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CASE REPORT Table of Contents   
Year : 2009  |  Volume : 52  |  Issue : 2  |  Page : 263-264
Acute osteomyelitis caused by Rhodococcus equi in an immunocompetent child

1 Department of Microbiology, Jawaharlal Institute of Post Graduate Medical Education and Research, Puducherry - 605 006, India
2 Department of Orthopedics, Jawaharlal Institute of Post Graduate Medical Education and Research, Puducherry - 605 006, India

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Rhodococcus equi is an unusual pathogen causing infections mostly in immunocompromised patients, particularly in those with human immunodeficiency virus (HIV). It has rarely been reported to affect immunocompetent hosts, where it usually presents as an isolated extrapulmonary lesion. We report a case of osteomyelitis caused by this organism in an immunocompetent host.

Keywords: Immunocompetent host, osteomyelitis, Rhodococcus equi

How to cite this article:
Sistla S, Karthikeyan S, Biswas R, Parija SC, Patro DK. Acute osteomyelitis caused by Rhodococcus equi in an immunocompetent child. Indian J Pathol Microbiol 2009;52:263-4

How to cite this URL:
Sistla S, Karthikeyan S, Biswas R, Parija SC, Patro DK. Acute osteomyelitis caused by Rhodococcus equi in an immunocompetent child. Indian J Pathol Microbiol [serial online] 2009 [cited 2022 Nov 27];52:263-4. Available from:

   Introduction Top

Rhodococcus equi has been regarded as an almost exclusive zoopathogenic microbe causing necrotizing pneumonias in horses. [1] The first human infection was reported in a patient with autoimmune hepatitis on steroid therapy. Thereafter, more than 200 cases of R. equi infections have been reported, with the vast majority of them in immunocompromised patients. [2] There have been a few case reports of R. equi infections in immunocompetent hosts, although the course and the manifestations of the disease may differ from that seen in immunocompromised patients. [3] The natural habitat of R. equi is soil contaminated with animal manure, with infection being acquired by inhalation, inoculation or ingestion. Although the organism is easily cultured from specimens, it may be misdiagnosed as a contaminant, usually diphtheriods. [2] We report a case of osteomyelitis in an immunocompetent child caused by this organism.

   Case Report Top

A-15-year-old boy involved in a road traffic accident was admitted to the orthopedic ward of our hospital in August 2004. He had sustained multiple injuries, including compound fracture of the inferior pubic ramus and posterior urethral injury. There was extensive soft tissue injury over both the iliac crests. He underwent wound debridment, open reduction with screw fixation for the fracture neck of the right femur and a split skin graft for the raw areas. The patient was treated with IV ceftriaxone 1gm twice a day for 5 days. A suprapubic cystostomy was performed and the patient was on regular follow-up for the next few months, with altered gait and inability to squat as the only complaints.

In May 2005, the boy returned to the hospital with pain in the right hip joint, which had been persisting for 10 days. On examination, the patient was febrile, with tenderness and restricted movement in the right hip. A sinus with seropurulent discharge was observed at the affected site. A plain X-ray of the area revealed periosteal reaction and radiolucent areas suggestive of acute osteomyelitis. A pus sample aspirated from the depth of the wound was sent to the microbiology laboratory.

Microbiological investigations

On direct Grams staining of the pus, a number of neutrophils were seen without any bacteria. Colonies on blood agar after 48h of aerobic incubation were 1-2mm in diameter, orange red colored and nonhemolytic. A Gram stain of the colony revealed irregular, short, gram-positive bacilli with occasional coccoid forms. It was identified as R. equi based on the following characters: growth on nutrient agar with a typical pigment, nonmotile, acid fast with 1% H 2 SO 4 , positive for catalase, urease, nitrate reductase and lipase and negative for oxidase, gelatinase, lecithinase and hydrolysis of casein, xanthine, hypoxanthine and tyrosine. The organism was susceptible to erythromycin, gentamycin and vancomycin and resistant to penicillin. Blood culture was sterile and the enzyme-linked immunosorbent assay for HIV1/2 antibodies was negative. Hematological investigations revealed a leukocyte count of 15,000/mm 3 with 70% neutrophils, hemoglobin of 12gm/100ml and Erythrocyte sedimentation rate (ESR) of 100mm/h.

The patient was treated initially with IV ceftriaxone, which was changed to erythromycin (250mg six hourly for a period of 4 weeks) later following the culture report. There was a complete resolution of symptoms.

   Discussion Top

R. equi was first isolated in 1923 from the lungs of foals in Sweden. It has been isolated from a variety of land and water animals like cattle, crocodiles and even wild birds. The organism is present in soil all over the world except in Antarctica, in fresh and sea water and in the intestines of blood sucking arthropods. [2]

Human infections with this organism occur rarely through different routes such as inhalation, inoculation and ingestion. Other routes of acquisition, including nosocomial and person-to-person transmission, have been reported. [2] The possibility that our patient could have acquired the organism from the hospital cannot be ruled out in the light of his multiple visits to the hospital.

After the first human case in 1967, there have been more than 200 case reports in the literature, most of them in immunocompromised patients, particularly in those with HIV and in transplant recipients. [1],[4] Till 2006, there were 24 cases of R. equi infection in immunocompetent hosts. The clinical manifestations, course and response to therapy differ significantly between immunocompromised and immunocompetent patients. Immunocompromised patients usually present with necrotizing pneumonia with or without sepsis, have a high mortality rate and require prolonged treatment with multiple antibiotics. In contrast, immunocompetent patients, most of them children, present with extrapulmonary lesions like abscesses, osteomyelitis, septic arthritis, etc., have a low mortality rate and respond to a shorter course of antibiotics, usually with a single agent. [1],[2],[5],[6] Our patient was HIV negative, with no other obvious cause of immunosuppression. His clinical presentation, course and response to therapy also parallel other reports in immunocompetent patients. A Medline search revealed three other case reports of R. equi infection from India. One was in a 3-year-old female with protein energy malnutrition [7] whereas another was from a HIV-positive patient [8] and the third was from an apparently immunocompetent adult with brain abscess. [9]

R. equi may easily be dismissed as a contaminant in the laboratory as it resembles diphtheroids. As the typical orange red pigment may not appear for 4-7 days, a high index of suspicion needs to be maintained to avoid misidentification. Fortunately, our strain produced pigment within 48 h, arousing our suspicion of R. equi . Recently, several new species of Rhodococcus have been described, like R. rhodochrous, R. fascians and R. globerulis , which are difficult to distinguish phenotypically from R. equi . [10] Standard treatment regimens for R. equi have not been established although a combination of antibiotics with drainage of abscess forms the mainstay of therapy. R. equi is susceptible to many antibiotics in vitro , although penicillin should not be used for therapy because resistance develops very easily. [2] Erythromycin is the most commonly used drug, which was also used in our patient with excellent results. This is possibly due to the good intracellular penetration of the antibiotic.

   Conclusion Top

R. equi has emerged as a rare human pathogen with particular significance in immunocompromised patients. Increased awareness of this organism among clinicians and microbiologists would aid in timely diagnosis and management of these patients.

   Acknowledgements Top

The authors gratefully acknowledge the help rendered by Dr. Mary V. Jesudassan, former head of the Department of Clinical Microbiology, Christian Medical College, Vellore in confirming the identity of the isolate.

   References Top

1.Votava, M, Skalka B, Hrstkova H, Tejkalova R, Dvorska L. Review of 105 cases of isolation of Rhodococcus equi in humans. Cas Lek Cesk 1997;136:51-3.  Back to cited text no. 1    
2.Weinstock DM, Brown AE. Brown Rhodococcus equi : An emerging pathogen. Clin Infect Dis 2002;34:1379-85.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Kedlaya I, Ing MB, Wong SS. Rhodococcus equi Infections in Immunocompetent Hosts: Case report and review. Clin Infect Dis 2001;32:E39-46.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Torres-Tortosa M, Arrizabalaga J, Villanueva JL, Galvez J, Leyes M, Valencia ME, et al . Prognosis and clinical evaluation of infection caused by Rhodococcus equi in HIV-infected patients: A multicenter study of 67 cases. Chest 2003;123:1970-6.  Back to cited text no. 4    
5.Verville TD, Huycke MM, Greenfield RA, Fine DP, Kuhls TL, Slater LN. Rhodococcus equi infections of humans: 12 cases and a review of the literature. Medicine (Baltimore) 1994;73:119-32.  Back to cited text no. 5  [PUBMED]  
6.Ulivieri S, Oliveri G. Cerebellar abscess due to Rhodococcus equi in an immunocompetent patient: Case report and literature review. J Neurosurg Sci 2006;50:127-9.  Back to cited text no. 6  [PUBMED]  
7.Sarangi G, Chayani N, Mahapatra A, Mahapatra D, Paty BP, Parida B. Bacteremia due to Rhodococcus equi : A case report. Indian J Pathol Microbiol 2004;47:553-5.  Back to cited text no. 7    
8.Mistry NF, Dholakia Y, D'Souza DT, Taylor M, Hoffner S, Birdi TJ. Rhodococcus and Mycobacterium tuberculosis : Masquerade or mixed infection. Int J Tuberc Lung Dis 2006;10:351-3.  Back to cited text no. 8  [PUBMED]  [FULLTEXT]
9.Kamboj M, Kalra A, Kak V. Rhodococcus equi brain abscess in a patient without HIV. J Clin Pathol 2005;58:423-5.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]
10.Conville PS, Witebsky FG. In: Borriello SP, Murray PR, Funke G, editors. Topley and Wilsons Microbiology and Microbial infections. vol 2. 10 th ed. American society for Microbiology. Washington, DC: 2005.p. 1166-68.   Back to cited text no. 10    

Correspondence Address:
Sujatha Sistla
Department of Microbiology, JIPMER, Puducherry - 605 006
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.48940

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