Diagnosing Rhodococcus equi infections in a setting where tuberculosis is highly endemic: a double challenge

Rhodococcus equi bacteremia with necrotizing pneumonia and brain abscess in a newly diagnosed HIV patient in Saudi Arabia: A case report and review of literature

Rhodococcus equi is a Gram-positive coccobacillus that falls within the category of aerobic actinomycetes. The Rhodococcus genus belongs to the nocardioform bacteria group. This microorganism has been found in various settings, including natural environments, animals, and particularly in individuals with compromised immune systems, such as those living with HIV. Notably, there is an increasing number of reports concerning R. equi infections in transplant recipients and even individuals with a normally functioning immune system. Traditionally, R. equi has been primarily associated with pulmonary infections, but there is a growing body of evidence documenting its involvement in extrapulmonary infections. In this report, we present a case involving a newly diagnosed HIV patient who experienced R. equi -induced necrotizing pneumonia, bacteremia, and a brain abscess in newly diagnosed HIV patient. It is important to note that a direct Gram stain may potentially lead to misclassification of such microorganisms as contaminants. Microbiologists should therefore prioritize the careful examination of colony morphology, biochemical reactions, and consider the limitations of automated machine databases. Furthermore, they should correlate their identification findings with clinical data to ensure optimal patient care and management, especially in the context of an immunocompromised state.

Pulmonary Talaromycosis: A Window into the Immunopathogenesis of an Endemic Mycosis

Talaromycosis is an invasive mycosis caused by the thermally dimorphic saprophytic fungus Talaromyces marneffei (Tm) endemic in Asia. Like other endemic mycoses, talaromycosis occurs predominantly in immunocompromised and, to a lesser extent, immunocompetent hosts. The lungs are the primary portal of entry, and pulmonary manifestations provide a window into the immunopathogenesis of talaromycosis. Failure of alveolar macrophages to destroy Tm results in reticuloendothelial system dissemination and multi-organ disease. Primary or secondary immune defects that reduce CD4+ T cells, INF-γ, IL-12, and IL-17 functions, such as HIV infection, anti-interferon-γ autoantibodies, STAT-1 and STAT-3 mutations, and CD40 ligand deficiency, highlight the central roles of Th1 and Th17 effector cells in the control of Tm infection. Both upper and lower respiratory infections can manifest as localised or disseminated disease. Upper respiratory disease appears unique to talaromycosis, presenting with oropharyngeal lesions and obstructive tracheobronchial masses. Lower respiratory disease is protean, including alveolar consolidation, solitary or multiple nodules, mediastinal lymphadenopathy, cavitary disease, and pleural effusion. Structural lung disease such as chronic obstructive pulmonary disease is an emerging risk factor in immunocompetent hosts. Mortality, up to 55%, is driven by delayed or missed diagnosis. Rapid, non-culture-based diagnostics including antigen and PCR assays are shown to be superior to blood culture for diagnosis, but still require rigorous clinical validation and commercialisation. Our current understanding of acute pulmonary infections is limited by the lack of an antibody test. Such a tool is expected to unveil a larger disease burden and wider clinical spectrum of talaromycosis.

Rhodoccocus Equi Pneumonia and Paradoxical Immune Reconstitution Inflammatory Syndrome in a Patient with Acquired Immune Deficiency Syndrome (AIDS)

Patient: Male, 47

Final Diagnosis: Rhodococcus equi pneumonia • paradoxical immune reconstitution inflammatory syndrome

Symptoms: Cough • fever • shorthness of breath

Medication: —

Clinical Procedure: —

Specialty: Infectious Diseases