A hospital-associated measles outbreak among individuals not targeted for vaccination in eastern China, 2014

Background An outbreak of measles occurred in early 2014 among individuals not targeted for vaccination—adults, and infants too young to vaccinate, in Xiangshan County, Zhejiang Province, in eastern China. Objective We conducted an investigation to identify risk factors responsible for this outbreak and to provide evidence-based recommendations for measles elimination strategies in China. Methods Measles was diagnosed using national standard case definitions. In a case-control study, 20 randomly selected measles patients were matched with controls selected from the same village or community as each case in a 1:2 case-to-control ratio. Controls were matched on age, within 5 years, and gender. We compared exposure histories during the 7–21 days before rash onset of the case and the same time period for the matched controls. We also conducted a measles antibody seroprevalence survey of a convenient sample of residual serum obtained from healthy patients during routine care in a hospital. Results The outbreak consisted of 45 measles cases, with an attack rate of 8.9/100,000 total population. Among cases, 91.1% (41/45) were adults (ranged 23–51 years) who had unknown vaccination histories; the other cases were infants younger than 8 months of age. The case-control study showed major risk factors to be a visit to Hospital X (ORMH = 7.3, 95% CI: 1.8–30.7) and treatment in an IV room in Hospital X (ORMH = 11.0, 95% CI: 1.3–96.1). The seroprevalence survey showed that 88.8% of adults had measles IgG antibodies, and that 100% of children 2–19 years of age were seropositive. Conclusions The outbreak was primarily among age groups not targeted for vaccination—primarily adults, but with some children too young to vaccinate. Visiting a hospital was the major risk factor for measles transmission. We conclude that in addition to maintaining high 2-dose coverage with measles vaccine, working with hospital infection control programs to implement evidence-based strategies to prevent or limit hospital transmission is an important action for eliminating measles in eastern China.