Assessment of Effectiveness of Non-pharmaceutical Interventions in a School Outbreak of Influenza A, Lamphun Province, November 2007

Abstract

         In mid-November 2007, an influenza outbreak was detected in a primary school in Lamphun Province. A study was conducted to describe epidemiological characteristics, to evaluate effectiveness of school closure and non-pharmaceutical interventions, and to assess response capacity of local public health agencies. An active case finding was conducted by reviewing influenza case reports and hospital records. A suspect influenza case was defined as a student/staff in School M who developed fever with at least one of the following symptoms: sore throat, cough, sputum, running nose, headache, myalgia, arthralgia or vomiting during November 1-30, 2007. A confirmed case was identified by at least one positive laboratory result for influenza virus. A basic reproduction number (R0) was estimated and a survey was carried-out to determine a secondary attack rate in households. Effectiveness of public health interventions was assessed resulting in on. Of 248 students and staff members, 109 met a suspect case definition. Overall attack rate of 45.6 percent. Median age of the cases was 10 years. Class-specific attack rate, where the first case occurred, was the highest at 68.8 percent. The secondary attack rate was 12.0 percent. Estimated R0 was 3.4. Non-pharmaceutical public health interventions including 7-day school closure, case isolation at home or in a field hospital, mask use, active surveillance, and community participation in control activities resulted in limited spreading of the influenza A outbreak. Enhanced influenza surveillance in a school setting and mobilization of health resources to further support local rapid response teams  are necessary for pandemic influenza preparedness.

Key words: influenza A, school closure, social distancing, non-pharmaceutical intervention, effectiveness