Hepatitis A risk factors

Travelers
Persons from developed countries who travel to developing countries are at substantial risk for acquiring hepatitis A. Such persons include tourists, immigrants and their children returning to their country of origin to visit friends or relatives, military personnel, missionaries, and others who work or study abroad in countries that have high or intermediate endemicity of hepatitis A. Hepatitis A remains one of the most common vaccine-preventable diseases acquired during travel. One study estimated the risk among persons who did not receive IG or vaccine before departure to be four to 30 cases per 100,000 months of stay in developing countries. The risk might be higher among travelers staying in areas with poor hygienic conditions, varies according to the region and the length of stay, and appears to be increased even among travelers who reported observing protective measures and staying in urban areas or luxury hotels (CDC, unpublished data, 2005). In the United States, children account for approximately 50% of reported travel-related cases. In one study of Hispanic children in San Diego with hepatitis A, two thirds reported international travel (to Mexico) during the incubation period; travel was the only exposure associated with infection in a case-control study. Travelers who acquire hepatitis A during their trips also might transmit to others on their return.

MSM
Hepatitis A outbreaks among MSM have been reported frequently. Cyclic outbreaks have occurred in urban areas in the United States, Canada, Europe, and Australia and can occur in the context of an outbreak in the larger community. Seroprevalence surveys have not consistently demonstrated an elevated prevalence of anti-HAV compared with a similarly aged general population. Certain studies have identified specific sex practices associated with illness, whereas others have not demonstrated such associations. Since 1996, ACIP has recommended hepatitis A vaccination of MSM. Although precise data are lacking, vaccine coverage appears to be low.

Users of Injection and Noninjection Drugs
During the preceeding 2 decades, outbreaks have been reported with increasing frequency among users of injection and noninjection drugs in Australia, Europe, and North America. In the United States, outbreaks have frequently involved users of injected and noninjected methamphetamine, who have accounted for up to 48% of reported cases during outbreaks. Cross-sectional serologic surveys have demonstrated that injection-drug users have a higher prevalence of anti-HAV than the general U.S. population. Transmission among injection-drug users probably occurs through both percutaneous and fecal-oral routes. Since 1996, ACIP has recommended hepatitis A vaccination of users of illicit drugs, but vaccine coverage data are not available.

Persons with Clotting-Factor Disorders
During 1992-1993, outbreaks of hepatitis A were reported in Europe among persons with clotting-factor disorders who had been administered solvent-detergent-treated, "high-purity" factor VIII concentrates that presumably had been contaminated from plasma donors incubating hepatitis A. In the United States, data from one serologic study suggested that persons with hemophilia might be at increased risk for HAV infection. HAV is resistant to solvent-detergent treatment, and during 1995-1996, one study identified six patients with clotting-factor disorders who had hepatitis A after having been administered solvent-detergent-treated factor VIII and factor IX concentrates. However, changes in viral inactivation procedures, high hepatitis A vaccine coverage, and improved donor screening have decreased the risk for HAV transmission from clotting factors. During May 1998-July 2002, no new cases of HAV infection attributed to blood products were identified in an analysis of serosurveillance data from 140 participating hemophilia treatment centers.

Persons Working with Nonhuman Primates
Outbreaks of hepatitis A have been reported among persons working with nonhuman primates that are susceptible to HAV infection, including Old and New World species. Primates that were infected were those that had been born in the wild, not those born and raised in captivity.

Risk for Severe Adverse Consequences of Hepatitis A Among Persons with Chronic Liver Disease
Although not at increased risk for HAV infection, persons with chronic liver disease are at increased risk for fulminant hepatitis A. Death certificate data indicate a higher prevalence of chronic liver disease among persons who died of fulminant hepatitis A compared with persons who died of other causes.

Food-Service Establishments and Food Handlers
Foodborne hepatitis A outbreaks are recognized relatively infrequently in the United States. Outbreaks typically are associated with contamination of food during preparation by an HAV-infected food handler; a single infected food handler can transmit HAV to dozens or even hundreds of persons. However, the majority of food handlers with hepatitis A do not transmit HAV. Food handlers are not at increased risk for hepatitis A because of their occupation. However, among the approximately 40,000 adults with hepatitis A reported during 1992--2000 for whom an occupation was known, 8% were identified as food handlers, reflecting the large number of persons employed in the food service industry. Evaluating HAV-infected food handlers is a common and labor-intensive task for public health departments. In a 1992 common-source outbreak involving 43 persons, the estimated total medical and disease control cost was approximately $800,000.

Outbreaks associated with food, especially green onions and other raw produce, that has been contaminated before reaching a food-service establishment have been recognized increasingly in recent years. Low attack rates are common, and outbreaks often have been recognized in association with a single restaurant in which no infected food handler was identified on subsequent investigation.

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.