Po-Yung Cheng

Centers for Disease Control and Prevention, Атланта, Michigan, United States

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Publications (21)116.7 Total impact

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    ABSTRACT: Little is known about factors associated with maintenance of hemagglutinin inhibition (HAI) antibodies after influenza vaccination in older adults. Adults ≥50 years of age were vaccinated prior to the 2009-10 influenza season. Serum was drawn pre-vaccination (S1), 21-28 days post-vaccination (S2), and after the influenza season (S3) for HAI assays. Seroconversion was defined as ≥ 4-fold increase S1 to S2 or if S1 < 10 by an S2 ≥ 40) and seroprotection was defined as S2 ≥ 40. Maintenance of antibody response was measured in participants with an S2 ≥ 40, and defined as an S3 ≥ 40. We enrolled 510 participants during Fall 2009 at Vanderbilt University Medical Center and Marshfield Clinic Research Foundation. Participants' mean age was 64 years with 62% female and 96% white. Seroconversion and seroprotection rates were lowest for influenza A H1N1 (12% and 26%, respectively), highest for influenza A H3N2 (45% and 82%), and intermediate for influenza B (28% and 72%). Of the participants with an S2 ≥ 40, 36% (46/126), 71% (289/407), and 74% (263/354) maintained an S3 ≥ 40 for H1N1, H3N2, and B influenza vaccine strains, respectively. S1 HAI titer was strongly associated with both post-vaccination seroprotection and maintaining seroprotection at S3 for all three influenza antigens. Age, sex, body mass index, self-reported stress, and vaccination site were not consistently associated with vaccine response or maintenance of response. Pre-vaccination antibody titer was the only study variable consistently and positively associated with both serologic response to vaccination and maintenance of response. Antibody responses were lowest for the H1N1 vaccine strain. CLINICALTRIALS: gov Identifier: NCT02401893.
    BMC Infectious Diseases 04/2015; 15(1):195. DOI:10.1186/s12879-015-0926-8 · 2.56 Impact Factor
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    ABSTRACT: Infectious diseases in poultry can spread quickly and lead to huge economic losses. In the past decade, on multiple continents, the accelerated spread of highly pathogenic avian Influenza A (H5N1) virus, often through informal trade networks, has led to the death and culling of hundreds of millions of poultry. Endemic poultry diseases like Newcastle disease and fowl typhoid can also be devastating in many parts of the world. Understanding trade networks in unregulated systems can inform policy decisions concerning disease prevention and containment. From June to December 2008 we conducted a cross-sectional survey of backyard farmers, market traders, and middlemen in 5/8 provinces in Kenya. We administered a standardized questionnaire to each type of actor using convenience, random, snowball, and systematic sampling. Questionnaires addressed frequency, volume, and geography of trade, as well as biosecurity practices. We created a network diagram identifying the most important locations for trade. Of 380 respondents, 51% were backyard farmers, 24% were middlemen and 25% were market traders. Half (50%) of backyard farmers said they raised poultry both for household consumption and for sale. Compared to market traders, middlemen bought their poultry from a greater number of villages (median 4.2 villages for middlemen vs. 1.9 for market traders). Traders were most likely to purchase poultry from backyard farmers. Of the backyard farmers who sold poultry, 51% [CI 40-63] reported selling poultry to market traders, and 54% [CI 44-63] sold to middlemen. Middlemen moved the largest volume of poultry on a weekly basis (median purchases: 187 birds/week [IQR 206]; median sales: 188 birds/week [IQR 412.5]). The highest numbers of birds were traded in Nairobi - Kenya's capital city. Nairobi was the most prominent trading node in the network (61 degrees of centrality). Many smaller sub-networks existed as a result of clustered local trade. Market traders were also integral to the network. The informal poultry trade in Kenya is dependent on the sale of backyard poultry to middlemen and market traders. These two actors play a critical role in poultry movement in Kenya; during any type of disease outbreak middlemen should be targeted for control- and containment-related interventions. Published by Elsevier B.V.
    Preventive Veterinary Medicine 04/2015; DOI:10.1016/j.prevetmed.2015.03.021 · 2.51 Impact Factor
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    ABSTRACT: Excess mortality due to seasonal influenza is substantial, yet quantitative estimates of the benefit of annual vaccination programs on influenza-associated mortality are lacking. We estimated the numbers of deaths averted by vaccination in four age groups (0.5 to 4, 5 to 19, 20 to 64 and ≥65 yrs.) for the nine influenza seasons from 2005/6 through 2013/14. These estimates were obtained using a Monte Carlo approach applied to weekly U.S. age group-specific estimates of influenza-associated excess mortality, monthly vaccination coverage estimates and summary seasonal influenza vaccine effectiveness estimates to obtain estimates of the number of deaths averted by vaccination. The estimates are conservative as they do not include indirect vaccination effects. From August, 2005 through June, 2014, we estimated that 40,127 (95% confidence interval [CI] 25,694 to 59,210) deaths were averted by influenza vaccination. We found that of all studied seasons the most deaths were averted by influenza vaccination during the 2012/13 season (9398; 95% CI 2,386 to 19,897) and the fewest during the 2009/10 pandemic (222; 95% CI 79 to 347). Of all influenza-associated deaths averted, 88.9% (95% CI 83 to 92.5%) were in people ≥65 yrs. old. The estimated number of deaths averted by the US annual influenza vaccination program is considerable, especially among elderly adults and even when vaccine effectiveness is modest, such as in the 2012/13 season. As indirect effects ("herd immunity") of vaccination are ignored, these estimates represent lower bound estimates and are thus conservative given valid excess mortality estimates. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
    Vaccine 03/2015; 99. DOI:10.1016/j.vaccine.2015.02.042 · 3.49 Impact Factor
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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; 42(11). DOI:10.1097/CCM.0000000000000545 · 6.15 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; 33(6). DOI:10.1097/INF.0000000000000283 · 3.14 Impact Factor
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    ABSTRACT: Historically, American Indian/Alaska Native (AI/AN) people have experienced a disproportionate burden of infectious disease morbidity compared with the general US population. We evaluated whether a disparity in influenza hospitalizations exists between AI/AN people and the general US population. We used Indian Health Service hospital discharge data (2001-2011) for AI/AN people and 13 State Inpatient Databases (2001-2008) to provide a comparison to the US population. Hospitalization rates were calculated by respiratory year (July-June). Influenza-specific hospitalizations were defined as discharges with any influenza diagnoses. Influenza-associated hospitalizations were calculated using negative binomial regression models that incorporated hospitalization and influenza laboratory surveillance data. The mean influenza-specific hospitalization rate/100 000 persons/year during the 2001-2002 to 2007-2008 respiratory years was 18.6 for AI/AN people and 15.6 for the comparison US population. The age-adjusted influenza-associated hospitalization rate for AI/AN people (98.2; 95% confidence interval [CI], 51.6-317.8) was similar to the comparison US population (58.2; CI, 34.7-172.2). By age, influenza-associated hospitalization rates were significantly higher among AI/AN infants (<1 year) (1070.7; CI, 640.7-2969.5) than the comparison US infant population (210.2; CI, 153.5-478.5). American Indian/Alaska Native people had higher influenza-specific hospitalization rates than the comparison US population; a significant influenza-associated hospitalization rate disparity was detected only among AI/AN infants because of the wide CIs inherent to the model. Taken together, the influenza-specific and influenza-associated hospitalization rates suggest that AI/AN people might suffer disproportionately from influenza illness compared with the general US population.
    03/2014; 1(1):ofu031. DOI:10.1093/ofid/ofu031
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    ABSTRACT: Re-emergence in 2003 of human cases of avian H5N1 and the resultant spread of the disease highlighted the need to improve the capacity of countries to detect and contain novel viruses. To assess development in this capacity, the Centers for Disease Control and Prevention (CDC) produced a tool for assessing a country's capability in 12 critical areas related to pandemic preparedness, including monitoring and identifying novel influenza viruses. Capabilities the CDC tool assesses range from how well a country has planned and is prepared for an outbreak to how prepared a country is to respond when a pandemic occurs. Included in this assessment tool are questions to determine whether a country has a detailed preparedness plan and the laboratory capacity to identify various strains of influenza quickly and accurately. The tool was used first in 2008 when 40 countries in collaboration with CDC calculated baseline scores and used a second time in 2010 by 36 of the original 40 countries to determine whether they had improved their preparedness. Using basic mathematical comparison and statistical analyses, we compared data at the aggregate capability level as well as at the indicator and country levels. Additionally, we examined the comments of respondents to the assessment questionnaire for reasons (positive and negative) that would explain changes in scores from 2008 to 2010. Analysis of results of two assessments in 36 countries shows statistically significant improvement in all 12 capabilities on an aggregate level and 47 of 50 indicators.
    Influenza and Other Respiratory Viruses 12/2013; DOI:10.1111/irv.12214 · 1.90 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; 8(1). DOI:10.1111/irv.12209 · 1.90 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; 58(3). DOI:10.1093/cid/cit736 · 9.42 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; DOI:10.1093/cid/cit551 · 9.42 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; 188(6). DOI:10.1164/rccm.201212-2341OC · 11.99 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. DOI:10.2471/BLT.12.116871 · 5.11 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 06/2013; 8(6):e66312. DOI:10.1371/journal.pone.0066312 · 3.53 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 02/2013; 8(2):e55016. DOI:10.1371/journal.pone.0055016 · 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; 7(5). DOI:10.1111/irv.12022 · 1.90 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. DOI:10.1093/cid/cis574 · 9.42 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. DOI:10.1093/infdis/jis467 · 5.78 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. DOI:10.1016/S1473-3099(12)70121-4 · 19.45 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. DOI:10.1093/cid/cis211 · 9.42 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. DOI:10.2105/AJPH.2008.151944 · 4.23 Impact Factor