Estimating Sensitivity of Laboratory Testing for Influenza in Canada through Modelling

Saboui

Lee

et al. 2017

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BackgroundA regression‐based study design has commonly been used to estimate the influenza burden; however, these estimates are not timely and many countries lack sufficient virological data. Alternative approaches that would permit a timelier assessment of the burden, including a sentinel surveillance approach recommended by the World Health Organization (WHO), have been proposed. We aimed to estimate the hospitalization burden attributable to influenza, respiratory syncytial virus (RSV), and other respiratory viruses (ORV) and to assess both the completeness of viral identification among respiratory inpatients in Canada and the implications of adopting other approaches.MethodsRespiratory inpatient records were extracted from the Canadian Discharge Abstract Database from 2003 to 2014. A regression model was used to estimate excess respiratory hospitalizations attributable to influenza, RSV, and ORV by age group and diagnostic category and compare these estimates with the number with a respiratory viral identification.ResultsAn estimated 33 (95% CI: 29, 38), 27 (95% CI: 22, 33), and 27 (95% CI: 18, 36) hospitalizations per 100 000 population per year were attributed to influenza, RSV, and ORV, respectively. An influenza virus was identified in an estimated 78% (95% CI: 75, 81) and 17% (95% CI: 15, 21) of respiratory hospitalizations attributed to influenza for children and adults, respectively, and 75% of influenza‐attributed hospitalizations had an ARI diagnosis.ConclusionsHospitalization rates with respiratory viral identification still underestimate the burden. Approaches based on acute respiratory case definitions will likely underestimate the burden as well, although each proposed method should be compared with regression‐based estimates of influenza‐attributed burden as a way of assessing their validity.

Section: Discussionmentioning

confidence: 99%

Burden of influenza, respiratory syncytial virus, and other respiratory viruses and the completeness of respiratory viral identification among respiratory inpatients, Canada, 2003‐2014

Saboui

Lee

et al. 2017

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“…The very strong association of the negative results with influenza and RSV confirmations necessitated the estimation and removal of false negatives. Using a similar Poisson regression model, negative samples attributed to influenza, RSV, PIV, or adenovirus were assumed to be false negatives 21 . Negative samples minus the model estimated false negatives were considered ‘other ILI.’ Results for adenovirus were combined with ‘other ILI’ to simplify reporting.…”

Section: Methodsmentioning

confidence: 99%

Role of influenza and other respiratory viruses in admissions of adults to Canadian hospitals

Langley

Tam

2008

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Objective We sought to estimate age‐specific hospitalization rates attributed to influenza and other virus for adults. Methods Admissions from Canada’s national hospitalization database (Canadian Institute of Health Information), from 1994/95 to 1999/2000, were modeled as a function of proxy variables for influenza, respiratory syncytial virus (RSV) and other viral activity, seasonality and trend using a Poisson regression model and stratified by age group. Results The average annual influenza‐attributed hospitalization rate for all adults, 20 years of age or older, over the study period, which included three severe seasons, was an estimated 65/100 000 population (95% CI 63–67). Among persons aged 65 and over, 270–340 admissions per 100 000 population per year were attributed to influenza, while 30–110, 60–90 and 130–350 per 100 000 were attributed to RSV, parainfluenza (PIV) and other respiratory viruses, respectively. Although marked season‐to‐season variation in age‐specific hospitalization rates attributable to influenza was observed in persons 50 years of age and older, increasing risk with age was preserved at all time periods. Conclusions Influenza, RSV, PIV and other respiratory viruses were all associated with morbidity requiring hospitalization, while influenza was responsible for peak respiratory admissions. The burden of health care utilization associated with respiratory viruses is appreciable beginning in the sixth decade and increases significantly with age.

“…Although the percent positive is often used, as this approach would normalize for the unusually high testing rates early in the pandemic period, the use of this normalized variable did not capture peak influenza activity well in the Canadian setting. 3 The percent positive time series can also be strongly influenced by testing procedures and false-negative tests results, 12 which is likely contributed to the poor performance during periods of peak influenza activity. With laboratory confirmation in over 50% of admissions attributed H1N1, the expected precision of the model results for the pandemic period is fairly high.…”

Section: Model Fitmentioning

confidence: 99%

“…Through-out the 2009 pandemic period, priority was given in Canada to the use of laboratory testing for the diagnosis of influenza in hospitalized patients. Despite similar recommendations in the United States, the US Centers for Disease Control and Prevention (CDC) aware that incomplete testing and false negative results 12 were contributing to a significant underestimation of the true H1N1 ⁄ 2009 burden, 13 started correcting for under-ascertainment using a multiplier model as of July 2009. 14 In December 2009, the World Health Organization (WHO) recommended that the burden of the pandemic be assessed using statistical methods similar to those used to assess the burden of seasonal influenza.…”

Section: Introductionmentioning

confidence: 99%

Statistical estimates of respiratory admissions attributable to seasonal and pandemic influenza for Canada

McGeer

Morris

2012

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Background The number of admissions to hospital for which influenza is laboratory confirmed is considered to be a substantial underestimate of the true number of admissions due to an influenza infection. During the 2009 pandemic, testing for influenza in hospitalized patients was a priority, but the ascertainment rate remains uncertain.Methods The discharge abstracts of persons admitted with any respiratory condition were extracted from the Canadian Discharge Abstract Database, for April 2003–March 2010. Stratified, weekly admissions were modeled as a function of viral activity, seasonality, and trend using Poisson regression models.Results An estimated 1 out of every 6·4 admissions attributable to seasonal influenza (2003–April 2009) were coded to J10 (influenza virus identified). During the 2009 pandemic (May–March 2010), the influenza virus was identified in 1 of 1·6 admissions (95% CI, 1·5–1·7) attributed to the pandemic strain. Compared with previous H1N1 seasons (2007/08, 2008/09), the influenza-attributed hospitalization rate for persons <65 years was approximately six times higher during the 2009 H1N1 pandemic, whereas for persons 75 years or older, the pandemic rate was approximately fivefold lower.Conclusions Case ascertainment was much improved during the pandemic period, with under ascertainment of admissions due to H1N1/2009 limited primarily to patients with a diagnosis of pneumonia.