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/100,000 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.

Figure 1

Number of influenza cases retrospectively identified from review of hospital discharge records of patients aged <18 years, by month and year of admission – Nebraska, influenza seasons 2001–2002* through 2006–2007.