Spring 2009 H1N1 influenza outbreak in King County, Washington.
BACKGROUND
In April 2009, King County, Washington, experienced a sustained outbreak of 2009 H1N1 influenza A. This report describes the epidemiology of that outbreak in King County, home to a diverse population of 1.9 million people.


METHODS
The 2 primary sources of data are case investigations of reported laboratory-confirmed 2009 H1N1 influenza A and a population-based syndromic surveillance system that captures data from emergency departments (EDs). A syndromic category for influenza-like illness was defined based on chief complaint and diagnosis.


RESULTS
ED visits for influenza-like illness peaked quickly in the first week of the outbreak and remained high for approximately 6 weeks, with school-age children accounting for the greater number of ED visits, followed by young adults. Children ages 0 to 4 years had the highest rate of hospitalization. Among reported cases, blacks, Asians, and Hispanics were more likely to be hospitalized. Predisposing factors associated with admission were immune compromise, chronic lung disease, chronic heart disease, pregnancy, diabetes, and asthma. Of people receiving antiviral treatment, 34% started their medication more than 2 calendar days after the onset of illness. Mean days between illness onset and antiviral treatment were greater for blacks, Hispanics, and foreign language speakers.


CONCLUSIONS
The spring 2009 influenza A H1N1 outbreak disproportionately affected children, young adults, and racial and ethnic minorities. Opportunities exist to improve the timeliness of antiviral treatment. Potential barriers to care for racial and ethnic minorities should be proactively addressed to ensure prompt evaluation and treatment.
Kwan-Gett
Tao Sheng
TS
Public Health-Seattle & King County, 401 Fifth Ave, CNK-0900, Seattle, WA 98104, USA. tao.kwan-gett@kingcounty.gov
Baer
Atar
A
Duchin
Jeffrey S
JS
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000998:Antiviral Agents / Q000008:administration & dosage; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D003422:Critical Care / Q000706:statistics & numerical data; D004196:Disease Outbreaks; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D007256:Information Systems / Q000458:organization & administration; D008297:Male; D008875:Middle Aged; D011635:Public Health Administration / Q000379:methods / Q000706:statistics & numerical data; D044469:Racial Groups / Q000706:statistics & numerical data; D012307:Risk Factors; D018571:Sentinel Surveillance; D014861:Washington / Q000453:epidemiology; D055815:Young Adult
D000998:Antiviral Agents