Vaccine-associated measles in the low-incidence country of Korea over a 10-year period.

As the incidence of measles decreases, cases reported as suspected measles will increasingly involve rash associated with measles vaccination itself. In this study, we assessed vaccine-associated measles cases reported in Korea between 2002 and 2012 using a standardized assessment and following by the World Health Organization case definition criteria. We retrospectively analyzed data regarding (i) wild-type measles and (ii) vaccine-associated measles in patients aged 12-23 months. The presence or absence of fever, rash, cough, coryza, conjunctivitis, and Koplik spots were reviewed. Males were more likely to be reported with vaccine-associated measles than with wild-type measles (68% vs. 47%, P < 0.05). The number of patients with wild-type measles peaked between April and July, whereas that of patients with vaccine-associated measles remained relatively constant throughout the year. However, after excluding the cases reported during the 2007 outbreak in Korea, the trend was similar between the two groups. Cough, coryza, and conjunctivitis were more likely to be present in patients with wild-type measles (32-61% vs. 10-43%, P < 0.05); conversely, the absence of these symptoms was noted in most patients with vaccine-associated measles. We therefore conclude that cough, coryza, and conjunctivitis may be useful as key positive findings to distinguish between wild-type measles and vaccine-associated measles infection among 12-23-month-old patients in a country with a low incidence of measles.

Timely measles surveillance in the Republic of Korea, 2002-2009: impact of sentinel laboratory surveillance.

In order to sustain the elimination of measles, timely reporting is important. The surveillance data in Korea from 2002-2009 was analyzed to determine the effect of sentinel laboratory surveillance, which was introduced in 2006, on the timeliness of measles reporting. The data were stratified by two surveillance periods, (A) before and (B) after 2006, and by cases confirmed clinically and cases confirmed by laboratory measures. During Period A, 113 suspected cases were reported, and 241 during Period B. There was no difference in the proportion of timely reporting among cases confirmed clinically between the two periods, whereas the proportion of cases confirmed by laboratory measures has increased. The mean notification interval in cases confirmed by laboratory measures was shortened from 39 to 16 days. In Korea, sentinel laboratory surveillance has enhanced earlier detection of suspected cases that had not been reported, improving the timeliness of measles surveillance. Adopting this new method may improve the timely collection of cases in other countries.

Epidemiological features and surveillance performance of measles in the Republic of Korea, 2002-2011.

Measles was declared eliminated from the Republic of Korea in 2006; however, recently the number of reported cases has been gradually increasing. To address this issue, we summarized the measles surveillance data collected during 2002-2011, and aimed to evaluate the performance of the current surveillance system in Korea. We analyzed data from the national surveillance system to describe the occurrence of measles. Surveillance indicators proposed by the World Health Organization were used to evaluate the performance of the current measles surveillance system. Between 2002 and 2005, a gradual decrease in confirmed cases of measles was noted, whereas cyclical increases were noted from 2006 to 2011. Since 2006, confirmed cases of measles were more likely to be identified by laboratory methods. In general, the incidence of confirmed case was less than one per million in Korea; however, this figure increased in 2002 (1.3/million), 2007 (4.0), and 2010 (2.3). Most cases were occurred in the age groups 0-23 months and 12-17 years. Laboratory testing was performed in most suspected cases; however, the proportion of discarded cases was low. Overall, more than half of the reported cases experienced an onset of symptoms from April to June. The incidence of measles is relatively low in Korea, and the laboratory surveillance may have helped in identifying under-diagnosed cases within the country. It remains important to continuously assess the surveillance data to improve the surveillance performance.

Reemergence of measles in South Korea: implications for immunization and surveillance programs.

Following the implementation of the national measles elimination program, the Republic of Korea declared in 2006 that measles had been eliminated. However in 2011, a measles outbreak was reported in Gyeongnam Province in the southeastern part of the country. We conducted active case-based surveillance and analyzed the data of cases reported in 2011 to identify the factors contributing to the reemergence of measles in this province. Of 41 confirmed measles cases reported in Korea, 32 were from within the Gyeongnam Province. Among cases identified in the outbreak, 97% had inadequate history of immunization, 28% were not immunized at the recommended ages, and 22% were infants aged 6-11 months. The outbreak involved transmission in 3 hospitals, 1 kindergarten, 1 day-care center, and 3 households. Molecular analysis of measles virus isolates from 11 cases revealed the same D9 genotype, which was the first to be discovered in Korea. In conclusion, inadequate immunization coverage, non-timely immunization, infants under 12 months of age, nosocomial transmission, and international importation may play important roles in the reemergence of measles in Korea during the attempted sustained elimination of the disease.