title: A population-based study of neurologic manifestations of severe influenza A(H1N1)pdm09 in California.
abstract: BACKGROUND
  Reported influenza-associated neurologic complications are generally limited to case series or case reports. We conducted a population-based study of neurologic manifestations associated with severe and fatal influenza A(H1N1)pdm09 (2009 H1N1) cases.
  
  
  METHODS
  Medical records of patients with fatal or severe (hospitalized in intensive care unit) laboratory-confirmed 2009 H1N1 reported to the California Department of Public Health from 15 April 2009 through 31 December 2009 were reviewed to identify those with primary neurological manifestations. Cases with secondary neurologic manifestations (eg, hypoxia) were excluded. Primary influenza-associated neurologic complications (INCs) were classified into 4 groups: encephalopathy/encephalitis, seizures, meningitis, and other. Severe 2009 H1N1-associated neurologic incidence was calculated by using estimates of 2009 H1N1 illnesses in California.
  
  
  RESULTS
  Of 2069 reported severe or fatal 2009 H1N1 cases, 419 (20%) had neurologic manifestations. Of these, 77 (18%) met our definition of INCs: encephalopathy/encephalitis (n = 29), seizures (n = 44), meningitis (n = 3), and other (Guillain-Barré Syndrome) (n = 1). The median age was 9 years (range, 4 months-92 years); the highest rate of disease was among pediatric Asian/Pacific Islanders (12.79 per 1,000,000) compared with pediatric white, non-Hispanics (3.09 per 1,000,000), Hispanics (4.58 per 1,000,000), and blacks (6.57 per 1,000,000). The median length of stay (LOS) was 4 days (range, 1-142), and there were 4 fatalities. The estimated incidence of INCs was 1.2 per 100,000 symptomatic 2009 H1N1 illnesses.
  
  
  CONCLUSIONS
  Influenza-associated neurologic complications were observed in 4% of patients with fatal or severe 2009 H1N1. They were observed most often in pediatric patients, and Asian/Pacific Islanders appear to be overrepresented compared with the California population. Most patients with INCs had a relatively short LOS, and there were few fatalities.
authors.affiliation: Communicable Disease and Emergency Response Branch, Division of Communicable Disease Control, Department of Public Health, Richmond, CA 94804, USA. carol.glaser@cdph.ca.gov
authors.forename: Carol A
authors.initials: CA
authors.lastname: Glaser
authors.forename: Kathleen
authors.initials: K
authors.lastname: Winter
authors.forename: Kara
authors.initials: K
authors.lastname: DuBray
authors.forename: Kathleen
authors.initials: K
authors.lastname: Harriman
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Uyeki
authors.forename: James
authors.initials: J
authors.lastname: Sejvar
authors.forename: Sabrina
authors.initials: S
authors.lastname: Gilliam
authors.forename: Janice K
authors.initials: JK
authors.lastname: Louie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002140:California / Q000453:epidemiology; D020805:Central Nervous System Viral Diseases / Q000453:epidemiology* / Q000821:virology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D020275:Guillain-Barre Syndrome / Q000453:epidemiology / Q000821:virology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology* / Q000821:virology*; D008297:Male; D008875:Middle Aged; D012640:Seizures / Q000453:epidemiology* / Q000821:virology*