Kyle J. Popovich

Are Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Replacing Traditional Nosocomial MRSA Strains?

BACKGROUND Recent studies have suggested that community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection is encroaching on health care settings. We describe the epidemiology of hospital-onset community-associated MRSA bloodstream infections using phenotypic and genotypic analysis. METHODS Using an update of an established rule derived from antibiotic susceptibilities, we inferred genotypes (i.e., community [CG] or hospital [HG]) for 208 MRSA isolates from hospital-onset (>72 h after hospital admission) bloodstream infections during 2000-2006. We compared demographic characteristics, risk factors, and outcomes of patients infected with CG or HG strains. RESULTS Total hospital-onset MRSA bloodstream infection incidence density rates for the periods January 2000-June 2003 and July 2003-December 2006 (0.215 cases per 1000 patient-days and 0.207 cases per 1000 patient-days, respectively) were stable (risk ratio, 1.0; 95% confidence interval, 0.7-1.3; P = .79, period 2 vs. period 1). However, the risk that these bloodstream infections were due to CG strains doubled (risk ratio, 1.9; 95% confidence interval, 1.2-3.1; P = .01), whereas the risk due to HG strains decreased (risk ratio, 0.7; 95% confidence interval, 0.46-0.93; P = .02). After adjustment for comorbidities in multivariate analysis, no significant risk factors for or outcomes of infections due to CG versus HG strains were detected. Patients infected with HG strains showed a trend toward later day of acquisition of a positive blood culture, and those infected with CG strains showed trend toward greater risk of intensive care unit admission. CONCLUSION Although total hospital-onset MRSA bloodstream infection rates were relatively stable during 2000-2006, CG strains were responsible for an increasing proportion of cases (from 24% to 49%), suggesting replacement of traditional hospital-associated strains. For most risk factors and outcomes, patients infected with CG and HG strains were similar, suggesting that, thus far, CG strains are behaving like their traditional hospital-associated counterparts.

Effectiveness of routine patient cleansing with chlorhexidine gluconate for infection prevention in the medical intensive care unit.

BACKGROUND Controlled studies that took place in medical intensive care units (MICUs) have demonstrated that bathing patients with chlorhexidine gluconate (CHG) can reduce skin colonization with potential pathogens and can lessen the risk of central venous catheter (CVC)-associated bloodstream infection (BSI). OBJECTIVE To examine, without oversight of practice by research study staff, the effectiveness or real-world effect of patient cleansing with CHG on rates of CVC-associated BSI. DESIGN In the fall of 2005, the MICU at Rush University Medical Center discontinued bathing patients daily with soap and water and substituted skin cleansing with no-rinse, 2% CHG-impregnated cloths. This change was a clinical management decision without research input. SETTING A 21-bed MICU at Rush University Medical Center. PATIENTS Patients hospitalized in the MICU during the period from September 2004 through October 2006. METHODS In a pre-post study design, we gathered data from administrative and laboratory databases, infection control practitioner logs, and patient medical charts to compare rates of CVC-associated BSI and blood culture contamination between the baseline soap-and-water bathing period (September 2004-October 2005) and the CHG bathing period (November 2005-October 2006). Rates of secondary BSI, Clostridium difficile infection (CDI), ventilator-associated pneumonia (VAP), and urinary tract infection (UTI) served as control variables that were not expected to be affected by CHG bathing. RESULTS Bathing with CHG was associated with a statistically significant decrease in the rate of CVC-associated BSI (from 5.31 to 0.69 cases per 1,000 CVC-days; P = .006) and in the rate of blood culture contamination (from 6.99 to 4.1 cases per 1,000 patient-days; P = .04). Rates of secondary BSI, CDI, VAP, and UTI did not change significantly. CONCLUSIONS In our analysis of real-world practice, daily bathing of MICU patients with CHG was effective at reducing rates of CVC-associated BSI and blood culture contamination. Controlled studies are needed to determine whether these beneficial effects extend outside the MICU.

Multicenter Study of Clostridium difficile Infection Rates from 2000 to 2006

OBJECTIVE To compare incidence rates of Clostridium difficile infection (CDI) during a 6-year period among 5 geographically diverse academic medical centers across the United States by use of recommended standardized surveillance definitions of CDI that incorporate recent information on healthcare facility (HCF) exposure. METHODS Data on C. difficile toxin assay results and dates of hospital admission and discharge were collected from electronic databases. Chart review was performed for patients with a positive C. difficile toxin assay result who were identified within 48 hours after hospital admission to determine whether they had any HCF exposure during the 90 days prior to their hospital admission. CDI cases, defined as any inpatient with a stool toxin assay positive for C. difficile, were categorized into 5 surveillance definitions based on recent HCF exposure. Annual CDI rates were calculated and evaluated by use of the chi(2) test for trend and the chi(2) summary test. RESULTS During the study period, there were significant increases in the overall incidence rates of HCF-onset, HCF-associated CDI (from 7.0 to 8.5 cases per 10,000 patient-days; P < .001); community-onset, HCF-associated CDI attributed to a study hospital (from 1.1 to 1.3 cases per 10,000 patient-days; P = .003); and community-onset, HCF-associated CDI not attributed to a study hospital (from 0.8 to 1.5 cases per 1,000 admissions overall; P < .001). For each surveillance definition of CDI, there were significant differences in the total incidence rate between HCFs. CONCLUSIONS The increasing incidence rates of CDI over time and across healthcare institutions and the correlation of CDI incidence in different surveillance categories suggest that CDI may be a regional problem and not isolated to a single HCF within a community.

Community-associated methicillin-resistant Staphylococcus aureus and HIV: intersecting epidemics.

BACKGROUND Single-site studies have suggested a link between human immunodeficiency virus (HIV) and community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). METHODS Population-level incidence of HIV-infected patients with CA-MRSA versus community-associated methicillin-susceptible S. aureus (CA-MSSA) infection was assessed in the Cook County Health and Hospitals System (CCHHS), a multi-hospital and ambulatory care center. Rates in zip codes, including those with a high density of individuals with prior incarceration (ie, high-risk zip codes), were calculated. We did a nested case-control analysis of hospitalized HIV-infected patients with S. aureus skin and soft-tissue infections (SSTIs). RESULTS In CCHHS, the incidence of CA-MRSA SSTIs was 6-fold higher among HIV-infected patients than it was among HIV-negative patients (996 per 100,000 HIV-infected patients vs 157 per 100,000 other patients; P < .001). The incidence of CA-MRSA SSTIs among HIV-infected patients significantly increased from 2000-2003 (period 1) to 2004-2007 (period 2) (from 411 to 1474 cases per 100,000 HIV-infected patients; relative risk [RR], 3.6; P<.001), with cases in period 1 clustering in an area 6.3 km in diameter (P=.035) that overlapped high-risk zip codes. By period 2, CA-MRSA SSTIs among HIV-infected patients were spread throughout Cook County. USA300 was identified as the predominant strain by pulsed-field gel electrophoresis (accounting for 86% of isolates). Among hospitalized HIV-infected patients, the incidence of CA-MRSA increased significantly from period 1 to period 2 (from 190 to 779 cases per 100,000 HIV-infected patients; RR, 4.1; P<.001). Risks for CA-MRSA by multivariate analysis were residence in alternative housing (eg, shelters), residence in high-risk zip codes, younger age, and infection in period 2. CONCLUSIONS HIV-infected patients are at markedly increased risk for CA-MRSA infection. This risk may be amplified by overlapping community networks of high-risk patients that may be targets for prevention efforts.

Phenotypic Prediction Rule for Community-Associated Methicillin-Resistant Staphylococcus aureus

ABSTRACT Recent studies have suggested that community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are encroaching upon nosocomial settings. We assessed the performance characteristics of a rule using the antimicrobial phenotype to predict genotype. This rule could be applied for epidemiologic purposes to describe the trend in CA-MRSA infections over time.

Multicenter study of surveillance for hospital-onset Clostridium difficile infection by the use of ICD-9-CM diagnosis codes.

OBJECTIVE To compare incidence of hospital-onset Clostridium difficile infection (CDI) measured by the use of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) discharge diagnosis codes with rates measured by the use of electronically available C. difficile toxin assay results. METHODS Cases of hospital-onset CDI were identified at 5 US hospitals during the period from July 2000 through June 2006 with the use of 2 surveillance definitions: positive toxin assay results (gold standard) and secondary ICD-9-CM discharge diagnosis codes for CDI. The chi(2) test was used to compare incidence, linear regression models were used to analyze trends, and the test of equality was used to compare slopes. RESULTS Of 8,670 cases of hospital-onset CDI, 38% were identified by the use of both toxin assay results and the ICD-9-CM code, 16% by the use of toxin assay results alone, and 45% by the use of the ICD-9-CM code alone. Nearly half (47%) of cases of CDI identified by the use of a secondary diagnosis code alone were community-onset CDI according to the results of the toxin assay. The rate of hospital-onset CDI found by use of ICD-9-CM codes was significantly higher than the rate found by use of toxin assay results overall (P < .001), as well as individually at 3 of the 5 hospitals (P < .001 for all). The agreement between toxin assay results and the presence of a secondary ICD-9-CM diagnosis code for CDI was moderate, with an overall kappa value of 0.509 and hospital-specific kappa values of 0.489-0.570. Overall, the annual increase in CDI incidence was significantly greater for rates determined by the use of ICD-9-CM codes than for rates determined by the use of toxin assay results (P = .006). CONCLUSIONS Although the ICD-9-CM code for CDI seems to be adequate for measuring the overall CDI burden, use of the ICD-9-CM discharge diagnosis code for CDI, without present-on-admission code assignment, is not an acceptable surrogate for surveillance for hospital-onset CDI.

Community-Associated Methicillin-Resistant Staphylococcus aureus Colonization Burden in HIV-Infected Patients

BACKGROUND The epidemic of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has had a disproportionate impact on patients with human immunodeficiency virus (HIV). METHODS We evaluated CA-MRSA colonization burden (number of colonized sites per total number sampled) among HIV-infected and HIV-negative inpatients within 72 hours of hospitalization. From March 2011 through April 2012, we obtained cultures from nasal and extranasal sites (throat, axilla, inguinal, perirectal, and chronic wound if present) and collected risk factor data. RESULTS Of 745 patients (374 HIV-infected, 371 HIV-negative), 15.7% were colonized with CA-MRSA at any site: 20% of HIV and 11% of HIV-negative patients (relative prevalence=1.8, P=.002). HIV-infected patients had a higher prevalence of nasal, extranasal, and exclusive extranasal colonization as well as higher colonization burden. Perirectal and inguinal areas were the extranasal sites most frequently colonized, and 38.5% of colonized patients had exclusive extranasal colonization. Seventy-three percent of isolates were identified as USA300. Among HIV-infected patients, male sex, younger age, and recent incarceration were positively associated whereas Hispanic ethnicity was negatively associated with higher colonization burden. Among HIV-negative patients, temporary housing (homeless, shelter, or substance abuse center) was the only factor associated with higher colonization burden. Predictors of USA300 included HIV, younger age, illicit drug use, and male sex; all but 1 colonized individual with current or recent incarceration carried USA300. CONCLUSIONS HIV-infected patients were more likely to have a higher CA-MRSA colonization burden and carry USA300. In certain populations, enhanced community and outpatient-based infection control strategies may be needed to prevent CA-MRSA cross-transmission and infection.

Relationship between Chlorhexidine Gluconate Skin Concentration and Microbial Density on the Skin of Critically Ill Patients Bathed Daily with Chlorhexidine Gluconate

OBJECTIVE AND DESIGN Previous work has shown that daily skin cleansing with chlorhexidine gluconate (CHG) is effective in preventing infection in the medical intensive care unit (MICU). A colorimetric, semiquantitative indicator was used to measure CHG concentration on skin (neck, antecubital fossae, and inguinal areas) of patients bathed daily with CHG during their MICU stay and after discharge from the MICU, when CHG bathing stopped. PATIENTS AND SETTING MICU patients at Rush University Medical Center. METHODS CHG concentration on skin was measured and skin sites were cultured quantitatively. The relationship between CHG concentration and microbial density on skin was explored in a mixed-effects model using gram-positive colony-forming unit (CFU) counts. RESULTS For 20 MICU patients studied (240 measurements), the lowest CHG concentrations (0-18.75 μg/mL) and the highest gram-positive CFU counts were on the neck (median, 1.07 log(10) CFUs; [Formula: see text]). CHG concentration increased postbath and decreased over 24 hours ([Formula: see text]). In parallel, median log(10) CFUs decreased pre- to postbath (0.78 to 0) and then increased over 24 hours to the baseline of 0.78 ([Formula: see text]). A CHG concentration above 18.75 μg/mL was associated with decreased gram-positive CFUs ([Formula: see text]). In all but 2 instances, CHG was detected on patient skin during the entire interbath (approximately 24-hour) period (18 [90%] of 20 patients). In 11 patients studied after MICU discharge (80 measurements), CHG skin concentrations fell below effective levels after 1-3 days. CONCLUSION In MICU patients bathed daily with CHG, CHG concentration was inversely associated with microbial density on skin; residual antimicrobial activity on skin persisted up to 24 hours. Determination of CHG concentration on the skin of patients may be useful in monitoring the adequacy of skin cleansing by healthcare workers.

Validity of ICD-9-CM coding for identifying incident methicillin-resistant Staphylococcus aureus (MRSA) infections: is MRSA infection coded as a chronic disease?

BACKGROUND AND OBJECTIVE Investigators and medical decision makers frequently rely on administrative databases to assess methicillin-resistant Staphylococcus aureus (MRSA) infection rates and outcomes. The validity of this approach remains unclear. We sought to assess the validity of the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) code for infection with drug-resistant microorganisms (V09) for identifying culture-proven MRSA infection. DESIGN Retrospective cohort study. METHODS All adults admitted to 3 geographically distinct hospitals between January 1, 2001, and December 31, 2007, were assessed for presence of incident MRSA infection, defined as an MRSA-positive clinical culture obtained during the index hospitalization, and presence of the V09 ICD-9-CM code. The κ statistic was calculated to measure the agreement between presence of MRSA infection and assignment of the V09 code. Sensitivities, specificities, positive predictive values, and negative predictive values were calculated. RESULTS There were 466,819 patients discharged during the study period. Of the 4,506 discharged patients (1.0%) who had the V09 code assigned, 31% had an incident MRSA infection, 20% had prior history of MRSA colonization or infection but did not have an incident MRSA infection, and 49% had no record of MRSA infection during the index hospitalization or the previous hospitalization. The V09 code identified MRSA infection with a sensitivity of 24% (range, 21%-34%) and positive predictive value of 31% (range, 22%-53%). The agreement between assignment of the V09 code and presence of MRSA infection had a κ coefficient of 0.26 (95% confidence interval, 0.25-0.27). CONCLUSIONS In its current state, the ICD-9-CM code V09 is not an accurate predictor of MRSA infection and should not be used to measure rates of MRSA infection.

Predictors of Clinical Virulence in Community-Onset Methicillin-Resistant Staphylococcus aureus Infections: The Importance of USA300 and Pneumonia

BACKGROUND Though USA300 community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) has emerged as a major public health concern in the United States, its relative virulence is unknown. We sought to evaluate if the USA300 strain of CO-MRSA causes more severe infections than other MRSA (ie, USA100, -500, -800, and others) strains. METHODS An epidemiologic study was conducted from 2000 to 2007 to measure rates of severe infection. A matched case-control study was conducted from 2004 to 2006 to assess the relationship of strain type, syndrome, and severity of infection. Severe illness was defined as CO-MRSA infections with medical intensive care unit (MICU) admission or death within 1 week of admission. Controls were those with CO-MRSA infection without MICU admission. RESULTS We found an incidence of 75 cases per 100000 people of CO-MRSA infection in 2000, which increased to a rate of 396 per 100000 in 2007 (relative risk [RR], 5.3; 95% confidence interval [CI], 4.47-6.27). The incidence of severe infections increased from 5 cases per 100000 in 2000 to 17 per 100000 in 2007 (RR, 3.4; 95% CI; 1.67-6.43). USA300 strains were negatively associated with severe clinical courses or death as compared with other MRSA strain types. The highest risk of severe infection was found in those with pulmonary embolic infiltrates and bacteremia in the setting of USA300 infection (odds ratio, 31.41; 95% CI, 6.40-154.23). CONCLUSIONS Our findings suggest that USA300 infections are negatively associated with severe clinical courses, suggesting less virulence than other MRSA strains, except in the setting of pneumonia with septic pulmonary emboli.