Letter to the editor: the increasing hepatitis a incidence in Korea: is it possible within a limited time?

Dear Editor

We read with interest the recent article published by Seo et al. [1] in your journal. In order to define the pattern of hepatitis A incidence based on area characteristics, the authors performed a study using data from the registered national population of Korea and the national health insurance between 2004 and 2008. Among 73 459 individuals who had acute hepatitis A virus (HAV) infection, the incidence rates of HAV were 15.6 (per 100 000) in 2004 and the rate increased to 61.7 (per 100 000) in 2008 [1]. HAV infection is a major problem worldwide involving 10 million people each year. It is known as a self-limited, acute disease that usually spreads through oral-fecal routes [2]. Thanks to improvements in socioeconomic and sanitary conditions in many countries, its epidemiology has been changing through decades, but an important question remains about the detection methods that were used.

One of the basic points that remained ambiguous was related to the inclusion criteria used in patient selection, that is, to determine who were HAV infected patients; Seo et al. [1] used the International Classification of Diseases. Due to the nonspecific clinical presentations of acute hepatitis A, the detection of anti-HAV IgM antibodies in the serum for obtaining a definitive diagnosis is mandatory. Another study from Korea revealed that the optimal time for repeating the HAV test in clinically suspicious acute hepatitis A patients with a negative initial HAV test appears to be at least 2 days after the peak-alanine aminotranferase day [3]. Therefore, relying on only the disease classification could not reveal the real incidence rate of HAV. In addition, other factors such as symptomatic or asymptomatic and icteric or non-icteric cases should be considered.

The authors reported that the incidence rate of HAV increased dramatically from 15.6 to 61.7 over the course of four years (2004 to 2008), which seems to some extent a strange result because it does not seem that such a major alteration took place in sanitary conditions of Korea. Or was there an epidemic in the country? Actually these strange changes may be caused by an outbreak, for instance, of water pollution, food poisoning, or similar causes. Otherwise, such a change in the incidence rate as described could happen over the course of decades not years. There have been some reports in the literature that have declared that epidemiological shifts in the HAV pattern require the passing of a decade [4,5]. Consequently, following improvements in socio-economic and hygienic conditions, the mean age of HAV infection has been altered from children to adults. In another interpretation, HAV infection in older ages could lead to a symptomatic disease, which could increase reporting of the infected cases.