Chapter 3Infectious Diseases Related To Travel
Umid M. Sharapov, Eyasu H. Teshale
Hepatitis A virus (HAV) is an RNA virus classified as a picornavirus.
Through direct person-to-person contact; contaminated water, ice, or shellfish harvested from sewage-contaminated water; or from contaminated raw fruits, vegetables, or other foods. HAV is shed in the feces of infected people. The virus reaches peak levels 1–2 weeks before onset of symptoms and diminishes rapidly after liver dysfunction or symptoms appear, which is concurrent with the appearance of circulating antibodies to HAV. Infants and children, however, may shed virus for up to 6 months after infection.
Common throughout the developing world, where infections most frequently are acquired during early childhood and are usually asymptomatic or mild. In these countries, a high proportion of adults in the population are immune to HAV, and epidemics of hepatitis A are uncommon. In developed countries, infection is less common, but communitywide outbreaks may occur. Hepatitis A is one of the most common vaccine-preventable infections acquired during travel. In the United States the most frequently identified risk factor for hepatitis A is international travel. Risk is highest for those who live in or visit rural areas, trek in backcountry areas, or frequently eat or drink in settings of poor sanitation. However, cases of travel-related hepatitis A can also occur in travelers to developing countries with “standard” tourist itineraries, accommodations, and eating behaviors.
Incubation period averages 28 days (range, 15–50 days). Infection may be asymptomatic or may range in severity from a mild illness lasting 1–2 weeks to a severely disabling disease lasting several months. Clinical manifestations include the abrupt onset of fever, malaise, anorexia, nausea, and abdominal discomfort, followed within a few days by jaundice. The likelihood of having symptoms with HAV infection is related to the age of the infected person. In children aged <6 years, most (70%) infections are asymptomatic; if illness does occur, its duration is usually <2 months. Ten percent of infected people have prolonged or relapsing symptoms over a 6- to 9-month period. The overall case-fatality ratio is 0.3%; however, the ratio is 1.8% among adults aged >50 years.
Anti-HAV IgM in serum or ≥4-fold rise in specific antibodies in paired sera.
Supportive care only.
Vaccination or immune globulin (IG), and food and water precautions.
Two monovalent hepatitis A vaccines and a combined hepatitis A and hepatitis B (Twinrix) vaccine are licensed in the United States (Table 3-02). The immunogenicity of the combination vaccine is equivalent to that of the monovalent hepatitis vaccines when tested after completion of the licensed schedule.
Indications for Use
All susceptible people traveling for any purpose, frequency, or duration to countries with high or intermediate HAV endemicity should be vaccinated or receive IG before departure. Currently, international travel is considered the number one risk factor for HAV infection in the United States. Although the Advisory Committee for Immunization Practices recommends hepatitis A vaccination for people traveling to countries with high or intermediate HAV endemicity, published maps may not be the best guide in determining endemicity in developing countries. Prevalence patterns of HAV infection may vary among regions within a country, and missing or obsolete data present a challenge. Countries where the prevalence of HAV infection is decreasing have increasing numbers of susceptible people, and there is a risk of large outbreaks of hepatitis A. In addition, in recent years, large outbreaks of hepatitis A were reported in developed countries among people who had been exposed to either food handlers with hepatitis A or imported food contaminated with HAV. Taking into account the complexity involved with interpreting hepatitis A risk maps and potential foodborne hepatitis A risk in countries with low endemicity, some expert travel clinicians advise people traveling outside the United States to consider hepatitis A vaccination regardless of their destination.
Vaccination is recommended for unvaccinated household members and other people who will have close personal contact (such as regular babysitters) with an international adoptee from a country of high or intermediate endemicity (see Chapter 7, International Adoption).
One dose of monovalent hepatitis A vaccine protects most healthy people aged ≤40 years. The vaccine series should be completed according to the licensed schedule for long-term protection.
Hepatitis A vaccine at the age-appropriate dose is preferred to IG; however, for optimal protection, adults aged >40 years, immunocompromised people, and people with chronic liver disease or other chronic medical conditions planning to depart to an area in <2 weeks should receive the initial dose of vaccine along with IG (0.02 mL/kg) at a separate injection site.
Travelers who are aged <12 months, are allergic to a vaccine component, or who otherwise elect not to receive vaccine should receive a single dose of IG (0.02 mL/kg), which provides effective protection against HAV infection for up to 3 months. Those who do not receive vaccination and plan to travel for >3 months should receive an IG dose of 0.06 mL/kg, which must be repeated if the duration of travel is >5 months.
Although vaccination of an immune traveler is not contraindicated and does not increase the risk for adverse effects, screening for total anti-HAV before travel can be useful in some circumstances to determine susceptibility and eliminate unnecessary vaccination. Postvaccination testing for serologic response is not indicated.
Other Vaccine Considerations
Using the vaccines according to the licensed schedules is preferable. However, an interrupted series does not need to be restarted. More than 95% of vaccinated people develop protective levels of anti-HAV 1 month after the first dose. Given their similar immunogenicity, a series that has been started with one brand of monovalent vaccine may be completed with the other brand. For children and adults who complete the primary series, booster doses of vaccine are not recommended.
Vaccine Safety and Adverse Reactions
Among adults, the most frequently reported side effects, occurring 3–5 days after a vaccine dose, are tenderness or pain at the injection site (53%–56%) or headache (14%–16%). Among children, the most common side effects reported are pain or tenderness at the injection site (15%–19%), feeding problems (8% in one study), or headache (4% in one study). No serious adverse events in children or adults have been found that could be attributed definitively to the vaccine, nor have increases in serious adverse events been identified among vaccinated people compared with baseline rates.
Precautions and Contraindications
These vaccines should not be administered to travelers with a history of hypersensitivity to any vaccine component. Twinrix should not be administered to people with a history of hypersensitivity to yeast. Because hepatitis A vaccine consists of inactivated virus and hepatitis B vaccine consists of a recombinant protein, no special precautions are needed for vaccination of immunocompromised travelers.
The safety of hepatitis A vaccine for pregnant women has not been determined. However, because hepatitis A vaccine is produced from inactivated HAV, the theoretical risk to either the pregnant woman or the developing fetus is thought to be low. The risk of vaccination should be weighed against the risk of hepatitis A among female travelers who might be at high risk for exposure to HAV.
Travelers who are exposed to HAV and who have not received hepatitis A vaccine or IG previously should be administered 1 dose of monovalent hepatitis A vaccine or IG (0.02 mL/kg) as soon as possible. The efficacy of IG or vaccine when administered >2 weeks after exposure has not been established. Information about the relative efficacy of vaccine compared with IG postexposure is limited.
For healthy people aged 12 months to 40 years, a dose of monovalent hepatitis A vaccine is recommended. For people aged >40 years, IG is preferred, but vaccine can be used if IG is unavailable. IG is recommended for people aged <12 months, people who are immunocompromised, people who have chronic liver disease, and people for whom vaccine is contraindicated. More detailed information can be found in the Advisory Committee on Immunization Practices recommendations at www.cdc.gov/mmwr/preview/mmwrhtml/mm5641a3.htm.
CDC website: www.cdc.gov/hepatitis/HAV
Table 3-02. Vaccines to prevent hepatitis A
|VACCINE||TRADE NAME (MANUFACTURER)||AGE (Y)||DOSE||ROUTE||SCHEDULE||BOOSTER|
|Hepatitis A vaccine, inactivated||Havrix (GlaxoSmithKline)||1–18
0.5 mL (720 ELU)
0, 6–12 mo
|Hepatitis A vaccine, inactivated||Vaqta (Merck & Co., Inc.)||
0.5 mL (25 U)
0, 6–18 mo
|Combined hepatitis A and B vaccine||Twinrix (GlaxoSmithKline)||
1.0 mL (720 ELU HAV + 20 μg HBsAg)
same as above
0, 1, 6 mo
0, 7, 21–30 d
Abbreviations: ELU, ELISA units of inactivated HAV; IM, intramuscular; U, units HAV antigen; HAV, hepatitis A virus; HBsAg, hepatitis B surface antigen.
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