Groups at Increased Risk for Hepatitis A : Part 2

by CDC

(Page 5 of 13)

Child Care Centers

Outbreaks among children attending child care centers and persons employed at these centers have been recognized since the 1970s, but their frequency has decreased as overall hepatitis A incidence among children has declined in recent years. Because infection among children is typically mild or asymptomatic, outbreaks often are identified only when adult contacts (typically parents) become ill. Poor hygiene among children who wear diapers and the handling and changing of diapers by staff contribute to the spread of HAV infection; outbreaks rarely occur in child care centers in which care is provided only to children who are toilet trained.

Although child care centers might have been the source of outbreaks of hepatitis A in certain communities, disease in child care centers more commonly reflects extended transmission from the community. Despite the occurrence of outbreaks when HAV is introduced into child care centers, results of serologic surveys do not indicate a substantially increased prevalence of HAV infection among staff at child care centers compared with prevalence among control populations.

Health-Care Institutions

Nosocomial HAV transmission is rare. Outbreaks have occasionally been observed in neonatal intensive-care units because of infants acquiring infection from transfused blood and subsequently transmitting hepatitis A to other infants and staff. Outbreaks of hepatitis A caused by transmission from adult patients to health-care workers are typically associated with fecal incontinence, although the majority of hospitalized patients who have hepatitis A are admitted after onset of jaundice, when they are beyond the point of peak infectivity. Data from serologic surveys of health-care workers have not indicated an increased prevalence of HAV infection in these groups compared with that in control populations.

Institutions for Persons with Developmental Disabilities

Historically, HAV infection was highly endemic in institutions for persons with developmental disabilities. As fewer children have been institutionalized and as conditions in institutions have improved, the incidence and prevalence of HAV infection have decreased, although outbreaks can occur in these settings.

Schools

In the United States, the occurrence of cases of hepatitis A in elementary or secondary schools typically reflects disease acquisition in the community. Child-to-child disease transmission in the school setting is uncommon; if multiple cases occur among children at a school, the possibility of a common source of infection should be investigated.

Workers Exposed to Sewage

Data from serologic studies conducted outside the United States indicate that workers who had been exposed to sewage had a possible elevated risk for HAV infection; however, these analyses did not control for other risk factors (e.g., socioeconomic status). In published reports of three serologic surveys conducted among U.S. wastewater workers and appropriate comparison populations, no substantial or consistent increase in the prevalence of anti-HAV was identified among wastewater workers. No work-related instances of HAV transmission have been reported among wastewater workers in the United States.

Strategy to Prevent and Control Hepatitis A Through Vaccination

With the availability of hepatitis A vaccines beginning in 1995, hepatitis A became a disease that was not only common but also vaccine-preventable. Use of these highly effective vaccines provided the opportunity to protect persons from infection, reduce disease incidence by preventing transmission, and ultimately eliminate indigenous HAV transmission.

Soon after hepatitis A vaccines became available in the United States, a strategy of routine vaccination of children was recognized to have the potential to achieve a sustained reduction in the overall incidence of hepatitis A by preventing infection among persons in age groups that accounted for at least one third of cases and eliminating a major source of infection for others. However, hepatitis A vaccines could not be readily incorporated into the routine infant and early childhood schedule because they were not licensed for children aged < 2 years. To overcome these logistical barriers to use of hepatitis A vaccines among children, a novel vaccination strategy was developed on the basis of distinct features of hepatitis A epidemiology and experience gathered from demonstration projects and other research and involving incremental implementation of routine childhood hepatitis A vaccination.

Initial recommendations primarily involved vaccination of persons in populations at increased risk for hepatitis A and, as the first step in the incremental strategy, of children living in communities with the highest disease rates. Vaccination of persons in groups at increased risk for hepatitis A (e.g., travelers) or its adverse outcomes (e.g., persons with chronic liver disease) provided protection to these persons but had little effect on national disease rates because the majority of cases did not occur among persons in these groups. Although routine vaccination of children living in communities with the highest rates of disease was effective in reducing disease rates in these communities, the impact on national disease incidence was limited because the majority of nationally reported cases occurred outside these communities.

A further step in the incremental implementation of routine vaccination of children was possible because areas with consistently elevated hepatitis A rates could be identified that contributed the majority of cases to the national disease burden. To date, the 1999 ACIP recommendations for routine vaccination of children living in these areas with consistently elevated rates have been implemented primarily by voluntary measures. The 2004 National Immunization Survey among children aged 24 - 35 months indicated first-dose coverage of approximately 54% in states for which vaccination is recommended, 27% in states for which it is to be considered, and 2% in the rest of the country. Although limited information on trends is available, these coverage estimates represent increases of 2% - 3% compared with the previous year. Coincident with implementation of these recommendations, national disease incidence has declined to historic lows, with the largest declines occurring in the age groups and parts of the country for which vaccination is recommended. The majority of disease (and the highest incidence) occurs in areas for which hepatitis A vaccination of children has not been recommended previously. Examination of historical incidence trends in these areas and theoretic models of incidence dynamics after introduction of a new vaccine suggest that incidence might increase again, although to what level is unknown.

A decade has passed since hepatitis A vaccines first became available in the United States. Multiple considerations make this an appropriate time to implement the final step in the incremental strategy, thereby bringing hepatitis A vaccination policy into line with that of other routinely recommended childhood vaccines. First, hepatitis A vaccine became available for children aged 12 - 23 months in 2005, allowing for its incorporation into the routine early childhood vaccination schedule. Second, as disease rates equalize across regions of the United States, questions remain regarding the validity and ultimate sustainability of the interim limited strategy. Continuation of this policy in light of current hepatitis A epidemiology means that vaccination of children is not presently recommended for the areas with the highest overall and age-specific disease incidence. Nationwide hepatitis A vaccination of children is likely to result in further narrowing of current demographic disparities and in lower overall rates. Ultimately, elimination of indigenous HAV transmission in the United States is an attainable goal.

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