Hepatitis A: Foodborne Outbreaks in Michigan and Maine—Should we Recommend Immunization?

Abstract & Commentary

Synopsis: Two hundred thirteen cases of hepatitis A in schoolchildren in Michigan were shown by hepatitis A genetic analysis to be transmitted by specific batches of frozen strawberries grown in Mexico and processed in California. These were widely distributed for school lunch programs. Apparently, sporadic cases in Maine and other states were subsequently linked to the same source.

Sources: Hutin YJ, et al. A multistate, foodborne outbreak of hepatitis A. N Engl J Med 1999;340:595-602; Koff RS. The case for routine childhood vaccination against hepatitis A. N Engl J Med 1999;340:644-645.

Hutin and associates on the national hepatitis a investigation Team of the Centers for Disease Control and Prevention (CDC) investigated a large outbreak of cases of hepatitis A that occurred in February and March 1997. The cases occurred almost exclusively in schoolchildren and school employees in two counties in Michigan. There had been no cases of hepatitis A reported in these counties in the preceding year. Information was obtained concerning how often a subject ate school lunch and which food items were eaten during seven school days, beginning 32 days before the peak incidence of the disease. The same information was obtained from an equal number of randomly selected classmates who did not develop hepatitis A. During the same period, 39 cases were reported from Maine and similar dietary information was obtained. In both Michigan and Maine, there was a strong association between consumption of strawberry shortcake and the subsequent development of hepatitis A. Polymerase chain reaction analyses of viruses isolated from patients in Michigan and Maine revealed an identical sequence of RNA indicating that the same virus caused the disease. It was possible to trace the strawberries responsible for the Michigan outbreak. The same RNA sequences were also found in small numbers of cases that occurred in the same general period in several other states that had received the same batches of frozen strawberries. These berries had been grown in Mexico, processed and frozen in California, and distributed though the Department of Agriculture for school lunch programs. The source of contamination was found to be probably related to unsanitary field conditions in Mexico.

In an accompanying editorial, Koff points out the increasing vulnerability of individuals in the United States to hepatitis A infections because of a falling rate (30%) of naturally acquired immunity and the increasing importation of vegetables and fruits from less developed countries where hepatitis A is endemic. The Advisory Committee on Immunization Practices (ACIP) of the CDC has recommended hepatitis A immunizations for some high-risk groups, including persons traveling or working in underdeveloped countries where hepatitis A is endemic, homosexual males, patients with chronic liver disease, and Native and Alaskan Americans. However, universal immunization has not yet been advocated. Koff believes that the time is appropriate to institute universal hepatitis A immunization in U.S. children.

Comment by Hal B. Jenson, MD, FAAP

Although we have two highly effective and safe inactivated hepatitis A vaccines, they are not licensed for use in children younger than 2 years of age because of reduced efficacy. This age limit and the cost of yet another childhood vaccine have dampened enthusiasm for universal hepatitis A immunization. Hepatitis A infection most frequently occurs as sporadic cases but also occurs in the clusters and outbreaks such as these in Michigan and Maine described by Hutin et al that continue to occur and place a strain on public health departments. Physicians must provide postexposure immunoglobulin prophylaxis, and parents must take time from home and work to obtain medical care following exposure. These cases exemplify the dilemma we face to determine whether the currently available vaccines are appropriate for universal use.

In his accompanying editorial, Koff points out the increasing vulnerability of individuals in the United States to hepatitis A infections because of a falling rate (< 30%) of naturally acquired immunity, higher susceptibility of younger persons, and the increasing importation of vegetables and fruits from developing countries where hepatitis A is endemic and sanitation may be sub-optimal. The ACIP has recommended routine hepatitis A immunization for persons traveling to or working in underdeveloped countries where hepatitis A is endemic, homosexual and bisexual males, persons with chronic liver disease, recipients of clotting factors, users of illicit drugs, as well as for children in high-risk communities such as Native and Alaskan Americans and children in selected areas of high hepatitis A endemicity. This

approach has resulted in different hepatitis A vaccination recommendations in different areas. The state of Oklahoma recently enacted universal childhood hepatitis A immunization statewide for all children, and in the next year, Texas is implementing hepatitis A immunization for 32 counties along the Texas-Mexico border.

However, universal immunization for the entire country has not yet been recommended. Koff believes that the

time is appropriate to institute universal hepatitis A immunization in U.S. children. These outbreaks demonstrate our vulnerability to global health problems despite never even leaving the confines of middle America. More and more of us, including children, are international travelers and would benefit from routine immunization in childhood.

We face barriers with hepatitis A vaccination that we have not let impede us with other vaccines. We instituted Haemophilus influenzae type b vaccination with the original polyribosyl ribitol phosphate (PRP) vaccine while the conjugate vaccines were being developed, to at least provide protection for all children 2 years of age and older. While combined hepatitis A and B vaccination beginning in infancy may be possible, the available hepatitis A vaccines are effective in children 2 years of age and older. We implemented universal hepatitis B vaccination in childhood even though hepatitis B, like hepatitis A, is predominantly a disease of adults and, therefore, the full public health benefit may take years or decades to realize. It is certainly appropriate to vaccinate early in life, against both hepatitis B and hepatitis A, to provide maximum protection. We have instituted universal vaccination against varicella, which, like hepatitis A, has a high rate of complete recovery but is associated with approximately 80-100 deaths annually in the United States.

We have the means by implementing universal hepati-tis A vaccination to prevent much disease and even some deaths each year. However, it remains to be determined if we have the will and the determination.

Which of the following statements is true regarding hepatitis A infections?

    a. They can be reliably prevented in children younger than 2 years of age with current vaccines.
    b. Universal vaccination is currently advised in areas of high epidemicity for hepatitis A.
    c. Specific viral strains responsible for local outbreaks cannot be identified with tests currently available.
    d. They have a high rate of acute and long-term mortality.