Pandemic (H1N1) 2009–associated Deaths Detected by Unexplained Death and Medical Examiner Surveillance

During the pandemic (H1N1) 2009 outbreak, Minnesota, New Mexico, and Oregon used several surveillance methods to detect associated deaths. Surveillance using unexplained death and medical examiner data allowed for detection of 34 (18%) pandemic (H1N1) 2009–associated deaths that were not detected by hospital-based surveillance.

illness (ILI) based on pre-or postmortem fi ndings as well as sudden deaths in previously healthy persons <50 years of age. Each state expanded its EIP Infl uenza Surveillance statewide during the pandemic (H1N1) 2009 pandemic. In addition, hospitalized persons with ILI, including decedents, were reported to the state health department by physicians, infection preventionists, and hospital pathologists.
Pre-and/or postmortem specimens, including nasopharyngeal, nasal, or throat swabs; nasal or endotracheal aspirates; bronchial alveolar lavage specimens; sputum; frozen and fi xed respiratory tissue; and serum specimens, were tested at state laboratories or at CDC for pandemic (H1N1) 2009 virus. Tests included PCR, virologic culture, immunohistochemistry, serology, and infl uenza antigen detection. In a few instances, it was not possible to characterize the virus beyond infl uenza type A because of limited specimen availability; these cases were assumed to be pandemic (H1N1) 2009. Because UNEX and Med-X are not mutually exclusive, all pandemic (H1N1) 2009associated deaths were determined to be UNEX/Med-X cases if they were captured through either of those programs ( Figure 1).
Data were collected on underlying medical conditions, symptoms, and clinical outcomes from medical records, case investigations, and autopsy reports. In Minnesota and New Mexico, all decedents with positive laboratory A total of 194 pandemic (H1N1) 2009-associated deaths were detected in this analysis, 160 (82%) through hospital surveillance and 34 (18%) through UNEX/Med-X. The additional surveillance resulted in the detection of 21% more total cases than hospital surveillance alone. Minnesota had the highest proportion of UNEX/Med-Xdetected cases with 24% (16/66); Oregon had the lowest with 11% (8/76) ( Table 1). Decedents detected by using UNEX/Med-X were more frequently of a nonwhite race (47% vs. 23%); an increased percentage of deaths of American Indians/Alaska Natives was detected through UNEX/Med-X versus hospital surveillance (21% vs. 4%).
UNEX/Med-X decedents were more likely to have had an autopsy performed (85% vs. 17%) and were more likely to have died in their residences (53% vs. 8%) than decedents detected by hospital surveillance. The median age of UNEX/Med-X decedents was 37.5 years, compared with 51.0 years for hospital surveillance decedents (p<0.001) ( Table 1). The percentage of UNEX/Med-X decedents among age groups decreased with increasing age (62.5% among those 0-4 years of age compared with 2.6% among those >65 years of age; Figure 2).
More hospital surveillance than UNEX/Med-X decedents (89% vs. 68%) were determined to have >1 underlying condition. Specifi c underlying conditions were more frequently identifi ed among hospital surveillance than UNEX/Med-X decedents, except for obesity (Table 2). Pneumonia, including viral pneumonia, was frequently reported among decedents. Acute respiratory distress syndrome was documented for 37% of hospital and 15% of UNEX/Med-X decedents. Two previously healthy children with nasopharyngeal swabs positive for infl uenza had evidence at autopsy of viral myocarditis.

Conclusions
UNEX/Med-X surveillance captured 11%-24% of pandemic (H1N1) 2009-associated deaths in the 3 states. Other estimates of deaths resulting from pandemic (H1N1) 2009 may be increased with better data on nonhospitalized and sudden unexplained deaths (7,8). Estimates from surveillance in New York, New York, which included medical examiner and unexplained respiratory causerelated death surveillance, indicate 17% of decedents died at home and 6% had not sought any prior medical care (9)(10)(11).
UNEX/Med-X decedents were younger and more often previously healthy than hospital surveillance decedents, a fi nding that would change the estimated impact of pandemic (H1N1) 2009 among those populations in particular. Consistent with other studies (12), larger racial/ ethnic disparities, particularly among Native American/ Alaska Native populations, may be detected by UNEX/ Med-X than have been detected through other surveillance methods. Although we were unable to determine the cause of these disparities, the fi ndings warrant further study and attention to these populations regarding public health resources.
Even with an emphasis on deaths among those <50 years of age, UNEX and Med-X programs are critical for detecting severe illnesses that rapidly progress to death and could otherwise go undetected. Partnering with medical examiners and pathologists to identify infectious causerelated deaths among persons who were previously healthy is important to give a clear picture of the entire mortality spectrum.
Although it is important to accurately measure the impact of a disease, it is perhaps more important to quickly identify new serious disease threats. Approximately one tenth to one quarter of the infl uenza deaths detected in this study, and particularly those in younger, healthier persons, were not detected by hospital surveillance when infl uenza awareness was at its peak. This fi nding argues for surveillance systems like UNEX and Med-X as a means of quickly detecting emerging, severe infectious disease threats. Because pathogens are likely to emerge over broad geographic areas, we recommend a standardized approach to death investigations to fully understand the epidemiologic and clinical features of illness caused by a particular pathogen.