Insights into unplanned K-12 school closures in the United States, August 1, 2011 to December 31, 2012

Background: School closure is a potential mitigation strategy in influenza pandemic. However, data about unplanned school closures occurring during non-pandemic years are limited. We describe characteristics of unplanned school closures in the US during two academic years. Purpose: To enhance knowledge base regarding unplanned school closures in the US. Significance: This study will inform emergency preparedness by helping determine the potential impact unplanned school closures have on students and families. Methods: Unplanned school closures lasting ≥1 day were identified through systematic searches of web-based search engines and were verified via the school or local news websites. The number of affected schools and students were calculated based on publically available school data. Results: From August, 1, 2011 ¨C December 31, 2012, a total of 42,555 unplanned school closures were identified. Of these, 41,072 (97%) schools participated in 5,134 district-wide closures, while 1,483 (3%) were individual school closures. Approximately 22 million K-12 students in 49 states were impacted. The average duration of closures was 2.2 days (range=1-20 days). Most frequently reported reasons for closures included weather events (22,679 [53%]) and natural disasters (16,246[38%]). Overall, 274 (0.6%) closures were due to infectious disease outbreaks. During fall of 2012, 106 influenza-related closures occurred, compared to zero during fall of 2011. Conclusions: Unplanned school closures occur frequently and affect a significant number of schools and students each year. Although a small proportion of school closures were related with infectious disease, a substantial number of influenza-related closures occurred in the fall semester of 2012/13.