A case-control study of risk factors for death from 2009 pandemic influenza A(H1N1): Is American Indian racial status an independent risk factor?

Historically, American Indian/Alaska Native ( AI/AN ) populations have suffered excess morbidity and mortality from influenza. We investigated the risk factors for death from 2009 pandemic influenza A( H1N1 ) in persons residing in five states with substantial AI/AN populations. We conducted a case-control investigation using pandemic influenza fatalities from 2009 in Alaska, Arizona, New Mexico, Oklahoma and Wyoming. Controls were outpatients with influenza. We reviewed medical records and interviewed case proxies and controls. We used multiple imputation to predict missing data and multivariable conditional logistic regression to determine risk factors. We included 145 fatal cases and 236 controls; 22% of cases were AI/AN. Risk factors ( P < 0·05 ) included: older age [adjusted matched odds ratio ( mOR ) 3·2, for > 45 years vs. < 18 years], pre-existing medical conditions ( mOR 7·1 ), smoking ( mOR 3·0 ), delayed receipt of antivirals ( mOR 6·5 ), and barriers to healthcare access ( mOR 5·3 ). AI/AN race was not significantly associated with death. The increased influenza mortality in AI/AN individuals was due to factors other than racial status. Prevention of influenza deaths should focus on modifiable factors ( smoking, early antiviral use, access to care ) and identifying high-risk persons for immunization and prompt medical attention.