Notes from the Field: Outbreak of 2009 Pandemic Influenza A (H1N1) Virus at a Large Public University in Delaware, April–May 2009

Background In late April 2009, the first documented 2009 pandemic influenza A (pH1N1) virus infection outbreak in a university setting occurred in Delaware, with large numbers of students presenting with respiratory illness. At the time of this investigation, little was known about the severity of illness, effectiveness of the vaccine, or transmission factors of pH1N1 virus infection. We characterized illness, determined the impact of this outbreak, and examined factors associated with transmission. Methods Health clinic records were reviewed. An online survey was administered to all students, staff, and faculty to assess influenza-like illness (ILI), defined as documented or subjective fever with cough or sore throat. Results From 26 April-2 May 2009, the health clinic experienced a sharp increase in visits for respiratory illness, with 1080 such visits among a total of 1430 student visits, and then a return to baseline visit levels within 2 weeks. More than 500 courses of oseltamivir were distributed, and 24 cases of influenza A (pH1N1) virus infection were confirmed. Of 29,000 university students and faculty/staff, 7450 (30%) responded to the survey. ILI was reported by 604 (10%) of the students and 73 (5%) of the faculty/staff. Travel to Mexico (relative risk [RR], 2.9; 95% confidence interval [CI], 1.8-4.7) and participation in "Greek Week" activities (RR, 2.2; 95% CI, 1.8-2.8) were associated with ILI. Recipients of the 2008-2009 seasonal influenza vaccine had the same risk of ILI as nonrecipients (RR, 1.0). Four (3%) of the students with ILI were hospitalized; there were no deaths. Conclusions pH1N1 spread rapidly through the University of Delaware community with a surge in illness over a 2-week period. Although initial cases appear to be associated with travel to Mexico, a rapid increase in cases was likely facilitated by increased student interactions during Greek Week. No protective effect from receiving seasonal influenza vaccine was identified. Although severe illness was rare, the outbreak caused a substantial burden and challenge to the university health care system. Preparedness efforts in universities and similar settings should include enhancing health care surge capacity.