Circumstance: Pandemic influenza A(H1N1) egressed quickly in California in April 2009. Explorative comparabilities with seasonal flu indicate that pandemic 2009 influenza A(H1N1) disproportionately impacts younger ages and induces normally meek disease.

Objective: To distinguish the clinical and epidemiological characteristics of pandemic 2009 influenza A(H1N1) instances that resulted in hospitalization or death.

Conception, Setting, and Participants: Statewide increased public health surveillance of California residents who were hospitalized or passed away with research lab evidence of pandemic 2009 influenza A(H1N1) infection reported to the California Department of Public Health between April 23 and August 11, 2009.

Primary Result: Assess features of hospitalized and lethal cases.

Outcomes: During the study time period there were 1088 cases of hospitalization or death due to pandemic 2009 flu A(H1N1) infection reported in California. The average age was twenty-seven years (scope, <1-92 years) and 68% (741/1088) had risk components for seasonal influenza complications. 66 percent (547/833) of those with chest radiograms executed had infiltrates and 31% (340/1088) necessitated intensive care. Rapid antigen examinations were falsely negative in 34% (208/618) of cases assessed. Secondary bacterial contagion was discovered in 4% (46/1088). Twenty-one percent (183/884) received no antiviral drug treatment. Gross fatality was 11% (118/1088) and was greatest (18%-20%) in individuals aged fifty years or older. The primary causes of demise were viral pneumonia and acute respiratory distress syndrome.

Determinations: In the introductory 16 weeks of the present-day pandemic, the average age of hospitalized infected cases was younger than is common with seasonal flu. Babies had the steepest hospitalization rates and individuals aged fifty years or older had the greatest mortalities when hospitalized. Most cases had established risk components for complications of seasonal flu.