RISK FACTORS FOR DEATH FROM 2009 PANDEMIC INFLUENZA A (H1N1): IS AMERICAN INDIAN / ALASKA NATIVE RACIAL STATUS AN INDEPENDENT RISK FACTOR?
During the 2009 H1N1 influenza A pandemic, the indigenous people of the United States (American Indians/Alaska Natives (AI/AN)) suffered a 4-fold increased mortality compared with the overall population. This is similar to the well-established increased mortality due to pneumonia and influenza among AI/AN people. The underlying causes for the high mortality from seasonal influenza and 2009 pandemic H1N1 influenza among AI/AN persons are unknown, but theories range from undescribed genetic susceptibilities to underlying social determinants of health.
METHODS:
We conducted a case-control study using laboratory-confirmed pandemic influenza fatalities from 2009 in Alaska, Arizona, New Mexico, Oklahoma and Wyoming. Controls were outpatients with influenza, matched by state and date. We reviewed medical records and interviewed case proxies and controls for medical, behavioral and socio-demographic factors. We first used univariate analysis, then used multiple imputation to predict missing data. We used multivariable conditional logistic regression to determine risk factors.
RESULTS:
We included 145 fatal cases and 236 controls; 22% were AI/AN. Risk factors from multivariable logistic regression (p-value < 0.05) included: older age (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. Among AI/AN persons, risk factors for influenza mortality included pre-existing medical conditions (MOR 3.5), obesity (body-mass index > 30) (MOR 3.7) and smoking (5.4). No interaction effects were detected in the final model.
CONCLUSIONS:
The increased influenza mortality among AI/ANs in these states was due to factors other than racial status. Prevention of influenza deaths should focus on modifiable factors (smoking cessation, early antiviral use, access to care, weight reduction) and identifying medically high-risk persons for immunization and prompt medical attention for influenza-like illnesses.