A labourer involved with repair-work of sewers was admitted with fever, jaundice and renal failure. The most appropriate test to diagnose the infection in this patient is:

This patient is suffering from Leptospirosis which is common in sewerage workers. The most appropriate test to diagnose the infection is microscopic agglutination test using live antigen, which is complicated but sensitive. The diagnosis of leptospirosis is primarily serologic. The standard serologic test (microscopic agglutination) is often limited to reference laboratories. Ref: Textbook of Microbiology By Ananthanarayan and Panicker, 6th Edition, Page 359 ; Ray C.G., Ryan K.J. (2010). Chapter 37. Spirochetes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.