Po-Yung Cheng

University Center Rochester, Rochester, Minnesota, United States

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Publications (17)101.45 Total impact

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    ABSTRACT: Influenza is the most common vaccine-preventable disease in the United States; however, little is known about the burden of critical illness due to influenza virus infection. Our primary objective was to estimate the proportion of all critical illness hospitalizations that are attributable to seasonal influenza.
    Critical care medicine. 08/2014;
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    ABSTRACT: SUMMARY Death certificate reports and laboratory-confirmed influenza deaths probably underestimate paediatric deaths attributable to influenza. Using US mortality data for persons aged <18 years who died during 28 September 2003 to 2 October 2010, we estimated influenza-attributable deaths using a generalized linear regression model based on seasonal covariates, influenza-certified deaths (deaths for which influenza was a reported cause of death), and occurrence during the 2009 pandemic period. Of 32 783 paediatric deaths in the death categories examined, 853 (3%) were influenza-certified. The estimated number of influenza-attributable deaths over the study period was 1·8 [95% confidence interval (CI) 1·3-2·8] times higher than the number of influenza-certified deaths. Influenza-attributable deaths were 2·1 (95% CI 1·5-3·4) times higher than influenza-certified deaths during the non-pandemic period and 1·1 (95% CI 1·0-1·8) times higher during the pandemic. Overall, US paediatric deaths attributable to influenza were almost twice the number reported by death certificate codes in the seasons prior to the 2009 pandemic.
    Epidemiology and Infection 05/2014; · 2.87 Impact Factor
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    ABSTRACT: Young children are at increased risk of severe outcomes from influenza illness, including hospitalization. We conducted a case-control study to identify risk factors for influenza-associated hospitalizations among children in U.S. Emerging Infections Program sites. Cases were children 6-59 months of age hospitalized for laboratory-confirmed influenza infections during 2005-08. Age- and zip-code-matched controls were enrolled. Data on child, caregiver, and household characteristics were collected from parents and medical records. Conditional logistic regression was used to identify independent risk factors for hospitalization. We enrolled 290 (64%) of 454 eligible cases and 1,089 (49%) of 2,204 eligible controls. Risk for influenza hospitalization increased with maternal age <26 years (odds ratio [OR] 1.8, 95% confidence interval [CI] 1.1-2.9); household income below the poverty threshold (OR 2.2, CI 1.4-3.6); smoking by >50% of household members (OR 2.9, CI 1.4-6.6); lack of household influenza vaccination (OR 1.8, CI 1.2-2.5); and presence of chronic illnesses, including hematologic/oncologic (OR 11.8, CI 4.5-31.0), pulmonary (OR 2.9, CI 1.9-4.4), and neurologic (OR 3.8, CI 1.6-9.2) conditions. Full influenza immunization decreased the risk among children aged 6-23 months (OR 0.5, CI 0.3-0.9) but not among those 24-59 months of age (OR 1.5, CI 0.8-3.0; p-value for difference = 0.01). Chronic illnesses, young maternal age, poverty, household smoking, and lack of household influenza vaccination increased the risk of influenza hospitalization. These characteristics may help providers to identify young children who are at greatest risk for severe outcomes from influenza illness.
    The Pediatric Infectious Disease Journal 03/2014; · 3.57 Impact Factor
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    ABSTRACT: Limited data are available from Central and Eastern Europe on risk factors for severe complications of influenza. Such data are essential to prioritize prevention and treatment resources and to adapt influenza vaccination recommendations. To use sentinel surveillance data to identify risk factors for fatal outcomes among hospitalized patients with severe acute respiratory infections (SARI) and among hospitalized patients with laboratory-confirmed influenza. Retrospective analysis of case-based surveillance data collected from sentinel hospitals in Romania during the 2009/2010 and 2010/2011 winter influenza seasons was performed to evaluate risk factors for fatal outcomes using multivariate logistic regression. During 2009/2010 and 2010/2011, sentinel hospitals reported 661 SARI patients of which 230 (35%) tested positive for influenza. In the multivariate analyses, infection with influenza A(H1N1)pdm09 was the strongest risk factor for death among hospitalized SARI patients (OR: 6·6; 95% CI: 3·3-13·1). Among patients positive for influenza A(H1N1)pdm09 virus infection (n = 148), being pregnant (OR: 7·1; 95% CI: 1·6-31·2), clinically obese (OR: 2·9;95% CI: 1·6-31·2), and having an immunocompromising condition (OR: 3·7;95% CI: 1·1-13·4) were significantly associated with fatal outcomes. These findings are consistent with several other investigations of risk factors associated with influenza A(H1N1)pdm09 virus infections. They also support the more recent 2012 recommendations by the WHO Strategic Advisory Group of Experts on Immunization (SAGE) that pregnant women are an important risk group for influenza vaccination. Ongoing sentinel surveillance can be useful tool to monitor risk factors for complications of influenza virus infections during each influenza season, and pandemics as well.
    Influenza and Other Respiratory Viruses 11/2013; · 1.47 Impact Factor
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    ABSTRACT: Background. Each year, the US Flu VE Network examines the effectiveness of influenza vaccines in preventing medically-attended acute respiratory illnesses caused by influenza. Methods. Patients with acute respiratory illnesses of <7 days duration were enrolled at ambulatory care facilities in five communities. Specimens were collected and tested for influenza by real-time reverse transcriptase polymerase chain reaction. Receipt of influenza vaccine was defined based on documented evidence of vaccination in medical records or immunization registries. Vaccine effectiveness was estimated in adjusted logistic regression models by comparing the vaccination coverage in those who tested positive for influenza with those who tested negative. Results. The 2011-2012 season was mild and peaked late, with circulation of both type A viruses and both lineages of type B. Overall adjusted vaccine effectiveness was 47% (95% confidence interval [CI], 36 to 56) in preventing medically-attended influenza; vaccine effectiveness was 65% (95% CI, 44 to 79) against type A (H1N1) pdm09, but only 39% (95% CI, 23 to 52) against type A (H3N2). Estimates of vaccine effectiveness against both type B lineages were similar (overall 58%, 95% CI, 35 to 73). An apparent negative effect of prior year vaccination on current year effectiveness estimates was noted, particularly for A (H3N2) outcomes. Conclusions. Vaccine effectiveness in the 2011-2012 season was modest overall, with lower effectiveness against the predominant A (H3N2) virus. This may be related to modest antigenic drift, but past history of vaccination might also play a role.
    Clinical Infectious Diseases 11/2013; · 9.37 Impact Factor
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    ABSTRACT: During 2009-2010, we examined 217 cases hospitalized with laboratory-confirmed pandemic influenza in nine FluSurv-NET sites and 413 age- and community-matched controls and found a single dose of monovalent non-adjuvanted influenza A(H1N1)pdm09 vaccine was 50% (95% CI=13%-71%) effective in preventing hospitalization associated with A(H1N1)pdm09 virus infection.
    Clinical Infectious Diseases 08/2013; · 9.37 Impact Factor
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    ABSTRACT: Rationale: The incidence of influenza-associated acute respiratory failure is unknown. Objectives: We conducted this study to estimate the population-based incidence of influenza-associated acute respiratory failure hospitalizations. Methods: This is a cohort study from January 2003 through March 2009 using hospitalization databases for Arizona, California, and Washington from the Healthcare Cost and Utilization Project and influenza surveillance data for regions encompassing these states. Acute respiratory failure requiring mechanical ventilation was defined by ICD-9-CM code. We used negative-binomial regression modeling to estimate the incidence of influenza-associated events. Measurements and Main Results: The incidence of influenza-associated acute respiratory failure was 2.7 per 100,000 person-years (95% CI 0.2, 23.5), and during the influenza season, 3.8% of all respiratory failure hospitalizations were attributable to influenza. Compared with adults aged 18-49 years, the incidence rate ratio (IRR) for influenza-associated acute respiratory failure was lower among children aged 1-4 years (0.9) and 5-17 years (0.3). However, the IRR was higher among adults aged 50-64 years (4.8), 65-74 years (10.4), 75-84 years (19.9), and 85 years and older (33.7). Results were similar with more sensitive and specific outcome definitions and in a sensitivity analysis using only Arizona-specific outcome and surveillance data. Conclusion: Our data indicate that influenza was an important contributor to respiratory failure hospitalizations during 2003-2009. Physicians should consider influenza testing and empiric antiviral therapy for hospitalized patients with severe acute respiratory disease during periods of influenza activity. Influenza has a greater effect on respiratory failure in the elderly, for whom better prevention measures are needed.
    American Journal of Respiratory and Critical Care Medicine 07/2013; · 11.04 Impact Factor
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    ABSTRACT: To determine trends in mortality from respiratory disease in several areas of Latin America between 1998 and 2009. The numbers of deaths attributed to respiratory disease between 1998 and 2009 were extracted from mortality data from Argentina, southern Brazil, Chile, Costa Rica, Ecuador, Mexico and Paraguay. Robust linear models were then fitted to the rates of mortality from respiratory disease recorded between 2003 and 2009. Between 1998 and 2008, rates of mortality from respiratory disease gradually decreased in all age groups in most of the study areas. Among children younger than 5 years, for example, the annual rates of such mortality - across all seven study areas - fell from 56.9 deaths per 100 000 in 1998 to 26.6 deaths per 100 000 in 2008. Over this period, rates of mortality from respiratory disease were generally highest among adults older than 65 years and lowest among individuals aged 5 to 49 years. In 2009, mortality from respiratory disease was either similar to that recorded in 2008 or showed an increase - significant increases were seen among children younger than 5 years in Paraguay, among those aged 5 to 49 years in southern Brazil, Mexico and Paraguay and among adults aged 50 to 64 years in Mexico and Paraguay. In much of Latin America, mortality from respiratory disease gradually fell between 1998 and 2008. However, this downward trend came to a halt in 2009, probably as a result of the (H1N1) 2009 pandemic.
    Bulletin of the World Health Organisation 07/2013; 91(7):525-32. · 5.25 Impact Factor
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    ABSTRACT: Influenza A (H1N1)pdm09 (2009 H1N1) re-circulated as the predominant virus from January through February 2011 in China. National surveillance of 2009 H1N1 as a notifiable disease was maintained to monitor potential changes in disease severity from the previous season. To describe the characteristics of hospitalized cases with 2009 H1N1 infection and analyze risk factors for severe illness during the 2010-2011winter season in China, we obtained surveillance data from hospitalized cases with 2009 H1N1 infection from November 2010 through May 2011, and reviewed medical records from 701 hospitalized cases. Age-standardized risk ratios were used to compare the age distribution of patients that were hospitalized and died due to 2009 H1N1 between the 2010-2011winter season to those during the 2009-2010 pandemic period. During the 2010-2011 winter season, children less than 5 years of age had the highest relative risk of hospitalization and death, followed by adults aged 65 years or older. Additionally, the relative risk of hospitalized cases aged 5-14 and 15-24 years was lower compared to children less than 5 years of age. During the winter season of 2010-2011, the proportions of adults aged 25 years or older for hospitalization and death were significantly higher than those during the 2009-2010 pandemic period. Being male, having a chronic medical condition, delayed hospital admission (≥3 days from onset) or delayed initiation of antiviral treatment (≥5 days from onset) were associated with severe illness among non-pregnant patients ≥2 years of age. We observed a change in high risk groups for hospitalization for 2009 H1N1 during the winter months immediately following the pandemic period compared to the high risk groups identified during the pandemic period. Our nationally notifiable disease surveillance system enabled us to understand the evolving epidemiology of 2009 H1N1 infection after the pandemic period.
    PLoS ONE 01/2013; 8(2):e55016. · 3.53 Impact Factor
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    ABSTRACT: The goal of influenza vaccination programs is to reduce influenza-associated disease outcomes. Therefore, estimating the reduced burden of influenza as a result of vaccination over time and by age group would allow for a clear understanding of the value of influenza vaccines in the US, and of areas where improvements could lead to greatest benefits. To estimate the direct effect of influenza vaccination in the US in terms of averted number of cases, medically-attended cases, and hospitalizations over six recent influenza seasons. Using existing surveillance data, we present a method for assessing the impact of influenza vaccination where impact is defined as either the number of averted outcomes or as the prevented disease fraction (the number of cases estimated to have been averted relative to the number of cases that would have occurred in the absence of vaccination). We estimated that during our 6-year study period, the number of influenza illnesses averted by vaccination ranged from a low of approximately 1.1 million (95% confidence interval (CI) 0.6-1.7 million) during the 2006-2007 season to a high of 5 million (CI 2.9-8.6 million) during the 2010-2011 season while the number of averted hospitalizations ranged from a low of 7,700 (CI 3,700-14,100) in 2009-2010 to a high of 40,400 (CI 20,800-73,000) in 2010-2011. Prevented fractions varied across age groups and over time. The highest prevented fraction in the study period was observed in 2010-2011, reflecting the post-pandemic expansion of vaccination coverage. Influenza vaccination programs in the US produce a substantial health benefit in terms of averted cases, clinic visits and hospitalizations. Our results underscore the potential for additional disease prevention through increased vaccination coverage, particularly among nonelderly adults, and increased vaccine effectiveness, particularly among the elderly.
    PLoS ONE 01/2013; 8(6):e66312. · 3.53 Impact Factor
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    ABSTRACT: Please cite this paper as: Azziz-Baumgartner et al. (2012) Incidence of influenza-associated mortality and hospitalizations in Argentina during 2002-2009. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12022. Background  We estimated rates of influenza-associated deaths and hospitalizations in Argentina, a country that recommends annual influenza vaccination for persons at high risk of complications from influenza illness. Methods  We identified hospitalized persons and deaths in persons diagnosed with pneumonia and influenza (P&I, ICD-10 codes J10-J18) and respiratory and circulatory illness (R&C, codes I00-I99 and J00-J99). We defined the influenza season as the months when the proportion of samples that tested positive for influenza exceeded the annual median. We used hospitalizations and deaths during the influenza off-season to estimate, using linear regression, the number of excess deaths that occurred during the influenza season. To explore whether excess mortality varied by sex and whether people were age <65 or ≥65 years, we used Poisson regression of the influenza-associated rates. Results  During 2002-2009, 2411 P&I and 8527 R&C mean excess deaths occurred annually from May to October. If all of these excess deaths were associated with influenza, the influenza-associated mortality rate was 6/100 000 person-years (95% CI 4-8/100 000 person-years for P&I and 21/100 000 person-years (95% CI 12-31/100 000 person-years) for R&C. During 2005-2008, we identified an average of 7868 P&I excess hospitalizations and 22 994 R&C hospitalizations per year, resulting in an influenza-associated hospitalization rate of 2/10 000 person-years (95% CI 1-3/10 000 person-years) for P&I and 6/10 000 person-years (95% CI 3-8/10 000 person-years) for R&C. Conclusion  Our findings suggest that annual rates of influenza-associated hospitalizations and death in Argentina were substantial and similar to neighboring Brazil.
    Influenza and Other Respiratory Viruses 12/2012; · 1.47 Impact Factor
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    ABSTRACT: Background. Influenza vaccines may be reformulated annually because of antigenic drift in influenza viruses. However, the relationship between antigenic characteristics of circulating viruses and vaccine effectiveness (VE) is not well understood. We conducted an assessment of the effectiveness of US influenza vaccines during the 2010-2011 season. Methods. We performed a case-control study comparing vaccination histories between subjects with acute respiratory illness with positive real-time reverse transcription polymerase chain reaction for influenza and influenza test-negative controls. Subjects with acute respiratory illness of ≤7 days duration were enrolled in hospitals, emergency departments, or outpatient clinics in communities in 4 states. History of immunization with the 2010-2011 vaccine was ascertained from vaccine registries or medical records. Vaccine effectiveness was estimated in logistic regression models adjusted for study community, age, race, insurance status, enrollment site, and presence of a high-risk medical condition. Results. A total of 1040 influenza-positive cases and 3717 influenza-negative controls were included from the influenza season, including 373 cases of influenza A(H1N1), 334 cases of influenza A(H3N2), and 333 cases of influenza B. Overall adjusted VE was 60% (95% confidence interval [CI], 53%-66%). Age-specific VE estimates ranged from 69% (95% CI, 56%-77%) in children aged 6 months-8 years to 38% (95% CI, -16% to 67%) in adults aged ≥65 years. Conclusions. The US 2010-2011 influenza vaccines were moderately effective in preventing medically attended influenza during a season when all 3 vaccine strains were antigenically similar to circulating viruses. Continued monitoring of influenza vaccines in all age groups is important, particularly as new vaccines are introduced.
    Clinical Infectious Diseases 07/2012; 55(7):951-959. · 9.37 Impact Factor
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    ABSTRACT: Background. Although influenza is a vaccine-preventable disease that annually causes substantial disease burden, data on virus activity in tropical countries are limited. We analyzed publicly available influenza data to better understand the global circulation of influenza viruses. Methods. We reviewed open-source, laboratory-confirmed influenza surveillance data. For each country, we abstracted data on the percentage of samples testing positive for influenza each epidemiologic week from the annual number of samples testing positive for influenza. The start of influenza season was defined as the first week when the proportion of samples that tested positive remained above the annual mean. We assessed the relationship between percentage of samples testing positive and mean monthly temperature with use of regression models. Findings. We identified data on laboratory-confirmed influenza virus infection from 85 countries. More than one influenza epidemic period per year was more common in tropical countries (41%) than in temperate countries (15%). Year-round activity (ie, influenza virus identified each week having ≥10 specimens submitted) occurred in 3 (7%) of 43 temperate, 1 (17%) of 6 subtropical, and 11 (37%) of 30 tropical countries with available data (P = .006). Percentage positivity was associated with low temperature (P = .001). Interpretation. Annual influenza epidemics occur in consistent temporal patterns depending on climate.
    The Journal of Infectious Diseases 07/2012; 206(6):838-46. · 5.85 Impact Factor
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    ABSTRACT: 18,500 laboratory-confirmed deaths caused by the 2009 pandemic influenza A H1N1 were reported worldwide for the period April, 2009, to August, 2010. This number is likely to be only a fraction of the true number of the deaths associated with 2009 pandemic influenza A H1N1. We aimed to estimate the global number of deaths during the first 12 months of virus circulation in each country. We calculated crude respiratory mortality rates associated with the 2009 pandemic influenza A H1N1 strain by age (0-17 years, 18-64 years, and >64 years) using the cumulative (12 months) virus-associated symptomatic attack rates from 12 countries and symptomatic case fatality ratios (sCFR) from five high-income countries. To adjust crude mortality rates for differences between countries in risk of death from influenza, we developed a respiratory mortality multiplier equal to the ratio of the median lower respiratory tract infection mortality rate in each WHO region mortality stratum to the median in countries with very low mortality. We calculated cardiovascular disease mortality rates associated with 2009 pandemic influenza A H1N1 infection with the ratio of excess deaths from cardiovascular and respiratory diseases during the pandemic in five countries and multiplied these values by the crude respiratory disease mortality rate associated with the virus. Respiratory and cardiovascular mortality rates associated with 2009 pandemic influenza A H1N1 were multiplied by age to calculate the number of associated deaths. We estimate that globally there were 201,200 respiratory deaths (range 105,700-395,600) with an additional 83,300 cardiovascular deaths (46,000-179,900) associated with 2009 pandemic influenza A H1N1. 80% of the respiratory and cardiovascular deaths were in people younger than 65 years and 51% occurred in southeast Asia and Africa. Our estimate of respiratory and cardiovascular mortality associated with the 2009 pandemic influenza A H1N1 was 15 times higher than reported laboratory-confirmed deaths. Although no estimates of sCFRs were available from Africa and southeast Asia, a disproportionate number of estimated pandemic deaths might have occurred in these regions. Therefore, efforts to prevent influenza need to effectively target these regions in future pandemics. None.
    The Lancet Infectious Diseases 06/2012; 12(9):687-95. · 19.97 Impact Factor
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    ABSTRACT: Age-specific comparisons of influenza and respiratory syncytial virus (RSV) hospitalization rates can inform prevention efforts, including vaccine development plans. Previous US studies have not estimated jointly the burden of these viruses using similar data sources and over many seasons. We estimated influenza and RSV hospitalizations in 5 age categories (<1, 1-4, 5-49, 50-64, and ≥65 years) with data for 13 states from 1993-1994 through 2007-2008. For each state and age group, we estimated the contribution of influenza and RSV to hospitalizations for respiratory and circulatory disease by using negative binomial regression models that incorporated weekly influenza and RSV surveillance data as covariates. Mean rates of influenza and RSV hospitalizations were 63.5 (95% confidence interval [CI], 37.5-237) and 55.3 (95% CI, 44.4-107) per 100000 person-years, respectively. The highest hospitalization rates for influenza were among persons aged ≥65 years (309/100000; 95% CI, 186-1100) and those aged <1 year (151/100000; 95% CI, 151-660). For RSV, children aged <1 year had the highest hospitalization rate (2350/100000; 95% CI, 2220-2520) followed by those aged 1-4 years (178/100000; 95% CI, 155-230). Age-standardized annual rates per 100000 person-years varied substantially for influenza (33-100) but less for RSV (42-77). Overall US hospitalization rates for influenza and RSV are similar; however, their age-specific burdens differ dramatically. Our estimates are consistent with those from previous studies focusing either on influenza or RSV. Our approach provides robust national comparisons of hospitalizations associated with these 2 viral respiratory pathogens by age group and over time.
    Clinical Infectious Diseases 04/2012; 54(10):1427-36. · 9.37 Impact Factor
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    ABSTRACT: Most estimates of US deaths associated with influenza circulation have been similar despite the use of different approaches. However, a recently published estimate suggested that previous estimates substantially overestimated deaths associated with influenza, and concluded that substantial numbers of deaths during a future pandemic could be prevented because of improvements in medical care. We reviewed the data sources and methods used to estimate influenza-associated deaths. We suggest that discrepancies between the recent estimate and previous estimates of the number of influenza-associated deaths are attributable primarily to the use of different outcomes and methods. We also believe that secondary bacterial infections will likely result in substantial morbidity and mortality during a future influenza pandemic, despite medical progress.
    American Journal of Public Health 10/2009; 99 Suppl 2:S225-30. · 3.93 Impact Factor
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    ABSTRACT: A wide range of methods have been used for estimating influenza-associated deaths in temperate countries. Direct comparisons of estimates produced by using different models with US mortality data have not been published. Compare estimates of US influenza-associated deaths made by using four models and summarize strengths and weaknesses of each model. US mortality data from the 1972-1973 through 2002-2003 respiratory seasons and World Health Organization influenza surveillance data were used to estimate influenza-associated respiratory and circulatory deaths. Four models were used: (i) rate-difference (using peri-season or summer-season baselines), (ii) Serfling least squares cyclical regression, (iii) Serfling-Poisson regression, (iv) and autoregressive integrated moving average models. Annual estimates of influenza-associated deaths made using each model were similar and positively correlated, except for estimates from the summer-season rate-difference model, which were consistently higher. From the 1976/1977 through the 2002/2003 seasons the, the Poisson regression models estimated that an annual average of 25,470 [95% confidence interval (CI) 19,781-31,159] influenza-associated respiratory and circulatory deaths [9.9 deaths per 100,000 (95% CI 7.9-11.9)], while peri-season rate-difference models using a 15% threshold estimated an annual average of 22,454 (95% CI 16,189-28,719) deaths [8.6 deaths per 100,000 (95% CI 6.4-10.9)]. Estimates of influenza-associated mortality were of similar magnitude. Poisson regression models permit the estimation of deaths associated with influenza A and B, but require robust viral surveillance data. By contrast, simple peri-season rate-difference models may prove useful for estimating mortality in countries with sparse viral surveillance data or complex influenza seasonality.
    Influenza and Other Respiratory Viruses 02/2009; 3(1):37-49. · 1.47 Impact Factor