A Rare Dual Infection in a Homeless Patient: Diagnostic Challenges of <i>Naganishia</i> <i>diffluens</i> and <i>Bartonella</i> <i>quintana</i> Co-Infection

We report a case of dual infection with Naganishia diffluens (formerly Cryptococcus diffluens) and Bartonella quintana in a homeless patient in Mexico City. The patient exhibited sporotrichoid lesions along the lymphatic channels. This typical presentation initially suggested a fungal infection caused by Sporothrix species, which are common in such lesions in Mexico. Additionally, the presence of lice infestation raised suspicions of Bartonella infection, as human body lice often transmit it and is a concern in homeless populations. The infections were conclusively identified through a comprehensive diagnostic approach that included microbiological culture on PDA media, microscopic examination, molecular identification via PCR, and amplification and sequencing of the internal transcribed spacer (ITS) region for fungi, as well as the gltA gene for Bartonella. Immunological confirmation was also performed with a precipitin assay using patient serum tested against fungal extracts. Naganishia diffluens was isolated from skin lesion scrapings, and Bartonella quintana was identified from a blood sample. This case underscores the importance of employing thorough laboratory techniques for accurate diagnosis and effective management of similar cases.