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

Prognosis and clinical evaluation of infection caused by Rhodococcus equi in HIV-infected patients: a multicenter study of 67 cases

OBJECTIVE

To assess the clinical characteristics and the factors that influenced the prognosis of patients with HIV and infection caused by Rhodococcus equi.

DESIGN

Observational, multicenter study in 29 Spanish general hospitals.

SETTING

These hospitals comprised a total of 20,250 beds for acute patients and served a population of 9,716,880 inhabitants.

PATIENTS

All patients with HIV and diagnosed R equi infection until September 1998.

RESULTS

During the study period, 19,374 cases of AIDS were diagnosed. Sixty-seven patients were included (55 male patients; mean +/- SD age, 31.7 +/- 5.8 years). At the time of diagnosis of R equi infection, the mean CD4+ lymphocyte count was 35/ micro L (range, 1 to 183/ micro L) and the stage of HIV infection was A3 in 10.4% of patients, B3 in 31.3%, C3 in 56.7%, and unknown in 1.5%. R equi was most commonly isolated in sputum (52.2%), blood cultures (50.7%), and samples from bronchoscopy (31.3%). Chest radiographic findings were abnormal in 65 patients (97%). Infiltrates were observed in all of them, with cavitations in 45 patients. The most active antibiotics against the strains isolated were vancomycin, amikacin, rifampicin, imipenem, ciprofloxacin, and erythromycin. After a mean follow-up of 10.7 +/- 12.8 months, 23 patients (34.3%) died due to causes related to R equi infection and 6 other patients showed evidence of progression of the infection. The absence of highly active antiretroviral therapy (HAART) was independently associated with mortality related to R equi infection (relative risk, 53.4; 95% confidence interval, 1.7 to 1,699). Survival of patients treated with HAART was much higher than that of patients who did not receive this therapy.

CONCLUSIONS

Infection by R equi is an infrequent, opportunistic complication of HIV infection and occurs during advanced stages of immunodepression. In these patients, it leads to a severe illness that usually causes a bacteremic, cavitary pneumonia, although HAART can improve the prognosis.

Medical management of pneumonia caused by Rhodococcus equi in a renal transplant recipient

Rhodococcus equi is an animal pathogen that occasionally causes opportunistic infections in immunocompromised patients. The most common clinical picture is one of necrotizing pneumonia with a tendency toward cavitation and the formation of abscesses. We report a case of pneumonia caused by R equi in a renal transplant patient. An excellent response was shown to antibiotic treatment. Symptoms regressed, and the progressive disappearance of the lesion was confirmed on follow-up computed tomography scans. Surgical intervention or other invasive procedures were not required. To our knowledge, 14 cases of infection by R equi in solid-organ transplant patients have been described to date. Nine were recipients of a renal allograft. Surgery was required in many of these patients, and all the renal transplant recipients required the use of invasive therapeutic techniques, such as pleural drainage. This is the first case of a renal transplant recipient in whom radiologic presentation was as a solid nodule without ensuing cavitation that resolved exclusively with antibiotic treatment.

Septic arthritis caused by a gram-negative bacterium representing a new species related to the Bordetella-Alcaligenes complex

A knee-joint exudate culture yielded on two occasions a gram-negative bacterium. Regular methods for speciation did not provide an identification. The infection was successfully treated with ciprofloxacin. The unknown isolate, CCUG 36768, was subjected to further investigation, including 16S rDNA sequencing, protein profiling, cellular fatty acid analysis, and various biochemical tests, in order to produce a species identification. The 1469 bp-long 16S rDNA sequence did not reveal identity with any known species sequence. CCUG 36768 clustered in a group of species, including Alcaligenes defragrans, Denitrobacter permanens, Taylorella equigenitalis, Alcaligenes faecalis, and four strains of Alcaligenes species without a specific species name. Bordetella species also showed a high degree of similarity with CCUG 36768. Protein profiling, cellular fatty acid analysis and computer-assisted analysis of biochemical profiles indicated similarity with Bordetella-Alcaligenes species, often close to B. holmesii and B. avium. API 20 NE indicated the profile of Moraxella species of poor identity. It is concluded that CCUG 36768 represents a new bacterial species of pathogenic potential in humans. It is related to the Bordetella-Alcaligenes group. Powerful new methods for speciation are available and it is recommended that unknown isolates from normally sterile sites be submitted for further analysis. Several isolates are required for the definition of new species.

Rhodococcus equi infection in transplant recipients: case report and review of the literature

BACKGROUND

Rhodococcus equi is an opportunistic pathogen that usually causes infection in immunocompromised hosts, mainly human immunodeficiency virus-positive patients, yet solid organ transplant recipients may be affected as well. Infections in this group of patients have not been sufficiently analyzed.

METHODS

We report an R equi pneumonia in a heart transplant recipient and review another 11 cases.

RESULTS

Infection appeared a mean of 49 months (range 1-180) after transplantation. Lung was primarily involved in 10 cases (83.3%). The remaining two cases presented with a paravertebral abscess and a purulent pericarditis. Invasive techniques were necessary to reach the diagnosis in nine cases. One patient healed with surgical resection of the lesion; the remaining 11 received antimicrobial agents. Six of them required additional surgical treatment. Three patients died.

CONCLUSIONS

Clinicians should consider R equi when evaluating a solid organ recipient with an asymptomatic lung nodule. Microbiology laboratories should be alerted in these cases because it could be mistaken for a contaminant diphtheroid and will not respond to the standard empirical therapy.