Methicillin resistance of Staphylococcus species among health care and nonhealth care workers undergoing cataract surgery

Purpose:

The purpose of this study is to characterize the bacterial flora of the ocular and periocular surface in cataract surgery patients and to determine the prevalence of methicillin resistance among staphylococcal isolates obtained from health care workers (HCWs) and non-HCWs.

Methods:

In this prospective, multicenter, case series study, eyelid and conjunctival cultures were obtained from the nonoperative eye of 399 consecutive cataract patients on the day of surgery prior to application of topical anesthetics, antibiotics, or antiseptics. Speciation and susceptibility testing were performed at the Dean A. McGee Eye Institute. Logistic regression was utilized to evaluate whether any factors were significant in predicting the presence of methicillin-resistant staphylococcal isolates.

Results:

Staphylococcus epidermidis (62.9%), followed by S. aureus (14.0%), was the most frequently isolated organism. Methicillin-resistant S. epidermidis accounted for 47.1% (178/378) of S. epidermidis isolates, and methicillin-resistant S. aureus accounted for 29.5% (26/88) of S. aureus isolates. Methicillin-resistant staphylococcal isolates were found in 157 of 399 (39.3%) patients, the majority (89.2%) of whom were non-HCWs. The likelihood of being colonized with methicillin-resistant organisms increased with age (odds ratio [OR], 1.27; 95% confidence interval [CI]: 1.02–1.58; P = 0.04) but decreased with diabetes (OR, 0.51; 95% CI: 0.29–0.89; P = 0.02). Being a HCW (OR, 1.25; 95% CI: 0.61–2.58; P = 0.54) was not a risk factor for colonization with methicillin-resistant organisms.

Conclusion:

Patients without exposure to health care environments are as likely as HCWs to be colonized with methicillin-resistant organisms. Increasing methicillin resistance with age may partially explain the increased risk of endophthalmitis reported with older age.

Respiratory syncytial virus and Staphylococcus aureus coinfection in children hospitalized with pneumonia

Respiratory syncytial virus (RSV) infection might facilitate bacterial infection. We describe 5 patients with RSV among 30 children admitted to pediatric hospitals in Atlanta between October 1, 2006 and April 30, 2007 with community-onset Staphylococcus aureus pneumonia. RSV-S. aureus patients were younger and had less medical comorbidity than those without RSV.

The economic effect of screening orthopedic surgery patients preoperatively for methicillin-resistant Staphylococcus aureus

BACKGROUND AND OBJECTIVE

Patients undergoing orthopedic surgery are susceptible to methicillin-resistant Staphylococcus aureus (MRSA) infections, which can result in increased morbidity, hospital lengths of stay, and medical costs. We sought to estimate the economic value of routine preoperative MRSA screening and decolonization of orthopedic surgery patients.

METHODS

A stochastic decision-analytic computer simulation model was used to evaluate the economic value of implementing this strategy (compared with no preoperative screening or decolonization) among orthopedic surgery patients from both the third-party payer and hospital perspectives. Sensitivity analyses explored the effects of varying MRSA colonization prevalence, the cost of screening and decolonization, and the probability of decolonization success.

RESULTS

Preoperative MRSA screening and decolonization was strongly cost-effective (incremental cost-effectiveness ratio less than $6,000 per quality-adjusted life year) from the third-party payer perspective even when MRSA prevalence was as low as 1%, decolonization success was as low as 25%, and decolonization costs were as high as $300 per patient. In most scenarios this strategy was economically dominant (ie, less costly and more effective than no screening). From the hospital perspective, preoperative MRSA screening and decolonization was the economically dominant strategy for all scenarios explored.

CONCLUSIONS

Routine preoperative screening and decolonization of orthopedic surgery patients may under many circumstances save hospitals and third-party payers money while providing health benefits.

Identification and eradication of methicillin-resistant Staphylococcus aureus colonization in the neonatal intensive care unit: results of a national survey

We surveyed members of the Society for Healthcare Epidemiology of America to assess current practice with regard to identifying and eradicating methicillin-resistant Staphylococcus aureus (MRSA) colonization in the neonatal intensive care unit (NICU). Although most respondents (86%) screened patients for MRSA colonization, variation existed in the number of anatomic sites sampled and in the use of culture at NICU admission, empirical institution of isolation precautions, and MRSA decolonization therapy. Evidence-based prevention strategies for MRSA transmission and infection are needed.

Risk factors associated with mupirocin resistance in meticillin-resistant Staphylococcus aureus

Implementation of meticillin-resistant Staphylococcus aureus (MRSA) decolonisation programmes has been increasing and the emergence of mupirocin resistance has been reported. However, the patient-level risk factors associated with mupirocin resistance are not clear. In this study, independent predictors of mupirocin resistance in MRSA among Providence Veterans Affairs Medical Center patients with MRSA-positive culture dates between 1 July 2004 and 30 June 2008 were identified using a frequency-matched case-control study. Forty cases (mupirocin-resistant) were matched on culture date quarter and year to 270 controls (mupirocin-susceptible). The adjusted conditional logistic regression model identified three significant independent predictors associated with mupirocin resistance in MRSA: (1) exposure to mupirocin in the year prior to the culture date [odds ratio (OR): 9.84; 95% confidence interval (CI): 2.93-33.09]; (2) Pseudomonas aeruginosa infection in the year before the culture-related admission (4.85; 1.20-19.61); and (3) cefepime use in the year prior to culture (2.80; 1.03-7.58). In sensitivity analyses, previous mupirocin exposure was associated with low-level [minimum inhibitory concentration (MIC) 8-128mg/L; 23 cases, 202 controls; OR: 6.32; 95% CI: 1.58-25.33] and high-level (MIC ≥256mg/L; 17 cases, 151 controls; OR: 11.18; 95% CI: 1.89-66.30) mupirocin resistance. To our knowledge, this is the first case-control study to reveal a strong association between previous mupirocin exposure and subsequent mupirocin resistance in MRSA, with demonstrated robustness in low- and high-level mupirocin resistance. Mupirocin susceptibility monitoring is critical for facilities instituting decolonisation with mupirocin as increased use may reduce effectiveness through resistance.

Methicillin-resistant Staphylococcus aureus colonization in HIV-infected outpatients is common and detection is enhanced by groin culture

SUMMARYAlthough high rates of clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) have been reported in HIV-infected adults, data on MRSA colonization are limited. We enrolled HIV-infected adults receiving care at the Atlanta VA Medical Center. Swabs from each participant's nares and groin were cultured with broth enrichment for S. aureus. Of 600 HIV-infected adults, 79 (13%) were colonized with MRSA and 180 (30%) with methicillin-susceptible S. aureus. MRSA pulsed-field gel electrophoresis types USA300 (n=44, 54%) and USA500/Iberian (n=29, 35%) predominated. Inclusion of groin swabs increased MRSA detection by 24% and USA300 detection by 38%. In multivariate analysis, MRSA colonization compared to no MRSA colonization was associated with a history of MRSA clinical infection, rarely or never using condoms, and contact with prisons and jails. In summary, the prevalence of MRSA colonization was high in this study of HIV-infected adults and detection of USA300 was enhanced by groin culture.

Prevalence and characteristics of Staphylococcus aureus colonization among healthcare professionals in an urban teaching hospital

OBJECTIVE

To determine the prevalence of asymptomatic carriage of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) among healthcare professionals (HCPs) who experience varying degrees of exposure to ambulatory patients and to genetically characterize isolates.

METHODS

This single-center, cross-sectional study enrolled 256 staff from the intensive care units, emergency department, and prehospital services of an urban tertiary care university hospital in 2008. Occupational histories and nasal samples for S. aureus cultures were obtained. S. aureus isolates were genetically characterized with the use of spa typing and screened for mecA. MRSA isolates underwent further characterization.

RESULTS

S. aureus was isolated from 112 of 256 (43.8%) HCPs, including 30 of 52 (57.7%) paramedics, 51 of 124 (41.1%) nurses, 11 of 28 (39.3%) clerical workers, and 20 of 52 (38.5%) physicians. MRSA was isolated from 17 (6.6%) HCPs, including 1 (1.9%) paramedic, 13 (10.5%) nurses, 1 (3.6%) clerical worker, and 2 (3.8%) physicians. Among S. aureus isolates, 15.2% were MRSA. MRSA prevalence was 9.6% (12/125) in emergency department workers, 5.1% (4/79) in intensive care unit workers, and 1.9% (1/52) in emergency medical services workers. Compared with paramedics, who had the lowest prevalence of methicillin resistance among S. aureus isolates (1 of 30 [3.3%] isolates), nurses, who had the highest prevalence (13 of 51 [25.4%] isolates), had an odds ratio of 9.92 (95% confidence interval, 1.32-435.86; P = .02) for methicillin resistance. Analysis of 15 MRSA isolates revealed 7 USA100 strains, 6 USA300 strains, 1 USA800 strain, and 1 EMRSA-15 strain. All USA300 strains were isolated from emergency department personnel.

CONCLUSIONS

The observed prevalence of S. aureus and MRSA colonization among HCPs exceeds previously reported prevalences in the general population. The proportion of community-associated MRSA among all MRSA in this colonized HCP cohort reflects the distribution of the USA300 community-associated strain observed increasingly among US hospitalized patients.

Prevalence of USA300 strain type of methicillin-resistant Staphylococcus aureus among patients with nasal colonization identified with active surveillance

BACKGROUND

USA300 is the most prevalent strain type of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), but the proportion of patients colonized with USA300 strains and their risk for infection are largely unknown.

OBJECTIVE

To determine the prevalence of USA300 strains among MRSA nasal colonizing isolates in our hospital, to identify risks for USA300 nasal colonization, and to determine risks of developing infection for nasally colonized patients.

METHODS

Retrospective cohort study of patients found to be nasally colonized with MRSA through active surveillance at a tertiary care hospital from January 2005 through December 2007. MRSA isolates were identified as USA300 or non-USA300. Risks for colonization and infection were identified with logistic regression.

RESULTS

Among 1,306 MRSA nasal isolates, 307 (24%) were USA300 strains, and this proportion significantly increased over time (17.4% in 2005 and 26.7% in 2007; P = .003). African American race was an independent risk for USA300 nasal colonization (odds ratio [OR], 1.81 [95% confidence ratio {CI}, 1.38-2.38]). Older age (OR, 0.97 [95% CI, 0.96-0.98]) and female sex (OR, 0.74 [95% CI, 0.56-0.97]) decreased risk. Among nasally colonized patients, 238 (18.2%) developed infection. Increased length of stay (OR, 1.03 [95% CI, 1.01-1.06]) independently increased risk for infection among patients nasally colonized with USA300 MRSA, and female sex decreased risk (OR, 0.48 [95% CI, 0.24-0.95]). Increased length of stay (OR, 1.03 [95% CI, 1.02-1.04]) and treatment in an intensive care unit (OR, 1.64 [95% CI, 1.10-2.44]) independently increased risk for infection among patients nasally colonized with non-USA300 MRSA, and female sex decreased risk (OR, 0.67 [95% CI, 0.47-0.94]).

CONCLUSION

The proportion of MRSA nasally colonized patients with USA300 strains significantly increased during the study, and risks included African American race. Strain type had no significant effect on the proportion of patients who developed infection, and risk factors for infection were similar.

Prevalence of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus carriage in three populations

BACKGROUND

A higher prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization is reported in healthcare workers compared with nonhealthcare workers.

HYPOTHESIS

The prevalence of MRSA colonization differed in people and pets in households with healthcare workers as compared with households without healthcare workers.

SUBJECTS

A person and 1 dog or cat from 586 households defined as either a nonhealthcare (n = 213), veterinary healthcare (n = 211), or human healthcare (n = 162) worker household.

METHODS

Prospective cross-sectional study. Samples from humans and pets were cultured in vitro. Staphylococcus aureus was identified as methicillin sensitive (MSSA) or MRSA with mecA polymerase chain reaction. Pulsed-field gel electrophoresis and spa-typing were used to characterize relatedness of S. aureus and MRSA and assign USA types.

RESULTS

The prevalence of MSSA and MRSA in humans was 21.5% (126/586) and 5.63% (33/586), respectively, and 7.85% (46/586) and 3.41% (20/586), respectively, in pets. There were no differences in prevalences of either MSSA or MRSA between household types. The proportion of MRSA among all S. aureus isolates in humans and pets was 20.8% (33/159) and 30.3% (20/66), respectively. In < 1.0% (4/586) of households, the same strain of MRSA was found in both a person and a pet.

CONCLUSIONS AND CLINICAL IMPORTANCE

There were no differences in the prevalences of MSSA or MRSA between healthcare worker and nonhealthcare worker households. Pets and people colonized with S. aureus were as likely to be colonized with MRSA. Colonization of a person and their pet with the same strain of MRSA was rare.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-associated methicillin-resistant Staphylococcus aureus strains in pediatric intensive care unit

Virulent community-associated methicillin-resistant Staphylococcus-aureus (CA-MRSA) strains have spread rapidly in the United States. To characterize the degree to which CA-MRSA strains are imported into and transmitted in pediatric intensive care units (PICU), we performed a retrospective study of children admitted to The Johns Hopkins Hospital PICU, March 1, 2007-May 31, 2008. We found that 72 (6%) of 1,674 PICU patients were colonized with MRSA. MRSA-colonized patients were more likely to be younger (median age 3 years vs. 5 years; p = 0.02) and African American (p<0.001) and to have been hospitalized within 12 months (p<0.001) than were noncolonized patients. MRSA isolates from 66 (92%) colonized patients were fingerprinted; 40 (61%) were genotypically CA-MRSA strains. CA-MRSA strains were isolated from 50% of patients who became colonized with MRSA and caused the only hospital-acquired MRSA catheter-associated bloodstream infection in the cohort. Epidemic CA-MRSA strains are becoming endemic to PICUs, can be transmitted to hospitalized children, and can cause invasive hospital-acquired infections. Further appraisal of MRSA control is needed.

Non-suppurative cellulitis: risk factors and its association with Staphylococcus aureus colonization in an area of endemic community-associated methicillin-resistant S. aureus infections

Suppurative methicillin-resistant Staphylococcus aureus (MRSA) skin infections are common and associated with MRSA colonization, but little is known about non-suppurative cellulitis and its relationship with MRSA colonization in areas endemic for community-associated MRSA. We prospectively enrolled patients hospitalized for non-suppurative cellulitis (n=50) and matched controls (n=100) and found S. aureus colonization was similar in cases and controls (30% vs. 25%, P=0·95). MRSA was uncommon in cases (6%) and controls (3%) (P=0·39). All MRSA isolates were USA300 by pulsed-field gel electrophoresis. Independent risk factors for non-suppurative cellulitis were diabetes (OR 3·5, 95% CI 1·4-8·9, P=0·01) and homelessness in the previous year (OR 6·4, 95% CI 1·9-20·9, P=0·002). These findings suggest that MRSA may only rarely be causative of non-suppurative cellulitis.

A veterinary perspective on methicillin-resistant staphylococci

OBJECTIVE

To familiarize the reader with the epidemiology, diagnosis, and infectious and zoonotic potential of methicillin-resistant staphylococci.

DATA SOURCES

Original research publications, scientific reviews and abstracts, case reports, and conference proceedings.

HUMAN DATA SYNTHESIS

Staphylococcus aureus is a common human commensal organism; acquisition of genes encoding an altered penicillin-binding protein confers resistance to beta-lactam antimicrobial drugs. Methicillin-resistant S. aureus (MRSA) are often resistant to non-beta-lactam antimicrobial drugs as well. Originally described as an important cause of nosocomial infection, MRSA colonization and infection are now often identified in humans outside healthcare settings. Like other S. aureus, MRSA may be present without clinical illness. However, when they do cause infection the consequences can be extremely serious.

VETERINARY DATA SYNTHESIS

The major domestic animal species, including pets and livestock, may become contaminated, colonized, or infected with methicillin-resistant staphylococci, including MRSA. Dogs and cats are more likely to be colonized/infected with Staphylococcus pseudintermedius than S. aureus, but this pathogen can acquire genes encoding methicillin resistance (ie, MRSP). Diagnosis of MRSA or MRSP has implications not only for treatment of infected animals, but for potential zoonotic transmission.

CONCLUSIONS

MRSA infection is an important cause of morbidity and mortality in humans. Animals may be contaminated, colonized, or infected with MRSA, with implications for the animal's health and as a potential reservoir for human infection. Staphylococci other than S. aureus may also acquire genes for methicillin resistance, and these species can also result in animal and occasionally human morbidity or mortality.

Ecological temporal stability of Staphylococcus aureus nasal carriage

We described the colonization dynamics of Staphylococcus aureus in a group of 266 healthy carriers over a period of approximately 1 year. We used precise genotyping methods, i.e., amplified fragment length polymorphism (AFLP), spa typing, and double-locus sequence typing (DLST), to detect changes in strain identity. Strain change took place rather rarely: out of 89 carriers who had initially been colonized, only 7 acquired a strain different from the original one. Approximately one-third of the carriers eliminated the colonization, and a similar number became newly colonized. Some of these events probably represent detection failure rather than genuine colonization loss or acquisition. Lower bacterial counts were associated with increased probability of eliminating the colonization. We have confirmed a high mutation rate in the spa locus: 6 out of 53 strains underwent mutation in the spa locus. There was no overall change in S. aureus genotype composition.

Staphylococcal colonization of caretakers of children who have community-acquired skin and soft tissue infections

PURPOSE

Colonization with Staphylococcus aureus is considered a risk factor for the rising incidence of pediatric community-acquired skin and soft tissue infections (CA-SSTIs), and intrafamily spread is thought to be the source of colonization.

METHODS

A prospective study was conducted to determine skin and nasal staphylococcal colonization rates among the caretakers of CA-SSTI patients and those of nonabscess controls. A questionnaire regarding risk factors was administered to all participants. Fisher's Exact test and the chi(2) test were used for statistical analysis.

RESULTS

Forty-six patients and their caretakers were enrolled in both the study and control groups. Of the caretakers in the study group, 19.6% (n = 9) had staphylococcal colonization of nares; and 2.2% (n = 1), skin. In the control group, 17.4% (n = 8) had nasal colonization; and none had skin colonization. Of the children in the study group, 58.7% (n = 27) had a family history of CA-SSTI compared with only 17.4% (n = 8) of controls (P = .0001). Of CA-SSTI patients, 45.7% (n = 21) had prior abscesses compared with 6.5% (n = 3) of controls (P = .0001). No other risk factor was identified.

CONCLUSION

There was no increase in nasal or skin staphylococcal colonization among caretakers of children with CA-SSTI. Family and personal histories of CA-SSTI were the only identified risk factors for CA-SSTI.

The human nasal microbiota and Staphylococcus aureus carriage

Background

Colonization of humans with Staphylococcus aureus is a critical prerequisite of subsequent clinical infection of the skin, blood, lung, heart and other deep tissues. S. aureus persistently or intermittently colonizes the nares of ∼50% of healthy adults, whereas ∼50% of the general population is rarely or never colonized by this pathogen. Because microbial consortia within the nasal cavity may be an important determinant of S. aureus colonization we determined the composition and dynamics of the nasal microbiota and correlated specific microorganisms with S. aureus colonization.

Methodology/Principal Findings

Nasal specimens were collected longitudinally from five healthy adults and a cross-section of hospitalized patients (26 S. aureus carriers and 16 non-carriers). Culture-independent analysis of 16S rRNA sequences revealed that the nasal microbiota of healthy subjects consists primarily of members of the phylum Actinobacteria (e.g., Propionibacterium spp. and Corynebacterium spp.), with proportionally less representation of other phyla, including Firmicutes (e.g., Staphylococcus spp.) and Proteobacteria (e.g. Enterobacter spp). In contrast, inpatient nasal microbiotas were enriched in S. aureus or Staphylococcus epidermidis and diminished in several actinobacterial groups, most notably Propionibacterium acnes. Moreover, within the inpatient population S. aureus colonization was negatively correlated with the abundances of several microbial groups, including S. epidermidis (p = 0.004).

Conclusions/Significance

The nares environment is colonized by a temporally stable microbiota that is distinct from other regions of the integument. Negative association between S. aureus, S. epidermidis, and other groups suggests microbial competition during colonization of the nares, a finding that could be exploited to limit S. aureus colonization.

Community-associated meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) is endemic in hospitals worldwide, and causes substantial morbidity and mortality. Health-care-associated MRSA infections arise in individuals with predisposing risk factors, such as surgery or presence of an indwelling medical device. By contrast, many community-associated MRSA (CA-MRSA) infections arise in otherwise healthy individuals who do not have such risk factors. Additionally, CA-MRSA infections are epidemic in some countries. These features suggest that CA-MRSA strains are more virulent and transmissible than are traditional hospital-associated MRSA strains. The restricted treatment options for CA-MRSA infections compound the effect of enhanced virulence and transmission. Although progress has been made towards understanding emergence of CA-MRSA, virulence, and treatment of infections, our knowledge remains incomplete. Here we review the most up-to-date knowledge and provide a perspective for the future prophylaxis or new treatments for CA-MRSA infections.

Community-associated methicillin-resistant Staphylococcus aureus nasal carriage in a college student athlete population

OBJECTIVE

This study evaluated the prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) nasal carriage, risk factors for nasal carriage, and antibiotic susceptibility patterns in college student athletes.

DESIGN

Cross-sectional study.

SETTING

Methicillin-resistant Staphylococcus aureus nasal samples and data collection forms were obtained at athletic team training rooms at 2 colleges.

PARTICIPANTS

: The study population included 277 college student athletes older than 18 years.

INTERVENTIONS

A nasal swab was obtained from each athlete after completion of a data collection form. Variables collected on the data collection form included age, sex, race/ethnicity, athletic team, recent health care exposure(s), history of CA-MRSA exposure, recent antibiotic treatment(s), sharing towels, razors or soap, nose picking, and on-campus or off-campus living.

MAIN OUTCOME MEASURES

Prevalence of CA-MRSA nasal carriage and antibiotic susceptibility patterns was analyzed. Risk factors for nasal carriage were also evaluated.

RESULTS

Five positive CA-MRSA nasal carriers (4 men and 1 woman) were identified of 277 sampled; a prevalence of 1.8%. Two institutions were involved in the study. Institution 1 had 4 positive CA-MRSA nasal carriers of 124 sampled (3.2%). Institution 2 had 1 positive CA-MRSA nasal carrier of 153 sampled (0.65%). No risk factors were found to be significantly associated with positive CA-MRSA nasal carriage.

CONCLUSIONS

The prevalence of CA-MRSA nasal carriage in college student athletes in East Tennessee (1.8%) seems similar to what has been reported in the general population (1.5%).

The prevalence of carriage of meticillin-resistant staphylococci by veterinary dermatology practice staff and their respective pets

It has been shown that people and pets can harbour identical strains of meticillin-resistant (MR) staphylococci when they share an environment. Veterinary dermatology practitioners are a professional group with a high incidence of exposure to animals infected by Staphylococcus spp. The objective of this study was to assess the prevalence of carriage of MR Staphylococcus aureus (MRSA), MR S. pseudintermedius (MRSP) and MR S. schleiferi (MRSS) by veterinary dermatology practice staff and their personal pets. A swab technique and selective media were used to screen 171 veterinary dermatology practice staff and their respective pets (258 dogs and 160 cats). Samples were shipped by over-night carrier. Human subjects completed a 22-question survey of demographic and epidemiologic data relevant to staphylococcal transmission. The 171 human-source samples yielded six MRSA (3.5%), nine MRSP (5.3%) and four MRSS (2.3%) isolates, while 418 animal-source samples yielded eight MRSA (1.9%) 21 MRSP (5%), and two MRSS (0.5%) isolates. Concordant strains (genetically identical by pulsed-field gel electrophoresis) were isolated from human subjects and their respective pets in four of 171 (2.9%) households: MRSA from one person/two pets and MRSP from three people/three pets. In seven additional households (4.1%), concordant strains were isolated from only the pets: MRSA in two households and MRSP in five households. There were no demographic or epidemiologic factors statistically associated with either human or animal carriage of MR staphylococci, or with concordant carriage by person-pet or pet-pet pairs. Lack of statistical associations may reflect an underpowered study.

The development and validation of a simulation tool for health policy decision making

Computer simulations have been used to model infectious diseases to examine the outcomes of alternative strategies for managing their spread. Methicillin resistant Staphylococcus aureus (MRSA) skin and soft tissue infections have become prominent in many communities and efforts are underway to reduce the spread of this organism both in hospitals and communities. Currently, there are few tools for policy makers to use to examine the outcome of various choices when making decisions about MRSA. Using the example of MRSA, we describe, in this paper, a rigorous approach for development and validation of a tool that simulates the spread of MRSA infections. We used sensitivity analyses in a novel way and validated the simulation results against local data over time. Our approach for simulation development and validation is generalizeable to simulations of other diseases.

Characterization and persistence of Staphylococcus aureus strains isolated from the anterior nares and throats of healthy carriers in a Mexican community

Healthy carriers of Staphylococcus aureus strains have an important role in the dissemination of this bacterium. To investigate the presence of S. aureus in the throat and anterior nares, samples from 1,243 healthy volunteers in a Mexican community were examined. The percentage of healthy carriers was 59.8%. Results showed that colonization of the throat occurred more frequently than that of the nares (46.5% versus 37.1%, P<0.0001). Of the S. aureus carriers, 22.2% were exclusive nasal carriers and 38% were exclusive throat carriers. A total of 1,039 strains were isolated; 12.6% were shown to be methicillin-resistant S. aureus (MRSA). Of MRSA strains, 32.1% were isolated from exclusive throat carriers. Most of the strains isolated from the anterior nares and throat of the same carriers were the same or related; however, some were different. Pulsed-field gel electrophoresis (PFGE) pattern analysis of the MRSA strains isolated from the exclusive nasal carriers or exclusive throat carriers showed that they belong to different clusters. A 6-year prospective study was performed to investigate the persistence of S. aureus in the throat. Results showed that 13% of subjects were persistent carriers. Most of them were colonized with the same clone of S. aureus throughout the time of the study, and just three had different clones. Antimicrobial susceptibility testing showed that 91.1% of the strains were penicillin resistant. The presence of mecA and nucA genes (in order to confirm methicillin resistance) and of thermostable nuclease of S. aureus was examined. This study showed that some strains of S. aureus regularly colonized the throats of healthy people and could persist for years.

Methicillin-resistant Staphylococcus aureus in food products: cause for concern or case for complacency?

The widespread use of antimicrobial agents, in combination with insufficient infection control measures, is the main driver of the current pandemic of antimicrobial resistance in human pathogens. The use of antimicrobials in food animal production also contributes, because resistant organisms and resistance genes can spread from animals to humans by direct contact or through the food chain. An important, traditionally human, pathogen, methicillin-resistant Staphylococcus aureus (MRSA), is currently endemic in many hospitals around the world and has also emerged in the community. Recently, a new reservoir of MRSA has been identified in food production animals and people in contact with these animals. This involves a specific clone, multilocus sequence type 398 (ST398), which has spread extensively among animals. ST398 has also been found in up to 11.9% of retail meat samples in several surveys from different parts of the world, posing a potential threat to human health.

Importance of colonization site in the current epidemic of staphylococcal skin abscesses

OBJECTIVE

The goal was to compare rectal and nasal Staphylococcus aureus colonization rates and S aureus pulsed-field types (PFTs) for children with S aureus skin and soft-tissue abscesses and normal control subjects.

METHODS

Sixty consecutive children with S aureus skin and soft-tissue abscesses that required surgical drainage and 90 control subjects were enrolled. Cultures of the nares and rectum were taken in both groups. S aureus isolates from all sites were characterized through multiple-locus, variable-number, tandem-repeat analysis, pulsed-field gel electrophoresis, staphylococcal cassette chromosome mec typing for methicillin-resistant S aureus isolates, and determination of the presence of Panton-Valentine leukocidin genes.

RESULTS

S aureus was detected significantly more often in the rectum of children with abscesses (47%) compared with those in the control group (1%; P = .0001). Rates of nasal colonization with S aureus were equivalent for children with abscesses (27%) and control subjects (20%; P = .33). S aureus recovered from the rectum was identical to S aureus in the abscess in 88% of cases, compared with 75% of nasal isolates. PFT USA300, staphylococcal cassette chromosome mec type IV, and Panton-Valentine leukocidin genes were significantly increased in the S aureus isolates from children with abscesses compared with those from control subjects.

CONCLUSIONS

Skin and soft-tissue abscesses in the current epidemic of community-associated staphylococcal disease are strongly associated with rectal colonization by PFT USA300. Nasal colonization in children does not seem to be a risk factor.

Topical antibacterial agents

Decreased systemic toxicity, ease of application, and increased concentrations at the target site are some of the important advantages topical antibacterial agents offer. This article reviews the literature on selected indications for these agents and provides in-depth examination of specific agents for the prophylaxis and treatment of skin and wound infections.

Perioperative management of neurosurgical patients with methicillin-resistant Staphylococcus aureus

Object

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has posed a challenge in the treatment of neurosurgical patients. The authors investigated the impact of MRSA colonization and infection in the neurosurgical population at a community-based, tertiary care referral center.

Methods

Hospitalized patients under the care of the Kaiser Permanente inpatient neurosurgery service were prospectively entered into a database. In Phase I of the study, 492 consecutive patients were followed. Per hospital policy, the 260 patients from this group who were admitted to the intensive care unit (ICU) underwent screening for MRSA based on nasal swab cultures and a review of their medical history for prior MRSA infections. These patients were designated as either MRSA positive (17 patients, 6.5% of screened patients) or MRSA negative (243 patients). The 232 patients admitted to non-ICU nursing units did not undergo MRSA screening and were designated as unscreened. In Phase II of the study, the authors reviewed 1005 neurosurgical admissions and completed a detailed chart review in 62 MRSA-positive patients (6.2%). Eleven patients received nonoperative treatment. Five patients presented with community-acquired neurosurgical infections, and the causative organism was MRSA in 3 cases. Forty-six patients underwent 55 procedures, and the authors reviewed their perioperative management.

Results

In Phase I of the study, the authors found that for the MRSA-positive, MRSA-negative, and unscreened groups, the rates of postoperative neurosurgical wound infections caused by all pathogens were 23.5, 4.1, and 1.3%, respectively. For MRSA wound infections, the rates were 23.5, 0.8, and 0%, respectively. In Phase II, patients with MRSA were noted to have the following clinical features: male sex in 63%, a malignancy in 39.1%, diabetes in 34.8%, prior MRSA infection in 21.7%, immunosuppressed state in 17.4%, and a traumatic injury in 15.2%. The rate of postoperative neurosurgical wound infection in patients who received MRSA-specific prophylactic antibiotic therapy (usually vancomycin) was 7.4% (27 procedures) compared with 32.1% (28 procedures) in patients who received the standard treatment (usually cefazolin) (p = 0.04). Wound care for ICU patients was standardized for postoperative Days 0–7 with chlorhexidine cleaning at bandage changes at 3-day intervals. Wound cultures from neurosurgical site infections in patients with prior MRSA colonization or infection grew MRSA in 7 of 11 patients.

Conclusions

Neurosurgical patients identified with MRSA colonization or a prior history of MRSA infections benefit from specific perioperative care, including prophylactic antibiotics active against MRSA (such as vancomycin) and postoperative wound care with coverings and chlorhexidine antisepsis to reduce MRSA wound colonization.

Epidemiology of methicillin-susceptible Staphylococcus aureus in a university medical center day care facility

BACKGROUND

Few data are available on methicillin-susceptible Staphylococcus aureus (MSSA) colonization in day care. We performed a study in a child care center on a medical university campus to study the epidemiology of MSSA in this population.

METHODS

A cross-sectional study was done on 104 day care attendees and 32 adult employees of the child care center. Swab samples were taken from the nose, oropharynx, axilla, groin, and perirectal area of children, from the nose and oropharynx of employees, and from the environment. Parents and employees completed questionnaires. Swabs were placed in broth, then plated on agar and identified as MSSA by routine methods. Molecular typing was performed.

RESULTS

The prevalence of MSSA was 21.15% in children and 28.13% in employees. MSSA was found in 8.72% of environmental samples. Univariate analysis identified 3 risk factors and 5 protective factors for MSSA colonization. In multivariable analysis, only 2 variables remained significantly related to MSSA colonization, with older age remaining as a risk factor and receipt of beta-lactams approaching significance as being protective. Many of the isolates were indistinguishable by molecular typing.

CONCLUSIONS

The prevalence of MSSA colonization in children and care providers in a university medical center child care center is similar to that of the general population. Children colonized with MSSA tended to be older and to have received fewer courses of antibiotics than children who did not have MSSA. The relatedness of many of the isolates indicates that transmission of MSSA occurred at this child care center.

Community-associated methicillin-resistant Staphylococcus aureus immune evasion and virulence

Staphylococcus aureus is a significant cause of human infections globally. Methicillin-resistant S. aureus (MRSA) emerged in the early 1960s and is now endemic in most healthcare facilities. Although healthcare-associated MRSA infections remain a major problem in most industrialized countries, those caused by community-associated MRSA (CA-MRSA) are now the most abundant cause of bacterial infections in the community in some parts of the world, such as the United States. The basis for the emergence and subsequent success of CA-MRSA is incompletely defined. However, the ability of the pathogen to cause disease in otherwise healthy individuals is likely attributed, in part, to its ability to circumvent killing by the innate immune system, which includes survival after phagocytosis by neutrophils. In this review, we discuss the role of neutrophils in host defense against S. aureus and highlight progress made toward understanding mechanisms of CA-MRSA virulence and pathogenesis.

Risks for methicillin-resistant Staphylococcus aureus colonization or infection among patients with HIV infection

BACKGROUND

Risks for methicillin-resistant Staphylococcus aureus (MRSA) among those with HIV infection have been found to vary, and the epidemiology of USA-300 community-acquired (CA) MRSA has not been adequately described.

METHODS

We conducted a retrospective review of HIV-infected out-patients from January 2002 to December 2007 and employed multivariate logistic regression (MLR) to identify risks for MRSA colonization or infection. Pulsed-field gel electrophoresis (PFGE) was used to identify USA-300 strains.

RESULTS

Seventy-two (8%) of 900 HIV-infected patients were colonized or infected with MRSA. MLR identified antibiotic exposure within the past year [odds ratio (OR) 3.4; 95% confidence interval (CI) 1.5-7.7] and nadir CD4 count <200 cells/microL (OR 2.5; 95% CI 1.2-5.3) as risks for MRSA colonization or infection. Receipt of antiretroviral therapy (ART) within the past year was associated with decreased risk (OR 0.16; 95% CI 0.07-0.4). Eighty-nine percent of available strains were USA-300. MLR identified skin or soft tissue infection (SSTI) as the only predictor for infection with USA-300 (OR 5.9; 95% CI 1.4-24.3).

CONCLUSION

Significant risks for MRSA among HIV-infected patients were CD4 count nadir <200 cells/microL and antibiotic exposure. Only the presence of an SSTI was associated with having USA-300, and thus the use of patient characteristics to predict those with USA-300 was limited. In addition, ART within the previous year significantly reduced the risk of MRSA colonization or infection.

The environment as a factor in methicillin-resistant Staphylococcus aureus transmission

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) has become a leading cause of infectious disease morbidity and mortality in the United States. The epidemiology of the organism has changed, with novel strains emerging in the community among individuals lacking any healthcare contact. Although direct human-to-human transmission via skin contact is one way for this organism to spread, transmission via environmental contamination of fomites or through air are other potential ways that the organism can be acquired. As such, an improved understanding of MRSA transmission is needed to implement maximally effective control and prevention interventions. We review the research documenting the role of the environment in MRSA spread.

Common wound colonizers in patients with epidermolysis bullosa

One of the major morbidities of patients with epidermolysis bullosa is the tendency to develop chronic wounds, which predisposes them to multiple complications including life-threatening infections, failure to thrive, and squamous cell carcinomas. Chronic wounds frequently become colonized with bacteria, and we sought to identify the most common microorganisms isolated on cultures from patients with epidermolysis bullosa. We conducted a retrospective review of positive wound, nasal, and blood cultures, including bacterial, fungal and viral, in 30 patients with epidermolysis bullosa. Staphylococcus sp., Streptococcus sp., diptheroids, Pseudomonas aeruginosa, and Candida sp. were the most commonly isolated microorganisms in wound cultures from our epidermolysis bullosa patients. Two patients had viral cultures that grew herpes simplex virus type-1. Bacterial colonization of chronic wounds can lead to infections and may also impact wound healing. Results from this study provide data on which to base empiric antibiotic choice in patients with epidermolysis bullosa when needed and may be useful in planning strategies for decolonization and improved wound healing in this population.

Skin infection in children colonized with community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

The relationship between community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) nasal colonization and subsequent infection in children is unknown. We sought to define risk factors for skin and soft tissue infection (SSTI) in community children.

METHODS

A prior study measured S. aureus nasal colonization prevalence for 1300 community children. To detect subsequent SSTI in these children or a household member, surveys were administered 6 and 12 months following enrollment.

RESULTS

SSTIs were reported by 56/708 (8.1%) respondents during the initial 6-month interval. SSTI developed in 6/26 (23%) initially colonized with MRSA, 16/194 (8%) with methicillin-sensitive S. aureus colonization, and 34/474 (7%) not colonized with S. aureus (MRSA vs. not MRSA, univariate analysis, p = 0.014). In multivariable analysis, factors associated with SSTI included history of SSTI in the child during the year preceding enrollment (p < 0.01) and SSTI in household contacts during the follow-up interval (p<0.01); MRSA nasal colonization approached statistical significance (p = 0.08).

CONCLUSIONS

In the current era of community MRSA transmission, SSTI is a disease of households, with recurrences in index cases and occurrences among household contacts. Children with MRSA colonization may be at risk for subsequent SSTI. Further study of MRSA transmission dynamics in households and preventive strategies should receive high priority.

Reemergence of antibiotic-resistant Staphylococcus aureus in the genomics era

Staphylococcus aureus is the leading cause of bacterial infections in developed countries and produces a wide spectrum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Although S. aureus infections were historically treatable with common antibiotics, emergence of drug-resistant organisms is now a major concern. Methicillin-resistant S. aureus (MRSA) was endemic in hospitals by the late 1960s, but it appeared rapidly and unexpectedly in communities in the 1990s and is now prevalent worldwide. This Review focuses on progress made toward understanding the success of community-associated MRSA as a human pathogen, with an emphasis on genome-wide approaches and virulence determinants.

Screening for Staphylococcus aureus carriage in pregnancy: usefulness of novel sampling and culture strategies

OBJECTIVE

The purpose of this study was to determine the most sensitive strategy for the detection of Staphylococcus aureus among pregnant women and newborn infants.

STUDY DESIGN

We obtained cultures for S aureus from 5 body sites of women at 35-37 weeks' gestation. We obtained cultures from their newborn infants before hospital discharge.

RESULTS

Of 209 women who were screened, 29% of the women had at least 1 culture that was positive for S aureus; 5% of infants were S aureus carriers. The sensitivities of each site for S aureus detection were 52% nares, 50% throat, 13% rectum, 8% vagina, and 10% skin. The most sensitive combination of 2 sites was nares and throat (88%). Perinatal transmission of S aureus occurred in 4 women. Maternal methicillin-resistant S aureus carriage rate was 1%. Two infants carried the USA300 methicillin-resistant S aureus.

CONCLUSION

Screening single body sites is insensitive for the detection of S aureus carriage in pregnancy. Sampling nares and throat is essential to the identification of S aureus carriers.

Fatal co-infection with swine origin influenza virus A/H1N1 and community-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) co-infection has been described previously in association with respiratory tract infection caused by seasonal influenza A viruses, but not with swine origin influenza A (H1N1) virus (S-OIV). We report the clinical and pathological findings of the first death with fulminant co-infection by CA-MRSA. Since early empirical treatment with beta-lactam plus fluoroquinolone or macrolides is often initiated before specimen collections, bacterial co-infection in S-OIV may have been under-reported.

Community-associated meticillin-resistant Staphylococcus aureus infections: epidemiology, recognition and management

Meticillin-resistant Staphylococcus aureus (MRSA) is an important cause of infection, particularly in hospitalized patients and those with significant healthcare exposure. In recent years, epidemic community-associated MRSA (CA-MRSA) infections occurring in patients without healthcare risk factors have become more frequent. The most common manifestation of CA-MRSA infection is skin and soft tissue infection, although necrotizing pneumonia, sepsis and osteoarticular infections can occur. CA-MRSA strains have become endemic in many communities and are genetically distinct from previously identified MRSA strains. CA-MRSA may be more capable colonizers of humans and more virulent than other S. aureus strains. Specific mechanisms of pathogenicity have not been elucidated, but several factors have been proposed as responsible for the virulence of CA-MRSA, including the Panton-Valentine leukocidin, phenol-soluble modulins and type I arginine catabolic mobile element. The movement of CA-MRSA strains into the nosocomial setting limits the utility of using clinical risk factors alone to designate community- or healthcare-associated status. Identification of unique genetic characteristics and genotyping are valuable tools for MRSA epidemiological studies. Although the optimum pharmacological therapy for CA-MRSA infections has not been determined, many CA-MRSA strains remain broadly susceptible to several non-beta-lactam antibacterial agents. Empirical antibacterial therapy should include an MRSA-active agent, particularly in areas where CA-MRSA is endemic.

Waves of resistance: Staphylococcus aureus in the antibiotic era

Staphylococcus aureus is notorious for its ability to become resistant to antibiotics. Infections that are caused by antibiotic-resistant strains often occur in epidemic waves that are initiated by one or a few successful clones. Methicillin-resistant S. aureus (MRSA) features prominently in these epidemics. Historically associated with hospitals and other health care settings, MRSA has now emerged as a widespread cause of community infections. Community or community-associated MRSA (CA-MRSA) can spread rapidly among healthy individuals. Outbreaks of CA-MRSA infections have been reported worldwide, and CA-MRSA strains are now epidemic in the United States. Here, we review the molecular epidemiology of the epidemic waves of penicillin- and methicillin-resistant strains of S. aureus that have occurred since 1940, with a focus on the clinical and molecular epidemiology of CA-MRSA.