Influenza Diagnosis and Point-of-Care Testing

January 2007

Influenza Diagnosis and Point-of-Care Testing

Search Strategy: Recognizing Influenza diagnosis is an annual issue, you turn to PUBMED Clinical Queries searching “Influenza” under the diagnosis tab requesting initially a narrow/specific search yielding 5695 hits. You conduct a second search of JAMA and then combine the two search results to yield 30 citations, the second of which is a systematic review of influenza’s clinical diagnosis. Similarly, searching “Emergency Medicine” combined with the clinical query search of “Influenza” yields four citations including a recent Annals of Emergency Medicine review of unaided clinical diagnosis, clinical decision rule guided diagnosis, and rapid Influenza testing. Finally, a general PUBMED search of “Influenza Point of Care Test” yields 23 references, two of which concern use of these bedside tests in ED children.

A 39-year old lawyer presents to your ED in mid-December with one-day history of fever, sore throat, and myalgias. He denies any prior medical history. Review of your hospital records reveals no prior ED evaluations or hospital admissions. His physical exam is unremarkable except for a temperature of 38.6C and rhinnorhea. You’ve not seen or heard of a confirmed case of Influenza in your community yet, but you contemplate whether today’s case might be your first taste of an impending long winter.

Your ED has recently debated the merits of rapid testing for Influenza. A quick search on Google Scholar reveals several commercially available rapid tests including Directigen Flu A + B, QuickVue, ZstatFlu-II, Xpect Flu a/B, FLU OIA A/B, and BinaxNow Influenza A & B (Rapids Tests for Influenza, Current Infectious Disease Reports 2005; 7: 187). You wonder whether any of these tests are superior to another or even more importantly, the utility of any of these tests above and beyond your clinical impression. Motivated, you turn eagerly to the medical literature.

PICO Question

Population: ED patients presenting with possible Influenza

Intervention: Rapid testing added to clinical impression

Comparison: Clinical impression alone

Outcome: Diagnostic accuracy, appropriate utilization of anti-viral therapy, impact influenza related morbidity and mortality.

Years

First years: Does This Patient Have Influenza? JAMA 2005; 293: 987-997.

Second years: Effect of Point-of-Care Influenza Testing on Management of Febrile Children. Acad EM 2006; 13: 1259-1268.

Third years: Accuracy and Impact of a Point-of-Care Rapid Influenza Test in Young Children with Respiratory Illnesses. Arch Pediatr Adolesc Med 2006; 160: 713-718.

Fourth years: Performance Characteristics of Clinical Diagnosis, a Clinical Decision Rule, and a Rapid Influenza Test in the Detection of Influenza Infection in a Community Sample of Adults. Ann EM 2005; 46: 412-419.

Articles

Article 1: Does This Patient Have Influenza? JAMA 2005;293: 987-997
ANSWER KEY

Article 2: Effect of Point-of-Care Influenza Testing on Management of Febrile Children, Acad EM2006; 13:1259-1268
ANSWER KEY

Article 3: Accuracy & Impact of a Point-of-Care Rapid Influenza Test in Young Children with Respiratory Illness, Arch Pediatr Adolesc Med 2006: 160:713-718
ANSWER KEY

Article 4: Performance Characteristics of Clinical Diagnosis, a Clinical Decision Rule, and a Rapid Influenza Test in the Detection of Influenza Infection in a Community Sample of Adults, Annals EM 2005; 46:412-419
ANSWER KEY

Bottom Line

The bottom of the PGY-I Answer Key has valuable links to the CDC to monitor weekly Influenza Activity state-by-state. Also, a link is provided to the CDC for their evaluation of available Point-of-Care tests.

A few final points about Influenza:

  • Children shed more virus than adults which probably explains the enhanced sensitivity of POC tests in children relative to adults.
  • Neuraminidase inhibits are expensive, but when used within 48-hours of symptom onset may reduce symptom duration by 24-48 hours and confer up to 50% reduction in complications leading to hospitalization.
  • Influenza testing may also be important for surveillance (early in flu season) or for deciding when to offer prophylaxis to potentially high-risk contacts of the index patient.
  • Another influenza pandemic is not an if but rather a when. Be prepared by maintaining an emergency kit in your house, alternative means of communication with family/friends when phones are disrupted, and getting the influenza vaccine each year.