Surveillance for Japanese Encephalitis in Vietnam, 1998–2007

Abstract

Japanese encephalitis (JE) is recognized as an important public health problem in Vietnam. A JE immunization program was introduced in 1997 in high-risk districts and expanded to additional districts over subsequent years. We reviewed national acute encephalitis syndrome (AES) surveillance data for 1998–2007 and analyzed more detailed data regarding JE from five northern provinces in 2004 and 2005. The annual reported incidence of AES in Vietnam ranged from 3.0 to 1.4 cases per 100,000 population with a decreasing trend over the 10-year period. The mean annual incidence of AES was highest in the northern region of the country. Of 421 AES cases from five northern provinces with laboratory results reported, 217 (52%) had laboratory evidence of recent JEV infection. As Vietnam moves closer to control of JE through immunization, accurate JE surveillance data will be important to evaluate and guide the program.

Dengue Associated Acute Encephalitis Syndrome Cases in Son La Province, Vietnam in 2014

“…Other AES agents, including bacteria and parasites, have been suggested as causative agents of AES for patients negative for antiflavivirus antibodies (2,(14)(15)(16)(17). In Vietnam, anti-JEV IgM positivity among AES patients varies from 17 to 71 (9). DENV infection, another mosquito borne disease in humans, has become an important epidemic disease in Vietnam.…”

“…Those that were positive for both antibodies had JEV IgM P N ratio higher than that of DENV. The incidence of JEV was more common in northern Vietnam than in central and southern Vietnam (9). According to AES surveillance guidelines, a clinical case of AES with JEV-specific IgM antibody positivity in a single sample of CSF or serum as detected by an IgM-capture ELISA is considered a laboratoryconfirmed case (10).…”

“…In 1997, JE vaccine was introduced in high-risk areas in northern Vietnam and subsequently to its other parts (8). From 1998 to 2007, the mean annual incidence of AES was 2.4 cases per 100,000 population (9). A slightly decreasing trend of incidence of encephalitis was noted after the introduction of JE vaccine; in addition, no JE epidemics, which were similar to those prior to the introduction of the vaccine, had been reported (9).…”

“…From 1998 to 2007, the mean annual incidence of AES was 2.4 cases per 100,000 population (9). A slightly decreasing trend of incidence of encephalitis was noted after the introduction of JE vaccine; in addition, no JE epidemics, which were similar to those prior to the introduction of the vaccine, had been reported (9). In most parts of the country, immunization with JE vaccine covers children aged 1-5 years (9).…”

“…cases. Usually, the northwest regions, which include Son La Province, have a high incidence of AES (＞6.0 cases per 100,000 population) compared to other parts of the country despite the introduction of JE vaccine (9 In this study, using samples from Son La Province, Vietnam, we aimed to describe the proportion of encephalitic patients due to JEV during the reported JE outbreak and to evaluate whether DENV was also a causative agent.…”