Abstract
BackgroundThe weekly proportion of laboratory tests that are positive for influenza is used in public health surveillance systems to identify periods of influenza activity. We aimed to estimate the sensitivity of influenza testing in Canada based on results of a national respiratory virus surveillance system.Methods and FindingsThe weekly number of influenza-negative tests from 1999 to 2006 was modelled as a function of laboratory-confirmed positive tests for influenza, respiratory syncytial virus (RSV), adenovirus and parainfluenza viruses, seasonality, and trend using Poisson regression. Sensitivity was calculated as the number of influenza positive tests divided by the number of influenza positive tests plus the model-estimated number of false negative tests. The sensitivity of influenza testing was estimated to be 33% (95%CI 32–34%), varying from 30–40% depending on the season and region.ConclusionsThe estimated sensitivity of influenza tests reported to this national laboratory surveillance system is considerably less than reported test characteristics for most laboratory tests. A number of factors may explain this difference, including sample quality and specimen procurement issues as well as test characteristics. Improved diagnosis would permit better estimation of the burden of influenza.
Highlights
Influenza virus infection is associated with considerable morbidity and mortality[1,2,3], laboratory confirmation of clinical illness is the exception rather than the rule
The estimated sensitivity of influenza tests reported to this national laboratory surveillance system is considerably less than reported test characteristics for most laboratory tests
Sources of data Weekly respiratory virus identifications from September 1999 to August 2006 were obtained from the Respiratory Virus Detection Surveillance System (RVDSS), Public Health Agency of Canada [19,20]
Summary
Influenza virus infection is associated with considerable morbidity and mortality[1,2,3], laboratory confirmation of clinical illness is the exception rather than the rule. Clinicians do not routinely seek laboratory confirmation for several reasons: diagnosis will often not alter patient management, a paucity of real-time, accurate, inexpensive testing methods [4] and because influenza is not recognized as the etiology of the clinical presentation[5]. The performance characteristics of currently available tests for influenza vary considerably and the overall sensitivities of these tests when used in routine practice are dependent on the type of specimen collected, the age of the patient and point in their illness in which they are sampled [4,9,13,14,15]. We aimed to estimate the sensitivity of influenza testing in Canada based on results of a national respiratory virus surveillance system
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