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Published on: August 2, 2011
Accuracy and interpretation of rapid influenza tests in children
Carlos G Grijalva1, Katherine A Poehling, Kathryn M Edwards
1Preventive Medicine Department, Vanderbilt University Medical Center, Nashville, TN 37232-2637, USA.
Insights
Rapid influenza diagnostic tests are most accurate when local infection rates are high. Their predictive value decreases significantly when influenza prevalence falls below 10%.
Area of Science:
- Pediatric Infectious Diseases
- Diagnostic Accuracy Studies
- Epidemiology
Background:
- Rapid antigen detection tests for influenza offer timely diagnosis but their interpretation is limited by prevalence.
- Understanding test characteristics in routine clinical practice is crucial for effective decision-making.
Purpose of the Study:
- To determine the optimal timing for using rapid influenza tests based on their predictive value.
- To assess how influenza prevalence influences the accuracy of rapid diagnostic tests.
Main Methods:
- Children under 5 hospitalized with respiratory illness were enrolled; influenza was confirmed via culture and PCR.
- Rapid influenza tests were compared to the gold standard to calculate sensitivity and specificity.
- Weekly influenza prevalence in outpatient settings was monitored to estimate trends in predictive values.
Main Results:
- Rapid influenza tests demonstrated an overall sensitivity of 63% and specificity of 97%.
- Positive predictive values exceeded 80% when influenza prevalence was 15% or higher.
- Predictive values dropped below 70% when prevalence was less than 10%.
Conclusions:
- Influenza prevalence fluctuates significantly within and between seasons.
- Rapid influenza tests have limited utility in low-prevalence settings (<10%).
- Effective use of rapid tests necessitates local surveillance data and prompt communication to clinicians.
Background:
Influenza rapid antigen detection (rapid tests) can provide timely identification of infection and aid in clinical decision-making. Although the interpretation of test results depends on test characteristics and influenza prevalence, this information is limited in routine clinical practice.
Objective:
We sought to assess the times at which rapid tests are most predictive of influenza infection.
Methods:
The New Vaccine Surveillance Network enrolled children aged < 5 years who were hospitalized with respiratory symptoms or fever from October 2000 through September 2004. Nasal and throat swabs were obtained, and influenza virus was detected by culture and reverse-transcription polymerase chain reaction. Provider-ordered rapid influenza tests were compared with the criterion standard (culture and reverse-transcription polymerase chain reaction) to determine their sensitivity and specificity. The New Vaccine Surveillance Network also enrolled children in outpatient settings during the 2002-2003 and 2003-2004 influenza seasons and determined the weekly influenza prevalence among symptomatic children. Trends in weekly predictive values of the rapid tests were estimated over the influenza seasons.
Results:
Rapid influenza tests had an overall sensitivity of 63% and specificity of 97%. In 2002-2003, the prevalence of influenza in symptomatic outpatient children peaked at 21% and stayed above 10% for approximately 4 weeks. In contrast, in 2003-2004, influenza prevalence peaked at 60% and remained above 20% for approximately 6 weeks. The positive predictive value of the rapid tests approached 80% when influenza prevalence was > or = 15% but decreased to < 70% when influenza prevalence was < 10%.
Conclusions:
Influenza prevalence varies between and within seasons. On the basis of our estimates, rapid tests are of limited use when prevalence is < 10%. The appropriate interpretation of rapid influenza tests requires local influenza surveillance and timely communication of this information to the practitioners.
