Sacroiliitis and osteomyelitis caused by serotype 3 Streptococcus pneumoniae in a previously healthy adult: a case report Yoshiro Hadano,1 Bin Chang2 1Department of Infectious Diseases, St. Mary’s Hospital, Kurume, Fukuoka, Japan; 2Department of Bacteriology I, National Institute of Infectious Diseases, Shinjuku-ku, Tokyo, Japan Abstract: Streptococcus pneumoniae is a rare cause of pyogenic sacroiliitis and osteomyelitis. A case of pneumococcal sacroiliitis and osteomyelitis is reported herein. The patient was a previously healthy 54-year-old man with a 3-day history of fever and a 3-week history of increasing right-side thigh pain. Computed tomography showed bone destruction of the right sacroiliac joint with perifocal abscess formation in the right iliac muscle. The patient was diagnosed with pyogenic sacroiliitis and osteomyelitis with a right iliac muscle abscess. Mucoid serotype 3 S. pneumoniae was obtained by culture of abscess. The patient was successfully treated with an 8-week course of antibiotics. Keywords: Streptococcus pneumoniae, pyogenic sacroiliitis, osteomyelitis, serotype 3, invasive pneumococcal diseases