BACKGROUND: Pelvic-abdominal actinomycosis is a rare chronic condition caused by an anaerobic, gram-negative rod-shaped commensal bacterium of the Actinomyces species. When Actinomyces becomes pathogenic, it frequently causes a chronic infection with granulomatous abscess formation with pus. Due to diversity in clinical and radiological presentation, actinomycosis can easily be mistaken for several other conditions. Peritonitis without preceding abscess formation caused by Actinomyces species has been described in only few cases before in literature.

CASE REPORT: We report a case of spontaneous pelvic-abdominal peritonitis with presence of pneumoperitoneum and absence of preceding abscesses due to acute actinomycosis mimicking a perforation of the proximal jejunum in a 42-year-old female with an intra-uterine contraceptive device in place. Explorative laparotomy revealed 2 liters of odorless pus but no etiological explanation for the peritonitis. The intra-uterine contraceptive device was removed. Cultivation showed growth of Actinomyces turicensis. The patient was successfully treated with penicillin.

CONCLUSIONS: In the case of primary bacterial peritonitis or lower abdominal pain without focus in a patient with an intra-uterine device in situ, Actinomyces should be considered as a pathogen.

Keywords: Diagnosis, Differential, Actinomycosis - etiology, Intestinal Perforation - diagnosis, Intrauterine Devices - adverse effects, Jejunal Diseases - diagnosis, Peritonitis - microbiology