Epidemiological Characteristics Of Measles And Its Influencing Factors In Zhejiang Province

Backgrounds and ObjectivesMeasles is a contagious disease accounting for nearly half the global burden of vaccine-preventable deaths, with122,000deaths estimated in2012. In2005, the World Health Organization (WHO) Regional Committee for the Western Pacific Region (WPR) prompted that measles should be eliminated by2012. In accordance with this strategy, in China,2012was also setted as the target year for measles elimination and the measles incidence, in cases per100,000, decreased from9.95in2008to a historic low of0.46in2012. However, the goal of measles elimination has not been achieved. Therefore, it was necessary to describe the epidemiological characteristics of measles and explore its influencing factors in China.Against the background of increasing immunization coverage, the mean annual measles incidence reported in Zhejiang, in cases per100,000, was1057.95between1951and1965,332.96between1966and1977,103.68between1978and1985, and10.62between1986and2004, with an obvious decrease. However, since2004, the resurgence started and measles outbreaks had occurred periodically. Moreover, few studies on epidemiology of measles were reported in Zhejiang. This study aimed to explore the epidemiological characteristics of measles and its influencing factors in Zhejiang, China, offer strategies that may be applicable in the broad context of measles elimination.Materials and Methods Measles data in this study was from the measles surveillance system. In Zhejiang, measles surveillance data was permitted to flow from the hospitals and county-level CDC to provincial CDC through a web-based computerized reporting system (National Notifiable Diseases Reporting System, NNDRS). Suspected cases were defined as any person with fever and a generalized, characteristic maculopapular rash (i.e. non-vesicular), and any of following:coryza (i.e. running nose), cough, or conjunctivitis (i.e. red eyes). An epidemiological investigation was conducted on suspected cases for information on possible source of infection. Laboratory confirmation serological testing was performed by measuring measles-specific immunoglobulin M (IgM). Both the epidemiological information and experimental results were recorded and uploaded into the system, which composed several data bases.The descriptive study was based on the surveillance data set of measles from all11prefectures in Zhejiang Province between2004and2011. The spatiotemporal evolution of measles epidemic and the demographic distribution of cases were explored. Spearman correlation analysis was used to assess associations between measles incidence and population density and proportion of floating populations.The case-control study was based on the surveillance data set of measles between2009and2011. Cases were persons who developed signs and symptoms of measles and were either laboratory confirmed or epidemiologically linked. Controls were excluded cases in the same system. A2-level binary logistic regression was conducted to evaluate the association between measles and related factors.ResultsA total of44,210measles cases were reported during the8-year period. A higher proportion of cases occurred in young adults aged20-34years and infants aged<1year. Two large measles epidemics occurred in2005(14453cases, incidence of31.41/100,000) and2008(12850cases, incidence of27.41/100,000). The counties reporting higher measles incidence had higher population density (spearman correlation coefficient=0.612, P<.0001) and proportion of inter-provincial floating populations (spearman correlation coefficient=0.748, P<.0001) than those reporting lower incidence. A total of5607cases and3686controls were recruited. A comparison on symptoms between cases and controls revealed that the cases had a higher proportion of fever (98.03%vs.93.62%), rash (99.36%vs.98.55%), cough (86.96%vs.62.34%), coryza (72.72%vs.53.29%), conjunctivitis (66.30%vs.45.90%), maculopapular rash (35.83%vs.14.29%) than controls. Moreover, the frequency of fever (98.62%vs.97.34%), cough (88.35%vs.85.31%), coryza (77.77%vs.66.75%), maculopapular rash (37.81%vs.33.49%) were higher in pediatric cases than in adult cases. The infants aged<1year were susceptible for measles. Scattered children (OR=1.992,95%CI (1.304-3.044)) were risk factors for measles. On the contrary, being vaccinated against measles (1dose of measles-containing vaccine(MCVl):OR=0.366,95%CI (0.310-0.431); MCV2:OR=0.181,95%CI (0.142-0.231))and being in collective units (OR=0.524,95%CI (0.436-0.630)) were protective factors for measles.ConclusionsSurveillance data demonstrates a higher proportion of young adults and infant cases contribute to measles epidemic in Zhejiang. Moreover, there appear to be annually recurring peaks (March to May) for measles. No coherent spatiotemporal patterns of measles epidemics are observed. Results also indicate that population density and proportion of inter-provincial floating populations are potential factors for measles epidemic. Scattered children are risk factors for measles. These findings highlight the necessity of timely vaccination of floating populations.