Monday, October 26, 1998

1. Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

Outbreaks reported to DHMH from 10/19-10/23:

2 outbreaks: Escherichia serogroup fergosonii in a health care facility- 2 cases which have yet to be epidemiologically linked. Scabies in a long term care facility.

2. The Johns Hopkins Hospital. Information provided by Dr. Angelique Wolf, Department of Pathology.

Case Report: This sixteen year old adolescent male with a history of recurrent pancreatitis of unknown etiology presented to The JHH with symptoms of sharp periumbilical pain and emesis, similar to his previous bouts of acute pancreatitis. He was first diagnosed with pancreatitis approximately one year ago in September of '97 and at that time underwent a cholecystectomy with symptomatic relief. Since then he has had three hospital admissions for recurrent episodes of acute pancreatitis with multiple ERCPs and stent placements and has required parenteral nutrition for the last seven months. On admission he was afebrile with signs and symptoms consistent with acute pancreatitis. Pertinent laboratory findings included the following: amylase 624; lipase 204; AST 16; ALT 26; alk phos 140; t. bili 1.2; WBC 12,200; PMNs 81%; lymphs 95; monos 2%. He developed spiking fevers up to 101.4 F on hospital day seven. Blood was drawn from the patient's central venous line and all bottles turned positive on day two of culture. Gram stain from the broth revealed pleomorphic gram-positive bacilli, often forming pallisades. Colony morphology and biochemical profiles were suggestive of Rhodococcus species. This was validated by gas liquid chromatography and Rhodococcus equi was confirmed using 16s ribosomal studies. The patient was effectively treated with vancomycin and gentamicin, and the central line was removed.

Organism: R. equi (formerly Corynebacterium equi) is an unusual gram-positive obligate aerobic actinomycete, initially isolated from horses in 1923, that has been well recognized as a pathogen in farm animals and can be isolated from the feces of herbivirus and swine. It has been found as a soil saprophyte in the agricultural environment and has been grown from marine and fresh water. Since the first reported case of human infection in 1967, R. equi has been increasingly recognized as an important pathogen in the immunocompromised host.

Clinical Manifestations: R. equi is a facultative intracellular pathogen that lives inside macrophages causing granulomatous inflammation and eventual caseous necrosis. The lung is the most common primary site of infection. The typical clinical presentation is that of fever, chills, and cough in an immunocompromised host with an insidious onset of a necrotizing cavitary pneumonia. The majority of patients with disease, in order of frequency, are immunocompromised secondary to HIV infection hematopoetic neoplasms, renal transplantation, or chronic steroid therapy. Less than a third of R. equi-infected patients have a history of contact with farm animals, soil, or both. Patients most commonly acquire this infection from the air, either through inhalation or the settling of dust on a central line. The organism frequently causes bacteremia usually secondary to an invasive pulmonary, soft tissue, or cutaneous infection. Rare case reports of localized R. equi infections involving the skin or eyes have occurred in patients without any known immunologic abnormality presumably due to soil contamination. A case of catheter-associated R. equi sepsis has been described in a patient who was receiving long-term parenteral nutrition with an indwelling central venous catheter.

Laboratory Diagnosis: R.. equi in culture is a gram-positive pleomorphic coccobacillus that varies in microscopic morphology depending on incubation time and growth conditions. Successive Gram stains show a progressive change from distinct bacillary forms in nutrient broth to distinct cocci on solid media. Microscopically the organisms resemble other coryneform bacteria and may easily be confused with the diphtheroids. At times, a small number of cells may stain weakly acid-fast by the modified Kinyoun method. Early in their growth cycles Rhodococcus can be confused with Nocardia since the organisms can be filamentous or branching.

The colony morphology is diverse: pale yellow to salmon-pink, moist or slimy, and 1 to 3 mm colonies. The organisms are catalase positive, oxidase negative, nonsporeforming, non-motile, indole negative, weakly urease positive, CAMP positive, and noncarbohydrate fermenters. Differentiation between species of the genera Rhodococcus, Gordona, and Tsukamurella can be difficult based on biochemical profiles alone. Because the cell walls of Rhodococcus contain mycolic acids, gas-liquid chromatography analysis is efficacious in separating rhodococci from the Nocardiae and other aerobic actinomycetes and provides additional data for species identification. Ribotyping provides the ultimate confirmation for species identification and can be used for differentiation of isolates.

Treatment: Antimicrobial therapy of infections due to the rhodococci is not standardized; therefore, susceptibility testing is recommended. In vitro rhodococcal isolates in humans are normally susceptible to erythromycin, rifampin, vancomycin, TMP-SMX, tetracycline, ampicillin-sulbactam, amoxicillin-clavulanic acid, the aminoglycosides, and imipenem. Agents with good activity as well as good penetration into macrophages include gentamicin, tobramycin, and ciprofloxacin. Vancomycin is also efficacious, either alone or in combination with another agent. The use of penicillins, penicillinase-resistant penicillins and extended spectrum cephalosporins is not recommended since these agents are likely inactive or show moderate activity against Rhodococcus.

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