Rat bite fever as a presenting illness in a patient with AIDS.

The etiology of culture-negative septic arthritis is poorly characterised in persons infected with human immunodeficiency virus (HIV). New molecular methods may assist in the investigation of culture-negative infections of sterile sites, including septic arthritis. We describe the first case of septic arthritis due to the cause of rat bite fever (RBF), Streptobacillus moniliformis, confirmed by 16S rRNA sequence analysis, in a patient with newly diagnosed HIV infection.