HEV is an enterically transmitted RNA virus that can cause outbreaks or sporadic disease, and large outbreaks are typical in developing countries with contaminated water. Genotypes 1 and 2 exclusively infect humans, whereas genotypes 3 and 4 infect humans, pigs, and other animals.
"Our study represents the first attempt to estimate the annual global impact of hepatitis E," lead author David Rein, PhD, from the National Opinion Research Center (NORC) at the University of Chicago, Illinois, said in a news release, noting that although an HEV vaccine exists, it has not yet been widely implemented.
In the study, Dr. Rein and colleagues modeled the disease burden of HEV genotypes 1 and 2 in 9 of the 21 regions defined for the Global Burden of Diseases, Injuries, and Risk Factors study.
The areas represented about 4.7 billion people, or 72.8% of the world's population in 2005, and encompassed Central, East, South, and Southeast Asia; North Africa and the Middle East; and Central, East, South, and West Sub-Saharan Africa.
The team (representing a collaboration between researchers from NORC, the World Health Organization, and RTI International) also estimated the annual incidence of infection to estimate symptomatic, asymptomatic, and mortality cases. They deduced that 20.1 million people across the 9 regions were infected with HEV (95% credible interval [CrI], 2.8 - 37.0 million), resulting in 3.4 million symptomatic cases (95% CrI, 0.5 - 6.5 million), 70,000 deaths (95% CrI, 12,400 - 132,732 deaths), and 3000 stillbirths (95% CrI, 1892 - 4424 deaths).
Although only some of those infected with HEV develop symptoms, the probability was estimated to be 0.198 (95% CrI, 0.167 - 0.229), with the risk for related death being 0.019 (95% CrI, 0.017 - 0.021) in nonpregnant cases and 0.198 (95% CrI, 0.169 - 0.227) in pregnant women.
The pattern of HEV infection was consistent across the regions, with the largest incident increase occurring in young people aged from 5 through 20 years (average, 17 years; range, from 8 years in North Africa to 21 years in East Asia).
North Africa accounted for 14.3% of all global HEV infections, but only 8.3% of symptomatic cases and 8.1% of deaths, which the authors attribute to the younger average age of infection in that region.
The greatest proportion (60.6%) of estimated HEV cases occurred in East and South Asia, accounting for 64.7% of HEV deaths.
The authors caution that the study is limited in several respects: the researchers only estimated the incidence of HEV genotypes 1 and 2, leaving out genotype 3 (which prevalently occurs in Europe and the United States) and genotype 4.
In addition, the data used to estimate the prevalence and incidence of HEV infection are "sparse and uncertain," and the estimates have yet to be verified; the global stillbirth estimate, for example, according to studies published in 2010 may be 14.5% lower than the rates used.
"Future studies work should explore the probability of disease from genotype 3 HEV infections; the probability of symptomatic illness given infection and how this probability varies by age, gender, and pregnancy status," the authors write, noting the importance of collecting population-based data on HEV antibody status.
The study was undertaken as part of the Global Burden of Diseases, Injuries, and Risk Factors study and prepared independently of the final estimates of study results. The authors have disclosed no relevant financial relationships.
Hepatology. 2012;55:988-997. Abstract
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Cite this: Hepatitis E Infected More Than 20 Million Worldwide Annually - Medscape - Mar 29, 2012.