Utvärdering av tularemispecifik diagnostik

Abstract

Background. Tularemia is a zoonotic infection caused by the bacterium Francisella tularensis. Laboratory diagnosis consists primarily of serological methods. Enzyme- linked immunosorbent assay (ELISA) is performed at the Laboratory Medicine, Norrland’s University Hospital in Umeå. A rapid serological test, Virapid tularemia, is also used there and at the Laboratory Medicine, Östersund ́s Hospital. It is considered important to compare Virapid with ELISA as this has not been done previously on this material. Research question. How well does Virapid agree with ELISA? To what extent are there clinical indications for current tularemia when the result of Virapid and/or ELISA is positive? Is the result for either test (Virapid and ELISA) better than the other in detecting a current infection with tularemia? Materials and methods. In total, 2443 serum samples analyzed between 2011 and 2025 at Norrland’s University Hospital and 304 serum samples analyzed at Östersund ́s hospital between 2022 and 2025 were included. For all samples, simultaneous analysis had been performed with Virapid and ELISA. Sixty-two patient records were reviewed to determine correlation to current tularemia. Results. In the Umeå material, the sensitivity for Virapid in comparison with ELISA was 55.8% and the specificity was 93.9%. The corresponding values in the Östersund material were 67.9% and 92.8%. A comparison was made between ELISA and Virapid in relation to current tularemia with similar outcomes; the former assay showed a sensitivity of 88.9% and a specificity of 87.1% and the latter 83,3% and 86,4%, respectively. Conclusion. A relatively large discrepancy was seen between Virapid and ELISA. For both ELISA and Virapid, there were positive samples that did not correlate to a current infection. The result indicates that borderline responses for ELISA have low predictive value. Larger studies are required to further investigate how Virapid and ELISA relate to each other and to current tularemia.