Anne Matlow

Mupirocin-Resistant, Methicillin-Resistant Staphylococcus aureus Strains in Canadian Hospitals

ABSTRACT Mupirocin resistance in Staphylococcus aureus is increasingly being reported in many parts of the world. This study describes the epidemiology and laboratory characterization of mupirocin-resistant methicillin-resistant S. aureus (MRSA) strains in Canadian hospitals. Broth microdilution susceptibility testing of 4,980 MRSA isolates obtained between 1995 and 2004 from 32 Canadian hospitals was done in accordance with CLSI guidelines. The clinical and epidemiologic characteristics of strains with high-level mupirocin resistance (HLMupr) were compared with those of mupirocin-susceptible (Mups) strains. MRSA strains were characterized by pulsed-field gel electrophoresis (PFGE) and typing of the staphylococcal chromosomal cassette mec. PCR was done to detect the presence of the mupA gene. For strains with mupA, plasmid DNA was extracted and subjected to Southern blot hybridization. A total of 198 (4.0%) HLMupr MRSA isolates were identified. The proportion of MRSA strains with HLMupr increased from 1.6% in the first 5 years of surveillance (1995 to 1999) to 7.0% from 2000 to 2004 (P < 0.001). Patients with HLMupr MRSA strains were more likely to have been aboriginal (odds ratio [OR], 3.7; 95% confidence interval [CI], 1.5 to 9.4; P = 0.006), to have had community-associated MRSA (OR, 2.2; 95% CI, 1.0 to 5.0; P = 0.05), and to have been colonized with MRSA (OR, 1.7; 95% CI, 1.0 to 3.0; P = 0.04). HLMupr MRSA strains were also more likely to be resistant to fusidic acid (21% versus 4% for mupirocin-susceptible strains; P < 0.001). All HLMupr MRSA strains had a plasmid-associated mupA gene, most often associated with a 9-kb HindIII fragment. PFGE typing and analysis of the plasmid profiles indicate that both plasmid transmission and the clonal spread of HLMupr MRSA have occurred in Canadian hospitals. These results indicate that the incidence of HLMupr is increasing among Canadian strains of MRSA and that HLMupr MRSA is recovered from patients with distinct clinical and epidemiologic characteristics compared to the characteristics of patents with Mups MRSA strains.

The use of Streptococcus pneumoniae nasopharyngeal isolates from healthy children to predict features of invasive disease

BACKGROUND The role of sampling nasopharyngeal carriage isolates of Streptococcus pneumoniae to determine characteristics of isolates causing invasive disease has not been established. METHODS Data were compared from two 1995 studies of S. pneumoniae in Metropolitan Toronto and Peel Region (population, 3.1 million). The first was a prospective survey of nasopharyngeal (NP) carriage in child care centers. The second was a prospective surveillance for all cases of invasive disease. RESULTS There were 545 NP S. pneumoniae isolates obtained from 532 children and 96 cases of invasive S. pneumoniae disease in children. The prevalences of reduced antibiotic susceptibility in the NP carriage and invasive studies, respectively, were: penicillin (16% vs. 11%, P=0.29); erythromycin (12% vs. 7%, P=0.25); and multiresistant (16% vs. 12%, P=0.34). The power to rule out a difference between the groups was <30% for each comparison. Trimethoprim/sulfamethoxazole resistance was more common in NP carriage isolates than invasive isolates (38% vs. 23%, P=0.02). Serotype 14 was more common in invasive isolates, whereas serogroup 6 was more common in NP carriage isolates. Antibiotic-resistant isolates were predominantly serogroups 6, 19 and 23 in both studies. CONCLUSIONS Nasopharyngeal carriage isolates of S. pneumoniae reflect the antibiotic susceptibility rates of invasive isolates found in the same period for most antibiotics. However, even a large study like this may have limited power to detect a difference. The most common NP carriage serotypes are the same as the invasive isolates, although the rank order of specific serotypes is different. Routine surveys of S. pneumoniae NP carriage are not feasible because of the cost of serotyping and limited power of the observations, unless sample sizes are extremely large.

Methicillin-Resistant Staphylococcus aureus Colonization or Infection in Canada: National Surveillance and Changing Epidemiology, 1995-2007

OBJECTIVE To determine the incidence and describe the changing epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection in Canadian hospitals from 1995-2007. SETTING Forty-eight hospitals participating in the Canadian Nosocomial Infection Surveillance Program. DESIGN Prospective, laboratory-based surveillance for incident cases of MRSA colonization or infection among hospitalized patients. METHODS Clinical and epidemiologic data were obtained by review of hospital records. Standard criteria were used to determine whether MRSA colonization or infection was present and whether the MRSA strain was healthcare associated or community associated. A representative subset of isolates was characterized by use of pulsed-field gel electrophoresis and staphylococcal cassette chromosome (SCC) mec typing. RESULTS From 1995 to 2007, a total of 37,169 hospitalized patients were newly identified as either infected or colonized with MRSA, and the overall incidence of both MRSA colonization and MRSA infection increased from 0.65 to 11.04 cases per 10,000 patient-days (P < .001). Of these 37,169 patients, 11,828 (32%) had an MRSA infection, and infection rate increased from 0.36 to 3.43 cases per 10,000 patient-days. The proportion of community-associated MRSA strains increased from 6% to 23% (P < .001). The most common genotype (47% of isolates) was CMRSA-2 (USA100/800); in 2007, CMRSA-10 (USA300) was the second most common strain (27% of isolates), associated with SCCmec type IV. Patients with CMRSA-10 were predominantly from western Canada and were more likely to be children (odds ratio [OR], 10.0 [95% confidence interval {CI}, 7.4-13.4]) and to have infection (OR, 2.3 [95% CI, 1.9-2.7]), especially skin and/or soft tissue infection (OR, 5.9 [95% CI, 5.0-6.9]). CONCLUSIONS The overall incidence of both MRSA colonization and MRSA infection increased 17-fold in Canadian hospitals from 1995 to 2007. There has also been a dramatic increase in cases of community-associated MRSA infection due to the CMRSA-10 (USA300) clone. Continued surveillance is needed to monitor the ongoing evolution of MRSA colonization or infection in Canada and globally.

Apparent lower rates of streptococcal toxic shock syndrome and lower mortality in children with invasive Group A streptococcal infections compared with adults

Since 1985 there have been worldwide reports of increases in severe invasive Group A streptococcal (IGAS) infections. We reviewed the charts of all children with IGAS infections (defined as isolation of Group A streptococcus from a normally sterile site) presenting to our institution over a 7-year period (January, 1985, to December, 1991) and the literature. Streptococcal toxic shock syndrome required hypotension and multisystem organ involvement. Twenty-four patients (mean age, 4.96 +/- 4.4 years) were identified with IGAS infection. One patient (presenting in 1989) met the criteria for probable streptococcal toxic shock syndrome and none died. Eight of 19 Group A streptococcal isolates tested were streptococcal pyrogenic exotoxin (SPE) A producers, most (90%) had the speC gene and all had the speB gene and produced the toxin. No M or T type predominated. The low rates of streptococcal toxic shock syndrome and fatalities among children with IGAS infection are consistent with other pediatric but not with adult series. The apparent differences in outcome of IGAS between children and adults were not explained by the virulence factors we examined and may warrant further investigation.

Defining Bloodstream Infections Related to Central Venous Catheters in Patients With Cancer: A Systematic Review

The objective of this review was to determine whether consistent definitions were used in published studies of bloodstream infections due to central venous catheters in patients with cancer (ie, catheter-related or catheter-associated bloodstream infections). Review of 191 studies reporting catheter-related or catheter-associated bloodstream infections in patients with cancer revealed a lack of uniformity in these definitions. We grouped definitions by type, with 39 articles failing to cite or report a definition. Definitions included those of the Centers for Disease Control and Prevention (n = 39) and the Infectious Diseases Society of America (n = 18). The criteria included in the definitions in studies were also tabulated. Clinical manifestations were frequently included. Definitions used have been highly variable; comparability of risk factors, incidence, management, and outcomes of such infections is difficult to achieve across studies. Future research should focus on development of a common definition of catheter-related and catheter-associated bloodstream infections for both adults and children with cancer.

The Role of Nurse Understaffing in Nosocomial Viral Gastrointestinal Infections on a General Pediatrics Ward

OBJECTIVE To examine the relationship between nurse staffing levels and the rate of nosocomial viral gastrointestinal infections (NVGIs) in a general pediatrics population. DESIGN Retrospective descriptive study. SETTING A general pediatrics ward at The Hospital for Sick Children in Toronto, Ontario, Canada, a 320-bed, tertiary-care pediatric institution. RESULTS Forty-three NVGIs were detected in 37 patients of 2,929 admissions (1.3%). The monthly NVGI rate correlated significantly with the monthly night patient-to-nurse ratio (r = 0.56) and the monthly day patient-to-nurse ratio (r = 0.50). The nursing hours per patient-day during the preinfection period (PIP) were significantly lower than those during the nonpreinfection period (NPIP; 12.5 vs 13.0). There was no difference between the PIP and the NPIP day patient-to-nurse ratios (3.31 vs 3.32), but there was a significant difference between the PIP and the NPIP night patient-to-nurse ratios (3.26 vs 3.16). The incidence of NVGIs in the 72-hour period after any day when the nursing hours per patient-day were less than 10.5 was 6.39 infections per 1,000 patient-days, compared with 2.17 infections per 1,000 patient-days in periods with more than 10.5 nursing hours per patient-day (rate ratio, 2.94; 95% confidence interval, 2.16 to 4.01). CONCLUSION Nurse understaffing contributed to an increased NVGI rate in our general pediatrics population, and should be assessed as a risk factor in outbreak investigations.

Nosocomial urinary tract infections at a pediatric hospital

Although the epidemiology of nosocomial urinary tract infections (NUTIs) is well-described in the adult population, there is little information on children. We therefore reviewed all our patients with NUTIs, to determine their age, underlying diagnoses, microorganisms involved, use of catheters and secondary bacteremias. During a 2-year period at our institution, NUTIs accounted for 10% of all nosocomial infections (0.8 infections/100 admissions). Of 44948 patients admitted during this period 0.7% (n = 318) acquired 351 episodes of NUTI. The patient ages ranged from 5 days to 21 years. The highest rates of NUTIs per ward (NUTI/100 admissions or transfers to the ward) were seen in the neonatal surgery (4.8), hematology/oncology (2.7), infant neurosurgery (2.1) and neonatal intensive care units (1.9). The most common organisms isolated were Escherichia coli (26%), Enterococccus sp. (15%), Pseudomonas sp. (13%), Klebsiella sp. (10%) and coagulase-negative Staphylococcus (9%). Catheterrelated infections accounted for 48% of all the NUTIs. Secondary bacteremia occurred rarely, with an incidence of 2.9% (n = 7). We conclude that NUTIs represent an important proportion (10%) of nosocomial infections in our population of hospitalized children, but secondary bacteremia is uncommon.

Neonatal Escherichia coli infections: concerns regarding resistance to current therapy

Currently recommended antibiotic treatment of suspected neonatal sepsis is ampicillin and an aminoglycoside. Recently, we observed increasing ampicillin and gentamicin resistance in strains of Escherichia coli isolated from neonates at our institution. We therefore reviewed clinical and laboratory records of all neonates with systemic infection, hospitalized from 1994 through 1998, from whom E. coli was isolated from blood and/or cerebrospinal fluid. The influence of perinatal variables (e.g. rupture of foetal membranes > 24 h, group B Streptococcus (GBS) colonization, urinary tract infection during pregnancy and the use of antepartum and/or intrapartum antibiotics), and neonatal variables (e.g. gestational age, age at onset of sepsis (early: 72h, late: >72h), number of E. coli septic recurrences, and associated underlying medical and/or surgical conditions) on antimicrobial susceptibilities of invasive E. coli isolates was studied. Twenty‐three neonates with invasive E. coli infection were identified; most [19 (83%)] presented as late‐onset sepsis (LOS). Ampicillin‐resistant E. coli were isolated in 75% and 53% of neonates in the early‐ and late‐onset groups, respectively. Gentamicin resistance was found in 50% of early‐onset sepsis (EOS) isolates compared with 16% in the late‐onset group. Isolates from two neonates with EOS were resistant to both ampicillin and gentamicin. One neonate with EOS and three with LOS had recurrent E. coli sepsis; all isolates were ampicillin‐resistant and one was gentamicin‐resistant. All these neonates were initially treated with ampicillin and gentamicin. Both groups had associated underlying medical and/or surgical conditions (50% early‐onset, 47% late‐onset). Maternal GBS colonization occurred in 2 (50%) versus 3 (16%) of EOS and LOS cases, respectively. All GBS colonized women received intrapartum ampicillin prior to delivery.

Detection and Characterization of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Isolates in Canada: Results from the Canadian Nosocomial Infection Surveillance Program, 1995-2006

ABSTRACT We describe the epidemiology of heterogeneously resistant Staphylococcus aureus (hVISA) identified in Canadian hospitals between 1995 and 2006. hVISA isolates were confirmed by the population analysis profiling-area under the curve method. Only 25 hVISA isolates (1.3% of all isolates) were detected. hVISA isolates were more likely to have been health care associated (odds ratio [OR], 5.1; 95% confidence interval [CI], 1.9 to 14.2) and to have been recovered from patients hospitalized in central Canada (OR, 3.0; 95% CI, 1.2 to 7.4). There has been no evidence of vancomycin “MIC creep” in Canadian strains of methicillin (meticillin)-resistant S. aureus, and hVISA strains are currently uncommon.

Sustained endemicity of Burkholderia cepacia complex in a pediatric institution, associated with contaminated ultrasound gel.

OBJECTIVE To determine whether contaminated ultrasound gel is the source of intermittent outbreaks of nosocomial infection due to Burkholderia cepacia complex in patients without cystic fibrosis since 1992. DESIGN A prospective clinical and in vitro study of all in-use bottles of ultrasound gel, as well as a retrospective analysis of archived bacterial strains, were performed. Handling of gel for clinical purposes throughout the hospital was evaluated. Gel and archived clinical isolates of B. cepacia complex were speciated to genomovar level and characterized by pulsed-field gel electrophoresis, and the pulsed-field gel electrophoresis patterns were compared. SETTING The Hospital for Sick Children, a 300-bed, tertiary care, pediatric academic health sciences center in Toronto, Canada. PATIENTS All patients without cystic fibrosis from whom B. cepacia complex was recovered at the Hospital for Sick Children since 1992. RESULTS No standardized protocol for storage or handling of ultrasound gel was found. Gel from 39% of bottles grew either B. cepacia (genomovar I) or Burkholderia stabilis (genomovar IV). These isolates had pulsed-field gel electrophoresis patterns identical to 2 of the 7 clinical pulsed-field gel electrophoresis types that are responsible for 88% of clinical isolates. CONCLUSIONS Contaminated ultrasound gel contributed to nosocomial infection due to B. cepacia complex in this institution over the course of 10 years. Suggested guidelines for the handling of ultrasound gel are provided.