Pyogenic arthritis caused by capnocytophaga gingivalis in an immunocompetent three-year-old male.

Capnocytophaga gingivalis is most often isolated as normal oral flora or with periodontal disease. This organism is also associated with sepsis usually in immunocompromised hosts. We identified pyogenic arthritis caused by C. gingivalis in a 3-year-old immunocompetent male, whose clinical course closely resembled monoarticular onset pauciarticular juvenile rheumatoid arthritis. This is the first report of C. gingivalis septic arthritis in the world literature, but there are increasing reports of infections with this carbon dioxide-loving organism at other sites in non-immunocompromised individuals. The subacute presentation of the monoarthritis with this organism of low virulence led to a long delay in diagnosis and treatment. Any monoarthritis must continue to raise concern about infection.