Evaluation of a commercial immunochromatographic assay for the serologic diagnosis of tularemia

Tularemia is an infection caused by Francisella tularensis with a worldwide distribution in the northern hemisphere and diverse clinical manifestations. Serology plays an important role in the diagnosis of tularemia. A commercially available immunochromatographic assay (ICA) for the serologic diagnosis of tularemia (VIRapid Tularemia, Vircell, Granada, Spain) was evaluated, and the performance was compared with that of the current standard, the microagglutination test (MA). A panel of 221 sera from 109 cases of tularemia was tested as well as 236 sera from normal individuals or individuals with other infectious or autoimmune diseases. The ICA demonstrated 91.5% (κ = 0.91) agreement with the reference method (MA) and gave an overall sensitivity of 99.3% and a specificity of 94.6%. No cross-reactivity was observed in the ICA with serum samples from normal individuals and patients with autoimmune diseases and bacterial, viral, and parasitic infections, although 4 of 50 patients with brucellosis demonstrated positive results in the ICA. The performance of ICA was simple, and it requires no specialized equipment. The ease of use and significantly high sensitivity and specificity of ICA make it a good choice for diagnostic testing and a valuable field test to support a presumptive diagnosis of tularemia in remote areas.