Additional Information

Additional Information:

• If swab specimens are sent, collect 1 nasal eSwab for each patient. Refer to the Collection procedure on this Web Site.
• Lower respiratory tract specimens (Bronchial lavage, Bronchial Wash) are not suitable for testing in-house. Influenza testing on lower respiratory tract specimens must be forwarded to an outside laboratory for testing.

Other Information:

It is critical to note that false positive results are more likely during periods of low influenza activity when prevalence is moderate to low. A positive rapid test result must be clinically correlated with typical symptoms, which are fever of 100-104° F, fatigue, muscle aches, joint pain, headache, cough, and loss of appetite. Individuals who received nasally administered influenza A vaccine may have positive test results for up to three days after vaccination and should not be tested.

This test detects most strains of influenza A, but does not differentiate H1N1 from ‘seasonal’ influenza .

A negative rapid test result does not exclude influenza viral infection. False negative test results are more likely during peak activity when prevalence of disease is high

Swab specimens have a lower specificity and sensitivity than nasopharyngeal wash specimens (see Collection procedure for specimen collection) and are discouraged. If swabs are submitted, the preferred specimen is one (1) e-swabs from the nares.

Specimens to be used with rapid tests generally should be collected as close as is possible to the start of symptoms and usually no more than 4-5 days later in adults. In very young children, influenza viruses can be shed for longer periods; therefore, in some instances, testing for a few days after this period may still be useful.

When Is Use of Rapid Diagnostic Tests Beneficial?

Rapid diagnostic testing for influenza should be done only when the results will affect clinical decision making.

Testing during an outbreak of acute respiratory disease can determine if influenza is the cause.

During influenza season, testing of selected patients presenting with respiratory illnesses compatible with influenza can help establish whether influenza is present in a specific patient population and help health-care providers determine how to use their clinical judgment for diagnosing and treating respiratory illness. (Testing need not be done for all patients.)

Decisions regarding isolation for hospitalized patients must be made in the following context, regardless of a negative rapid test result:

•  Assess duration of symptoms for patients with flu-like symptoms who require admission. If they have been symptomatic for less than 5 days, isolation with Droplet Precautions is required. Patients who are more than 5 days post-onset do not require isolation.
• Discontinue isolation/Droplet Precautions when patients are more than 5 days post-onset of symptoms.
• Cohort only those patients who have identical symptoms of influenza.

For more information, the following references may be helpful:
Link to CDC Clinical Description and Lab Diagnosis of Influenza:
http://www.cdc.gov/flu/professionals/diagnosis/