Received on November 28, 2005
Accepted on July 6, 2006

Molecular Diagnostics and Genetics

First International Proficiency Study on West Nile Virus Molecular Detection

¹ Robert Koch Institute, Berlin, Germany
² Unité de Biologie des Infections Virales Emergentes, Institut Pasteur, Lyon, France
³ Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany

^* To whom correspondence should be addressed. E-mail: niedrigm{at}rki.de.

Background: West Nile virus (WNV) molecular detection is being conducted by a growing number of laboratories, but the degree of proficiency may vary between them. External quality control is needed.

Methods: We have conducted an international quality assurance study on WNV molecular detection. Participating laboratories tested noninfectious samples inactivated by heat and gamma irradiation. Participants received 7 coded lyophilized samples containing WNV of genetic lineages 1a, 1b, and 2 at 2600 to 18 000 000 RNA copies/mL, 3 samples containing heterologous flaviviruses, and 2 negative samples.

Results: Thirty laboratories participated. The average laboratory achieved 50% detection probability from 7762 copies/mL onward (probit analysis; 95% CI = 1174-24547 copies/mL). Lineages 1a and 1b were detected with equal efficiencies, but the lineage 2 strain (Ug37) was detected at significantly lower rates. Only 27% of participants were able to detect the 6 samples containing 1.8 x 10⁴ copies/mL. Three laboratories generated false-positive results in negative samples. Six of 30 laboratories reported correct strain identification in 3 samples containing non-WNV flaviviruses. We observed a significant positive correlation between the capability of detecting non-WNV flaviviruses and detecting WNV lineage 2.

Conclusions: Most participants showed good performance in detecting lineage 1 WNV, the predominant virus in the Northern Hemisphere. The inability of some laboratories to detect even highly concentrated lineage 2 WNV downgraded the overall outcome. The lineage 2 material received through this study will provide laboratories with the necessary template for improving their assays. Such material is otherwise hard to obtain.