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