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. 2011 Apr 5;6(4):e18221.
doi: 10.1371/journal.pone.0018221.

A review of adult mortality due to 2009 pandemic (H1N1) influenza A in California

Janice K Louie  1 , Cynthia Jean, Meileen Acosta, Michael C Samuel, Bela T Matyas, Robert Schechter
Affiliations

A review of adult mortality due to 2009 pandemic (H1N1) influenza A in California

Janice K Louie et al. PLoS One. .

Abstract

Background: While children and young adults had the highest attack rates due to 2009 pandemic (H1N1) influenza A (2009 H1N1), studies of hospitalized cases noted high fatality in older adults. We analyzed California public health surveillance data to better characterize the populations at risk for dying due to 2009 H1N1.

Methods and findings: A case was an adult ≥20 years who died with influenza-like symptoms and laboratory results indicative of 2009 H1N1. Demographic and clinical data were abstracted from medical records using a standardized case report form. From April 3, 2009-August 10, 2010, 541 fatal cases ≥20 years with 2009 H1N1 were reported. Influenza fatality rates per 100,000 population were highest in persons 50-59 years (3.5; annualized rate = 2.6) and 60-69 years (2.3; annualized rate = 1.7) compared to younger and older age groups (0.4-1.9; annualized rates = 0.3-1.4). Of 486 cases hospitalized prior to death, 441 (91%) required intensive care unit (ICU) admission. ICU admission rates per 100,000 population were highest in adults 50-59 years (8.6). ICU case-fatality ratios among adults ranged from 24-42%, with the highest ratios in persons 70-79 years. A total of 425 (80%) cases had co-morbid conditions associated with severe seasonal influenza. The prevalence of most co-morbid conditions increased with increasing age, but obesity, pregnancy and obstructive sleep apnea decreased with age. Rapid testing was positive in 97 (35%) of 276 tested. Of 482 cases with available data, 384 (80%) received antiviral treatment, including 49 (15%) of 328 within 48 hours of symptom onset.

Conclusions: Adults aged 50-59 years had the highest fatality due to 2009 H1N1; older adults may have been spared due to pre-existing immunity. However, once infected and hospitalized in intensive care, case-fatality ratios were high for all adults, especially in those over 60 years. Vaccination of adults older than 50 years should be encouraged.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Fatal cases of 2009 pandemic (H1N1) influenza A in California by date of death.
In California, mortality peaks due to 2009 pandemic (H1N1) influenza A coincided with two waves of 2009 H1N1 activity: April 3-October 3, 2009, and October 4, 2009-February 4, 2010. The influenza fatality rate remained highest for 50–59 year-olds during both time periods.
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References

    1. Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic (H1N1) 2009 Influenza. Clinical aspects of pandemic 2009 influenza A (H1N1) virus infection. N Engl J Med. 2010;362(18):1708–19.2. - PubMed
    1. Centers for Disease Control and Prevention (CDC) Use of influenza A (H1N1) 2009 monovalent vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. MMWR Recomm Rep. 2009;58(RR-10):1–83. - PubMed
    1. Fiore AE, Uyeki TM, Broder K, Finelli L, Euler GL, et al. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR Recomm Rep. 2010;59(RR-8):1–62. Erratum in: MMWR Recomm Rep 59(31):993. - PubMed
    1. Louie JK, Acosta M, Winter K, Jean C, Gavali S, et al. Factors associated with death or hospitalization due to pandemic 2009 influenza A (H1N1) infection in California. JAMA. 2009;302(17):1896–902. - PubMed
    1. National Heart Lung and Blood Institute. The Practical Guide: Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. 2000. Available at: http://www.nhlbi.nih.gov/guidelines/obesity/practgde.htm. Last accessed February 19, 2011.

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