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Bacteremia among Aortic-Valve Surgery Patients -- Boston

In the period March 19-April 6, 1981, 3 of 5 patients at a Boston hospital who had undergone thoracotomy for aortic-valve replacement, developed bacteremia; the causative agent was a strain of Enterobacter cloacae not previously isolated at this hospital.

Clinical onset of infection ranged from 4 days to 2 weeks after surgery; 2 patients had mediastinitis in addition to bacteremia. The infected patients ranged in age from 60 to 83 years. Two of the 3 had also had coronary-artery-bypass grafts (CABG), but 22 other patients who had CABG surgery without valve replacement within the same 19-day period after surgery did not subsequently become infected by E. cloacae.

Because 3 of 5 patients who had valve replacements had been infected by the same uncommon bacterial strain, and because 2 different types of valves had been used in surgery, an investigation was initiated to identify procedures or equipment used in this surgery that were not used in other types of open-heart surgery. The only piece of equipment used exclusively for aortic-valve surgery was an anaeroid manometer that measured the pressure of cardioplegia solution being injected into the coronary arteries. The manometer, approximately 1 foot of disposable tubing, and a stopcock were connected to sterile tubing extending from the bubble trap (reservoir) of the cardioplegia solution. The manometer was not sterilized or disinfected after each use, and the stopcocks and tubing were not changed on a regular basis. Although reflux of the cardioplegia solution into the manometer tubing had not been observed, it was believed this could have occurred as a result of changes in pressure and fluid levels during surgery.

Use of this system was stopped immediately. The inner surfaces of the manomoeter and tubing junction were cultured. The cultures were positive for E. cloacae of the same biotype that caused infection in the index patients. In addition, 3 subsequent aortic-valve replacements without use of the implicated manometer were observed, and multiple cultures were obtained during surgery; all cultures were negative for E. cloacae.

The infusion pressure of cardioplegia solution is now monitored only with a pressure transducer that is sterilized with ethylene oxide after each use and is connected to the bubble trap by sterile tubing and stopcocks. Reported by R Kalaidjian, RN, IB Tager, MD, Boston, Massachusetts; Hospital Infections Br, Bacterial Diseases Div, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Mediastinitis and bacteremia are not uncommon complications of cardiac surgery. In one large study, 3.4% of cardiac surgical procedures performed through a median sternotomy were complicated by mediastinitis; however, there were no clusters of infection caused by a single microbial strain (1). Clusters of postoperative mediastinitis and bacteremia caused by a single strain of bacteria do sometimes occur, although the source of infection for the clusters is not often identified. Over the past years, cases of bacteremia have occurred as a result of intravascular infusion of solutions contaminated by pressure transducers (2); these instruments have rarely been associated with sternal osteomyelitis and mediastinitis (3).

Unsterile anaeroid and mercury manometers are used frequently in a variety of medical and surgical settings to calibrate electronic-pressure-monitoring equipment, such as that used in cardiac catheterization studies. Only rarely has contamination of sterile lines or solution by calibration or monitoring procedures been clearly associated with infection (2). The outbreak investigation reported here clearly demonstrates that a risk exists and reemphasizes the need to keep sterile systems closed and to ensure that the internal surfaces of all equipment directly connected to a sterile system remain sterile.

References

  1. Bor D, Rose R, Modlin J, Weintraub R, Friedland G. Infectious mediastinitis--a common complication of cardiac surgery. In: Program and Abstracts, 20th Interscience Conference on Antimicrobial Agents and Chemotherapy, September 22-24, 1980, New Orleans, La. No. 623.

  2. Weinstein RA, Stamm WE, Kramer L, Corey L. Pressure monitoring devices. Overlooked source of nosocomial infection. JAMA 1976;236:936-8.

  3. Weinstein RA, Jones EL, Schwarzmann SW, Hatcher CR. Sternal osteomyelitis and mediastinitis after open-heart operation: pathogenesis and prevention. Ann Thorac Surg 1976;21:442-4.

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