Rhodococcus equi pneumonia and occult HIV infection

Rhodococcus equi infection in HIV-infected individuals: case reports and review of the literature

Rhodococcus equi is a gram-positive, coryneform bacterium that causes zoonotic infection mainly in horses and foals. It sometimes affects humans presenting as cavitary pneumonia. Immunocompromised patients, including HIV-infected patients, are more susceptible to R. equi infection. We present 10 cases of R. equi infection in HIV-positive patients admitted to our institute from 1991 to June 2008. Moreover, we have reviewed 272 cases of R. equi infection in HIV-infected persons, published from 1986 through 2008. With respect to the literature data, the R. equi strains isolated in our case series showed lower sensitivity to ceftriaxone, amoxicillin/clavulanic acid, and cotrimoxazole. Prompt diagnosis, early initiation of antiretroviral treatment and combined antimicrobial treatment seem to be effective to eradicate the infection and to improve the outcome.

Rhodococcus equi pneumonia in patients infected with the human immunodeficiency virus. Report of 2 cases and review of the literature

Rhodococcus equi is a cause of lung infection in immunosuppressed hosts. Since the start of the HIV epidemic, 76 cases of R. equi lung infection (MEDLINE 1985-96) affecting this population have been described. We report 2 additional cases and review the clinical data, radiological findings, treatment and outcome of these 78 patients. The mean age of these patients was 33 y; 69 were male. 71 met the criteria for AIDS (CDC 1993). Fever and cough were the presenting complaints in the majority of patients (84.3%). A single cavitary lung lesion in the upper lobes was the most common radiological finding (57.7%), although multiple cavitations, alveolar infiltrates and pleural effusion were also found. Treatment usually was based on synergistic antibiotic combinations for a long period of time determined on an individual basis. Surgery was performed only in 11 patients. Death attributable directly to R. equi infection is low (15.4%), however only half of the patients (53.8%) were completely cured. We conclude that R. equi infection should be strongly considered in any HIV patient who presents with cavitary lesions in the lung, especially if mycobacteria are not identified. Treatment must be based on synergistic antibiotic combinations, and surgery relegated to cases of chronic single cavitary lesions not responding to antibiotics.

Rhodococcus equi infection in non-HIV-infected patients. Two case reports and review

OBJECTIVE: To review two recent cases in HIV-negative subjects in the light of literature reports (52 patients without HIV infection till 1994). METHODS: Epidemiology (animal contacts, risk factors, year, country), clinical presentation, diagnostic methods (X-ray, tomography, microbiological techniques), therapeutic approach (antibiotics, surgery) and outcome were evaluated on the basis of clinical literature reports. RESULTS: Tumors constituted an important predisposing factor and less frequently hepatobiliary pathology, rheumatologic diseases, iatrogenic causes, psychiatric pathology and trauma. Exposure to animals was reported by 55% of the patients. Pneumonia and pleurisy, without preferential localization, were detected in 50% of the patients. Etiologic diagnosis was usually obtained after an invasive collection. Combined medical therapy and surgery were required by 27.8% of the patients, and 16.7% of the patients died. CONCLUSIONS: In recent years the number of Rhodococcus equi cases has been rising also in HIV-negative patients. The infection is ubiquitous. Accurate diagnosis and the prompt selection of the most appropriate therapy depend on close cooperation between clinicians and microbiologists.

Radiologic features of Rhodococcus equi pneumonia in AIDS

This report outlines the radiological features observed in three cases of Rhodococcus equi (R. equi) pneumonia in AIDS (acquired immunodeficiency syndrome) and reviews another 45 radiological reports published of this emerging opportunistic pneumonia in Human Immunodeficiency Virus (HIV) infected patients. The clinical signs in our three patients consisted in a subacute onset of respiratory symptoms and fever. A low lymphocyte count (< 200 cells/mm3), pulmonary infiltrates, and pleural effusion was present in all three cases. Cavitary pneumonia was observed in two patients, and pericardial effusion in another. In this series CD4 lymphocyte count < 200/mm3 was seen in 29 of the 48 patients (60.4%). All 48 patients had abnormal findings on chest radiographs. Abnormalities involved the upper lobes in 26 of the 48 patients (55%). Cavitation was reported in 37 of the 48 cases (77%). R. equi pneumonia may not be as the paucity of case reports suggest. Consequently, a cavitary pneumonia in HIV infected patients with a low CD4 lymphocyte count (< 200 mm3) with a subacute onset, an upper lobe predilection, and/or a poor response to conventional antibiotic therapy should be considered as suspect of R. equi infection.

Transfer of a CD4+ Th1 cell line to nude mice effects clearance of Rhodococcus equi from the lung

Rhodococcus equi, and intracellular respiratory pathogen, causes sever e granulomatous pneumonia in humans with AIDS and in young horses. Pulmonary clearance of R. equi requires functional CD4+ T cells and gamma interferon (IFN-gamma) expression from bronchial lymph node cells. The purpose of this study was to investigate whether R. equi-specific CD4+ Th1 cells could effect clearance of R. equi from the lung. Adoptive transfer of a clearance of R. equi from the lungs. In contrast, mice transfused with a R. equi-specific CD4+ Th2 cell line expressed interleukin-4 but not IFN-gamma mRNA, failed to clear pulmonary infection, and developed granulomas in the lung. Control mice, which did not receive cells, did not produce IFN-gamma or interleukin-4 and developed small pulmonary granulomas. These results clearly show that a Th1 response is sufficient to effect pulmonary clearance of R. equi.

Rhodococcus equi infection in HIV-positive subjects: a retrospective analysis of 24 cases

Rhodococcus equi causes a rare infection in immunocompromised hosts. We describe 24 cases of infection in patients with AIDS-related complex (ARC)/acquired immunodeficiency syndrome (AIDS). Pneumonia was always the first manifestation of R. equi infection, but extrapulmonary involvement was also observed. The main sources of bacteria were sputum, bronchial washings and blood. The strains isolated were mainly susceptible to erythromycin, vancomycin, teicoplanin, rifampicin, imipenem and aminoglycosides. Initial treatment should involve an intravenously administered antibiotic combination therapy including imipenem or vancomycin or teicoplanin, followed by orally administered maintenance combination therapy. Drug combinations should be investigated for serum bactericidal activity in vitro. Surgery does not increase survival time and should only be performed in cases that do not respond to antibiotic treatment. Presumptive risks of infection (contact with horses or farm dust, or cohabiting with people affected by R. equi infection) were present in more than 50% of patients. This finding, and the frequency of bacteria in the sputum, are not sufficient proof of transmission between humans, but do suggest the need for respiratory isolation of patients affected by R. equi pneumonia.

Cytokine modulation alters pulmonary clearance of Rhodococcus equi and development of granulomatous pneumonia

Rhodococcus equi, a facultative intracellular bacterium, causes chronic, often fatal granulomatous pneumonia in young horses and in humans with AIDS. The inability of host alveolar macrophages to kill intracellular R. equi results in the development of granulomas and progressive loss of pulmonary parenchyma. Clearance of the organism from the lung requires functional CD4+ T cells. The purpose of this study was to identify the cytokine effector mechanisms that mediate clearance of R. equi from the lung. Mice were treated with monoclonal antibodies (MAbs) to either gamma interferon (IFN-gamma) or interleukin-4 (IL-4) to determine the role of endogenous production of these cytokines in pulmonary clearance of R. equi. Mice treated with an anti-IL-4 or isotype control MAb cleared R. equi by 21 days postinfection and expressed increased levels of IFN-gamma mRNA, as detected by transcriptional analysis of bronchial lymph node CD4+ T cells. In contrast, mice treated with the anti-IFN-gamma MAb failed to express detectable IFN-gamma mRNA, expressed increased levels of IL-4 mRNA, failed to clear pulmonary infection, and developed pulmonary granulomas with large numbers of eosinophils. The enhancement of IL-4 mRNA expression and a predominance of eosinophils in pulmonary lesions of anti-IFN-gamma-treated mice suggest that a nonprotective Th2 response in involved in disease pathogenesis. The association of increased bronchial lymph node CD4+ T-cell IFN-gamma mRNA expression with pulmonary clearance of R. equi suggests that a Th1 response is protective.