Pediatric influenza‐associated myositis – Nebraska, 2001–2007

Abstract

Objective Influenza-associated myositis (IAM), characterized by severe lower-extremity myalgia and reluctance to walk, is a complication of influenza among children. We investigated IAM in Nebraska during six influenza seasons, 2001–2007. Methods During 2006–2007, we requested reports of severe influenza illness among persons aged <18 years and investigated medical records to identify and confirm IAM cases defined as severe myalgia with elevated serum creatinine kinase level in a patient aged <18 years, occurring within 7 days of laboratory confirmed influenza illness onset. Statewide hospital discharge data (HDD) were reviewed to identify retrospectively confirmed IAM cases during 2006–2007 and five previous seasons, by using surveillance data to define periods of influenza activity. Statewide IAM incidence was estimated for 2001–2002 through 2006–2007. Results During 2006–2007, a total of 13 IAM cases were confirmed by enhanced surveillance. Median age was 6 years (range, 4–11 years). Influenza diagnosis was established by viral isolation from six patients (one influenza A and five influenza B) and rapid diagnostic tests for seven. Twelve (92%) patients, including one who died, were hospitalized for a median of 3 days (range, 1–4 days). Review of HDD identified 12 retrospectively confirmed IAM cases during 2006–2007, including four not reported through enhanced surveillance, and only one during five previous seasons (2003–2004). The HDD-derived, retrospectively confirmed statewide IAM incidence estimates/1 00 000 population aged <18 years were 2·693 and 0·225 during 2006–2007 and 2003–2004, respectively. Conclusion An IAM epidemic occurred in Nebraska during the 2006–2007 influenza season.