From September 1, 2010 to January 13, 2011, 232 suspected measles cases were reported, of which 209 were either laboratory confirmed (n
127) or clinically diagnosed (n
82) cases. The estimated attack rate (based on laboratory-confirmed or clinically diagnosed cases combined) was 3.3/100,000, which was about 4 times as high as the overall attack rate in Zhejiang Province (0.83/100,000). The median age of these measles cases was 1y (range: 2 m to 47y). Children aged 8–11 m had the highest attack rate (171/100,000), followed by children aged 0–7 m (Table ). Measles cases were reported from all 11 districts and counties of Wenzhou City; 59% of the cases were reported from the 3 central urban districts where Hospital S, the largest pediatric hospital in Wenzhou City, is located.
Attack rate of measles, by age: Wenzhou City, China, September 1, 2010 to January 13, 2011
The age-specific epidemic curves showed that, for children not eligible for the MMIC and never became age-eligible for the routine vaccination before their illness onset (Age Group A), cases occurred continuously. For children not age-eligible for the MMIC but should have been routinely vaccinated after the MMIC (Age Group B), the number of cases increased quickly after the MMIC was completed. Among children eligible for the MMIC (Age Group C), cases occurred sporadically until mid-December, 2011, when the case count started to increase. Among older children who were not targeted by the MMIC (Age Group D), the number of cases started to increase after November, 2011 (Figure ).
Figure 1 Age-specific epidemic curves of measles infections: Wenzhou City, China, September 1, 2010 to January 13, 2011. Age Group A: Children aged <8 m at MMIC (born Jan. 1-Nov. 9, 2010), who had measles at <8 m (i.e., never became (more ...)
The estimated vaccination coverage in none of the age groups exceeded 85%, with the exception of the older children who were not the target of the MMIC (Age Group D). Specifically, for children not age-eligible for the MMIC but should have been routinely vaccinated after the MMIC (Age Group B), the estimated vaccination coverage was only 52%, far below the national target of 95% for measles elimination. Even for the children who were the target of the MMIC (Age Group C), the estimated vaccination rate was only 85%, substantially lower than the national target (Table ).
Estimated measles vaccination coverage for children aged 8 m-15y, by age group classified in relation to the nationwide measles mass immunization Campaign: Wenzhou City, China, September 1, 2010 to January 13, 2011*
Analysis of the case–control data, which involved 42 cases and 168 controls, showed that the measles vaccine was highly protective (ORM-H
0.026, 95% CI: 0.0028-0.24) in children aged 8-11 m; the vaccine effectiveness based on this odds ratio (9) was estimated to be 97.4% (95% CI: 76% to 99.7%). Additionally, visiting Hospital S was associated with more than a 5-fold increase in the odds of contracting measles (ORM-H
5.5, 95% CI: 2.7–11). Children aged 8–12 m were expectedly at higher odds of contracting measles than children aged <8 m (ORM-H
3.0, 95% CI: 1.5–6.3). When we further examined the exposures of the patients who had visited Hospital S 7–21 days before their illness onset, visiting the IV room was associated with a 7-fold increase in the odds of measles infection (ORM-H
7.2, 95% CI: 1.9–27) (Table ). In an analysis of unvaccinated children who had visited Hospital S 7–21 days before their illness onset, stratified by children’s age, we found that IV-room visit was associated with a 9-fold increase in the adjusted odds of measles infection (adjusted ORM-H
9.2, 95% CI: 1.5–59) (Table ).
Univariate analysis of factors for measles infection among children aged ≤1y: Wenzhou City, China, November-December, 2010
Association between visiting IV room in Hospital S and measles infection in children under 1 year of age, stratified by age group: Wenzhou City, China, November - December, 2010
An on-site inspection of Hospital S revealed that the hospital’s pediatric clinic had several physician offices. All pediatric patients visiting these physician offices shared the same IV room during treatment. The IV room had an area of about 500 m2, with approximately 400 chairs in the room for waiting patients. According to the hospital’s record, 1600–1700 bags or bottles of IV fluid were administered in this room daily. Typically a child was accompanied by two adults; hence 4800–5100 persons are crammed in the IV room on a daily basis, subjecting the children and accompanying adults to the risk of infection by various pathogens. The surfaces and floor of the IV room reportedly were cleaned and disinfected once every morning before the room was opened, but were not disinfected during the day.