Laboratory testing practices for West Nile virus in the United States.

We surveyed state public health and commercial diagnostic reference laboratories regarding current testing practices for West Nile virus (WNV). The majority of WNV testing is now performed in commercial diagnostic reference laboratories using commercially available Food and Drug Administration-cleared kits labeled for the presumptive diagnosis of WNV. However, only 25% of surveyed state public health or commercial diagnostic reference laboratories currently have the capacity to perform the recommended confirmatory testing. These findings indicate the need for both manufacturers and laboratories to monitor the performance of these WNV test kits. Further, clinicians should be aware of the limitations of these kits and the need for additional testing to confirm a diagnosis of WNV disease.