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Rhodococcus equi, a gram-positive, weakly acid-fast coccobacillus, initially isolated from horses, is becoming increasingly recognized as an important pathogen for immunosuppressed human hosts since the first human case was reported in 1967. A review of the English medical literature yielded 53 cases. During the last 11 years, the microbiology laboratories of the authors isolated the organism from 12 patients. Of the total 65 cases, 60 occurred in immunosuppressed patients with HIV infection, malignant neoplasms, or chronic immunosuppressive therapy. The lung is the most common primary site of infection. Typically, the lesion is densely infiltrated by histiocytes with multiple microabscesses. Intracellular gram-positive coccobacilli are easily demonstrated. R equi grows well on routine non-selective media at 35 degrees C. Previously, many cases may have been missed because the organism resembles oropharyngeal commensal diphtheroids. Clinical information with gram and Kinyoun strains on fresh isolates is helpful in recognizing the possibility of R equi infection.

Between mid-May and mid-October, 1973, 49 blood cultures from 14 patients in an intensive care unit were positive for flavobacterium species, Group II-b. We conducted an investigation to determine how patients were being infected with this unusual organism. Comparison of the 14 infected patients with 37 controls associated indwelling arterial catheters with subsequent flavobacterium bacteremia (p = 0.005). Risk of infection was greatest during the period in which blood gas determinations were done most frequently (the first three days of catheterization) and in which infected patients had more blood gas determinations than control patients with arterial catheters (p less than 0.05). Flavobacterium species was cultured from in-use arterial catheters, from stopcocks, and from ice in the intensive-care unit's ice machine; the catheters were probably contaminated by syringes that were cooled in ice before being used to obtain arterial specimens for blood gas determination. This outbreak calls attention to arterial monitoring systems as a potential source of nosocomial infection.

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