Search

Background: Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3)., Methodology/principal Findings: Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively)., Conclusions/significance: MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Objective: Interventions for reducing methicillin-resistant Staphylococcus aureus (MRSA) healthcare-associated disease require outcome assessment; this is typically done by manual chart review to determine infection, which can be labor intensive. The purpose of this study was to validate electronic tools for MRSA healthcare-associated infection (HAI) trending that can replace manual medical record review., Design and Setting: This was an observational study comparing manual medical record review with 3 electronic methods: raw culture data from the laboratory information system (LIS) in use by our healthcare organization, LIS data combined with admission-discharge-transfer (ADT) data to determine which cultures were healthcare associated (LIS + ADT), and the CareFusion MedMined Nosocomial Infection Marker (NIM). Each method was used for the same 7-year period from August 2003 through July 2010., Patients: The data set was from a 3-hospital organization covering 342,492 admissions., Results: Correlation coefficients for raw LIS, LIS + ADT, and NIM were 0.976, 0.957, and 0.953, respectively, when assessed on an annual basis. Quarterly performance for disease trending was also good, with R(2) values exceeding 0.7 for all methods., Conclusions: The electronic tools accurately identified trends in MRSA HAI incidence density when all infections were combined as quarterly or annual data; the performance is excellent when annual assessment is done. These electronic surveillance systems can significantly reduce (93% [in-house-developed program] to more than 99.9999% [commercially available systems]) the personnel resources needed to monitor the impact of a disease control program.

Background: Considerable hospital resources are dedicated to minimizing the number of methicillin-resistant Staphylococcus aureus (MRSA) infections. One tool that is commonly used to achieve this goal is surveillance for MRSA colonization. This process is costly, and false-positive test results lead to isolation of individuals who do not carry MRSA. The performance of this technique would improve if patients who are at high risk of colonization could be readily targeted., Methods: Five MRSA colonization prediction rules of varying complexity were derived in a population of 23,314 patients who were consecutively admitted to a US hospital and tested for colonization. Rules incorporated only prospectively collected, structured electronic data found in a patient's record within 1 day of hospital admission. These rules were tested in a validation cohort of 26,650 patients who were admitted to 2 other hospitals., Results: The prevalence of MRSA at hospital admission was 2.2% and 4.0% in the derivation and validation cohorts, respectively. Multivariable modeling identified predictors of MRSA colonization among demographic, admission-related, pharmacologic, laboratory, physiologic, and historical variables. Five prediction rules varied in their performance, but each could be used to identify the 30% of patients who accounted for greater than 60% of all cases of MRSA colonization and approximately 70% of all MRSA-associated patient-days. Most rules could also identify the 20% of patients with a greater than 8% chance of colonization and the 40% of patients among whom colonization prevalence was 2% or less., Conclusions: We report electronic prediction rules that can fully automate triage of patients for MRSA-related hospital admission testing and that offer significant improvements on previously reported rules. The efficiencies introduced may result in savings to infection control programs with little sacrifice in effectiveness.

Our three-hospital system began active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, with decolonization of positive patients, on all admissions starting 1 August 2005. A question not previously addressed is whether reduction of the incidence of MRSA disease would lower the total number of S. aureus clinical isolates recovered by the microbiology laboratory that are reported to health care providers. The decreases in the numbers of MRSA and total S. aureus clinical isolates for each year after August 2005 were highly statistically significant compared to the numbers in each of the prior 3 years (P < 0.0001).

Objective: We evaluated the usefulness of topical decolonization therapy for reducing the risk of methicillin-resistant Staphylococcus aureus (MRSA) infection among MRSA-colonized inpatients., Design: Retrospective cohort study., Setting and Intervention: Three hospitals with universal surveillance for MRSA; at their physician's discretion, colonized patients could be treated with a 5-day course of nasal mupirocin calcium 2%, twice daily, plus chlorhexidine gluconate 4% every second day., Patients and Methods: MRSA carriers were later retested for colonization (407 subjects; study 1) or followed up for development of MRSA infection (933 subjects; study 2). Multivariable methods were used to determine the impact of decolonization therapy on the risks of sustained colonization (in study 1) and MRSA infection (in study 2)., Results: Independent risk factors for sustained colonization included residence in a long-term care facility (odds ratio [OR], 1.8 [95% confidence interval [CI], 1.1-3.2]) and a pressure ulcer (OR, 2.3 [95% CI, 1.2-4.4]). Mupirocin at any dose decreased this risk, particularly during the 30-60-day period after therapy; mupirocin resistance increased this risk (OR, 4.1 [95% CI, 1.6-10.7]). Over a median follow-up duration of 269 days, 69 (7.4%) of 933 patients developed infection. Independent risk factors for infection were length of stay (hazard ratio [HR], 1.2 per 5 additional days [95% CI, 1.0-1.4]), chronic lung disease (HR, 1.7 [95% CI, 1.0-2.8]), and receipt of non-MRSA-active systemic antimicrobial agents (HR, 1.8 [95% CI, 1.1-3.1]). Receipt of mupirocin did not affect the risk of infection, although there was a trend toward delayed infection among patients receiving mupirocin (median time to infection, 50 vs 15.5 days; P=.06)., Conclusions: Mupirocin-based decolonization therapy temporarily reduced the risk of continued colonization but did not decrease the risk of subsequent infection.

Background: The effect of large-scale expanded surveillance for methicillin-resistant Staphylococcus aureus (MRSA) on health care-associated MRSA disease is not known., Objective: To examine the effect of 2 expanded surveillance interventions on MRSA disease., Design: Observational study comparing rates of MRSA clinical disease during and after hospital admission in 3 consecutive periods: baseline (12 months), MRSA surveillance for all admissions to the intensive care unit (ICU) (12 months), and universal MRSA surveillance for all hospital admissions (21 months)., Setting: A 3-hospital, 850-bed organization with approximately 40,000 annual admissions., Intervention: Polymerase chain reaction-based nasal surveillance for MRSA followed by topical decolonization therapy and contact isolation of patients who tested positive for MRSA., Measurements: Poisson and segmented regression models were used to compare prevalence density of hospital-associated clinical MRSA disease (bloodstream, respiratory, urinary tract, and surgical site) in each period. Rates of bloodstream disease with methicillin-susceptible S. aureus were used as a control., Results: The prevalence density of aggregate hospital-associated MRSA disease (all body sites) per 10,000 patient-days at baseline, during ICU surveillance, and during universal surveillance was 8.9 (95% CI, 7.6 to 10.4), 7.4 (CI, 6.1 to 9.0; P = 0.15 compared with baseline), and 3.9 (CI, 3.2 to 4.7; P < 0.001 compared with baseline and ICU surveillance), respectively. During universal surveillance, the prevalence density of MRSA infection at each body site had a statistically significant decrease compared with baseline. The methicillin-susceptible S. aureus bacteremia rate did not statistically significantly change during the 3 periods. In a segmented regression model, the aggregate hospital-associated MRSA disease prevalence density changed by -36.2% (CI, -65.4% to 9.8%; P = 0.17) from baseline to ICU surveillance and by -69.6% (CI, -89.2% to -19.6%]; P = 0.03) from baseline to universal surveillance. During universal surveillance, the MRSA disease rate decreased during hospitalization and in the 30 days after discharge; no further reduction occurred thereafter. Surveillance with clinical cultures would have identified 17.8% of actual MRSA patient-days, and ICU-based surveillance with polymerase chain reaction would have identified 33.3%., Limitation: The findings rely on observational data., Conclusion: The introduction of universal admission surveillance for MRSA was associated with a large reduction in MRSA disease during admission and 30 days after discharge.

Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) is believed to precede disease. It is therefore reasonable to expect that testing for nasal MRSA colonization could provide guidance in the choice of empirical therapy for infections. We conducted a retrospective review of 5,779 nasal MRSA tests performed within a 24-h period before or after a clinical culture showed the growth of any organism. A positive nasal MRSA test strongly predicted MRSA involvement at a clinical site (relative risk, 12.9 times higher than in the remainder of the population; 95% confidence intervals [CI], 10.4, 16.1). Nasal MRSA colonization also strongly predicted antimicrobial resistance in other organisms. A negative nasal test was less useful; only 217 of 323 patients (67.2%; 95% CI, 61.8, 72.3) with clinical cultures involving MRSA had detectable, concomitant nasal MRSA colonization. Patients with clindamycin-susceptible MRSA infections were less likely (59%) to have nasal colonization than those with clindamycin-resistant MRSA infections (71%; P = 0.042). Patients nasally colonized with MRSA were substantially more likely to have antibiotic-resistant floras in clinical specimens, and this should be considered when initiating therapy. However, nearly a third of MRSA-infected patients were not nasally colonized, suggesting that nasal colonization need not precede disease and that a negative test for nasal colonization would not rule out MRSA disease in settings of moderate or high prevalence.

We evaluated the use of the BD GeneOhm MRSA real-time PCR assay (BD Diagnostics, San Diego, CA) for the detection of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA). The initial evaluation consisted of 403 paired nasal swabs and was done using the specimen preparation provided with the kit and an in-house lysis method that was specifically developed to accommodate large-volume testing using a minimal amount of personnel time. One swab was placed in an achromopeptidase (ACP) lysis solution, and the other was first used for culture and then prepared according to the kit protocol. PCR was performed on both lysates, and results were compared to those for culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay were 98%, 96%, 77%, and 99.7% with the kit lysate and 98%, 95%, 75%, and 99.7% with the ACP lysate (P, not significant), respectively. The second evaluation was done after implementation of all-admission surveillance using PCR with ACP lysis and a sampling of 1,107 PCR-negative samples and 215 PCR-positive samples that were confirmed by culture. The results of this sampling showed an NPV of 99.9% and a PPV of 73.5% (prevalence, 6%), consistent with our initial findings. The BD GeneOhm MRSA assay is an accurate and rapid way to detect MRSA nasal colonization. When one is dealing with large specimen numbers, the ACP lysis method offers easier processing without negatively affecting the sensitivity or specificity of the PCR assay.

A real-time PCR assay was developed to identify common staphylococcal species. A single set of consensus primers was designed to amplify a portion of the 16S rRNA gene, and a pair of fluorescence resonance energy transfer probes was used to identify species based on the unique melt properties of the probes resulting from sequence variations in the amplicons from each species. Nine common staphylococcal strains (S. aureus, S. capitis, S. epidermidis, S. haemolyticus, S. hominis, S. lugdunensis, S. schleiferi, S. simulans, and S. warneri) were used for assay development. The species-specific melting profiles were validated by correctly identifying 36 of 37 coagulase-negative staphylococcal (CoNS) isolates identified by ribotyping. In a study of clinical isolates, the PCR/melt curve approach correctly identified 56/56 S. aureus isolates identified by coagulase/protein A latex agglutination. Fifty-four CoNS clinical isolates characterized using the API Staph assay were studied, with the PCR/melt curve approach yielding matching identifications for 32/54 (59%). The API Staph assay was unable to identify 18 CoNS isolates, and differing results were obtained for 4 isolates. Sequencing of the 22 discrepant or unidentified CoNS samples revealed that the PCR/melt curve results were correct for all but one isolate. Thus, PCR/melt curve analysis achieved a nearly 100% accuracy and performed better than biochemical testing. Performance of the PCR/melt curve approach requires less than 2 h after colony selection. This method thus provides a rapid and accurate approach to the identification of staphylococcal species in the clinical laboratory.

Nasal carriage of Staphylococcus aureus is considered a source of subsequent infection in health care settings. Utilization of real-time polymerase chain reaction (PCR) for detection of S. aureus has the potential to dramatically affect infection control practice by rapidly identifying S. aureus-colonized patients. We developed and validated the use of real-time PCR for detection of S. aureus colonization in two patient populations. Paired nasal swabs were collected from 299 neonates and from 151 adult patients at Evanston Hospital. One swab was used for culture and the other placed into a bacterial lysis solution containing achromopeptidase. The DNA liberated was used as the template for real-time PCR with primers for the femA gene. SYBR Green was used for amplicon detection. In the neonatal population the sensitivity, specificity, predictive value positive and predictive value negative for culture and PCR was 92% versus 96%, 100% versus 100%, 100% versus 100%, and 98% versus 99%, respectively. In the adults the results were 90% versus 100%, 100% versus 98%, 100% versus 96%, and 95% versus 100%, respectively. Real-time PCR was able to detect S. aureus in 2 hours compared to 1 to 4 days for culture and provided sensitivity equal to or greater than culture.

During an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in the neonatal intensive care units at two hospitals, we assessed several sites for detection of MRSA colonization. Nasal cultures found 32 of 33 MRSA-colonized patients (97%). Rectal cultures detected 29% of 24 MRSA-colonized patients identified by paired rectal and nasal samples and axillary samples found 22% of 9 MRSA-colonized patients identified by axillary samples paired with nasal swabs. There were no positive umbilical samples.