A Case Report of a Forehead Abscess Caused by Nocardia concava in a Patient with AIDS.

Nocardia species are obligate aerobic actinomycetes. Human nocardiosis typically occurs in immunocompromised hosts and most commonly manifests as primary suppurative pulmonary infection. Hematogenous dissemination can lead to extrapulmonary involvement, with the central nervous system being the most frequent secondary site, followed by skin and subcutaneous soft tissues; pericardium, lymph nodes, and joints are affected only rarely. A 50-year-old HIV-positive man was admitted with a 1-month history of oral blood blisters and ecchymoses of the extremities. A right forehead abscess that developed during hospitalization yielded pus that was identified as Nocardia concava by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and confirmed by 16S rRNA gene sequencing. Initial management included antiretroviral therapy, systemic glucocorticoids, and intravenous immunoglobulin; subsequent targeted antimicrobial therapy with linezolid plus trimethoprim-sulfamethoxazole, instituted upon microbiological confirmation, resulted in clinical improvement and discharge. To our knowledge, this is the first case report of forehead abscess infection caused by N. concava in an acquired immunodeficiency syndrome (AIDS) patient. Human infections due to this organism remain extremely rare. Moreover, the infection site in this case was not the commonly affected lung or central nervous system, typically involved in nocardiosis, which resulted in atypical clinical manifestations prone to missed diagnosis or misdiagnosis. In this case, precise etiological identification allowed for early definitive diagnosis and favorable clinical outcomes. This case underscores the importance of increased vigilance for rare Nocardia infections in severely immunocompromised patients. For unexplained skin and soft tissue abscesses, early etiological examination is critical, and targeted antimicrobial therapy based on drug susceptibility can significantly improve prognosis.