History and clinical findings: A 23-year-old woman was admitted with typical signs of an acute urinary tract infection: fever, pain on tapping over both renal areas and in both flanks, urgency and dysuria. She had a history of renal colic with spontaneous passage of a renal stone.
Investigations: There was marked leukocytosis and raised C-reactive protein, leukocyturia and haematuria, but no nitrites or protein in the urine. All blood and urine cultures were sterile and renal ultrasound was unremarkable.
Diagnosis, treatment and course: As signs and laboratory data indicated acute pyelonephritis (PN) she was treated with gyrase inhibiting antibiotics. But while symptoms improved, fever, leukocyturia and haematuria continued; no micro-organism could be demonstrated. Mycoplasma was therefore considered as a rare cause of PN. Special urine cultures then grew M. hominis, > 10(5) organisms/ml. On the basis of sensitivity tests doxycycline was administered. All symptoms quickly improved and all inflammation parameters and urine sediments became normal.
Conclusion: In rare instances M. hominis may be isolated as the causative organism of PN. If, in cases with appropriate symptoms, routine tests fail to demonstrate the causative agent, M. hominis should be included in the differential diagnosis.