This test should be considered if the result would alter treatment. Preferred specimens are a nasopharyngeal swab, a nasal aspirate, or a nasopharyngeal swab combined with an oropharyngeal swab. Swabs should have a synthetic tip (e.g., Dacron, polyester) and an aluminium or plastic shaft, and should be immediately placed and transported in 1 to 3 mL of viral transport medium.

Advantages are that the test is relatively easy to perform and results can be obtained as early as 30 minutes. Disadvantages are its low sensitivity (10% to 88%), average specificity (51% to 100%), and inability to determine the subtype of influenza A. [55]

A negative result does not rule out H1N1 swine influenza infection.

Treatment should not be withheld in patients at high risk of influenza complications (children, adults >65 years, pregnant women, those with comorbid conditions) while awaiting test results.

The most definitive test for diagnosing H1N1 swine influenza infection.

Treatment should not be withheld in patients at high risk of influenza complications (children, adults >65 years, pregnant women, those with comorbid conditions) while awaiting test results.

Results may not return in a timely fashion, so clinical utility of this test is limited.

Treatment should not be withheld in patients at high risk of influenza complications (children, adults >65 years, pregnant women, those with comorbid conditions) while awaiting test results.

Direct or indirect immunofluorescence assays can be used to distinguish between influenza A and influenza B viruses. The sensitivity is low, and a negative result does not exclude infection.

Treatment should not be withheld in patients at high risk of influenza complications (children, adults >65 years, pregnant women, those with comorbid conditions) while awaiting test results.

Not needed for routine cases, but WBC count may be raised if bacterial complications have developed.