[An outbreak of measles among unvaccinated migrant population in Zhejiang province, from June to August, 2010].

OBJECTIVE: On July 6, 2010, the parents of a patient with confirmed measles reported several suspected measles patients with fever and rash in their village. An investigation was carried out to verify and understand the cause of the outbreak.

METHODS: Several suspected cases had an onset of fever and rash in this and other neighboring villages during June 1 to August 3, 2010. A confirmed case was a suspected case with measles-specific IgM identified in the serum. We conducted door-to-door visits and searched the Chinese Center for Disease Control and Prevention Information System to identify cases, also conducted a retrospective cohort study among migrant children aged 8 months-14 years to identify risk factors related to measles.

RESULTS: We identified 19 measles cases (17 confirmed case, 2 suspected cases) in the village, and all of them were migrants. Children aged 1-2 years had the highest attack rate (13%). The primary case-patient had onset on the day she arrived in this village (June 4, 2010). Caretakers from an unlicensed private clinic were providing service in the village but did not report the outbreak to the public health authority. The outbreak was identified only after receiving a report from the parents of one of the patients, by that time the outbreak had lasted for one month. The measles vaccine coverage rate was 81% among the 315 migrant children aged 8 months-14 years. Among the 61 unvaccinated children, those who reportedly being contacted a measles patient had a higher attack rate (14/16, 88%) than those who did not (2/45, 4.4%) (Relative risk = 20, Fisher's exact 95% confidence interval: 5.7-94).

CONCLUSION: The low measles vaccine coverage among migrant children and lack of measures taken on the incident, timely isolation diagnosis/reporting by the caretakers from the unlicensed private clinic etc. had contributed to this prolonged outbreak. Measures need to be taken to improve the immunization services for migrant populations and to enhance measles surveillance programs in the area.