During 1991 and early 1992 an outbreak of MRSA occurred at The Toronto Hospital in the Surgical Intensive care Unit (SICU) secondary to an organism which was Staphaurex negative. The strain was resistant to methicillin, rifampin, cotrimoxazole, and macrolides. Initially it was unrecognized that this small cluster represented an outbreak since the organisms were not confirmed to be S. aureus. Of the 10 patients who were identified, 1 was colonized and 9 were infected including: wound infection (3): pneumonia (3); and bacteremia (3). Pulse-field gel electrophoresis (PFGE) of smal digested chromosomal DNA indicated that the isolates from these 10 patients were of colonial origin. It was found that 7 of the 10 infected/colonized patients had shared a room with another patient who had been colonized or infected with this particular MRSA strain during their stay in the SICU suggesting cross-infection on the hands of the health care workers. In one instance, one patient became colonized after sharing a room for <24 hours with another colonized patient and this patient upon transfer subsequently was responsible for dissemination on a general ward. As a result of this outbreak, a review of laboratory identification of MRSA and isolation practices was conducted and patients are now isolated immediately following suspicion of MRSA regardless of the Staphaurex result. This policy is pursued even on initial laboratory testing. A recent point prevalence survey at The Toronto Hospital, two years following the outbreak found no evidence of MRSA and ongoing prospective surveillance has identified only sporadic isolates since this outbreak. No further isolates of the Staphaurex negative MRSA have been identified.
INTRODUCTION
The Toronto Hospital had cluster of 10 cases of Methicillin-resistant Staphylococcus
aureus (MRSA), between November 14, 1991 and March 1992. The patients were all colonized
in November and December but two cases were not detected until January and March. Although
a small cluster of MRSA is not unusual, all isolates in this cluster were staphaurex negative.
Staphaurex (Murex Diagnostics Ltd., Dartford, England) is a rapid slide agglutination test that
identifies S. aureus in less than one minute. The lack of recognition of these isolates as S.aureus
delayed the expedient use of STOP isolation. When it was recognized that there was a cluster of
Staphaurex negative MRSA, we conducted an investigation with the following objectives.
OBJECTIVES
To identify patients who became colonized/infected with Staphaurex negative and
Rifampin resistant MRSA (SNMRSA) and investigate and report the suspected mode(s)
of transmission.
To characterize the Staphaurex negative cluster of MRSA to determine if the cluster of
cases was due to a single strain.
To develop and institute a program designed to avoid similar outbreaks using the data
collected on transmission of SNMRSA in this cluster.
Patient Population and Facility Description
The Toronto Hospital is a 1,220 bed, two site facility affiliated with the University of Toronto. The General site has a 900 bed capacity with 5 service specific Intensive Care Unit (ICU). Each unit has single, double and three bed rooms. The Surgical Intensive Care Unit (SICU) is a 16 bed unit that usually has a three day turnover. Some patients have remained in the unit for up to 6 months. The patients must be ventilator assisted to be admitted and to remain in the unit. The Medical Intensive Care Unit (MICU) is an 11 bed unit for ventilator supported medical patients with lengths of stay varying from one day to several weeks. All patients in MICU and SICU have a daily ECG and chest X-ray.
All patient care is based on Body Substance Precautions (BSP) protocols. There is a sink available at each bedside and one in the shared washroom adjacent to the room.
The General site has an average of 14 MRSA isolates a year. There had not been an
outbreak since 1982-3 (See Graph 1).
The Cluster
On November 20, 1991, the Infection Control Practitioners met to discuss an unusually high number of MRSA patients in the hospital (n=6). An initial review revealed that these cases were not related and all but two patients, one from each of the MICU and SICU, were community acquired. The patients from the MICU and SICU were infected with a strain of MRSA that was Staphaurex negative which was confirmed on a repeated Staphaurex testing with a new lot. A review of the literature revealed there had been previous instances of a Staphaurex negative Staphylococcus aureus infection but no association with a cluster or outbreak.
By December 28, 1991, 6 (2 patients were not found until January and March) other
patients who had been in the SICU and two others who had been in the same unit with a patient
who had been in the SIC were colonized and/or infected with SNMRSA (Figure 1). Four of
these patients shared a room with a colonized patient for one day with one of the four sharing
less than 24 hours.
Investigation
Of the 10 patients who were identified one was colonized and 9 were infected. All but two patients were colonized and/or infected in more than one site. Sites of infection were wound infection (5), pneumonia (3) and bacteraemia (3). The three bacteraemic patients died within three days of the identification of a positive culture. A fourth patient, who never cleared the bacteria from his incision in the following five months eventually became bacteremic and died.
This strain of SNMRSA was transmitted from two patients on isolation: one was between units (MICU and SICU) and one was on the same floor. Because nurses and physicals did not work in both MICU and SICU, other health care workers who worked in both units were observed and their practices were evaluated. Some of these health care workers included ECG technicians, X-ray technicians, hospital assistants, dietary staff, chaplaincy, occupational therapist, housekeeping staff, respirator therapists, physiotherapists, research and educational staff.
Nasal swabs if staff and patients were done in the SICU to identify possible carriers. A
total of 218 cultures were taken: 176 from staff and 42 from contact patients and family. There
was only one positive MRSA culture and it differed from the outbreak strain.
Strain Description and Characterization
The strain of S.aureus involved in this cluster was methicillin resistant and was also
resistant to trimethoprim-sulphamethoxazole, rifampin, and erythromycin. It was susceptible to
vancomycin and fusidic acid. The organism was unusual in that it was negative for agglutination
with the Staphaurex reagent which detects clumping factor and a protein A. However it was
DNAse positive, tube coagulase positive and had the typical colonial morphology and golden
pigment of S. aureus. Genomic typing by macrorestriction enzyme digestion (Sma 1) and
pulsed-field gel electrophoresis proved that the isolates were all of al single clonal origin.
Observational Findings
In an effort to determine the mode(s) of transmission, the Infection Control Practitioners reviewed the care and practices of several groups of health care workers. Several findings were noteworthy. ECG technicians failed to wipe or clean their equipment between patients, even those isolated with MRSA. ECG machines were never cleaned well and had an excess of old electrode jelly in all of the cups.
Several X-ray technicians were observed to have poor hygienic practices such as not washing their hands between patients, not cleaning gloves between patients, wearing one gown for all patients and not changing gowns or uniforms when soiled.
SICU primary care staff, particularly physicians were observed doing limited handwashes.
The practices of other support staff in the ICUs was found to be acceptable and did not appear to present much risk for transmitting organisms.
There ws one SICU nurse positive for MRSA nasally but it was not the outbreak strain.
Visitors in the unit were not taught the necessity of handwashing and so failed to do so.
For example, one lung transplant support group member visited several patients in the unit and
hugged and kissed each patient without washing hands when leaving a patient's room.
Interventions
A new procedure for cleaning and disinfecting the ECG machines was developed. An educational program was developed and delivered to all ECG staff.
The X-ray technicians received a review of Substance Precautions and an MRSA education program was developed and delivered to all X-ray technicians.
A hospital wide MRSA educational program, individualized to each service or unit was prepared and taught to all departments.
An educational program on handwashing was developed for visitors. Sign were posted in waiting rooms and on ICU doors explaining the necessity of good handwashing.
An educational program on transmission of infection and BSP was developed and delivered to pre and post lung transplant patients. The practice of lung transplant support group members visiting their peers in the ICU setting was discontinued.
The Infection Control Manual was revised explaining isolation procedures, detailing
MRSA and all isolation procedures relevant to it. The Clinical Microbiology manual
was revised so that the laboratory technologists notify Infection Control and the patient
ward that they suspect MRSA. The policy states that the technician suggest the nurse
place the patient on STOP isolation until the S. aureus is confirmed or not confirmed to
be methicillin-resistant.
CONCLUSION
The mode of transmission in this cluster was most likely transient hand carriage and/or unclean equipment.
Revision of the policy for isolation of suspected MRSA patients will likely result in isolation of some cases which will not be confirmed to be true MRSA isolates but will significantly reduce the potential for transmission of MRSA while confirmatory testing is done.
Education and re-education of staff about good handwashing and aseptic technique combined with regular review of each departments' practices facilitated the elimination of the SNMRSA from our institution. With a change in laboratory reporting and isolation of suspected MRSA the risk of nosocomial transmission of MRSA should be reduced.
REFERENCES
Neville LO, Billington OJ, Kibbler CC, and Gillespie SH. Methicillin resistant
Staphylococcus aureus without clumping factor, protein A, and DNAse. Lancet
1991:338:518.
Boyce JM. Patterns of Methicillin-resistant Staphylococcus aureus prevalence. Infect
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