High Incidence of Japanese Encephalitis, Southern China

To the Editor: Japanese encephalitis virus (JEV) remains a major source of illness and death in Asia (1). An estimated 67,900 cases occur each year in Asia; ≈33,900 cases— half the cases in the world—probably occur in the People's Republic of China (2). However, because reporting is incomplete in most countries where JE incidence is high, these estimates are based on scarce data. In China, a study conducted during 2006–2007 in sentinel hospitals in 1 prefecture each in Shandong, Hubei, Guangxi, and Hebei Provinces (all in the eastern half of China) found that 9.2% of patients with acute meningitis and encephalitis had JEV; adjusted incidence for each prefecture was 0.08–1.58 cases per 100,000 population (3). Incidence in these 4 prefectures is lower than that among children <14 years of age in JE-endemic countries, where estimated incidence is 5.4 cases per 100,000 population (2). To assess the need for strengthening existing JE surveillance and vaccination programs, we conducted a population-based study of JE incidence in 1 area of southern China. Dehong is a prefecture in western Yunnan Province, which borders Myanmar. The JE-susceptible population of Dehong Prefecture (residents <15 years of age) is 211,337. The 2 principal cities of Dehong Prefecture—Mangshi and Ruili—are busy commercial centers surrounded by areas of extensive rice cultivation. The mosquito vector of JEV, Culex tritaeniorhynchus, is predominant during summer (4). During 1988– 2007, JEV vaccination was available only at certain clinics and only for a fee; however, since 2008, vaccination with the live, attenuated SA 14–14–2 JEV vaccine (Chengdu Institute of Biologic Products, Chengdu, China) has been included in the national Expanded Program on Immunization at no charge. The recommendation for children is vaccination at 8 months and 2 years of age (5,6). To estimate JE incidence in Dehong Prefecture during January 1–December 31, 2010, we conducted an anonymous, unlinked study of all cases of encephalitis at the only 2 major children's hospitals in the region, Dehong Prefecture Hospital in Mangshi and Ruili City Hospital in Ruili. All eligible patients admitted to these hospitals were included in the study. Inclusion criteria were age <15 years, residency in Dehong Prefecture, clinical diagnosis of encephalitis, lumbar puncture performed (routine for encephalitis patients at these 2 hospitals), and cerebrospinal fluid (CSF) pleocytosis. After routine testing was completed, leftover CSF and serum samples were stored at-70°C until further testing, which was all conducted at the Chinese Center for Disease Control …