Analysis of the cause of increased measles incidence in Xinjiang, China in 2004

BACKGROUND: Increased number of measles cases were reported from Xinjiang province of China in 2004, relative to previous years. This study aimed to identify the direct cause for this increase in measles morbidity and the major reason for the relatively high measles incidence rate in Xinjiang. METHODS: The epidemiologic and laboratory surveillance data for measles cases of 2004 were analyzed and a seroepidemiologic investigation involving 1024 subjects, mainly children aged less than 15 years, was conducted in Xinjiang. A questionnaire including demographic and vaccination data was completed by interview and blood samples drawn from surveillance subjects. Sera were analyzed for measles IgM (cases) and IgG (cases and surveillance). Data were assessed for their relationship with high measles incidence rate. RESULTS: 6271 measles cases were reported from Xinjiang in 2004 with a morbidity of 33.7 cases per 100,000 population. 83 of the cases were children less than 12-year-old. 50 of the serum samples were measles IgM positive and 69 were measles IgG positive. 2014 serum samples were collected in the seroepidemiologic survey. The overall IgG antibody seropositivity rate was 89 , preschool children having the lowest seropositivity rate (86 ). There was a significant difference in IgG positive rates as well as IgG titers between unvaccinated and vaccinated subjects with each subsequent dose leading to further increase in titer. CONCLUSIONS: Low routine measles vaccine coverage was the major probable cause contributing to the increased measles cases in 2004 in Xinjiang and the high measles infection rate overall. The national 2-dose measles vaccination regimen is effective if delivered appropriately.