Surveillance for influenza hospitalizations in residents of washtenaw county, Michigan, 2012-13

Background: Influenza is a leading cause of hospitalization and death in the United States. The 2012-13 influenza season was moderately severe. Local public health surveillance can characterize populations at risk for severe outcomes of influenza in the community. Methods: Enhanced passive surveillance was conducted for laboratory-confirmed influenza hospitalizations in Washtenaw County, Michigan residents. Demographic and clinical data were obtained through review of medical records, immunization registry data and patient/family interviews. Data from 2012-13 were compared to the 2010-11 and 2011-12 influenza seasons and were analyzed using Epi Info 7.0. Results: During 2012-13, 199 influenza hospitalizations were reported, for a hospitalization rate (IHR) of 57.7/100,000. Age-specific IHRs were highest among residents >=65 years (309/100,000). The IHR among African-Americans was 93.3/100,000, 1.6 times higher than the rate among White residents. Similar proportions of adult and pediatric cases had underlying medical conditions (91% and 87%, respectively). Ninety-eight (49%) received influenza vaccine >= 2 weeks prior to admission. Thirty-four cases (17%) required admission to the intensive care unit, 12 (6%) required mechanical ventilation, and 8 (4%) died. Compared to previous influenza seasons, a higher proportion of cases were >=65 years of age, but no significant differences were observed in vaccination status or patient outcome. Discussion: The 2012-13 influenza season had significant impact on individuals >=65 years or with chronic medical conditions. Serious outcomes were observed in vaccinated individuals. There were racial disparities in hospitalization rates. Local influenza surveillance data should be used to target outreach efforts to populations at higher risk for severe outcomes.