Epidemiology of Acute Viral Conjunctivitis at a Junior High School - October 2007

Background: Acute conjunctivitis is a highly contagious disease that can quickly spread through the community. In October 2007, a junior high school reported an outbreak of acute conjunctivitis among its students and staff. We describe the epidemiology of the outbreak at this school. Methods: A questionnaire was designed to identify persons who became ill with conjunctivitis. The questionnaire was distributed to all students and staff at the school on October 17, 2007. A case was defined as a person who had red eyes or physician diagnosed acute, non-allergic conjunctivitis lasting for at least one day. A secondary case was defined as a family member who became ill one to seven days after a student became ill. Conjunctival swabs were taken for viral culture. Results: Of the 681 questionnaires distributed, the response rate was 93.2%. During September 1 and October 17, 2007, there were 246 cases of conjunctivitis (attack rate = 35.2%). Of these, 234 (95.1%) had red eyes, 184 (74.8%) had pain, 172 (70.0%) had increased tearing, and 48 (19.5%) had photophobia. Constitutional symptoms, mainly fever, were present in 32 (13.7%) cases. Of the 988 family members, 167 secondary cases were identified (secondary attack rate = 16.9%). The odds of a case being a first- or second-year student was higher than being a third-year student (odds ratio [OR] = 1.7; 95% confidence interval [CI]: 1.1–2.6 and OR = 2.5; 95% CI: 1.7–3.7, respectively). Virus was isolated from one of three conjunctival swabs taken, which yielded coxsackie A24 virus. Conclusions: Coxsackie A24 virus caused acute conjunctivitis affecting 35.2% of the population at this school. The outbreak was controlled after instituting increased awareness of the epidemic, enhanced hand hygiene practices, and strengthened disinfection measures of shared equipments. Younger students were at increased risk of disease possibly as the result of socio-behavioral differences.