Several studies have failed to detect Borrelia burgdorferi, which is the causative agent of Lyme disease, in patients from the southern United States.[5][6] This disease may be caused by the related bacterium Borrelia lonestari,[7][8] which is a spirochete first isolated in culture in 2004.[9] However, this conclusion is controversial since the spirochete is not detected in all cases of the syndrome,[6] which has led some authors to argue that the illness is not caused by a bacterial pathogen.[10]