Rare AIDS co-infection with Talaromyces marneffei and Rhodococcus equi reported

The case, published as a case report in BMC Infectious Diseases, describes how the combination of bone marrow culture, bronchoalveolar lavage fluid culture and targeted next-generation sequencing was needed to untangle the true cause of the man’s illness.

The patient arrived at hospital on June 25, 2025, after two months of fever, cough and progressive weight loss of nine kilograms. He carried a CD4+ T cell count of 72 cells per microlitre, a level of immunosuppression at which opportunistic infections become a constant threat. A local hospital had previously diagnosed him with pulmonary tuberculosis, a label that shaped his early treatment.

The pivotal clue was a laboratory finding that is easy to misread. Acid-fast positive cocci were observed in sputum smears on June 26. Because acid-fast staining is classically associated with mycobacteria, the appearance of acid-fast positive organisms can point clinicians toward tuberculosis, even when the organisms in question are not mycobacteria at all. R. equi is a coccus that retains the acid-fast stain, and the report’s authors emphasize that this property makes it easily mistaken for tuberculosis in HIV-positive patients.

Definitive answers came quickly once deeper sampling was performed. Bone marrow culture confirmed R. equi sepsis on June 27. Two days later, on June 29, bronchoalveolar lavage fluid culture and targeted next-generation sequencing identified co-infection with both R. equi and T. marneffei. The sequencing approach, which targets specific pathogen genetic material, allowed the team to detect organisms that conventional workup had missed or misattributed.

Once the etiology was clear, the antimicrobial regimen was adjusted to match the two pathogens. Levofloxacin, amikacin and azithromycin were directed at R. equi, while amphotericin B was initiated for T. marneffei. On June 30, the patient’s antiretroviral therapy was optimized to a regimen of tenofovir disoproxil fumarate, lamivudine and dolutegravir.

The clinical course was not smooth. On July 1, oral candidiasis was diagnosed and treated with sodium bicarbonate mouthwash. On July 7, the patient developed septic shock, with a blood pressure of 87 over 56 millimetres of mercury, requiring immediate resuscitation. By July 9 his condition had stabilized, and he was discharged on oral itraconazole, levofloxacin and antiviral therapy.

The report links the episode of septic shock to a probable immune reconstitution inflammatory syndrome, or IRIS, which the authors say emerged shortly after the antiretroviral regimen was optimized.

The authors draw several practical lessons from the case. First, R. equi, because of its acid-fast positivity, belongs on the differential diagnosis when HIV-positive patients present with findings suggestive of tuberculosis. Second, they argue that definitive etiological diagnosis through bone marrow aspiration and bronchoscopy, combined with targeted next-generation sequencing, is essential for distinguishing R. equi and T. marneffei co-infection from tuberculosis and enabling targeted combination therapy. Third, they advise clinicians to maintain a high index of suspicion for opportunistic co-infections in advanced AIDS when presentations are atypical.

As a single case report, the study documents one patient’s diagnostic pathway and outcome rather than testing any treatment strategy in a controlled setting. Its value lies in the diagnostic lesson it records: in a patient with profound immunosuppression and an atypical presentation, staining patterns alone can mislead, and culture combined with molecular sequencing identified a life-threatening co-infection that a tuberculosis label had obscured.

Subject of Research: A rare case of co-infection with Talaromyces marneffei and Rhodococcus equi in a patient with AIDS, initially misdiagnosed as tuberculosis.

Article Title: A case report of complex co-infection with Talaromyces marneffei and Rhodococcus equi in a patient with AIDS

Article References: Gao, L., Peng, Y., Li, Z., Cai, X., Feng, Y., Dong, X., & Xia, X. (2026). A case report of complex co-infection with Talaromyces marneffei and Rhodococcus equi in a patient with AIDS. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14333-z

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14333-z

Keywords: AIDS, Talaromyces marneffei, Rhodococcus equi, co-infection, opportunistic infection, tuberculosis misdiagnosis, targeted next-generation sequencing, immune reconstitution inflammatory syndrome, bone marrow culture, bronchoalveolar lavage, case report, BMC Infectious Diseases