Hepatitis E Seroprevalence and Seroconversion
Hepatitis E virus (HEV) is an important agent of acute hepatitis in developing regions worldwide and is increasingly associated with infections that were acquired in regions where HEV infection had not been considered to be endemic. HEV is also a distinctive, nonenveloped, positive‐strand RNA virus; it represents the only species in genus Hepevirus, family Hepeviridae, and only 1 serotype is recognized. There are, however, 4 known genotypes that infect certain mammals; among humans, HEV genotypes 1 and 2 appear to differ clinically and epidemiologically from genotypes 3 and 4. HEV genotype 1 is the primary cause of epidemic and sporadic hepatitis among residents and travelers in many developing countries, where the primary mode of transmission is suspected to be fecal‐oral but indirect; genotype 2 infections are thought to have similar characteristics on the basis of fewer studies that represent several nations. In industrialized countries where hepatitis E (ie, disease caused by HEV) is very unusual, infections with genotype 3 or 4 are relatively common and transmission is postulated to have a zoonotic component.
Most reported outbreaks have occurred in South Asia, commonly following monsoon rains or flooding that resulted in contamination of well water or public water supplies. Epidemic and sporadic hepatitis E may account for half to nearly all of the cases of acute viral hepatitis among young adults in affected areas. Infection may manifest with a range of severity from subclinical to acute hepatitis to even death. Clinical features can include jaundice, anorexia, hepatomegaly, abdominal pain and tenderness, nausea and vomiting, and fever. Without laboratory confirmation, hepatitis E is indistinguishable from other types of hepatitis. Epidemics of HEV infection are common throughout nonindustrialized countries and may be responsible for up to half of all cases of acute viral hepatitis among young adults in affected areas. Although hepatitis E is generally self‐limited and the case‐fatality rate is low (estimated to be 0.5%–4%), morbidity from widespread outbreaks in large populations, including military populations, is well documented. In addition, pregnant women in their third trimester may have case‐fatality rates that exceed 20%, and immunosuppressed individuals may develop chronic hepatitis. It has been reported in developing countries that the ratio of subclinical to clinical infections is 2:1 for sporadic cases and 7:1 during epidemics. Therefore, seroprevalence studies are typically the best approach to determine the number of persons who have been infected with HEV.
The prevalence of antibodies to HEV (anti‐HEV) in the United States (US) was initially estimated to be 0.4%–2% and was thought to be almost exclusively associated with foreign travel. However, more recent studies among various US populations have found rates as high as 21%. HEV seroprevalence rates among United Nations Peacekeepers from several less industrialized countries were reported to be between 3% (among soldiers from Haiti) and 62% (among soldiers from Pakistan), whereas the seroprevalence rate among US soldiers was relatively low at 2%.