A 14 YEAR SAGA OF THE EPIDEMIOLOGY AND CONTROL OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS(MRSA) AT A LARGE TERTIARY CARE INSTITUTION
J Burt, M Garcia, BA Jolley, C Kennedy, J Strauss, W Marshall, I Campbell, J Conly*,
Infection Control Unit and Dept. Of Microbiology, The Toronto Hospital, University of Toronto, Toronto, Ontario
MRSA is an important pathogen and a major cause of nosocomial infection. With several US centres reporting up to 40% of strains of S. Aureus as MRSA, there is growing concern about this organism in Canadian hospitals. A retrospective analysis of microbiology records from 1981-88 at The Toronto Hospital and from 1989-94 at The Toronto Hospital reveals an incidence of MRSA which has varied between 0.6-2.3% of all S. Aureus isolates. The rate of MRSA isolation has varied between 3-11/10000 admissions with the peak of 11/10000 admissions and 2.3% of all isolates noted during a cluster in 1982-83. Respiratory tract isolation accounted for 84-86% of MRSA isolates in 1982-83 but only 30-48% of isolates in 1993-94. Two clusters of MRSA have been identified, one in 1982-83 and the other in 1991-92 which was a Staphaurex negative strain. Epidemiologic data and phenotypic (antiobiogram and phage typing)markers implicated a specific strain associated with nasal carriage by staff in the 1982-83 outbreak and similar investigations plus genotypic markers(PFGE) implicated probable cross-transmission in the 1991-92 cluster. Whereas 88% of the MRSA isolates in 1982-83 were considered nosocomial, only 32% (p<0.001) were nosocomial in 1993-94 reflecting a higher proportion of patients colonized on admission or on transfer. Our experience with a strict isolation policy towards suspected MRSA suggest that nosocomial transmission of MRSA can be prevented within a large tertiary Canadian hospital.
Introduction
MRSA major nosocomial pathogen
Hospital outbreaks have occurred on world-wide basis
Prevalence varies depending on many factors-size of institution,patients
First appeared late 1960s Europe < 10 years after introduction methicillin
First isolates US in early 1970s
Percentage MRSA from all NNIS hospitals rose from 2.4% to 29% between 1975 and 1991
Epidemiology of MRSA Canada less well defined
MRSA acquired community setting in prairie provinces(Embil et al,1994)
Control efforts for MRSA controversial
Review of control measures by Boyce 1991 suggests chance eradication varies:<20 cases(100%);20-39 cases(70%);40 cases(10%)
Presence MRSA since 1978 TTH plus 1982-83 outbreak 78 cases prompted review of our experience
Methods
Retrospective analysis of Microbiology records 1981-1994
All MRSA isolates recorded "Phage Book"since 1979 (I Campbell)
Denominators :1981-84(1 month survey);1985-90(estimate);1991-94(annual report)
Admissions from Medical records
Susceptibilities 1981-89 Multiscan (semi-automated replicating system) 1989-94 Microscan (increased salt 1990,oxacillin screen plate 4mg/L 1991-present)
Phage typing-PHL Ministy of Health
Background
Currently 1200 bed tertiary care 2 -site medical school affiliated institution
Transplantation,oncology,neurosciences and cardiac care
Medical and surgical adult care
7 ICUs;40,000 patients/yr;334000pt day
Merged 1989 previously Western and General hospitals
MRSA Summary
| Year |
# (%) Urinary & Urinary Single Site Nonduplicate Organisms MRSA |
# Patients (%) MRSA |
# Isolates S. aureus Single Site Non-duplicate Organisms - Non-Urinary & Urinary |
| 1980 |
0 (Review of Phage
Book + S.A. Book) |
0 |
179‡ Oct only Est. 2004 |
| 1981 |
13 (0.6% |
12 |
183‡ (Est 2004) |
| 1982 |
47 (2.3%) |
43 (0.11%) |
170 ‡ “ “ |
| 1983 |
40 (2.0%) |
35 |
162 ‡ “ “ |
| 1984 |
14 (0.7%) |
14 |
141 ‡ “ “ |
| 1985 |
16 (0.8%) |
15 |
“ |
| 1986 |
20 (1.0%) |
20 |
“ “ |
| 1987 |
16 (0.8%) |
16 |
“ " |
| 1988 |
16 (0.8%) |
16 |
Not available (Est 2004) |
| 1989* |
14 (0.7%) |
14 |
“ " |
| 1990 |
15 (0.7%) |
13(.03) |
“ " |
| 1991 |
25 (1.5%) |
23(.05) |
1720 |
| 1992 |
30 (1.6%) |
25(.06) |
1821 |
| 1993 |
22 (0.8%) |
18(.05) |
2178 |
| 1994 |
33 (2.0%) |
27(.07) |
1662 |
* Merger of hospital labs
Nosocomial vs Community Acquired MRSA
- 1982-83 88% nosocomial with predominant phage type 82
- 1993-94 32% nosocomial wiyh no predomunant phage type
- 4/17 community acquired MRSA were transfers from other hospitals(out of country)
Conclusions
MRSA incidence has not increased in over 15 years
Continuing small no. of nosocomial cases each year cases
May be a shift towards more CA cases
Maximal barrier precautions should be used for MRSA patients
? need for a screening policy
