To explore differences in the prevalence of healthcare-associated infections (HAIs) according to survey methodology.

Repeated point and period prevalence survey strategies.

University-affiliated primary and tertiary care center.

Analysis of data collected from 2006 to 2012 from annual HAI prevalence surveys using definitions proposed by the US Centers for Disease Control and Prevention. The study design allowed the analysis of the same data in the format of a point or a period prevalence survey.

Pooled point and period HAI prevalence was 7.46% and 9.84% (+32%), respectively. This additional 32% was mainly attributable to infections of the lower respiratory tract (2.42% vs 3.20% [+32%]) and the urinary tract (1.76% vs 2.62% [+49%]). Differences in surgical site infections (1.02% vs 1.20% [+19%]) and bloodstream infections (0.76% vs 0.86% [+13%]) were smaller. HAI prevalence for the point and period methodology in acute and long-term care were 7.47% versus 9.38 (+26%) and 8.37% versus 11.89% (+42%), respectively. Differences were stable over time. Focusing on the 4 major HAIs (respiratory tract, urinary tract, surgical site, and bloodstream infections) misses one-quarter of all HAIs.

More HAIs are identified by the period prevalence method, especially those of shorter duration (lower respiratory and urinary tract), which would make this method more suitable to be used in long-term care. Results of the 2 study methods cannot be benchmarked against each other.

Infect Control Hosp Epidemiol 2014;35(6):674–684

To understand the prevalence of multidrug-resistant organism (MDRO) infections among nursing home (NH) residents and the potential for their spread between NHs and acute care hospitals (ACHs).

Descriptive analyses of MDRO infections among NH residents using all NH residents in the Long-Term Care Minimum Data Set (MDS) 3.0 between October 1, 2010 and December 31, 2011.

Analysis of MDS data revealed a very high volume of bidirectional patient flow between NHs and ACHs, indicating the need to study MDRO infections in NHs as well as in hospitals. A total of 4.24% of NH residents had an active MDRO diagnosis on at least 1 MDS assessment during the study period. This rate significantly varied by sex, age, urban/rural status, and state. Approximately 2% of NH discharges to ACHs involved a resident with an active diagnosis of infection due to MDROs. Conversely, 1.8% of NH admissions from an ACH involved a patient with an active diagnosis of infection due to MDROs. Among residents who acquired an MDRO infection during the study period, 57% became positive in the NH, 41% in the ACH, and 2% in other settings (eg, at a private home or apartment).

Even though NHs are the most likely setting where residents would acquire MDROs after admission to an NH (accounting for 57% of cases), a significant fraction of NH residents acquire MDRO infection at ACHs (41%). Thus, effective MDRO infection control for NH residents requires simultaneous, cooperative interventions among NHs and ACHs in the same community.

Despite implementation of recommended best practices, our central line-associated bloodstream infection (CLABSI) rates remained high. Our objective was to describe the impact of chlorhexidine gluconate (CHG) bathing on CLABSI rates in neonates.

Infants with a central venous catheter (CVC) admitted to the neonatal intensive care unit from April 2009 to March 2013 were included. Neonates with a birth weight of 1,000 g or less, aged less than 28 days, and those with a birth weight greater than 1,000 g were bathed with mild soap until March 31, 2012 (baseline), and with a 2% CHG-impregnated cloth starting on April 1, 2012 (intervention). Infants with a birth weight of 1,000 g or less, aged 28 days or more, were bathed with mild soap during the entire period. Neonatal intensive care unit nurses reported adverse events. Adjusted incidence rate ratios (aIRRs), using Poisson regression, were calculated to compare CLABSIs/1,000 CVC-days during the baseline and intervention periods.

Overall, 790 neonates with CVCs were included in the study. CLABSI rates decreased during the intervention period for CHG-bathed neonates (6.00 vs 1.92/1,000 CVC-days; aIRR, 0.33 [95% confidence interval (CI), 0.15-0.73]) but remained unchanged for neonates with a birth rate of 1,000 g or less and aged less than 28 days who were not eligible for CHG bathing (8.57 vs 8.62/1,000 CVC-days; aIRR, 0.86 [95% CI, 0.17-4.44]). Overall, 195 infants with a birth weight greater than 1,000 g and 24 infants with a birth weight of 1,000 g or less, aged 28 days or more, were bathed with CHG. There was no reported adverse event.

We observed a decrease in CLABSI rates in CHG-bathed neonates in the absence of observed adverse events. CHG bathing should be considered if CLABSI rates remain high, despite the implementation of other recommended measures.

To determine the prevalence, risk factors, and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) colonization at the time of admission to acute medical units and to develop a cost-effective screening strategy.

Nasal and groin screening cultures were performed for patients at admission to 15 acute medical units in all 7 catchment regions in Hong Kong. All MRSA isolates were subjected to spa typing.

The overall carriage rate of MRSA was 14.3% (95% confidence interval [CI], 13.5–15.1). MRSA history within the past 12 months (adjusted odds ratio [OR], 4.60 [95% CI, 3.28–6.44]), old age home residence (adjusted OR, 3.32 [95% CI, 2.78–3.98]), and bedbound state (adjusted OR, 2.19 [95% CI, 1.75–2.74]) were risk factors selected as MRSA screening criteria that provided reasonable sensitivity (67.4%) and specificity (81.8%), with an affordable burden (25.2%). spa typing showed that 89.5% (848/948) of the isolates were clustered into the 4 spa clonal complexes (CCs): spa CC1081, spa CC032, spa CC002, and spa CC4677. Patients colonized with MRSA spa types t1081 (OR, 1.77 [95% CI, 1.49–2.09]) and t4677 (OR, 3.09 [95% CI, 1.54–6.02]) were more likely to be old age home residents.

MRSA carriage at admission to acute medical units was prevalent in Hong Kong. Our results suggest that targeted screening is a pragmatic approach to increase the detection of the MRSA reservoir. Molecular typing suggests that old age homes are epicenters in amplifying the MRSA burden in acute hospitals. Enhancement of infection control measures in old age homes is important for the control of MRSA in hospitals.

Despite surveillance, the Quebec Healthcare-Associated Infections Surveillance Program saw no improvement in vascular access–associated bloodstream infections in hemodialysis (HD). We aimed to determine the infection control measures recommended and implemented in Quebec’s HD units, compliance of local protocols to infection control practice guidelines, and reasons behind the low prevalence of arteriovenous fistulas.

An online survey was elaborated on the basis of the Centers for Disease Control and Prevention (CDC) and National Kidney Foundation Kidney Disease Outcomes Quality Initiative guidelines. The questionnaire was validated (construct, content, face validity, and reliability) and sent to all HD units in Quebec (n = 40). Results were analyzed using descriptive statistics, linear regression, and Poisson regression.

Thirty-seven (93%) of 40 HD units participated. Thirty (94%) of the 32 centers where central catheters are inserted have written insertion protocols. Compliance with practice guidelines is good, except for full-body draping during catheter insertion (79%) and ointment use at insertion site (3%). Prevention measures for catheter maintenance are in accordance with guidelines, except for skin disinfection with at least 0.5% chlorhexidine and 70% alcohol (67% compliance) and regular antiseptic ointment use at the insertion site (3%). Before fistula cannulation, skin preparation is suboptimal; forearm hygiene is performed in only 61% of cases. Several factors explain the low rate of fistulas, including patient preference (69%) and lack of surgical resources (39%; P = .01).

Improvement in standardization of care according to practice guidelines is necessary. Fistula rate could be increased by improving access to surgical resources and patient education. Strategies are now being elaborated to address these findings.

Prevalence of multidrug-resistant (MDR) gram-negative (GN) bacteria is increasing globally and is complicated by patient movement between acute and long-term care facilities (LTCFs). In Asia, the contribution of LTCFs as a source of MDR GN infections is poorly described. We aimed to define the association between residence in LTCFs and MDR GN bloodstream infections (BSIs).

Secondary analysis of data from an observational cohort.

Two tertiary referral hospitals in Singapore, including the 1,400-bed Tan Tock Seng Hospital and the 1,600-bed Singapore General Hospital.

Adult patients with healthcare-onset (HCO) or hospital-onset (HO) GN BSI.

Patients were identified from hospital databases using standard definitions. Risk factors for both MDR GN HCO and HO BSI were analyzed using a multivariable logistic regression model.

A total of 675 episodes of GN BSI occurred over a 31-month period. Residence in a LTCF was an independent risk factor for developing MDR GN BSI (odds ratio [OR], 5.1 [95% confidence interval (CI), 2.2–11.9]; P < .01) when antibiotics were not used within the preceding 30 days. This risk persisted beyond the first 48 hours of hospitalization (OR, 3.4 [95% CI, 1.3–9.0]; P = .01). Previous culture growing an MDR organism (OR, 1.8 [95% CI, 1.3–2.7]; P < .01), previous antibiotic use (OR, 1.8 [95% CI, 1.2–2.6]; P < .01), and intensive care unit stay (OR, 2.2 [95% CI, 1.2–3.9]; P = .01), increased the risk of MDR GN BSI.

Residence in a LTCF is an independent risk factor for MDR GN BSI. Attempts to contain MDR GN bacteria in large Asian cities, where the proportion of the population that is elderly is projected to increase, should include infection prevention strategies that engage LTCFs.

To develop and validate a methodology for electronic surveillance of catheter-associated urinary tract infections (CAUTIs).

Diagnostic accuracy study.

A 425-bed university hospital.

A total of 1,695 unique inpatient encounters from November 2009 through November 2010 with a high clinical suspicion of CAUTI.

An algorithm was developed to identify incident CAUTIs from electronic health records (EHRs) on the basis of the Centers for Disease Control and Prevention (CDC) surveillance definition. CAUTIs identified by electronic surveillance were compared with the reference standard of manual surveillance by infection preventionists. To determine diagnostic accuracy, we created 2 × 2 tables, one unadjusted and one adjusted for misclassification using chart review and case adjudication. Unadjusted and adjusted test statistics (percent agreement, sensitivity, specificity, positive predictive value [PPV], negative predictive value [NPV], and κ) were calculated.

Electronic surveillance identified 64 CAUTIs compared with manual surveillance, which identified 19 CAUTIs for 97% agreement, 79% sensitivity, 97% sensitivity, 23% PPV, 100% NPV, and κ of .33. Compared with the reference standard adjusted for misclassification, which identified 55 CAUTIs, electronic surveillance had 98% agreement, 80% sensitivity, 99% specificity, 69% PPV, 99% NPV, and κ of .71.

The electronic surveillance methodology had a high NPV and a low PPV compared with the reference standard, indicating a role of the electronic algorithm in screening data sets to exclude cases. However, the PPV markedly improved compared with the reference standard adjusted for misclassification, suggesting a future role in surveillance with improvements in EHRs.

Infect Control Hosp Epidemiol 2014;35(6):685–691

The purpose of this study was to estimate the incidence of deep periprosthetic joint infections (PJIs) after primary total hip replacement (THR) in Sweden prior to the introduction of a national initiative to reduce these infections.

Prospective open cohort study with 2 years follow-up of each subject.

All THR-performing clinics in Sweden.

All patients registered for a primary THR in the Swedish Hip Arthroplasty Register between July 1, 2005, and December 31, 2008, were selected for the study (45,531 patients with 49,219 THRs) and were matched with the Swedish Prescribed Drug Register. All patients with a minimum of 4 weeks of continuous outpatient antibiotic treatment within 2 years after their primary THR (1,989 patients with 2,219 THRs) were selected for a medical records review, and the number of cases with PJI was determined.

The cumulative incidence of PJI within 2 years after primary THR was 0.9% (95% confidence interval, 0.85–1.02; n = 443), and 405 of these had been reoperated. The incidence rate of PJI for the first 3 months was 5 per 10,000 THR-weeks and, thereafter, 0.3 per 10,000 THR-weeks. Staphylococcus aureus and coagulase-negative staphylococci were the most common bacteria isolated.

This study describes a new method of national postoperative infection surveillance. The incidence is similar to previous smaller reports and is useful for monitoring changes over time to evaluate the national initiative to reduce infections.

To determine the durability of methicillin-resistant Staphylococcus aureus (MRSA)–free status after patients are removed from contact precautions and the association of specific clearance policy variables with survival

Retrospective cohort study from October 2007 to April 2013.

Veteran Affairs Boston Healthcare System.

Patients with a prior history of MRSA who were removed from contact precautions after deemed cleared of their MRSA status by infection prevention.

Active nasal screening results and clinical data from acute, long-term, and outpatient care facilities were evaluated to determine survival of MRSA-free status in a time-to-event analysis.

A total of 351 unique patients were followed for 107,112 patient-days. The median age was 68 years. Overall, 249 (71%) of patients remained MRSA-free, and 102 (29%) reverted to MRSA positive. The median MRSA-free survival was 880 days. Comorbidities, presence of indwelling devices, and the use of systemic antibiotics at the time of clearance screening were not associated with MRSA-free survival. More than 21,000 days of inpatient isolation days were avoided during the study period.

The majority of patients removed from contact precautions remained MRSA-free for more than 2 years. Antibiotic use at the time of clearance was not associated with reductions in MRSA-free survival. These findings can be used to simplify clearance criteria, promote clearance policies, and reduce patient isolation days.

Outbreaks of multidrug-resistant organisms have been linked to endoscope reprocessing lapses. Meticulous manual cleaning before high-level disinfection (HLD) is essential in reducing residual contamination that can interfere with HLD. Current reprocessing guidelines state that visual inspection is sufficient to confirm adequate cleaning.

Our aim was to evaluate contamination of clinically used endoscopes, using visual inspection and rapid indicator tests before and after manual cleaning. A second objective was to determine which rapid indicator instruments and methods could be used for quality improvement initiatives in endoscope reprocessing.

Clinical use study of endoscope reprocessing effectiveness.

Tertiary care teaching hospital with an inpatient endoscopy center.

Researchers sampled endoscopes used for gastrointestinal procedures before and after manual cleaning. The external surfaces and 1 channel of each endoscope were visually inspected and tested with rapid indicators to measure protein, blood, and adenosine triphosphate (ATP) contamination levels.

Multiple components were sampled during 37 encounters with 12 unique endoscopes. All bedside-cleaned endoscopes had high levels of ATP and detectable blood or protein, whether or not any residue was visible. Although there was no visible residue on any endoscopes after manual cleaning, 82% had at least 1 positive rapid indicator test.

Relying solely on visual inspection of endoscopes prior to HLD is insufficient to ensure reprocessing effectiveness. For quality assurance initiatives, tests of different endoscope components using more than 1 indicator may be necessary. Additional research is needed to validate specific monitoring protocols.

Determine the prevalence of extended-spectrum β-lactamase (ESBL)–producing Enterobacteriaceae (ESBL-PE) contamination of food and colonization of food handlers in a hospital kitchen and compare retrieved ESBL-PE strains with patient isolates.

Cross-sectional study.

A 2,200-bed tertiary care university hospital in Switzerland.

Food handlers.

Raw and prepared food samples were obtained from the hospital kitchen, with a comparator group from local supermarkets. Fecal samples collected from food handlers and selectively pre-enriched homogenized food samples were inoculated onto selective chromogenic media. Phenotypic confirmation of ESBL production was performed using the double disk method. Representative ESBL-PE were characterized using polymerase chain reaction (PCR) and sequencing for blaCTX-M, blaSHV, and blaTEM genes, and Escherichia coli strains were typed using phylotyping, repetitive element palindromic PCR, and multilocus sequence typing. Meat samples were screened for antibiotic residues using liquid chromatography time-of-flight mass spectrometry.

Sixty (92%) of the raw chicken samples were ESBL-PE positive, including 30 (86%) of the hospital samples and all supermarket samples. No egg, beef, rabbit, or cooked chicken samples were ESBL-PE positive. No antibiotic residues were detected. Six (6.5%) of 93 food handlers were ESBL-PE carriers. ESBL-PE strains from chicken meat more commonly possessed blaCTX-M-1 and blaCTX-M-2, whereas blaCTX-M-14and blaCTX-M-15 were predominant among strains of human origin. There was partial overlap in the sequence type of E. coli strains of chicken and human origin. No E. coli ST131 strains or blaCTX-M-15 genes were isolated from meat.

Although there is significant ESBL-PE contamination of delivered chicken meat, current preventive strategies minimize risks to food handlers, hospital staff, and patients.

To understand the genotypic spectrum of environmental contamination of Staphylococcus aureus in households and its persistence

Prospective longitudinal cohort investigation.

Index participants identified at 2 academic medical centers.

Adults and children with S. aureus skin infections and their household contacts in Los Angeles and Chicago.

Household fomites were surveyed for contamination at baseline and 3 months. All isolates underwent genetic typing.

We enrolled 346 households, 88% of which completed the 3-month follow-up visit. S. aureus environmental contamination was 49% at baseline and 51% at 3 months. Among households with a USA300 methicillin-resistant S. aureus (MRSA) body infection isolate, environmental contamination with an indistinguishable MRSA strain was 58% at baseline and 63% at 3 months. Baseline factors associated with environmental contamination by the index subject’s infection isolate were body colonization by any household member with the index subject’s infection isolate at baseline (odds ratio [OR], 10.93 [95% confidence interval (CI), 5.75–20.79]), higher housing density (OR, 1.47 [95% CI, 1.10–1.96]), and more frequent household fomite cleaning (OR, 1.62 [95% CI, 1.16–2.27]). Household environmental contamination with the index subject’s infection strain at 3 months was associated with USA300 MRSA and a synergistic interaction between baseline environmental contamination and body colonization by any household member with the index subject’s infection strain.

We found that infecting S. aureus isolates frequently persisted environmentally in households 3 months after skin infection. Presence of pathogenic S. aureus strain type in the environment in a household may represent a persistent reservoir that places household members at risk of future infection.

Infect Control Hosp Epidemiol 2014;35(11):1373–1382

The current central line–associated bloodstream infection (CLABSI) surveillance rate calculation does not account for multiple concurrent central venous catheters (CVCs). The presence of multiple CVCs creates more points of entry into the bloodstream, potentially increasing CLABSI risk. Multiple CVCs may be used in sicker patients, making it difficult to separate the relative contributions of multiple CVCs and comorbidities to CLABSI risk. We explored the relative impact of multiple CVCs, patient comorbidities, and disease severity on the risk of CLABSI.

Case-control study.

A total of 197 case patients and 201 control subjects with a CVC inserted during hospitalization at a tertiary care academic medical center from January 1, 2008, to December 31, 2010.

Multiple CVCs was the exposure of interest; the primary outcome was CLABSI. Multivariable logistic regression was conducted to estimate odds ratios (ORs) and 95% confidence intervals (CIs) describing the association between CLABSI and multiple CVCs with and without controlling for Acute Physiology and Chronic Health Evaluation (APACHE) II and Charlson comorbidity index (CCI) scores as measures of disease severity and patient comorbidities, respectively.

Patients with multiple CVCs (n = 78) showed a 4.2 (95% CI, 2.2–8.4) times greater risk of CLABSI compared with patients with 1 CVC after adjusting for CLABSI risk factors. When including APACHE II and CCI scores, multiple CVCs remained an independent risk factor for CLABSI (OR, 3.4 [95% CI, 1.7–6.9]).

Multiple CVCs is an independent risk factor for CLABSI even after adjusting for severity of illness. Adjustment for this risk may be necessary to accurately compare rates between hospitals.

Infect Control Hosp Epidemiol 2014;35(9):1140-1146

To identify current outpatient parenteral antibiotic therapy practice patterns and complications.

We administered an 11-question survey to adult infectious disease physicians participating in the Emerging Infections Network (EIN), a Centers for Disease Control and Prevention–sponsored sentinel event surveillance network in North America. The survey was distributed electronically or via facsimile in November and December 2012. Respondent demographic characteristics were obtained from EIN enrollment data.

Overall, 555 (44.6%) of EIN members responded to the survey, with 450 (81%) indicating that they treated 1 or more patients with outpatient parenteral antimicrobial therapy (OPAT) during an average month. Infectious diseases consultation was reported to be required for a patient to be discharged with OPAT by 99 respondents (22%). Inpatient (282 [63%] of 449) and outpatient (232 [52%] of 449) infectious diseases physicians were frequently identified as being responsible for monitoring laboratory results. Only 26% (118 of 448) had dedicated OPAT teams at their clinical site. Few infectious diseases physicians have systems to track errors, adverse events, or “near misses” associated with OPAT (97 [22%] of 449). OPAT-associated complications were perceived to be rare. Among respondents, 80% reported line occlusion or clotting as the most common complication (occurring in 6% of patients or more), followed by nephrotoxicity and rash (each reported by 61%). Weekly laboratory monitoring of patients who received vancomycin was reported by 77% of respondents (343 of 445), whereas 19% of respondents (84 of 445) reported twice weekly laboratory monitoring for these patients.

Although use of OPAT is common, there is significant variation in practice patterns. More uniform OPAT practices may enhance patient safety.

To explore the range of hospital policies for visitor use of personal protective equipment (PPE) when entering the room of patients under isolation precautions.

Survey using an online questionnaire.

Acute care hospitals registered in the North Carolina Statewide Program for Infection Control and Epidemiology (SPICE).

A total of 136 North Carolina hospitals were invited to participate in an online survey. The survey questionnaire was developed, reviewed, and pilot tested, and then it was distributed through SPICE listserv registered e-mail addresses. The survey was conducted from February 6 to March 30, 2012.

Among 93 respondent hospitals (response rate, 68.4%), 82 acute care hospitals (60.3%) were included in the analyses. Substantial variation was observed with regard to hospital policies for visitor PPE use when visiting patients under isolation precautions. A total of 71% of hospitals had a hospital visitor policy, and 96% of respondents agreed that hospitals should have a visitor policy. Only 14% of hospitals monitored visitor compliance with PPE. Reported compliance rates varied from “very low” to 97%. Many hospitals (28%) reported difficulties related to visitor compliance with isolation precautions, including hostility and refusal to comply.

Our study results illuminated hospital policy variations for visitor isolation precautions. Reported problems with hospital visitor policies (eg, different policies across departments or facilities) suggest the need for standard guidelines and for enhanced public awareness about the importance of visitor compliance with isolation precautions.

The risk of cross-infection from shared ultrasound probes in endorectal and vaginal ultrasonography due to low-level disinfection (LLD) is difficult to estimate because potential infections are also sexually transmitted diseases, and route of contamination is often difficult to establish. In France, the widely used standard for prevention of infections is through the use of probe covers and LLD of the ultrasound transducer by disinfectant wipes. We performed an in silico simulation based on a systematic review to estimate the number of patients infected after endorectal or vaginal ultrasonography examination using LLD for probes.

We performed a stochastic Monte Carlo computer simulation to produce hypothetical cohorts for a population of 4 million annual ultrasound examinations performed in France, and we estimated the number of infected patients for human immunodeficiency virus (HIV), herpes simplex virus, hepatitis B virus, hepatitis C virus, human papilloma virus, cytomegalovirus, and Chlamydia trachomatis. Modeling parameters were estimated by meta-analysis when possible.

The probability of infection from a contaminated probe ranged from 1% to 6%, depending on the pathogen. For cases of HIV infection, this would result in approximately 60 infected patients per year. For other common viral infections, the number of new cases ranged from 1,600 to 15,000 per year that could be attributable directly to ultrasound and LLD procedures.

Our simulation results showed that, despite cumulative use of probe cover and LLD, there were still some cases of de novo infection that may be attributable to ultrasound procedures. These cases are preventable by reviewing the currently used LLD and/or upgrading LLD to high-level disinfection, as recommended by the US Centers for Disease Control and Prevention.

To test the hypothesis that methicillin-susceptible Staphylococcus aureus (MSSA) carriage may protect against nosocomial methicillin-resistant S. aureus (MRSA) acquisition by competing for colonization of the anterior nares.

Prospective cohort and nested case-control study.

Swiss university hospital.

All adult patients admitted to 14 wards of the general medicine division between April 1 and October 31, 2007.

Patients were screened for MRSA and MSSA carriage at admission to and discharge from the division. Associations between nosocomial MRSA acquisition and MSSA colonization at admission and other confounders were analyzed by univariable and multivariable analysis.

Of 898 patients included, 183 (20%) were treated with antibiotics. Nosocomial MRSA acquisition occurred in 70 (8%) of the patients (case patients); 828 (92%) of the patients (control subjects) were free of MRSA colonization at discharge. MSSA carriage at admission was 20% and 21% for case patients and control subjects, respectively. After adjustment by multivariate logistic regression, no association was observed between MSSA colonization at admission and nosocomial MRSA acquisition (adjusted odds ratio [aOR], 1.2 [95% confidence interval (CI), 0.6–2.3]). By contrast, 4 independent predictors of nosocomial MRSA acquisition were identified: older age (aOR per 1-year increment, 1.05 [95% CI, 1.02–1.08]); increased length of stay (aOR per 1-day increment, 1.05 [95% CI, 1.02–1.09]); increased nursing workload index (aOR per 1-point increment, 1.02 [95% CI, 1.01–1.04]); and previous treatment with macrolides (aOR, 5.6 [95% CI, 1.8–17.7]).

Endogenous MSSA colonization does not appear to protect against nosocomial MRSA acquisition in a population of medical patients without frequent antibiotic exposure.