A rise in false-positive test results obtained with commercially available West Nile virus test kits has led the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), and state health departments to investigate the cause of the false positives. For the time being, the manufacturer of the kits has issued a voluntarily recall of the implicated tests.
The kit—an immunoglobulin M capture enzyme-linked immunosorbent assay (WNV IgM capture ELISA)—was manufactured by Inverness Medical (Princeton, NJ). On October 8, 2008, the manufacturer voluntarily recalled two lots of their PanBio WNV IgM capture ELISA kit. One lot (#07262) was only distributed in Canada. The other lot (#08118) was distributed from July to September 2008 to four laboratories in the United States.
The laboratories that used the recalled test kit include ViroMed (Minnetonka, MN), Meritcare Health System (Fargo, ND), Pennsylvania Department of Health (Exton, PA), and Baylor University Medical Center (Dallas, TX). Based on the investigation to date, this increase in false-positive results appears to be limited to these two lots of the PanBio kit.
The CDC and the FDA will continue to monitor and evaluate any additional reports of false-positive tests that may have resulted from previous lots.
False-positive test results occurred between July and September 2008, and may have led to an incorrect diagnosis in some patients. If a patient is still experiencing symptoms, additional evaluation and alternative diagnoses should be considered. State health departments can help health care providers decide if a new serum specimen should be obtained to test for WNV or another etiology.