Pam Tolomeo

Surveillance Cultures for Detection of Methicillin-Resistant Staphylococcus aureus: Diagnostic Yield of Anatomic Sites and Comparison of Provider- and Patient-Collected Samples

We studied provider- and patient-collected samples from multiple anatomic sites to determine the yield for detection of methicillin-resistant Staphylococcus aureus (MRSA). Sampling of multiple sites was required to achieve a sensitivity of more than 90% for MRSA colonization. Groin and perineum samples yielded positive results significantly more often for community-onset MRSA than for hospital-onset MRSA. Agreement rates between provider- and patient-collected swab specimens were excellent.

Test Characteristics of Perirectal and Rectal Swab Compared to Stool Sample for Detection of Fluoroquinolone-Resistant Escherichia coli in the Gastrointestinal Tract

ABSTRACT Among 63 patients enrolled in a prospective cohort study of gut colonization with fluoroquinolone-resistant Escherichia coli, the sensitivity of perirectal swab compared to stool sample was 90% (95% confidence interval [CI], 70 to 99%) and the specificity was 100% (95% CI, 91 to 100%). For rectal swab, the sensitivity was 90% (95% CI, 68 to 99%) and the specificity was 100% (95% CI, 91 to 100%).

Epidemiology of antimicrobial resistance among gram-negative organisms recovered from patients in a multistate network of long-term care facilities.

We identified 1,805 gram-negative organisms in cultures of urine samples obtained over a 10-month period from residents of 63 long-term care facilities. The prevalence of fluoroquinolone resistance in Escherichia coli was 51% (446 of 874 isolates), whereas the prevalences of ceftazidime and imipenem resistance in Klebsiella species were 26% and 6% (84 and 19 of 323 isolates), respectively. The prevalence of resistance varied significantly by facility type, size, and geographic location.

Potential Role of Pet Animals in Household Transmission of Methicillin-Resistant Staphylococcus aureus: A Narrative Review

In this narrative review, we found numerous reports suggesting that dogs and cats may play a role in household methicillin-resistant Staphylococcus aureus (MRSA) transmission and recurrent MRSA infection in human contacts. Future work should emphasize elucidating more clearly the prevalence of MRSA in household pets and characterize transmission dynamics of MRSA humans and pet animals.

Phenotypic and Genotypic Characterization of Fecal Escherichia coli Isolates with Decreased Susceptibility to Fluoroquinolones: Results from a Large Hospital-Based Surveillance Initiative

BACKGROUND The prevalence of fecal colonization with Escherichia coli that has reduced susceptibility to fluoroquinolones is unknown. A detailed characterization of such isolates is limited. METHODS We conducted 3 annual fecal surveillance initiatives at 2 hospitals from 2002 to 2004. All E. coli isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration [MIC] to levofloxacin, > or = 0.125 microg/mL) were identified. We characterized gyrA and parC mutations and organic solvent tolerance (OST). Isolates were compared using pulsed-field gel electrophoresis. RESULTS Of 789 fecal samples, 149 (18.9%) revealed E. coli with reduced susceptibility to fluoroquinolones. Of 149 isolates, 102 (68.5%) had a MIC > or = 8 microg/mL, 138 (92.6%) had > or = 1 gyrA mutation, 101 (67.8%) had > or = 1 parC mutation, and 59 (39.6%) demonstrated OST. Isolates with a MIC > or = 8 versus <8 microg/mL had more target mutations (median, 3 vs. 1; P<.001) and more often exhibited OST (51% vs. 15%; P<.001). Of 149 isolates, 144 (96.6%) demonstrated a MIC > or = 16 microg/mL to nalidixic acid. The prevalence of OST differed across study years (P = .01). There was no clonal spread of isolates. CONCLUSIONS Colonization by E. coli with reduced fluoroquinolone susceptibility is common, and fluoroquinolone-resistance characteristics differ significantly over time. Resistance to nalidixic acid may be useful in the identification of E. coli with early resistance mutations.

The shared microbiota of humans and companion animals as evaluated from Staphylococcus carriage sites

BackgroundStaphylococcus aureus and other coagulase-positive staphylococci (CPS) colonize skin and mucous membrane sites and can cause skin and soft tissue infections (SSTIs) in humans and animals. Factors modulating methicillin-resistant S. aureus (MRSA) colonization and infection in humans remain unclear, including the role of the greater microbial community and environmental factors such as contact with companion animals. In the context of a parent study evaluating the households of outpatients with community MRSA SSTI, the objectives of this study were 1) to characterize the microbiota that colonizes typical coagulase-positive Staphylococcus spp. carriage sites in humans and their companion pets, 2) to analyze associations between Staphylococcus infection and carriage and the composition and diversity of microbial communities, and 3) to analyze factors that influence sharing of microbiota between pets and humans.ResultsWe enrolled 25 households containing 56 pets and 30 humans. Sampling locations were matched to anatomical sites cultured by the parent study for MRSA and other CPS. Bacterial microbiota were characterized by sequencing of 16S ribosomal RNA genes. Household membership was strongly associated with microbial communities, in both humans and pets. Pets were colonized with a greater relative abundance of Proteobacteria, whereas people were colonized with greater relative abundances of Firmicutes and Actinobacteria. We did not detect differences in microbiota associated with MRSA SSTI, or carriage of MRSA, S. aureus or CPS. Humans in households without pets were more similar to each other than humans in pet-owning households, suggesting that companion animals may play a role in microbial transfer. We examined changes in microbiota over a 3-month time period and found that pet staphylococcal carriage sites were more stable than human carriage sites.ConclusionsWe characterized and identified patterns of microbiota sharing and stability between humans and companion animals. While we did not detect associations with MRSA SSTI, or carriage of MRSA, S. aureus or CPS in this small sample size, larger studies are warranted to fully explore how microbial communities may be associated with and contribute to MRSA and/or CPS colonization, infection, and recurrence.

Gastrointestinal tract colonization with fluoroquinolone-resistant Escherichia coli in hospitalized patients: changes over time in risk factors for resistance.

OBJECTIVE The prevalence of fluoroquinolone (FQ) resistance in Escherichia coli has increased markedly in recent years. Despite the important role of gastrointestinal tract colonization with FQ-resistant E. coli (FQREC), the prevalence of and risk factors for FQREC colonization among the general hospitalized patient population have not been described, to our knowledge. The objective of this study was to identify the prevalence of and risk factors for FQREC colonization among hospitalized patients. DESIGN Three-year case-control study. Case patients (ie, all subjects with FQREC colonization) were compared with control patients (ie, all subjects without FQREC colonization). SETTING Two large medical centers within an academic health system. PARTICIPANTS All patients hospitalized at the 2 study hospitals. MAIN OUTCOME MEASURE Three annual fecal surveillance surveys were conducted. All patients colonized with FQREC (levofloxacin minimum inhibitory concentration, >or=8 microg/mL) were identified. RESULTS Of the 774 subjects, 89 (11.5%) were colonized with FQREC. Although there was a significant association between prior FQ use and FQREC colonization on bivariable analysis (odds ratio [OR], 2.02 [95% confidence interval {CI}, 1.14-3.46]; P=.01), there was statistically significant effect modification by year of study (P=.005). In multivariable analyses, after controlling for the hospital and for the duration of hospitalization prior to sampling, the association between FQ use and FQREC colonization was as follows: adjusted OR (aOR), 0.97 (95% CI, 0.29-3.23) in 2002; aOR, 1.41 (95% CI, 0.57-3.50) in 2003; and aOR, 9.87 (95% CI, 3.67-26.55) in 2004. CONCLUSIONS The association between prior FQ use and FQREC colonization varied significantly by study year, suggesting that the clinical epidemiology of resistant organisms may change over time. Furthermore, in the context of recent work showing significant changes in FQREC prevalence as well as changes in FQ resistance mechanisms (specifically, efflux overexpression) over the same time period, these results suggest a previously unrecognized complexity in the relationship between the clinical and molecular epidemiology of FQ resistance.

The Prevalence of Fluoroquinolone Resistance Mechanisms in Colonizing Escherichia coli Isolates Recovered from Hospitalized Patients

BACKGROUND Fluoroquinolones are the most commonly prescribed antimicrobials. The epidemiology of fecal colonization with Escherichia coli demonstrating reduced susceptibility to fluoroquinolones remains unclear. METHODS During a 3-year period (15 September 2004 through 19 October 2007), all patients hospitalized for >3 days were approached for fecal sampling. All E. coli isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration [MIC] of levofloxacin, 0.125 microg/mL) were identified. We characterized gyrA and parC mutations and organic solvent tolerance. Isolates were compared using pulsed-field gel electrophoresis. RESULTS Of 353 patients colonized with E. coli demonstrating reduced fluoroquinolone susceptibility, 300 (85.0%) had 1 gyrA mutation, 161 (45.6%) had 1 parC mutation, and 171 (48.6%) demonstrated organic solvent tolerance. The mean numbers of total mutations (ie, gyrA and parC) for E. coli isolates with a levofloxacin MIC of 8 microg/mL versus <8.0 microg/mL were 2.70 and 0.82 (P < .001). Of the 136 E. coli isolates with a levofloxacin MIC of 8 microg/mL, 90 (66.2%) demonstrated a nalidixic acid MIC of 16 microg/mL. Significant differences were found over time in the proportion of E. coli isolates demonstrating gyrA mutation, parC mutation, and organic solvent tolerance. There was little evidence of clonal spread of isolates. Conclusions. Gastrointestinal tract colonization with E. coli demonstrating reduced susceptibility to levofloxacin is common. Although 40% of study isolates exhibited a levofloxacin MIC of <8 microg/mL (and would thus be missed by current Clinical and Laboratory Standards Institute breakpoints), nalidixic acid resistance may be a useful marker for detection of such isolates. Significant temporal changes occurred in the proportion of isolates exhibiting various resistance mechanisms.

Duration of Colonization and Determinants of Earlier Clearance of Colonization With Methicillin-Resistant Staphylococcus aureus

BACKGROUND The duration of colonization and factors associated with clearance of methicillin-resistant Staphylococcus aureus (MRSA) after community-onset MRSA skin and soft-tissue infection (SSTI) remain unclear. METHODS We conducted a prospective cohort study of patients with acute MRSA SSTI presenting to 5 adult and pediatric academic hospitals from 1 January 2010 through 31 December 2012. Index patients and household members performed self-sampling for MRSA colonization every 2 weeks for 6 months. Clearance of colonization was defined as negative MRSA surveillance cultures during 2 consecutive sampling periods. A Cox proportional hazards regression model was developed to identify determinants of clearance of colonization. RESULTS Two hundred forty-three index patients were included. The median duration of MRSA colonization after SSTI diagnosis was 21 days (95% confidence interval [CI], 19-24), and 19.8% never cleared colonization. Treatment of the SSTI with clindamycin was associated with earlier clearance (hazard ratio [HR], 1.72; 95% CI, 1.28-2.30; P < .001). Older age (HR, 0.99; 95% CI, .98-1.00; P = .01) was associated with longer duration of colonization. There was a borderline significant association between increased number of household members colonized with MRSA and later clearance of colonization in the index patient (HR, 0.85; 95% CI, .71-1.01; P = .06). CONCLUSIONS With a systematic, regular sampling protocol, duration of MRSA colonization was noted to be shorter than previously reported, although 19.8% of patients remained colonized at 6 months. The association between clindamycin and shorter duration of colonization after MRSA SSTI suggests a possible role for the antibiotic selected for treatment of MRSA infection.

Risk factors for fluoroquinolone resistance in Gram-negative bacilli causing healthcare-acquired urinary tract infections

The prevalence of urinary tract infections caused by fluoroquinolone-resistant Gram-negative bacilli (FQ-resistant GNB-UTIs) has been increasing. Previous studies that explored risk factors for FQ resistance have focused only on UTIs caused by Escherichia coli and/or failed to distinguish colonisation from infection. We conducted a case-control study at two medical centres within the University of Pennsylvania Health System to identify risk factors for FQ resistance among healthcare-acquired GNB-UTIs. Subjects with positive urine cultures for GNB and who met Centers for Disease Control and Prevention criteria for healthcare-acquired UTI were eligible. Cases were subjects with FQ-resistant GNB-UTI and controls were subjects with FQ-susceptible GNB-UTI matched to cases by month of isolation and species of infecting organism. In total, 251 cases and 263 controls were included from 1 January 2003 to 31 March 2005. Independent risk factors (adjusted odds ratio; 95% confidence interval) for FQ resistance included male sex (2.03; 1.21-3.39; P=0.007), African-American race (1.80; 1.10-2.94; P=0.020), chronic respiratory disease (2.58; 1.18-5.62; P=0.017), residence in a long term care facility (4.41; 1.79-10.88; P=0.001), hospitalisation within the past two weeks (2.19; 1.31-3.64; P=0.003), hospitalisation under a medical service (2.72; 1.63-4.54; P<0.001), recent FQ exposure (15.73; 6.15-40.26; P<0.001), recent cotrimoxazole exposure (2.49; 1.07-5.79; P=0.033), and recent metronidazole exposure (2.89; 1.48-5.65; P=0.002).