Epidemiology of zoonotic hepatitis E: a community-based surveillance study in a rural population in China

Abstract

Background: Hepatitis E is caused by two viral genotype groups: human types and zoonotic types. Current understanding of the epidemiology of the zoonotic hepatitis E disease is founded largely on hospital-based studies.

Methods: The epidemiology of hepatitis E was investigated in a community-based surveillance study conducted over one year in a rural city in eastern China with a registered population of 400,162.

Results: The seroprevalence of hepatitis E in the cohort was 38%. The incidence of hepatitis E was 2.8/10,000 person-years. Totally 93.5% of the infections were attributed to genotype 4 and the rest, to genotype 1. Hepatitis E accounted for 28.4% (102/359) of the acute hepatitis cases and 68.9% (102/148) of the acute viral hepatitis cases in this area of China. The disease occurred sporadically with a higher prevalence during the cold season and in men, with the male-to-female ratio of 3∶1. Additionally, the incidence of hepatitis E increased with age. Hepatitis B virus carriers have an increased risk of contracting hepatitis E than the general population (OR = 2.5, 95%CI 1.5-4.2). Pre-existing immunity to hepatitis E lowered the risk (relative risk = 0.34, 95% CI 0.21-0.55) and reduced the severity of the disease.

Conclusions: Hepatitis E in the rural population of China is essentially that of a zoonosis due to the genotype 4 virus, the epidemiology of which is similar to that due to the other zoonotic genotype 3 virus.

Figure 1. Sentinel surveillance of acute hepatitis in rural community.

A sentinel surveillance study of acute hepatitis was conducted over 12 months between 2006 and 2007 in 10 rural townships with a combined population of 400,162. A total of 1,428 suspected cases presented within 21 days of onset of symptoms to local healthcare centers or hospitals during this period and 359 of which were diagnosed with acute hepatitis, having elevated serum ALT levels of 2.5 to 116.7 ULN (Upper Limit of Normal). Paired acute and convalescent serum samples were obtained from 271 of the acute hepatitis patients and single acute samples, from 88 patients for differential diagnosis of acute hepatitis caused by hepatitis viruses.

Figure 2. Seasonal distribution of hepatitis E.

Hepatitis E cases detected as described in Table 1 occurred sporadically throughout 12 months with ≤2 cases in any one village over any 30 days period. Most (70.6%, 72/102) of the cases occurred in the months of October to March.

Figure 3. Age and gender distribution of hepatitis E.

Noted virtually all the hepatitis E cases (see Table 1) occurred after age 20 years, most of which, among men (shaded block) and few among women (open block). Incidence of the infection (line) increases with age, reaching peak levels after 60 years of age.

Figure 4. Acute marker profiles of hepatitis E.

Of the 102 hepatitis E cases in the present series (see Table 1), 11 (cases 92 to 102) were detected according to occurrence of IgM anti-HEV and HEV RNA in single acute serum samples and the others (cases 1 to 91), according to occurrence of these markers and also ≥4 fold rise of IgG anti-HEV levels in paired serum samples. Additional low avidity IgG anti-HEV test was done for some of the samples, including those tested positive for rising IgG anti-HEV (cases 1 to 8) alone and those positive for IgM anti-HEV alone (cases 88 to 91 and cases 99 to 102). (+) denotes a positive finding and (-), for a negative finding, for the acute marker in individual samples and blank space denotes test not performed. The resulting acute marker profiles of cases 10 to 102 featured a positive IgM anti-HEV, and variously accompanied low avidity IgG or the other acute markers, are consistent with responses to primary infection by hitherto immunologically naïve subjects. The profiles of cases 1 to 9, featuring rising IgG and a negative finding for the other markers, except one (case 9), who was also tested positive for HEV RNA, are consistent with anamnestic responses by immune subjects to reinfection. HEV: hepatitis E virus.