Actinomyces timonensis: A Novel Pathogen to Not Overlook in Immunocompetent Children With Recurrent Cutaneous Abscesses

To the Editors: Actinomyces timonensis is a newly identified species of the genus Actinomyces, first isolated from a 13-year-old girl with sacroiliitis.1 To date, no other human isolations have been reported. We present a case of recurrent cutaneous abscesses due to A. timonensis in a previously healthy 2-year-old girl, describing clinical management, follow-up and microbiology workup. She presented with a 5-month history of recurrent cutaneous abscesses despite multiple antibiotics. Born at 41 weeks via cesarean, her neonatal period was uneventful, and she had no significant past infections requiring hospitalization. The family history was negative for serious illnesses. One month before our assessment, she required surgical drainage for a subcutaneous mass in the left cervical region, followed by antibiotics (amoxicillin-clavulanate and cefixime). She was afebrile and systemically well; physical examination revealed multiple furuncles on chest and neck, impetiginized scalp lesions and cutaneous infections on her fingers (Fig. 1).FIGURE 1.: Recurrent abscesses in a immunocompetent child. A, B, and C: Patient before the treatment was carried out at our center. D: Resolution of the patient’s lesions at the end of the treatment.Blood tests were normal, with an initially elevated total IgE level (1434 kU/L), which later decreased. Immunologic investigations, including IgA, IgM, IgG and IgG subclasses, antibody titers to tetanus, Haemophilus influenzae, serotypes in the protein-conjugated pneumococcal vaccine and HIV tests were negative. Immune phenotype, natural killer cell function tests, nitroblue tetrazolium test and the dihydrorhodamine assay were normal. Culture analysis of the lesion swab revealed A. timonensis, identified with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Tests for Mycobacterium tuberculosis and nontuberculous mycobacteria were negative. The patient was initially treated with teicoplanin and later switched to meropenem based on susceptibility testing, followed by clindamycin. Skin lesions improved and resolved completely, with no recurrence over a 1-year follow-up. This is the first case of recurrent cutaneous abscesses due to A. timonensis in an immunocompetent child. Indeed, A. timonensis in children was isolated only from a 13-year-old girl with sacroiliitis.1 Actinomycosis is a slowly progressive bacterial infection caused by Actinomyces, rare in pediatric patients and often misdiagnosed. Actinomyces is a normal commensal in the human oropharynx, gastrointestinal and urogenital tracts, becoming pathogenic when mucous membranes are compromised. Cervicofacial actinomycosis is the most common form, associated with gingival disease, oral trauma, dental caries or immunocompromised states.2–4 Appropriate treatment typically requires prolonged intravenous antibiotics.5 Treatment details in the previously documented case of A. timonensis infection were not reported.1 Our patient received 3 weeks of intravenous antibiotics followed by 2 weeks of oral therapy, leading to resolution. The antibiotic regimen was based on susceptibility tests showing sensitivity to clindamycin, meropenem, penicillin G, piperacillin-tazobactam and vancomycin but resistance to metronidazole. No predisposing conditions including trauma, dental abnormalities or primary and acquired immunodeficiencies were found in our patient. In addition, oral swabs for A. timonensis were always negative. This case highlights the importance of considering actinomycosis in cases of subacute or chronic skin infections unresponsive to standard antibiotics, even in immunocompetent children. Prompt and accurate diagnosis is crucial for appropriate treatment and preventing recurrence or spread. Further studies are needed to understand effective treatment strategies for A. timonensis, given the scarcity of documented cases and antibiotic resistance data.