Diagnostic algorithm for acute Q fever in an outbreak setting introduced 1 May 2009 in the Jeroen Bosch Hospital, 's-Hertogenbosch, Netherlands. Abbreviations: ELISA MII-screen, enzyme-linked immunosorbent assay for immunoglobulin M antibodies to Coxiella burnetii phase II antigens; IFA, immunofluorescence assay; IgM-II antibodies, immunoglobulin M antibodies to C. burnetii phase II antigens; IgG-II antibodies, immunoglobulin G antibodies to C. burnetii phase II antigens; IgG-I antibodies, immunoglobulin G antibodies to C. burnetii phase I antigens.