Actinomycosis: etiology, clinical features, diagnosis, treatment, and management Florent Valour,1–3 Agathe Sénéchal,1,2 Céline Dupieux,2–4 Judith Karsenty,1,2 Sébastien Lustig,2,5 Pierre Breton,2,6 Arnaud Gleizal,2,7 Loïc Boussel,2,8,9 Frédéric Laurent,2–4, Evelyne Braun,1 Christian Chidiac,1–3 Florence Ader,1–3 Tristan Ferry1–3 1Service des Maladies Infectieuses et Tropicales, Hospices Civils de Lyon, Groupement Hospitalier Nord, Lyon, France; 2Université Claude Bernard Lyon 1, Lyon, France; 3Centre International de Recherche en Infectiologie, CIRI, INSERM U1111, CNRS UMR5308, ENS de Lyon, UCBL1, Lyon, France; 4Laboratoire de Bactériologie, Centre de Biologie du Nord, Hospices Civils de Lyon, Groupement Hospitalier Nord, Lyon, France; 5Chirurgie Orthopédique, Hospices Civils de Lyon, Groupement Hospitalier Nord, Lyon, France; 6Stomatologie et Chirurgie Maxillo-faciale, Hospices Civils de Lyon, Groupement Hospitalier Sud, Lyon, France; 7Chirurgie Maxillo-faciale, Hospices Civils de Lyon, Groupement Hospitalier Nord, Lyon, France; 8Radiologie, Hospices Civils de Lyon, Groupement Hospitalier Nord, Lyon, France; 9Creatis, CNRS UMR 5220, INSERM U1044, Université Lyon 1, INSA Lyon, Lyon, France Abstract: Actinomycosis is a rare chronic disease caused by Actinomyces spp., anaerobic Gram-positive bacteria that normally colonize the human mouth and digestive and genital tracts. Physicians must be aware of typical clinical presentations (such as cervicofacial actinomycosis following dental focus of infection, pelvic actinomycosis in women with an intrauterine device, and pulmonary actinomycosis in smokers with poor dental hygiene), but also that actinomycosis may mimic the malignancy process in various anatomical sites. Bacterial cultures and pathology are the cornerstone of diagnosis, but particular conditions are required in order to get the correct diagnosis. Prolonged bacterial cultures in anaerobic conditions are necessary to identify the bacterium and typical microscopic findings include necrosis with yellowish sulfur granules and filamentous Gram-positive fungal-like pathogens. Patients with actinomycosis require prolonged (6- to 12-month) high doses (to facilitate the drug penetration in abscess and in infected tissues) of penicillin G or amoxicillin, but the duration of antimicrobial therapy could probably be shortened to 3 months in patients in whom optimal surgical resection of infected tissues has been performed. Preventive measures, such as reduction of alcohol abuse and improvement of dental hygiene, may limit occurrence of pulmonary, cervicofacial, and central nervous system actinomycosis. In women, intrauterine devices must be changed every 5 years in order to limit the occurrence of pelvic actinomycosis. Keywords: Actinomyces spp., sulfur granule, osteomyelitis, lumpy jaw syndrome