Clinical impact of timely reporting of IgM for West Nile Virus

In 2002 diagnostic testing for West Nile Virus (WNV) infection was not ideal because commercial products were unavailable. Although testing was performed without charge by public health (PH), testing is not intended to be used for patient management and generally results are not available in a timely or reliable manner.

This study was conducted to determine the clinical impact of having WNV serology available by a diagnostic laboratory within a few days of sample collection.

An IgM immunoassay (FT, from Focus Technologies) was performed August 13, 2003 to October 31, 2003 Monday, Wednesday and Friday in our hospital's virology laboratory with split sample testing at PH. All results (positive and negative) were called to physicians.

Turn-around time for the FT assay was within 0-3 days; for PH, it was approximately 8 days. Of 95 samples, 6 were positive and 89 negative. For the FT negative samples, all were concordant with PH, but four FT positive samples (three sera and one cerebrospinal fluid) were discrepant. After resolution of the discrepancies, the FT test had a sensitivity of 100% and a specificity of 99%. Physicians reacted positively to having results faster. Fifty-eight percent of the results had clinical impact, 22% had undetermined impact, 13% were patient requests, and 4% had no impact. Concluding, the FT assay is 100% sensitive and 99% specific and in 58% there was clinical impact for WNV reporting in a timely manner.