Fast and accurate flu tests can guide therapy

Rapid tests can acc­urately diagnose flu and could help guide treatment opt­ions, but cannot rule flu out in pat­i­ents with similar symptoms, researchers have found.

Influenza testing may also drive more appropriate antibiotic use (Photograph: Istock)
Influenza testing may also drive more appropriate antibiotic use (Photograph: Istock)

Dr Caroline Chartrand and colleagues from the University of Montreal, Canada, argue that rapid tests could guide prompt treatment, infection control and decisions about investigations.

Rapid influenza tests may also drive more appropriate antibiotic use and these benefits could make routine use of such tests cost-effective in the long run, they said.

Dr Chartrand and her team examined the accuracy of rapid diagnostic tests for influenza-like illness. They said their findings showed that positive results were unlikely to be false-positives.

‘In the presence of a pos­itive rapid influenza diagnostic test in a patient with influenza-like illness, a clinician can confidently make the diagnosis of influenza and begin appropriate infection-control measures and antiviral therapy, if indica­ted, while forgoing unnecessary additional diagnostic testing and antibiotic prescription.’

These res­ults should be confirmed by other tests if the result is likely to affect patients bec­ause negative test results have a reasonable likelihood of being falsely negative, they added.

Dr Chartrand and her team carried out a meta-analysis of 159 studies evaluating 26 different rapid influenza diagnostic tests. They found that the tests were able to identify flu cases with 98% specificity, but could only find 62% of cases.

Sensitivity varied widely across different tests, which was partly explained by the tests’ lower sensitivity in adults than in chi­ldren and a lower sensitivity for influenza B than A.

However, point-of-care testing also showed no effect on the accuracy of rapid diagnostic tests. ‘This could be good news,’ the researchers said. ‘It is likely that it is when they are used as first-line tests they find their most useful application and have the most effect in the diagnostic work-up for influenza.’

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Ann Intern Med Online 2012

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