Epidemiologic Investigation of a Mumps Outbreak in a Middle School in Pohang, Korea: Effect of vaccination during outbreak

Park, Byung Chan; Cheong, Hae Kwan; Lim, Hyun Sul; Kim, Duck Soo; Kim, Doohie

Abstract

BACKGROUND: There was a widespread outbreak of mumps at elementary and middle schools in Pohang city in March 1999. We have carried out an epidemiologic survey to trace the source and mode of transmission of the outbreak, as well as evaluating the effect of vaccination as a measure of controlling the outbreak.
METHODS
Questionnaire survey on 959 students showed that attack rate was 10.7%. There was no significant difference between genders in terms of attack rates. However, second graders outnumbered other groups as 16.9%, comparing to 8.1% among first graders and to 7.0% in the third graders.
RESULTS
Cases of mumps were reported in 1998, primarily in the neighboring elementary schools. The disease was also reported earlier in 1999, sporadically. In March, however, number of the cases was sharply on the rise as the middle schools opened for a new semester. Our investigation revealed that infection stemmed from more than three different sources, particularly in the classes of second graders, and then spread to all students, corresponding to the distance between students. Effect of vaccination during the outbreak was pretty good: attack rate of the group vaccinated since May 1st, considering the maximum latent period of infections (21 days), was 0.8%, comparing to 5%. The efficiency of vaccination marked 84.8%.(95% confidence interval 79.66-89.94) Although the authors recommended the students to wear flue masks and wash their hands as often as possible to screen infections among the students, it turned out that such measures had little effect for the prevention of spread.
CONCLUSIONS
The number of mumps cases dropped remarkably among vaccinated the students the prevalent period of the disease. Authors concluded that is effective to control the outbreak if it is done at early stage.