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

Abstract

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 (OR(MH)=7.3, 95% CI: 1.8-30.7) and treatment in an IV room in Hospital X (OR(MH)=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.

Keywords: Adult measles outbreak; Measles; Non-targeted population; Nosocomial transmission; Outbreak.