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Journal Article

Prevalence of Colonization and Infection with Methicillin-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococcus and of Clostridium difficile Infection in Canadian Hospitals

Andrew E. Simor MD, Victoria Williams MPH, Allison McGeer MD, Janet Raboud PhD, Oscar Larios MD, Karl Weiss MD, Zahir Hirji CIC, Felicia Laing MSc, Christine Moore ART, Denise Gravel MSc and Community and Hospital Infection Control Association–Canada
Infection Control and Hospital Epidemiology
Vol. 34, No. 7 (July 2013), pp. 687-693
DOI: 10.1086/670998
Stable URL: http://www.jstor.org/stable/10.1086/670998
Page Count: 7
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Original Article

Prevalence of Colonization and Infection with Methicillin-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococcus and of Clostridium difficile Infection in Canadian Hospitals

Andrew E. Simor, MD,1,2
Victoria Williams, MPH,1
Allison McGeer, MD,2,3
Janet Raboud, PhD,2,4
Oscar Larios, MD,5
Karl Weiss, MD,6
Zahir Hirji, CIC,7
Felicia Laing, MSc,8
Christine Moore, ART,3
Denise Gravel, MSc,9 and
Community and Hospital Infection Control Association–Canada
1. Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
2. University of Toronto, Toronto, Ontario, Canada
3. Mount Sinai Hospital, Toronto, Ontario, Canada
4. University Health Network, Toronto, Ontario, Canada
5. University of Saskatchewan and Saskatoon Health Region, Saskatoon, Saskatchewan, Canada
6. Maisonneuve-Rosemont Hospital, Montreal, Quebec, Canada
7. Bridgepoint Health, Toronto, Ontario, Canada
8. Vancouver Coastal Health Authority, Vancouver, British Columbia, Canada
9. Centre for Communicable Diseases and Infection Control, Public Health Agency of Canada, Ottawa, Ontario, Canada
    Address correspondence to Andrew E. Simor, MD, Department of Microbiology, Sunnybrook Health Sciences Centre, B103-2075 Bayview Avenue, Toronto, Ontario M4N 3M5, Canada ().

Objective. To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Clostridium difficile infection (CDI) in Canadian hospitals.

Design. National point prevalence survey in November 2010.

Setting. Canadian acute care hospitals with at least 50 beds.

Patients. Adult inpatients colonized or infected with MRSA or VRE or with CDI.

Methods. The prevalence (per 100 inpatients) of MRSA, VRE, and CDI was determined. Associations between prevalence and institutional characteristics and infection control policies were evaluated.

Results. One hundred seventy-six hospitals (65% of those eligible) participated. The median (range) prevalence rates for MRSA and VRE colonization or infection and CDI were 4.2% (0%–22.1%), 0.5% (0%–13.1%), and 0.9% (0%–8.6%), respectively. Median MRSA and VRE infection rates were low (0.3% and 0%, respectively). MRSA, VRE, and CDI were thought to have been healthcare associated in 79%, 96%, and 84% of cases, respectively. In multivariable analysis, routine use of a private room for colonized/infected patients was associated with lower median MRSA infection rate (prevalence ratio [PR], 0.44 [95% confidence interval (CI), 0.22–0.88]) and VRE prevalence (PR, 0.26 [95% CI, 0.12–0.57]). Lower VRE rates were also associated with enhanced environmental cleaning (PR, 0.52 [95% CI, 0.36–0.75]). Higher bed occupancy rates were associated with higher rates of CDI (PR, 1.02 [95% CI, 1.01–1.03]).

Conclusions. These data provide the first national prevalence estimates for MRSA, VRE, and CDI in Canadian hospitals. Certain infection prevention and control policies were found to be associated with prevalence and deserve further investigation.

Keywords : MRSA VRE Clostridium difficile infection antibiotic resistance

The emergence of antibiotic-resistant organisms is a major public health concern. Methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and Clostridium difficile are of particular clinical significance in hospitalized patients. Infections caused by these pathogens have been associated with excess morbidity and mortality, prolonged hospital stay, and substantial excess healthcare costs. However, there continue to be significant gaps in our understanding of the epidemiology of antibiotic-resistant organisms in hospitals. Most of the available information comes from single institutions or small networks of hospitals. There are few published national prevalence data, and results vary depending on the surveillance methods employed.

In Canada, the incidence of colonization and infection with MRSA, VRE, and C. difficile has been reported by a national surveillance network involving primarily tertiary care hospitals.1-3 National prevalence rates of antimicrobial-resistant organisms have not previously been determined. Prevalence has been recognized as an important metric for assessing the burden of disease associated with antimicrobial resistance and for monitoring the effectiveness of various interventions.4-6 In this study, we determined the prevalence of colonization and infection with MRSA and VRE and of C. difficile infection (CDI) in Canadian hospitals. We were also interested in identifying institutional characteristics associated with their prevalence.

Methods

Study Design and Study Participants

A list of all accredited hospitals in Canada was obtained from the Canadian Healthcare Association. Hospitals providing acute care with at least 50 inpatient beds for adults were eligible; hospitals providing only pediatric, rehabilitation, psychiatric, or long-term care were excluded. Each participating hospital was asked to select 1 weekday between November 8 and November 21, 2010, for the prevalence survey. On that day, all adult (18 years of age or older) inpatients were identified by the hospital census. Adult inpatients colonized or infected with MRSA or VRE or who had CDI were also identified. The ethics review board at Sunnybrook Health Sciences Centre (Toronto, Ontario) approved the conduct of this study.

Study Definitions

At the time of the survey, it was standard in Canadian hospitals for patients with MRSA or VRE infection or colonization to be cared for with additional barrier precautions. Therefore, patients colonized or infected with MRSA or VRE were defined as those who were on additional precautions for either of these organisms on the day of the survey and who had a culture confirming the presence of the organism obtained on that day or previously. Patients were determined to have an infection caused by either of these organisms if they met National Healthcare Safety Network criteria.7 If infection criteria were not present, the patient was deemed to be colonized.

Patients were determined to have CDI if they had diarrhea (3 or more loose or watery stools within 24 hours), had laboratory confirmation with a positive C. difficile toxin assay, and were receiving treatment for this with either metronidazole or oral vancomycin on the day of the survey or if they had pseudomembranous colitis documented by sigmoidoscopy or colonoscopy within the previous 14 days.

MRSA or VRE were defined as healthcare associated if the initial identification of the organism was more than 48 hours after hospital admission; if the patient had been hospitalized or in a long-term care facility in the previous 12 months; if the patient had an indwelling medical device; or if the patient had had another significant healthcare exposure, such as ongoing dialysis, outpatient surgery, or chemotherapy.1 If none of these criteria were met, the organism was presumed to have been community associated. Healthcare-associated CDI was defined by the onset of symptoms 72 or more hours after hospital admission or if the patient had been discharged from a hospital or a long-term care facility within 8 weeks of the current hospital admission;3 other cases were deemed to have been community associated.

Data Collection

The number of admitted adult inpatients on the day of the survey was determined at each participating hospital. Patients with MRSA, VRE, or CDI were identified and their medical records reviewed by experienced infection control professionals. The data extracted included age, sex, hospital service, whether the patient met criteria for infection, whether the organism was thought to be healthcare or community associated, and whether the organism was first identified during the present admission. A separate questionnaire was completed describing hospital characteristics, including number of adult beds, type of facility (teaching or nonteaching), scope of medical services provided, and laboratory facilities for detection of MRSA, VRE, and C. difficile. Information was also obtained describing the facilities’ infection prevention and control policies regarding antibiotic-resistant organisms.

Data Analysis and Statistical Methods

The primary outcomes of interest were the prevalence of MRSA, VRE, and CDI, calculated as the number of cases of each per 100 adult inpatients identified on the survey date. Hospital characteristics of participating and nonparticipating facilities and differences between facility- and patient-level variables were compared using the χ2 test, Student t test, or 1-way ANOVA as appropriate. Prevalence of the 3 organisms was compared among categories of facility-level variables using Spearman rank correlation or Mann-Whitney U test for nonparametric distributions. Spearman correlation coefficients were calculated to determine the association of hospital prevalence of 1 antibiotic-resistant organism with that of any other resistant organism. Two-tailed P values less than 0.05 were considered to be significant.

Negative binomial regression models with robust standard errors were designed to evaluate the associations between the prevalence of infection associated with the antibiotic-resistant organisms and institutional characteristics and infection prevention and control policies. However, because VRE infections were uncommon, the model for VRE evaluated the combined prevalence of infection and colonization. The variables considered in these models were selected a priori on the basis of previously published data and guidelines regarding the control of transmission of these organisms.8-10 The variables were assessed for collinearity before model construction. Interactions between variables of interest were investigated, and none were identified. In order to account for the potential effect of regional or provincial infection prevention and control policies, provinces were forced into each model; since this had no effect on the results, the models presented do not include the provinces. The goodness-of-fit χ2 test was used to assess the goodness of fit of each final model. All analyses were performed using SPSS (ver. 16.0).

Results

Of the 406 accredited hospitals with 50 or more beds in Canada, 278 were thought to be eligible and were contacted; 183 agreed to participate and submitted adequate data. Seven hospitals were excluded because they had fewer than 50 acute care beds. Therefore, a total of 176 hospitals (with 40,054 beds), representing 65% of eligible hospitals and 58% of eligible hospital beds, were included. There was participation from all 10 Canadian provinces and from the Northwest Territories. The geographic distribution and size of eligible participating hospitals were similar to those of nonparticipating hospitals (Table 1). However, the proportion of teaching hospitals was higher among participating than nonparticipating sites. The mean bed occupancy rate on the survey date in the participating hospitals was 94% (range, 48%–122%).

Table 1. 
Characteristics of Eligible Participating and Nonparticipating Hospitals
CharacteristicParticipating hospitals ()Nonparticipating hospitals ()
Location
 Eastern Canada26 (15)10 (11)
 Central Canada103 (58)58 (61)
 Western Canada47 (27)27 (28)
Size, no. of beds
 50–20092 (52)60 (63)
 201–50074 (42)28 (30)
 >50010 (6)7 (7)
Type
 Teaching55 (31)6 (6)a
 Nonteaching121 (69)89 (94)

A total of 2,895 patients with MRSA, VRE, or CDI were identified: 1,930 (67%) colonized or infected with MRSA, 782 (27%) colonized or infected with VRE, and 485 (17%) with CDI. There were 278 (10%) patients coinfected or cocolonized with 2 of these organisms concurrently, and 12 (0.4%) were colonized or infected with all 3 organisms. The prevalence data are summarized in Table 2. Hospitals with higher prevalence of any 1 antibiotic-resistant organism were more likely to have higher prevalence of the other organisms (Spearman correlation coefficients for MRSA, VRE, and CDI ranged from 0.23 to 0.37; ). Prevalence of MRSA and CDI did not vary by region of the country or province, but VRE prevalence was lower in eastern Canada than in other regions (median prevalence, 0% in eastern Canada as compared with 0.7% and 1.3% in central and western Canada, respectively; ; Figure 1).

Table 2. 
Median Prevalence Rates of Methicillin-Resistant Staphylococcus aureus (MRSA), Vancomycin-Resistant Enterococcus (VRE), and Clostridium difficile Infection in Canadian Hospitals
OrganismNo. of patientsMedian prevalence per 100 inpatients (range)
Any organism2,8955.9 (0–25.0)
MRSA
 Colonization + infection1,9304.2 (0–22.1)
 Infection2460.3 (0–5.9)
VRE
 Colonization + infection7820.5 (0–13.1)
 Infection240 (0–1.8)
Clostridium difficile
 Infection4850.9 (0–8.6)

Figure 1. 

Median (range) prevalence (per 100 inpatients) of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and Clostridium difficile infection (CDI) by region of the country.

Characteristics of patients with MRSA, VRE, and CDI are summarized in Table 3. Patients with MRSA were more likely to have been identified by a clinical specimen (31.2%) and to have had an infection (12.8%) than were patients with VRE (9.2% identified by a clinical specimen; 3.1% infected; for all comparisons). Although all 3 organisms were acquired predominantly in healthcare settings, MRSA was thought to have been community associated (21.3%) more often than was VRE (3.8%) or CDI (15.7%; for both comparisons).

Table 3. 
Characteristics of Prevalent Cases with Methicillin-Resistant Staphylococcus aureus (MRSA), Vancomycin-Resistant Enterococcus (VRE), and Clostridium difficile Infection (CDI)
CharacteristicMRSAVRECDI
No. of patients1,930782485
Sex, male1,061 (54.7)414 (52.6)213 (44.2)a
Age, mean, years (SD)70.4 (16.9)71.0 (15.5)75.8 (14.3)a
Time in hospital before prevalence survey, days, median202923
Newly identified with resistant organism during current admission832 (43.1)435 (55.6)
Initial detection of MRSA or VRE
 In a screening specimen1,234 (63.9)689 (88.1)a
 In a clinical specimen602 (31.2)72 (9.2)
 Unknown94 (4.9)21 (2.7)
Infection/colonization status
 Colonized1,548 (80.2)727 (93.0)
 Infected246 (12.8)24 (3.1)a485 (100)
 Unknown136 (7.0)31 (3.9)
Sites of MRSA/VRE infection (of those infected)
 Skin/soft tissue99 (40.2)3 (12.5)
 Surgical site27 (11.0)3 (12.5)
 Pneumonia47 (19.1)0
 Urinary tract012 (50.0)
 Bloodstream infection34 (13.8)3 (12.5)
 Other or unknown39 (15.9)3 (12.5)
Acquisition of resistant organism
 Healthcare associated1,518 (78.6)752 (96.2)409 (84.3)
 Community associated412 (21.3)30 (3.8)a76 (15.7)
With another resistant organism (MRSA, VRE, CDI)229 (11.9)96 (12.3)97 (20.0)

In univariate analysis, the prevalence of MRSA and CDI did not vary by hospital size, annual number of admissions, or teaching facility status (data not shown). However, larger hospitals had higher VRE prevalence. Higher occupancy rates (greater than 95%) on the day of the survey were associated with higher prevalence of VRE (0.8% vs 0%; ) and of CDI (1.1% vs 0.5%; ). A policy to always accommodate a patient with MRSA, VRE, or CDI in a private room was standard in 58 (33.0%), 97 (55.1%), and 98 (55.7%) facilities, respectively, and such a policy was associated with lower prevalence of each organism.

In multivariable analysis, lower MRSA prevalence was associated with policies for routine use of a private room for patients with MRSA (prevalence ratio [PR], 0.44 [95% confidence interval (CI), 0.22–0.88]; ) and for use of an antiseptic soap for washing MRSA patients daily (PR, 0.74 [95% CI, 0.58–0.94]; ; Table 4). Teaching hospitals and hospitals with an inpatient pediatrics unit also had lower MRSA prevalence. Lower VRE prevalence was associated with policies for routine accommodation in a private room (PR, 0.26 [95% CI, 0.12–0.57]; ) and for enhanced environmental cleaning of rooms and medical equipment used by VRE patients (PR, 0.52 [95% CI, 0.36–0.75]; ). Higher MRSA and VRE prevalence was associated with a policy of screening for these organisms on admission to a hospital or to an intensive care unit. Only higher bed occupancy on the survey date was associated with higher CDI rates (PR per percent occupancy, 1.02 [95% CI, 1.01–1.03]; ).

Table 4. 
Covariates Associated with Prevalence of Methicillin-Resistant Staphylococcus aureus (MRSA) Infection, Vancomycin-Resistant Enterococcus (VRE) Infection/Colonization, and Clostridium difficile Infection (CDI) in Multivariate Models
MRSAVRECDI
CovariatesPR (95% CI)PPR (95% CI)PPR (95% CI)P
Occupancy rate1.00 (0.99–1.01).760.99 (0.98–0.99)<.0011.02 (1.01–1.03).002
No. of FTE ICPs/100 beds0.82 (0.60–1.14).240.67 (0.37–1.21).190.93 (0.78–1.10).41
Teaching hospital0.67 (0.50–0.90).0081.12 (0.64–1.97).681.02 (0.77–1.33).92
Inpatient pediatrics0.55 (0.42–0.73)<.001
Solid organ transplant unit1.53 (0.61–3.82).36
Universal admission screening1.26 (0.71–2.23).421.36 (1.08–1.71).01
ICU admission screening1.36 (1.05–1.76).021.39 (1.16–1.66)<.001
Nasal + extra nasal screening1.36 (0.49–3.77).55
Routine use of a private room0.44 (0.22–0.88).020.26 (0.12–0.57).0010.80 (0.49–1.31).38
Routine use of a surgical mask0.86 (0.53–1.38).53
Routine use of antiseptic soapa0.74 (0.58–0.94).02
Routine MRSA decolonizationb1.06 (0.58–1.92).85
Additional or enhanced environmental cleaning0.52 (0.36–0.75)<.0010.79 (0.40–1.54).48
Criteria to discontinue isolation precautionsc1.26 (0.64–2.49).510.77 (0.50–1.18).230.84 (0.66–1.06).15
Turnaround time ≥24 h for receipt of C. difficile lab test results0.84 (0.69–1.03).09

Discussion

The results of this study indicate that about 1 in 12 adults hospitalized in Canada are colonized or infected with MRSA, VRE, or C. difficile. In these hospitals, a median of 4.2% (mean, 5%) of inpatients was reported to be colonized or infected with MRSA, and a mean of 0.6% were infected. In comparison, mean MRSA prevalence rates in European hospitals have been reported to range from less than 1% (in hospitals in the Netherlands and Germany) to 24% (among orthopedic and trauma patients in a UK hospital).11 In 2 US national prevalence surveys for MRSA, the mean prevalence of combined colonization and infection among inpatients increased from 4.6% in 2006 to 6.6% in 2010, but MRSA infection prevalence decreased from 3.4% in 2006 to 2.5% in 2010.12,13 The apparent increase in overall MRSA prevalence in US hospitals was likely due to increased active surveillance to identify colonized patients. Active surveillance for MRSA is routine in almost all Canadian hospitals, and the observed ratio of infected to colonized patients with MRSA is lower in Canada than has been reported in the United States.

Fewer studies report the prevalence of VRE in hospitalized patients. In the United States, the prevalence of VRE on admission to an intensive care unit has been reported to range from 12% to 43%,14,15 and nearly one-third of adults in a stem cell transplant unit were colonized or infected with the organism.16 Although the incidence of VRE in Canadian hospitals has been increasing, rates remain low, and the vast majority of patients with VRE identified in Canada are colonized.2 Similarly, in this study, the VRE prevalence was low, and very few infected patients were identified.

The past decade has witnessed a striking increase in the incidence and severity of CDI around the world.17,18 Two previous national prevalence surveys of CDI have been reported, with results similar to those found in this study (median prevalence, 0.9%; mean prevalence, 1.3%): the mean prevalence of CDI in the United Kingdom and Ireland in 2006 was reported to be 1.7%19 and was 1.3% in the United States in 2008.20

In this study, we sought to determine whether certain institutional characteristics or infection prevention and control policies were associated with prevalence of MRSA, VRE, and CDI. Overcrowding and excess bed occupancy have previously been associated with higher incidence rates of MRSA infection and CDI.21-23 We could not assess staffing levels or overcrowding in this study. However, in the multivariable analysis, bed occupancy rate remained significantly associated with higher prevalence of CDI. In contrast, increased bed occupancy was associated with lower VRE prevalence, although the effect size was small. We are unable to explain this result, but perhaps there was unrecognized confounding by other covariates.

A few studies have examined the relationship between the prevalence of antibiotic-resistant organisms and measures of infection prevention and control activities.22,24-27 In 1 study involving 27 European hospitals, MRSA prevalence was not found to be associated with infection control infrastructure, hand hygiene, or antibiotic stewardship.22 However, in a French study, lower MRSA infection prevalence was associated with a higher composite of infection control activities designed to reduce nosocomial infections.25 In other European countries, more aggressive implementation of infection control measures appeared to be associated with lower MRSA prevalence.26,27 In this study, we attempted to determine whether any specific policies related to the control of antibiotic-resistant organisms were associated with prevalence. Lower prevalence of MRSA and VRE were found in facilities that routinely used private rooms to accommodate patients with these organisms. This finding is consistent with results of other studies28 and lends further support to published guidelines for the implementation of contact precautions in a private room for patients known to be colonized or infected with MRSA or VRE.9,29,30 The routine use of an antiseptic soap, such as chlorhexidine gluconate, for daily washing of patients with MRSA was associated with lower MRSA infection rates, as found in other studies.31 A policy of enhanced environmental cleaning of rooms used for patients with VRE was associated with lower VRE rates, consistent with reports indicating an important role for the hospital environment in VRE transmission.32,33

We believe that the results of this study are representative of Canadian adult acute care hospitals with at least 50 beds, since a large sample participated in the study and the participating sites were similar in several respects to nonparticipating hospitals. However, these results are not applicable to pediatric hospitals or to psychiatric, rehabilitation, or long-term care facilities. Because it was not feasible to ensure that all cases were culture confirmed on the survey date, it is possible that some cases may have been missed or that some were included when they were no longer colonized with MRSA or VRE. However, nearly half of the MRSA and VRE cases had been identified during the current admission, and the remainder were still in isolation precautions and presumed to have persistent carriage of these organisms.32,34 The study was subject to detection bias, since prevalence of colonization varies depending on screening practices at individual facilities, a variable we could not control. There may have been an underestimate of CDI cases, since only 9% of the participating hospital laboratories used polymerase chain reaction for detection of C. difficile toxin B, a more sensitive assay than the enzyme immunoassays used in most hospitals at the time of the survey. We did not have data regarding hand hygiene compliance or antibiotic utilization, and we were able to describe infection prevention and control policies but did not audit actual practices.

The results reported here represent the first national survey of the prevalence of MRSA, VRE, and CDI in Canadian hospitals and can be used as a baseline for future prevalence studies in Canada. The apparent association of prevalence with certain institutional infection prevention and control policies deserves further study.

Acknowledgments

We thank the infection control professionals at participating hospitals who collected and submitted data for the survey.

Potential conflicts of interest. All authors report no conflicts of interest relevant to this article. All authors submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and the conflicts that the editors consider relevant to this article are disclosed here.

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Acknowledgments

We thank the infection control professionals at participating hospitals who collected and submitted data for the survey.

Potential conflicts of interest. All authors report no conflicts of interest relevant to this article. All authors submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and the conflicts that the editors consider relevant to this article are disclosed here.

References

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