Uncommon lymphocutaneous cellulitis after insect bite: a case report of primary cutaneous nocardiosis and literature review.

Nocardia is a genus of aerobic actinomycetes that are usually responsible for opportunistic infection in immunocompromised patients. Less frequently nocardiosis can interest immunocompetent population, causing especially primary cutaneous infections. Cutaneous involvement by Nocardia spp. may occur mostly as one of four clinical manifestations: superficial cellulitis or abscess, mycetoma, lymphocutaneous (also defined "sporotrichoid") infection and secondary cutaneous involvement from systemic disease. Infections usually present after minor local injury, especially in traumatic outdoor activities (e.g. gardeners, farmers, road accidents), with subsequent environmental contamination of the wound. In sporadic cases cutaneous infection follows an insect bite. Microbiological diagnosis is often difficult to obtain and N. brasiliensis is the species isolated in most cases (80%). We present the case of a 45-year-old female with fever and a painful and necrotizing lesion on her right leg with secondary ascending lesions occurred on the homolateral knee and consensual groin lymphadenopathy after insect sting (maybe a spider bite). Cultures on skin biopsy identified Nocardia brasiliensis. Infection was completely healed after 5 months of targeted antibiotic therapy. In addition, we performed a literature review of all cutaneous nocardiosis cases in immunocompetent individuals, finding that only in 22 cases the infection presented after insect bite; in most of these cases lymphocutaneous manifestation was seen and N. brasiliensis was the Nocardia species isolated. Our case, along with others in literature, reveals that the real burden of soft-tissues nocardiosis seems low but probably many cases might go undiagnosed because of difficulties in microbiology diagnosis. Primary cutaneous nocardiosis should be included in the diagnostic pathway in cases of cellulitis following insect bite or sting, especially when localized to extremities.