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标题：Association of Age and Comorbidity on 2009 Influenza A Pandemic H1N1-Related Intensive Care Unit Stay in Massachusetts
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作者：Hilary E. D. Placzek ; Lawrence C. Madoff
期刊名称：American journal of public health
印刷版ISSN：0090-0036
出版年度：2014
卷号：104
期号：11
页码：e118-e125
DOI：10.2105/AJPH.2014.302197
语种：English
出版社：American Public Health Association
摘要：Objectives. We compared comorbidity measures by age group and risk factors for influenza-like illness (ILI)–related intensive care unit (ICU) stay during the 2009 seasonal influenza and influenza A (pH1N1) pandemic. Methods. We identified all patients discharged from Massachusetts hospitals with ILI-related diagnoses between October 1, 2008, and April 25, 2009, and pH1N1–related diagnoses between April 26 and September 30, 2009. We calculated the Diagnostic Cost Group (DxCG) risk score as a measure of comorbidity. We used logistic regression predictive models to compare ICU stay predictors. Results. Mean DxCG scores were similar for pH1N1 and seasonal influenza time periods (0.69 and 0.70). Compared with those aged 45 to 64 years, patients younger than 5, 5 to 12, and 13 to 18 years had an increased risk of pH1N1-related ICU stay. Within the pH1N1 cohort, an asthma diagnosis was highly predictive of ICU admission among those younger than 5, 5 to 12, and 13 to 18 years, and pregnancy among those aged 26 to 44 years. Conclusion. High-risk groups, including children with asthma or pregnant women, would benefit from improved surveillance and resource allocation during influenza outbreaks to prevent serious ILI-related complications. The emergence and spread of the novel influenza A (pH1N1) virus resulted in extraordinary influenza activity across the United States in 2009. 1 Severe influenza infection typically occurs in the very young, the elderly, and those with comorbid diseases. 2 However, studies have shown epidemiological differences between seasonal and pH1N1 patients stratified by age. The median age of hospitalized pH1N1 cases was younger than that normally seen with seasonal influenza, with infants with pH1N1 having the highest hospitalization rates. 3 In North America, 60% of all identified cases were younger than 18 years. 4 In one study, hospitalized patients with confirmed or probable pH1N1 infection ranged in age from 21 days to 86 years, but 45% of hospitalized cases were younger than 18 years, and only 5% of cases were aged 65 years or older. 5 Our previously published analysis of statewide 2009 pH1N1 epidemiological data in Massachusetts suggested that there were disproportionately large numbers of hospitalized pH1N1 cases among younger age groups. 6 Other work has shown that the pH1N1 attack rates were low in the general population, and high in children aged 5 to 19 years, and that estimated hospitalization and mortality rates per infection increased significantly with age. 7 The 2009 pH1N1 virus is a unique virus, but studies have found similarities between this pathogen and other influenza A viruses that have circulated in the past. Serum specimens analyzed by hemagglutination-inhibition testing for the presence of antibodies against pH1N1 found that most individuals born after 1944 lacked antibodies to the pandemic virus. 8,9 These findings suggest that previous exposure to seasonal influenza viruses or previous influenza vaccination had conferred some level of protective immunity against pH1N1. Other evidence indicates that the pH1N1 virus may have originated from the Spanish influenza virus and its descendants, which could explain the partial immunity exhibited in the older population. 9 Epidemiological assessments have shown that certain age-related trends occurred during the 2009 pH1N1 pandemic. Adults with pH1N1-related hospitalizations had significant complications and mortality despite being younger than patients with seasonal influenza. 10 However, statewide population-based comparisons of predictors of severe seasonal influenza and pH1N1 by age strata have not been conducted in the United States, and we do not yet know how comorbidity measures compare between age strata or between influenza seasons. To establish a baseline measure of comorbidity, we used validated risk adjustment calculation software, Diagnostic Cost Group (DxCG) Risk Analysis, to calculate individual-level baseline measures of comorbidity based on hierarchical condition categories (HCCs). 11 We calculated a risk-adjusted score for each patient discharged from any Massachusetts acute care hospital with influenza-like illness (ILI) between October 1, 2008, and September 30, 2009, and compared predictors of ILI-related intensive care unit (ICU) stay by age strata. Specific study objectives included (1) compare comorbidity measures by age group for those hospitalized during the pH1N1 pandemic and seasonal influenza time period in 2009, and (2) compare risk factors for ILI-related ICU stay for those hospitalized during the pH1N1 pandemic and seasonal influenza time period.