Validity Of The Screening Test For H1N1 (Swine) Flu
In a conversation at the place of work of one InsideSurgery editor this last week, a visiting official from the Centers for Disease Control (CDC) discussed the poor sensitivity and specificity of the screening test used in adults for detecting presence of the H1N1 virus.
The correct technique for sampling is a nasopharyngeal swab which requires an experienced technician to perform it correctly. Too often, the swab is not placed “far enough” up the nose.
If done correctly, the sampling is very uncomfortable for the few seconds it takes. As flu professionals say, if the patient does not want to slug the tester after the swab is obtained, it probably was not performed correctly.
Even in the setting of an adequate sample, the shedding of virus in adults is low, leading to a sensitivity (accuracy rate) of about 40%.
So, a negative screening for H1N1 in adults in no way rules out an infection with this worrisome influenza virus.