adverse side effects are rare with SIG and no transmission of viruses has been reported with SIG prepared in the U.S. that was used for this purpose. Because of the uncertain availability of SIG, we recommend using the inactivated hepatitis A vaccines (below). Travelers over the age of 50 years or those raised overseas may wish to be tested to see if they are immune to hepatitis A due to earlier acquisition of the disease while growing up. People who have been infected with hepatitis A have life-long immunity.
Two inactivated HAV vaccines are licensed for use in the U.S. and both are very effective and well-tolerated. One vaccination of either product provides immunity in ³95% within 4 weeks and for up to 20 years with a booster 6-12 months later. It is exciting to have this safe and highly effective vaccine option. We encourage travelers to visit their travel center at least 4 weeks prior to travel to take advantage of this vaccine, especially since we can't count on a reliable supply of SIG.
Enterically transmitted hepatitis E virus (HEV) has been found to be responsible for sporadic and epidemic acute hepatitis, especially in developing countries. Fatality rates for HEV range from 0.5 to 4 % for the general population, but up to 20% with pregnant women. Currently there is no effective prophylaxis for hepatitis E. The best prevention of infection to avoid potentially contaminated food and water.
Typhoid Fever (TF)
Typhoid fever is a bacterial infection caused by the bacterium Salmonella typhi that is transmitted by food and water that has been contaminated with the feces of chronic carriers or acutely ill patients. Unlike illness that is caused by other bacteria, the onset of TF may be insidious, with fever, malaise, anorexia, headache, and myalgia. Serious complications can include shock, heart valve infections, meningitis, or bone infections. This illness may be fatal if untreated. The worldwide incidence of TF varies from a low of < 1 case per 100,000 (U.S.), to ³100 cases per 100,000 in endemic areas such as Chile, Indonesia, and the Indian subcontinent. From 1975 to 1984, 62% of the average of 464 annual cases in the U.S. occurred among persons who had traveled to other countries.
The two typhoid vaccines that are currently available in the U.S. have been shown to protect only 70-90% of the recipients. Therefore, even vaccinated travelers should be cautious in selecting their food and water. Typhim Vi™ (typhoid Vi polysaccharide vaccine ViCPS) is an injectable killed vaccine derived from the capsular elements of the typhoid bacterium (S. typhi) This vaccine is very well tolerated, which is a marked improvement over the previously available injectable vaccine that is no longer available to American civilians. This vaccine is protective for 2 years following a single dose.
Live Oral Typhoid Vaccine Oral (Ty21a, Swiss Serum and Vaccine Institute), has been distributed in the U.S. since 1990. The vaccine contains an attenuated (live) strain of the bacterium S. typhi in enteric-coated capsules. Complete immunization requires four doses: each capsule is taken on alternate days with a cool drink not exceeding body temperature about 1 hour before a meal. Since this vaccine contains live bacteria, the tablets must be kept refrigerated and they must not be chewed or taken with antibacterial drugs or within 24 hours of the antimalarial drug mefloquine. The last dose should be taken at least one week prior to potential exposure to S. typhi. Adverse effects are rare, consisting of gastrointestinal tract upset and rash. One concern with this regimen is the large potential for non-compliance: 18% to 30% of travelers have been shown to be non-compliant with at least one or more of the instructions.
Typhoid vaccination is recommended for travelers to endemic areas such as Africa, Asia, SE Asia, and Central and South America, particularly for those planning to travel for extended periods (> 3 weeks), those traveling away from typical tourist areas, those expecting to come in contact with patients (health care workers), adventurous eaters, or those who take ulcer medications that decrease stomach acidity.
Cholera is a diarrheal disease caused by the bacterium Vibrio cholerae that is acquired by the ingestion of contaminated food or water. It is unusual for the western traveler to acquire cholera, although there are occasional outbreaks reported among groups of tourists associated with contaminated seafood. The diarrheal syndrome provoked by cholera is usually mild and self-limiting in adult travelers, but can be fatal for the very young who are especially prone to rapid and severe dehydration. Treatment is supportive. There is currently no cholera vaccine approved for use in the U.S.
Travelers diarrhea is defined as the occurrence of three or more watery stools each day or any number of stools accompanied by abdominal cramping, fever, or vomiting occurring in travelers from industrialized to developing countries. Travelers diarrhea occurs in 20-70% of travelers in the first two weeks of travel, and is most often caused by the bacterium Escherichia coli, although there are many potential bacterial, protozoal, and parasitic pathogens that can cause this syndrome. We recommend that the traveler carry a supply of an antibiotic, usually a quinolone, to take for 1-3 days in the event of moderate to severe watery diarrhea: this is very effective in shortening the duration of illness. It has been shown that the anti-motility agent loperamide plus antibiotic therapy significantly shortens the duration of diarrhea more that antibiotic alone. Anti-motility agents should be avoided with severe, bloody diarrhea. Diarrhea danger signs include persistent bloody diarrhea, high fever, vomiting, severe abdominal pain, prostration, and dehydration. Travelers should consult a physician if their symptoms are severe, are not improved after 24 hours of antibiotic treatment, or if there is continued vomiting.