Methicillin-resistant Staphylococcus aureus colonization of the groin and risk for clinical infection among HIV-infected adults

Data on the interaction between methicillin-resistant Staphylococcus aureus (MRSA) colonization and clinical infection are limited. During 2007–2008, we enrolled HIV-infected adults in Atlanta, Georgia, USA, in a prospective cohort study. Nares and groin swab specimens were cultured for S. aureus at enrollment and after 6 and 12 months. MRSA colonization was detected in 13%–15% of HIV-infected participants (n = 600, 98% male) at baseline, 6 months, and 12 months. MRSA colonization was detected in the nares only (41%), groin only (21%), and at both sites (38%). Over a median of 2.1 years of follow-up, 29 MRSA clinical infections occurred in 25 participants. In multivariate analysis, MRSA clinical infection was significantly associated with MRSA colonization of the groin (adjusted risk ratio 4.8) and a history of MRSA infection (adjusted risk ratio 3.1). MRSA prevention strategies that can effectively prevent or eliminate groin colonization are likely necessary to reduce clinical infections in this population.

Risk factors for community-associated methicillin-resistant Staphylococcus aureus colonisation in a large metropolitan area in Greece: An epidemiological study using two case definitions

The aim of this study was to evaluate the epidemiology and characteristics and to identify modifiable risk factors for community-associated (CA) MRSA colonisation in a region with high prevalence. A large patient population (n=2280) from two tertiary care centres in Athens (Greece) was evaluated. Demographics and potential risk factors for CA-MRSA colonisation were recorded prospectively. Presence of the Panton-Valentine Leukocidin (PVL) toxin and mecA gene was determined in all MRSA isolates. Two definitions for CA-MRSA were applied. Univariate and multivariate analyses to identify predictors of previously unknown CA-MRSA colonisation were performed. In total, 120 (5.3%) MRSA carriers were identified; in 67 the isolates were classified as CA-MRSA using criteria based on the CDC definition, compared with 35 based on a definition including PVL toxin positivity. Factors significantly associated with previously unknown CA-MRSA carriage (CDC definition) included being a child or adolescent (OR=3.6, 95% CI 1.5-8.6), belonging to the family of an index case (OR=2.4, 95% CI 1.2-4.8), and presence of any co-morbidity (OR=1.7, 95% CI 1.04-2.8) or chronic skin disease (OR=3.6, 95% CI=2.2-6.1). In multivariate analysis, presence of any co-morbidity was the only significant predictor (OR=4.9, 95% CI 1.07-22.5; P=0.04). No easily modifiable risk factor for previously unknown CA-MRSA colonisation was identified. The CDC-based epidemiological definition for CA-MRSA appears to be more sensitive in detection of CA-MRSA colonisation than a purely molecular definition based on presence of the PVL gene.

Impact of community-associated methicillin resistant Staphylococcus aureus on HIV-infected patients

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as an increasingly important pathogen, causing infections in persons who have no significant healthcare exposures. Persons with human immunodeficiency virus (HIV) infection have been disproportionately affected by CA-MRSA, with increased colonization and infection documented. Several factors are likely involved in the increased CA-MRSA burden observed among HIV-infected patients, including immune factors as well as healthcare and community exposures. Proposed community exposures that have been associated with increased CA-MRSA risk include substance abuse, incarceration, geographic area of residence, and social networks. This article explores these associations and reviews the current knowledge of the epidemiology, pathogenesis, clinical manifestations, and treatment of CA-MRSA in HIV-infected persons.

Seasonal H3N2 influenza A virus fails to enhance Staphylococcus aureus co-infection in a non-human primate respiratory tract infection model

Staphylococcus aureus community-acquired pneumonia is often associated with influenza or an influenza-like syndrome. Morbidity and mortality due to methicillin-resistant S. aureus (MRSA) or influenza and pneumonia, which includes bacterial co-infection, are among the top causes of death by infectious diseases in the United States. We developed a non-lethal influenza A virus (IAV) (H3N2)/S. aureus co-infection model in cynomolgus macaques (Macaca fascicularis) to test the hypothesis that seasonal IAV infection predisposes non-human primates to severe S. aureus pneumonia. Infection and disease progression were monitored by clinical assessment of animal health; analysis of blood chemistry, nasal swabs, and X-rays; and gross pathology and histopathology of lungs from infected animals. Seasonal IAV infection in healthy cynomolgus macaques caused mild pneumonia, but unexpectedly, did not predispose these animals to subsequent severe infection with the community-associated MRSA clone USA300. We conclude that in our co-infection model, seasonal IAV infection alone is not sufficient to promote severe S. aureus pneumonia in otherwise healthy non-human primates. The implication of these findings is that comorbidity factors in addition to IAV infection are required to predispose individuals to secondary S. aureus pneumonia.

Isolation of community-acquired methicillin-resistant Staphylococcus aureus in healthy carriers in a Mexican community

OBJECTIVES

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) clones are spreading rapidly among the population in many regions worldwide. Little information is available on CA-MRSA in Mexico. The aim of this study was to identify CA-MRSA strains in the nose and throat of healthy people in a Mexican community.

METHODS

A total of 131 MRSA strains from the nose and throat obtained from healthy people in Mexico City were characterized. The genes mecA, lukS-PV/lukF-PV, and ACME-arcA were detected by PCR. Staphylococcal cassette chromosome mec (SCCmec), pulsed-field gel electrophoresis (PFGE), and spa typing were performed.

RESULTS

Bacteria that had a Panton-Valentine leukocidin (PVL)-positive gene and SCCmec type IV or V were designated as CA-MRSA strains. We found that 21.4% of MRSA strains were CA-MRSA and that the percentage of CA-MRSA strains was similar in the nose and the throat. A great diversity of profiles was found in the strains identified by PFGE pattern and spa typing. Only one strain similar to the USA300 genotype was found; this strain carried the ACME-arcA gene.

CONCLUSIONS

CA-MRSA strains were detected in the nose and throat of healthy people. We identified a high level of genetic diversity among CA-MRSA strains in healthy people of Mexico City, which were different from the USA and pandemic clone profiles.

Staphylococcus aureus protein A promotes immune suppression

Staphylococcus aureus is a prominent cause of human infections worldwide and is notorious for its ability to acquire resistance to antibiotics. Methicillin-resistant S. aureus (MRSA), in particular, is endemic in hospitals and is the most frequent cause of community-associated bacterial infections in the United States. Inasmuch as treatment options for severe MRSA infections are limited, there is need for a vaccine that protects against such infections. However, recent efforts to generate a staphylococcal vaccine have met with little success in human clinical trials. These failures are somewhat puzzling, since the vaccine antigens tested promote opsonophagocytosis in vitro and confer protection in animal infection models. One possibility is that the pathogen inhibits (and/or fails to elicit) the development of protective immunity in humans. Indeed, S. aureus produces numerous molecules that can potentially promote immune evasion, including protein A (SpA), an immunoglobulin (Ig)-binding protein present on the bacterial surface and freely secreted into the extracellular environment. SpA binds the Fc region of antibody and the Fab regions of the B-cell receptor, processes that are known to block opsonophagocytosis and cause B-cell death in vitro. In a recent study, Falugi et al. [F. Falugi, H. K. Kim, D. M. Missiakas, and O. Schneewind, mBio 4(5):e00575-13, 2013] showed that vaccination with spa mutant S. aureus strains lacking antibody Fc- and/or Fab-binding capacity protects against subsequent challenge with the USA300 epidemic strain. The findings provide strong support for the idea that SpA promotes S. aureus immune evasion in vivo and form the foundation for a new approach in our efforts to develop a vaccine that prevents severe S. aureus infections.

The complex pathogenesis of bacteremia: from antimicrobial clearance mechanisms to the genetic background of the host

Bacteremia develops when bacteria manage to escape the host immune mechanisms or when the otherwise well-orchestrated immune response fails to control bacterial spread due to inherent or acquired immune defects that are associated with susceptibility to infection. The pathogenesis of bacteremia has some characteristic features that are influenced by the genetic signature of the host. In this review, the host defense mechanisms that help prevent bacteremia will be described and the populations who are at risk because of congenital or acquired deficiencies in such mechanisms will be defined. A special mention will be made to novel insights regarding host immune defense against the most commonly isolated organisms from patients with community-acquired bloodstream infections.

Effect of vitamin D3 supplementation on Staphylococcus aureus nasal carriage: a randomized, double-blind, placebo-controlled trial in healthy adults

Observational studies have reported an inverse association between serum 25-hydroxyvitamin D (25OHD) concentrations and Staphylococcus aureus nasal carriage; however, clinical trials of vitamin D supplementation are lacking. To assess the effect of vitamin D3 supplementation on persistent S. aureus nasal carriage we conducted a randomized, double-blind, placebo-controlled trial among 322 healthy adults. Participants were given an oral dose of either 200 000 IU vitamin D3 for each of 2 months, followed by 100 000 IU monthly or placebo in an identical dosing regimen, for a total of 18 months. Nasal swabs for S. aureus culture and serum for 25OHD measurement were obtained at baseline, 6, 12 and 18 months of study. The mean baseline concentration of 25OHD was 72 nM (SD 22 nM). Vitamin D3 supplementation increased 25OHD levels which were maintained at >120 nM throughout the study. Nasal colonization by S. aureus was found in 31% of participants at baseline. Persistent carriage, defined as those that had positive S. aureus nasal cultures for all post-baseline swabs, occurred in 20% of the participants but vitamin D3 supplementation was not associated with a reduction in persistent carriage (OR = 1.39, 95% CI 0.63-3.06). Risk factor analysis showed that only gender was significantly associated with carriage, where women were less likely to be carriers than men (relative risk 0.83, 95% CI 0.54-0.99). Serum 25OHD concentrations were not associated with the risk of carriage. In conclusion, monthly administration of 100 000 IU of vitamin D3 did not reduce persistent S. aureus nasal carriage.

Preoperative decolonization effective at reducing staphylococcal colonization in total joint arthroplasty patients

Staphylococcus decolonization prior to surgery is used to prevent surgical site infections (SSIs) after total joint arthroplasty (TJA). To determine if current treatment protocols result in successful decolonization of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA), 106 consecutive patients were screened for nasal MSSA/MRSA colonization pre-operatively and on the day of surgery. Colonized patients used intranasal mupirocin twice a day and chlorhexidine showers daily 5 days prior to surgery. Pre-operatively, 24 joints (22.0%) were positive for MSSA colonization and 5 joints (4.6%) were positive for MRSA colonization. On the day of surgery, 3 joints (2.8%) who underwent decolonization were positive for MSSA colonization and 0 joints were positive for MRSA colonization. The reduction in MSSA colonization was significant (P<0.001), while the eradication of MRSA colonization approached statistical significance (P=0.063). Current decolonization protocols using intranasal mupirocin and chlorhexidine washes are effective for reducing MRSA/MSSA colonization.

Medical and household characteristics associated with methicillin resistant Staphylococcus aureus nasal carriage among patients admitted to a rural tertiary care hospital

BACKGROUND

Methicillin resistant Staphylococcus aureus (MRSA) poses a threat to patient safety and public health. Understanding how MRSA is acquired is important for prevention efforts. This study investigates risk factors for MRSA nasal carriage among patients at an eastern North Carolina hospital in 2011.

METHODS

Using a case-control design, hospitalized patients ages 18 - 65 years were enrolled between July 25, 2011 and December 15, 2011 at Vidant Medical Center, a tertiary care hospital that screens all admitted patients for nasal MRSA carriage. Cases, defined as MRSA nasal carriers, were age and gender matched to controls, non-MRSA carriers. In-hospital interviews were conducted, and medical records were reviewed to obtain information on medical and household exposures. Multivariable conditional logistic regression was used to derive odds ratio (OR) estimates of association between MRSA carriage and medical and household exposures.

RESULTS

In total, 117 cases and 119 controls were recruited to participate. Risk factors for MRSA carriage included having household members who took antibiotics or were hospitalized (OR: 3.27; 95% Confidence Interval (CI): 1.24-8.57) and prior hospitalization with a positive MRSA screen (OR: 3.21; 95% CI: 1.12-9.23). A lower proportion of cases than controls were previously hospitalized without a past positive MRSA screen (OR: 0.40; 95% CI: 0.19-0.87).

CONCLUSION

These findings suggest that household exposures are important determinants of MRSA nasal carriage in hospitalized patients screened at admission.

A systematic literature review and meta-analysis of factors associated with methicillin-resistant Staphylococcus aureus colonization at time of hospital or intensive care unit admission

OBJECTIVE

Screening for methicillin-resistant Staphylococcus aureus (MRSA) in high-risk patients is a legislative mandate in 9 US states and has been adopted by many hospitals. Definitions of high risk differ among hospitals and state laws. A systematic evaluation of factors associated with colonization is lacking. We performed a systematic review of the literature to assess factors associated with MRSA colonization at hospital admission.

DESIGN

We searched MEDLINE from 1966 to 2012 for articles comparing MRSA colonized and noncolonized patients on hospital or intensive care unit (ICU) admission. Data were extracted using a standardized instrument. Meta-analyses were performed to identify factors associated with MRSA colonization.

RESULTS

We reviewed 4,381 abstracts; 29 articles met inclusion criteria (n = 76,913 patients). MRSA colonization at hospital admission was associated with recent prior hospitalization (odds ratio [OR], 2.4 [95% confidence interval (CI), 1.3-4.7]; P < .01), nursing home exposure (OR, 3.8 [95% CI, 2.3-6.3]; P < .01), and history of exposure to healthcare-associated pathogens (MRSA carriage: OR, 8.0 [95% CI, 4.2-15.1]; Clostridium difficile infection: OR, 3.4 [95% CI, 2.2-5.3]; vancomycin-resistant Enterococci carriage: OR, 3.1 [95% CI, 2.5-4.0]; P < .01 for all). Select comorbidities were associated with MRSA colonization (congestive heart failure, diabetes, pulmonary disease, immunosuppression, and renal failure; P < .01 for all), while others were not (human immunodeficiency virus, cirrhosis, and malignancy). ICU admission was not associated with an increased risk of MRSA colonization (OR, 1.1 [95% CI, 0.6-1.8]; P = .87).

CONCLUSIONS

MRSA colonization on hospital admission was associated with healthcare contact, previous healthcare-associated pathogens, and select comorbid conditions. ICU admission was not associated with MRSA colonization, although this is commonly used in state mandates for MRSA screening. Infection prevention programs utilizing targeted MRSA screening may consider our results to define patients likely to have MRSA colonization.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) isolates of swine origin form robust biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) colonization of livestock animals is common and prevalence rates for pigs have been reported to be as high as 49%. Mechanisms contributing to the persistent carriage and high prevalence rates of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains in swine herds and production facilities have not been investigated. One explanation for the high prevalence of MRSA in swine herds is the ability of these organisms to exist as biofilms. In this report, the ability of swine LA-MRSA strains, including ST398, ST9, and ST5, to form biofilms was quantified and compared to several swine and human isolates. The contribution of known biofilm matrix components, polysaccharides, proteins and extracellular DNA (eDNA), was tested in all strains as well. All MRSA swine isolates formed robust biofilms similar to human clinical isolates. The addition of Dispersin B had no inhibitory effect on swine MRSA isolates when added at the initiation of biofilm growth or after pre-established mature biofilms formed. In contrast, the addition of proteinase K inhibited biofilm formation in all strains when added at the initiation of biofilm growth and was able to disperse pre-established mature biofilms. Of the LA-MRSA strains tested, we found ST398 strains to be the most sensitive to both inhibition of biofilm formation and dispersal of pre-formed biofilms by DNaseI. Collectively, these findings provide a critical first step in designing strategies to control or eliminate MRSA in swine herds.

Growth and laboratory maintenance of Staphylococcus aureus

Staphylococcus aureus is a facultative anaerobic Gram-positive coccus and a member of the normal skin flora as well as the nasal passages of humans. S. aureus is also the etiological agent of suppurative abscesses, as first described by Sir Alexander Ogston in 1880. Ever since, studies on S. aureus have focused on the complex battery of virulence factors and regulators that allow for its swift transition between commensalism and pathogenic states and escape from host immune defenses. The success of this pathogen is further evidenced by its ability to acquire antibiotic resistance traits through mechanisms that often remain poorly understood.

Targeting imperfect vaccines against drug-resistance determinants: a strategy for countering the rise of drug resistance

The growing prevalence of antimicrobial resistance in major pathogens is outpacing discovery of new antimicrobial classes. Vaccines mitigate the effect of antimicrobial resistance by reducing the need for treatment, but vaccines for many drug-resistant pathogens remain undiscovered or have limited efficacy, in part because some vaccines selectively favor pathogen strains that escape vaccine-induced immunity. A strain with even a modest advantage in vaccinated hosts can have high fitness in a population with high vaccine coverage, which can offset a strong selection pressure such as antimicrobial use that occurs in a small fraction of hosts. We propose a strategy to target vaccines against drug-resistant pathogens, by using resistance-conferring proteins as antigens in multicomponent vaccines. Resistance determinants may be weakly immunogenic, offering only modest specific protection against resistant strains. Therefore, we assess here how varying the specific efficacy of the vaccine against resistant strains would affect the proportion of drug-resistant vs. -sensitive strains population-wide for three pathogens--Streptococcus pneumoniae, Staphylococcus aureus, and influenza virus--in which drug resistance is a problem. Notably, if such vaccines confer even slightly higher protection (additional efficacy between 1% and 8%) against resistant variants than sensitive ones, they may be an effective tool in controlling the rise of resistant strains, given current levels of use for many antimicrobial agents. We show that the population-wide impact of such vaccines depends on the additional effect on resistant strains and on the overall effect (against all strains). Resistance-conferring accessory gene products or resistant alleles of essential genes could be valuable as components of vaccines even if their specific protective effect is weak.

Occupational exposure to raw meat: a newly-recognized risk factor for Staphylococcus aureus nasal colonization amongst food handlers

Staphylococcus aureus contaminating raw meat may increase nasal colonization risk for occupationally-exposed food handlers. Food handlers from six catering establishments were nasally sampled for S. aureus and completed a questionnaire on carriage risk factors. Isolates were characterized for antibiotic susceptibility, spa type and, for methicillin-resistant strains, SCCmec type. Of 434 food handlers, 99 (22.8%) were colonized with S. aureus. Five isolates were methicillin-resistant belonging to SCCmec IV (2) and V (3). Resistance to tetracycline (20%), and erythromycin (16%) was high, but <10% to other antibiotics. Spa typing revealed 17% of isolates as t189, with 8% each t127 and t1081. Food handlers ever handling raw meat had a significantly higher colonization risk (OR=2.7; 95% CI: 1.7-4.5), increasing to 3.7 (95% CI: 2.0-6.8) for those always exposed. This is the first report of increased colonization risk in food handlers exposed to raw meat. This occupational hazard may increase infection risk, so improved compliance with workplace hygiene may be required.

Recurrent furunculosis: Efficacy of the CMC regimen--skin disinfection (chlorhexidine), local nasal antibiotic (mupirocin), and systemic antibiotic (clindamycin)

BACKGROUND

The treatment of recurrent furunculosis is poorly documented and represents a public health challenge. The medical care of this disease is often disappointing, especially as the disease evolution is uncertain and relapses occur. We report the efficacy and safety of our CMC regimen: skin disinfection (chlorhexidine), local nasal antibiotic (mupirocin), and systemic antibiotic (clindamycin).

METHODS

Patients attending our institution during the period 2006-2012 for recurrent furunculosis (≥ 4 episodes/y) were enrolled in the study. Clinical and bacteriological data were collected. Staphylococcus aureus colonization was also investigated in close contacts, and carriers were treated. Patients were treated with the CMC regimen: skin disinfection with chlorhexidine for 21 days, nasal mupirocin ointment for 5 days, and oral clindamycin 1800-2400 mg for 21 days.

RESULTS

Nineteen patients were included. Their mean age was 36 ± 14.5 y and the male to female sex ratio was 1.1. Screening swabs from all sites were S. aureus-positive in 63% (n = 12), including 4 methicillin-resistant S. aureus (MRSA). Before the CMC regimen, the median time to relapse was 31 days (mean 52 days). The mean number of recurrences was 5.5 ± 2.4/y. After the CMC regimen, among 16 patients who had a complete follow-up, 14 were healed beyond 9 months. Two recurrences occurred, 1 in an MRSA carrier and 1 in a patient with an insufficiently treated dermatosis. No serious side effect occurred that required the cessation of treatment.

CONCLUSIONS

There are 2 major routes involved in recurrent furunculosis: risk factors and staphylococcal colonization of close contacts. Our procedure is safe and effective, with 87% remission beyond 9 months. It merits testing on larger numbers of participants.

Prevalence and characteristics of community carriage of methicillin-resistant Staphylococcus aureus in Malta

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. Malta is one of the countries with the highest MRSA prevalence in Europe, as identified from hospital blood cultures [1]. However, community prevalence of MRSA has never previously been investigated. This study aimed at establishing the prevalence of community MRSA nasal colonization in Maltese individuals and identifying the clonal characteristics of the detected isolates. Nasal swabs were collected from 329 healthy individuals who were also asked to complete a brief questionnaire about risk factors commonly associated with MRSA carriage and infection. The swabs were transported and enriched in a nutrient broth supplemented with NaCl. The presence of MRSA was then determined by culturing on MRSA Select chromogenic agar and then confirming by several assays, including catalase, coagulase and PBP2a agglutination tests. The isolates were assayed for antibiotic susceptibilities and typed by microarray analysis to determine the clonal characteristics of each strain. The prevalence of MRSA nasal colonization in the healthy Maltese population was found to be 8.81% (95% confidence interval [CI], 5.75–11.87%), much higher than that found in other studies carried out in several countries. No statistical association was found between MRSA carriage and demographics or risk factors; however, this was hindered by the small sample size. Almost all the isolates were fusidic-acid resistant. The majority were found to belong to a local endemic clone (CC5) which seems to be replacing the previously prevalent European clone UK-EMRSA-15 in the country. A new clone (CC50-MRSA-V) was also characterized. The presence of such a significant community reservoir of MRSA increases the burdens already faced by the local healthcare system to control the MRSA epidemic. Colonization of MRSA in otherwise healthy individuals may represent a risk for endogenous infection and transmission to hospitalized patients after admission to a healthcare facility, leading to longer hospital stays and, consequently, increased healthcare costs.

Improved understanding of factors driving methicillin-resistant Staphylococcus aureus epidemic waves

Methicillin-resistant Staphylococcus aureus (MRSA) remains one of the most important causes of nosocomial infections worldwide. Since the global spread of MRSA in the 1960s, MRSA strains have evolved with increased pathogenic potential. Notably, some strains are now capable of causing persistent infections not only in hospitalized patients but also in healthy individuals in the community. Furthermore, MRSA is increasingly associated with infections among livestock-associated workers, primarily because of transmission from animals to humans. Moreover, many MRSA strains have gained resistance to most available antibiotics. In this review, we will present current knowledge on MRSA epidemiology and discuss new endeavors being undertaken to understand better the molecular and epidemiological underpinnings of MRSA outbreaks.

Mannitol utilisation is required for protection of Staphylococcus aureus from human skin antimicrobial fatty acids

Mannitol (Mtl) fermentation, with the subsequent production of acid, is a species signature of Staphylococcus aureus, and discriminates it from most other members of the genus. Inactivation of the gene mtlD, encoding Mtl-1-P dehydrogenase was found to markedly reduce survival in the presence of the antimicrobial fatty acid, linoleic acid. We demonstrate that the sugar alcohol has a potentiating action for this membrane-acting antimicrobial. Analysis of cellular metabolites revealed that, during exponential growth, the mtlD mutant accumulated high levels of Mtl and Mtl-P. The latter metabolite was not detected in its isogenic parent strain or a deletion mutant of the entire mtlABFD operon. In addition, the mtlD mutant strain exhibited a decreased MIC for H₂O₂, however virulence was unaffected in a model of septic arthritis.

Livestock-associated methicillin and multidrug resistant Staphylococcus aureus is present among industrial, not antibiotic-free livestock operation workers in North Carolina

Objectives

Administration of antibiotics to food animals may select for drug-resistant pathogens of clinical significance, such as methicillin-resistant Staphylococcus aureus (MRSA). In the United States, studies have examined prevalence of MRSA carriage among individuals exposed to livestock, but prevalence of multidrug-resistant S. aureus (MDRSA) carriage and the association with livestock raised with versus without antibiotic selective pressure remains unclear. We aimed to examine prevalence, antibiotic susceptibility, and molecular characteristics of S. aureus among industrial livestock operation (ILO) and antibiotic-free livestock operation (AFLO) workers and household members in North Carolina.

Methods

Participants in this cross-sectional study were interviewed and provided a nasal swab for S. aureus analysis. Resulting S. aureus isolates were assessed for antibiotic susceptibility, multi-locus sequence type, and absence of the scn gene (a marker of livestock association).

Results

Among 99 ILO and 105 AFLO participants, S. aureus nasal carriage prevalence was 41% and 40%, respectively. Among ILO and AFLO S. aureus carriers, MRSA was detected in 7% (3/41) and 7% (3/42), respectively. Thirty seven percent of 41 ILO versus 19% of 42 AFLO S. aureus-positive participants carried MDRSA. S. aureus clonal complex (CC) 398 was observed only among workers and predominated among ILO (13/34) compared with AFLO (1/35) S. aureus-positive workers. Only ILO workers carried scn-negative MRSA CC398 (2/34) and scn-negative MDRSA CC398 (6/34), and all of these isolates were tetracycline resistant.

Conclusions

Despite similar S. aureus and MRSA prevalence among ILO and AFLO-exposed individuals, livestock-associated MRSA and MDRSA (tetracycline-resistant, CC398, scn-negative) were only present among ILO-exposed individuals. These findings support growing concern about antibiotics use and confinement in livestock production, raising questions about the potential for occupational exposure to an opportunistic and drug-resistant pathogen, which in other settings including hospitals and the community is of broad public health importance.

Surveillance and management of multidrug-resistant microorganisms

Multidrug-resistant organisms are an established and growing worldwide public health problem and few therapeutic options remain available. The traditional antimicrobials (glycopeptides) for multidrug-resistant Gram-positive infections are declining in efficacy. New drugs that are presently available are linezolid, daptomicin and tigecycline, which have well-defined indications for severe infections, and talavancin, which is under Phase III trial for hospital-acquired pneumonia. Unfortunately the therapies available for multidrug-resistant Gram-negatives, including carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacteriaceae, are limited to only colistin and tigecycline. Both of these drugs are still not registered for severe infections, such as hospital acquired pneumonia. Consequently, as confirmed by scientific evidence, a multidisciplinary approach is needed. Surveillance, infection control procedures, isolation and antimicrobial stewardship should be implemented to reduce multidrug-resistant organism diffusion.

Methicillin-resistant Staphylococcus aureus infections

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen that has exploded into clinical prominence in a short period. New medications are available for the treatment of MRSA infections, each with its own pitfalls and caveats. However, the resistance profile of the bacteria is becoming more complex. Recent guidelines from the Infectious Diseases Society of America provide an evidence-based framework for the management of MRSA infections. This article provides additional practical advice on approaches to MRSA, including the detection, prevention, and management of a variety of its common presentations.

Identification of Staphylococcus aureus from enriched nasal swabs within 24 h is improved with use of multiple culture media

Nasal carriage of Staphylococcus aureus is commonly evaluated via culture-based methods. We found that parallel use of two media, Baird-Parker and CHROMagar™ Staph aureus, increased detection of S. aureus from a healthy population by 29 %. We suggest use of both media for optimal identification of S. aureus from healthy cohorts.

A basic dynamic transmission model of Staphylococcus aureus in the US population

We present a basic mathematical model of Staphylococcus aureus transmission in the USA based on natural history of infection and nationally representative data. We employed a Susceptible-Colonized-Infected-Recovered-Susceptible compartmental modelling framework with two different phenotypes of S. aureus: methicillin-susceptible (MSSA) and methicillin-resistant (MRSA). The model is dynamic and accounts for the US population growth. For model calibration/validation, we used published 1999–2005 S. aureus infection data in conjunction with the 2001–2004 National Health and Nutrition Examination Survey colonization data. Baseline model projections illustrated how MRSA might continue to expand and gradually replace MSSA over time, in the absence of intervention, if there is strong competition for colonization. The model-based estimate of the basic reproduction number (R₀) highlights the need for infection control. We illustrate the potential population-level impact of intervention with a hypothetical S. aureus vaccination component.

Risk factors for Staphylococcus aureus nasal colonization in Danish middle-aged and elderly twins

Staphylococcus aureus is a human commensal bacterium found in the nasal cavity and other body sites. Identifying risk factors for S. aureus nasal carriage is of interest, as nasal carriage is a risk factor for subsequent invasive infection. We recently investigated the influence of host genetics on S. aureus carriage in Danish middle-aged and elderly twins, which indicated no significant heritability that could account for the observed S. aureus carriage. In the present study, we performed a questionnaire-based study of S. aureus colonization on the same cohort of 2,196 Danish middle-aged and elderly twins to identify specific risk factors for S. aureus nasal colonization, including analyzing the paired twins (n = 478) that were discordant for S. aureus colonization. We found associations between risk factors and S. aureus nasal colonization among middle-aged and elderly twins, including age, male gender, psoriasis, and atopic diseases. Also, present living on a farm is clearly associated with S. aureus colonization, while smoking had a borderline statistically significant protective effect.

Obesity and Staphylococcus aureus nasal colonization among women and men in a general population

BACKGROUND

Obesity and diabetes mellitus (DM) have been linked to increased risk of infections, and Staphylococcus aureus nasal colonization is a major risk factor for developing infections with the microbe. We therefore sought to find whether body mass index (BMI) and waist circumference (WC) could be associated with S. aureus colonization independent of DM.

METHODOLOGY

S. aureus colonization was assessed by nasal swab cultures among 2,169 women and 1,709 men, aged 30-87 years, in the population-based Tromsø Staph and Skin Study in 2007-08. Height (cm), weight (kg), WC (cm), and glycated haemoglobin (HbA1c,%) were measured. Multivariable logistic regression analyses including information on DM, HbA1c, hormonal contraceptive use and other potential confounders were used.

RESULTS

In the female population, each 2.5 kg/m(2) increase in BMI was associated with a 7% higher odds of S. aureus nasal colonization (P = 0.01). When comparing obese and lean women aged 30-43 years, we observed that BMI ≥32.5 versus <22.5 kg/m(2) and WC ≥101 versus <80 cm was associated with a 2.60 and 2.12 times higher odds of S. aureus colonization, respectively (95% confidence intervals 1.35-4.98 and 1.17-3.85). Among men, high WC was also associated with S. aureus nasal colonization. The associations did not change significantly when the analysis was restricted to participants without signs of pre-diabetes (HbA1c <6.0%) among women and men, and to non-users of hormonal contraceptives among women.

CONCLUSION

Our results support that obesity is a possible determinant for S. aureus nasal colonization independent of DM, in particular for premenopausal women. The role of obesity at different ages and by sex should be addressed in future prospective studies of S. aureus colonization.

Evolution of community- and healthcare-associated methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a prominent cause of human infections globally. The high prevalence of infections is compounded by antibiotic resistance--a significant problem for treatment. Methicillin-resistant S. aureus (MRSA) is endemic in hospitals and healthcare facilities worldwide, and is an increasingly common cause of community-associated bacterial infections in industrialized countries. Although much focus is placed on the role of S. aureus as a human pathogen, it is in fact a human commensal organism that has had a relatively long coexistence with the human host. Many S. aureus infections can be explained by host susceptibility or other predisposing risk factors. On the other hand, the emergence/re-emergence of successful S. aureus clones (referred to as epidemic waves) suggests a rapid bacterial adaption and evolution, which includes the emergence of antibiotic resistance and increased virulence and/or transmissibility. It is within this context that we review our understanding of selected S. aureus epidemic waves, and highlight the use of genome sequencing as a means to better understand the evolution of each lineage.

MRSA nasal colonization in children: prevalence meta-analysis, review of risk factors and molecular genetics

BACKGROUND

We report a meta-analysis of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization prevalence in children and a review of the risk factors as well as molecular genetic characterization.

METHODS

All relevant studies reporting prevalence data on MRSA nasal colonization in children published between January 2000 and August 2010 were retrieved from the MEDLINE database and analyzed.

RESULTS

After screening 544 studies, 50 studies were included. We obtained an estimate of MRSA prevalence of 2.7% (95% confidence interval [CI]: 2.2-3.1); of 5.2% (95% CI: 3.1-7.3) in children with underlying conditions and of 2.3% (95% CI: 1.8-2.7) in healthy children; 5.4% (95% CI: 3.1-7.7) in children recruited in hospitals and 3% (95% CI: 2.4-3.6) in children recruited in the community. Staphylococcal cassette chromosome mec type IV is the most diffused cassette globally.

CONCLUSION

The hospital remains the environment where the microorganism circulates most. Children with underlying conditions could act as vectors of microorganisms between the hospital and the community. MRSA prevention strategies should be tailored to each specific institution, taking into account the nosocomial prevalence of MRSA nasal colonization and infections, and the prevalence of nasal colonization in the community that refers to the specific health care center.

Cohorting based on nasal methicillin-resistant Staphylococcus aureus status: an opportunity to share more than a room

BACKGROUND

Hospital roommates are cohorted with similarly colonized patients to decrease methicillin-resistant Staphylococcus aureus (MRSA) transmission risk. However, little is known about differences in S aureus nasal and extranasal carriage between hospital roommates who are in MRSA or non-MRSA designated rooms.

METHODS

Patients sharing hospital rooms were cultured for S aureus in the nose, throat, and other body sites. Differences in S aureus methicillin and mupirocin susceptibility and USA300 type were evaluated.

RESULTS

Eighty-two patients comprising 48 roommate pairs were studied. Among 6 roommate pairs in MRSA rooms, 3 (50%) had differences in carriage based on having methicillin-susceptible S aureus at an extranasal body site. In non-MRSA rooms, 19 (45%) roommate pairs had differences in S aureus carriage. Extranasal colonization was significantly associated with discordance between roommates, P < .001. Antibiotic exposure, ward type, and the duration of room sharing were not associated with discordance.

CONCLUSION

Patients have almost a 50% chance of having differences in S aureus colonization compared with their hospital roommate, even in MRSA-designated rooms. Cohorting by MRSA status at the time of admission may not be as effective a control strategy as horizontal measures that do not rely on known colonization with S aureus or other pathogens.

Evaluation of genetically inactivated alpha toxin for protection in multiple mouse models of Staphylococcus aureus infection

Staphylococcus aureus is a major human pathogen and a leading cause of nosocomial and community-acquired infections. Development of a vaccine against this pathogen is an important goal. While S. aureus protective antigens have been identified in the literature, the majority have only been tested in a single animal model of disease. We wished to evaluate the ability of one S. aureus vaccine antigen to protect in multiple mouse models, thus assessing whether protection in one model translates to protection in other models encompassing the full breadth of infections the pathogen can cause. We chose to focus on genetically inactivated alpha toxin mutant HlaH35L. We evaluated the protection afforded by this antigen in three models of infection using the same vaccine dose, regimen, route of immunization, adjuvant, and challenge strain. When mice were immunized with HlaH35L and challenged via a skin and soft tissue infection model, HlaH35L immunization led to a less severe infection and decreased S. aureus levels at the challenge site when compared to controls. Challenge of HlaH35L-immunized mice using a systemic infection model resulted in a limited, but statistically significant decrease in bacterial colonization as compared to that observed with control mice. In contrast, in a prosthetic implant model of chronic biofilm infection, there was no significant difference in bacterial levels when compared to controls. These results demonstrate that vaccines may confer protection against one form of S. aureus disease without conferring protection against other disease presentations and thus underscore a significant challenge in S. aureus vaccine development.

Methicillin-resistant staphylococcus aureus nasal colonization prevalence among Emergency Medical Services personnel

INTRODUCTION

The prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among Emergency Medical Services (EMS) personnel is not well studied. Methicillin-resistant Staphylococcus aureus colonization can be a health hazard for both EMS personnel and patients. The aim of this study was to quantify the prevalence of MRSA colonization among EMS personnel. This study will help the scientific community understand the extent of this condition so that further protocols and policies can be developed to support the health and wellbeing of EMS personnel. Hypothesis/ Problem The hypothesis of this study was that the prevalence of MRSA colonization among EMS personnel is significantly higher than among the general population.

METHODS

This was a cross-sectional study. A total of 110 subjects were selected from two major US Mid-Atlantic fire departments. Methicillin-resistant Staphylococcus aureus colonization was detected by nasal swabbing. Nasal swabs were inoculated onto a special agar medium (C-MRSAgar) with polymerase chain reaction testing performed. One-sided binomial distribution at the Study Size 2.0 Web calculator was used. Using the Web calculator, p (H0 proportion) = 1.5%; a difference (H1-H0) 'Δ' = 4.53% can be detected at α = 5% and power = 80% with N = 110.

RESULTS

Samples were collected from 110 volunteers. Seven samples were positive for MRSA, resulting in a prevalence of 7/110 or 6.4% (95% CI, 1.8%-11%; P < .0003) compared with a 1.5% prevalence of MRSA colonization among the general population.

CONCLUSION

There is evidence that EMS personnel have a higher prevalence of MRSA colonization than the general population. This can be a risk to patients and can be recognized as an occupational hazard.

Dynamic pattern and genotypic diversity of Staphylococcus aureus nasopharyngeal carriage in healthy pre-school children

OBJECTIVES

It is common wisdom that persistent carriage of Staphylococcus aureus is more frequent in young children than in adults. The objectives of this study were to assess the S. aureus temporal carriage pattern among a healthy community of pre-school children, with concomitant description of genotype diversity, toxin-encoding genes and antibiotic resistance.

METHODS

Among 333 children 3-6 years of age, S. aureus nasopharyngeal carriage was assessed over one school year by culture of three sequential nasopharyngeal aspirates. Identification, methicillin resistance and toxin production profile were determined by PCR. Genotyping was performed by spa sequencing and multilocus sequence typing (MLST).

RESULTS

Out of 830 samples collected, 286 (34%) yielded S. aureus from 185 carriers (55%). Based on consecutive genotype analysis, only 40/268 (15%) children could be classified as persistent carriers, and the remaining 118 (44%) showed intermittent carriage. spa typing revealed 82 types clustered into 13 spa clonal complexes (CCs). Fourteen strains isolated from 11 (3%) children were methicillin-resistant S. aureus (MRSA), half of these strains belonged to the commonly hospital-associated spa t008-ST8-SCCmec IV. Methicillin-susceptible S. aureus (MSSA) were genotypically more diverse. Toxic shock syndrome toxin and egc1/2 complexes were highly prevalent (24%). Contrastingly, Panton-Valentine leucocidin (PVL) was carried only by three MSSA strains (0.6% of children). Exfoliative toxins were detected in 10 (3.5%) MSSA strains, of which 5 were related to the impetigo clone CC121.

CONCLUSIONS

Although S. aureus nasopharyngeal carriage was high among healthy pre-school children, persistent carriage seems to be less frequent than previously reported. The prevalence of MRSA carriage was 3%, but was not associated with PVL.

Presence, distribution, and molecular epidemiology of methicillin-resistant Staphylococcus aureus in a small animal teaching hospital: a year-long active surveillance targeting dogs and their environment

Methicillin-resistant Staphylococcus aureus (MRSA) is known to be present in small animal veterinary clinical environments. However, a better understanding of the ecology and dynamics of MRSA in these environments is necessary for the development of effective infectious disease prevention and control programs. To achieve this goal, a yearlong active MRSA surveillance program was established at The Ohio State University (OSU) Veterinary Medical Center to describe the spatial and molecular epidemiology of this bacterium in the small animal hospital. Antimicrobial susceptibility testing, staphylococcal chromosomal cassette mec (SCCmec) typing, pulsed-field gel electrophoresis (PFGE) typing, and dendrogram analysis were used to characterize and analyze the 81 environmental and 37 canine-origin MRSA isolates obtained during monthly sampling events. Overall, 13.5% of surfaces were contaminated with MRSA at 1 or more sampling times throughout the year. The majority of the environmental and canine isolates were SCCmec type II (93.8% and 86.5%, respectively) and USA100 (90.1% and 86.5%, respectively). By PFGE analysis, these isolates were found to be closely related, which reflects a low diversity of MRSA strains circulating in the hospital. For 5 consecutive months, 1 unique pulsotype was the most prevalent across the medical services and was recovered from a variety of surfaces and hospital locations. Carts/gurneys, doors, and examination tables/floors were the most frequently contaminated surfaces. Some surfaces maintained the same pulsotypes for 3 consecutive months. Molecular analysis found that incoming MRSA-positive dogs were capable of introducing a new pulsotype into the hospital environment during the surveillance period. Our results suggest that once a MRSA strain is introduced into the hospital environment, it can be maintained and spread for extended periods of time. These findings can aid in the development of biosecurity and biocontainment protocols aimed at reducing environmental contamination and potential exposures to MRSA in veterinary hospital staff, clients, and patients.

Patient and provider perspectives on methicillin-resistant Staphylococcus aureus: a qualitative assessment of knowledge, beliefs, and behavior

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of healthcare-associated infection. Individuals with spinal cord injuries and disorders (SCI/D) are at high risk of MRSA colonization and infection. The Department of Veterans Affairs (VA) released guidelines to prevent the spread of MRSA in Veterans with SCI/D; however, available patient educational materials did not address the unique issues for this population.

OBJECTIVE

To assess perceptions of SCI/D providers and Veterans with SCI/D regarding MRSA and their educational needs about MRSA prevention, with an ultimate goal of developing patient educational materials that address the issues unique to SCI/D.

METHODS

Purposive samples of SCI/D providers (six groups) and Veterans with SCI/D (one group) at two VA facilities participated in 60-90-minute focus group sessions. Qualitative data were analyzed using latent content and constant comparative techniques to identify focal themes.

PARTICIPANTS

Thirty-three providers (physicians and nurses working in inpatient, outpatient, and homecare settings) and eight Veterans participated.

RESULTS

Three overarching themes emerged from the analysis: knowledge about MRSA, hand hygiene, and barriers to educating Veterans with SCI/D.

CONCLUSIONS

SCI/D providers and Veterans with SCI/D identified gaps in general MRSA knowledge, gaps in knowledge of good hand hygiene practices and of required frequency of hand hygiene, and barriers to educating Veterans with SCI/D during inpatient stays. Future educational materials and strategies should address these gaps.

Tip of the iceberg? The emergence of antibiotic-resistant organisms in the IBD population

Inflammatory bowel disease (IBD) patients have risk factors for acquisition of antibiotic-resistant organisms such as MRSA. In a recent study, we have shown a rising prevalence of MRSA infection among hospitalized IBD patients. This population is at increased risk of infection and its associated mortality. These findings underscore the need for infection control measures in the hospital setting.

Bacterial colonization and resistance patterns in 133 patients undergoing a primary hip- or knee replacement in Southern Sweden

BACKGROUND AND PURPOSE

Prosthetic joint infections can be caused by bacteria derived from the patient's skin. The aim of the study was: (1) to determine which bacteria colonize the nose and groin in patients planned for primary hip or knee arthroplasty, (2) to determine the antimicrobial resistance patterns, and (3) to monitor changes in bacterial colonization and resistance patterns connected to surgery.

PATIENTS AND METHODS

2 weeks before scheduled primary hip or knee arthroplasty, culture samples were taken from the anterior nares and from the groin of 133 consecutive patients. At surgery, cloxacillin was given prophylactically and cement with gentamicin was used. 2 weeks after surgery, another set of samples were taken from 120 of these patients. Bacterial findings and resistance patterns were analyzed.

RESULTS

Preoperatively, 95% of the patients had coagulase-negative staphylococci (CNS) in the groin and 77% in the nose. The proportion of patients with a methicillin-resistant CNS in the groin increased from 20% preoperatively to 50% postoperatively (p < 0.001), and the proportion of patients with a gentamicin-resistant CNS in the groin increased from 5% to 45% (p < 0.001). 28% of the patients had Staphylococcus aureus in the nose preoperatively, and 7% in the groin. Methicillin-resistant Staphylococcus aureus (MRSA) was found in the nose of 1 patient.

INTERPRETATION

In southern Sweden, beta-lactams were effective against 99% of the Staphylococcus aureus strains and 80% of the CNS strains colonizing the patients undergoing primary hip or knee arthroplasty. Gentamicin protects against most CNS strains in cemented primary joint replacements.

Household risk factors for colonization with multidrug-resistant Staphylococcus aureus isolates

Antimicrobial resistance, particularly in pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), limits treatment options and increases healthcare costs. To understand patient risk factors, including household and animal contact, potentially associated with colonization with multidrug-resistant MRSA isolates, we performed a prospective study of case patients colonized with MRSA on admission to a rural tertiary care hospital. Patients were interviewed and antimicrobial resistance patterns were tested among isolates from admitted patients colonized with MRSA in 2009-10. Prevalence of resistance was compared by case-patient risk factors and length-of-stay outcome among 88 MRSA case patients. Results were compared to NHANES 2003-04. Overall prevalence of multidrug resistance (non-susceptibility to ≥ four antimicrobial classes) in MRSA nasal isolates was high (73%) and was associated with a 1.5-day increase in subsequent length of stay (p = 0.008). History of hospitalization within the past six months, but not antimicrobial use in the same time period, was associated with resistance patterns. Within a subset of working-age case patients without recent history of hospitalization, animal contact was potentially associated with multidrug resistance. History of hospitalization, older age, and small household size were associated with multidrug resistance in NHANES data. In conclusion, recent hospitalization of case patients was predictive of antimicrobial resistance in MRSA isolates, but novel risk factors associated with the household may be emerging in CA-MRSA case patients. Understanding drivers of antimicrobial resistance in MRSA isolates is important to hospital infection control efforts, relevant to patient outcomes and to indicators of the economic burden of antimicrobial resistance.

Methicillin-Resistant Staphylococcus aureus Carriage among Students at a Historically Black University: A Case Study

Background. Black people in the USA is afflicted with a higher rate of methicillin-resistant Staphylococcus aureus (MRSA) infection. This study determined the prevalence of MRSA carriage among black college students at a university setting. Methods. Hand and nasal swabs were collected and screened for MRSA by mannitol fermentation, coagulase, and DNase activities and their resistance to oxacillin. MRSA isolates were analyzed for antimicrobial resistance pattern, genetic profile for staphylococcal cassette chromosome mec (SCCmec) type, pulsed-field type, multilocus sequence type (ST), and the presence of Panton-Valentine leukocidin (PVL) gene. Results. MRSA was isolated from 1 of the 312 (0.3%) hand swabs and 2 of the 310 (0.65%) nasal swabs, respectively. All isolates lack multidrug resistance and have type IV SCCmec, characteristic of community-associated MRSA. These isolates were a ST8-MRSA-IVa-PVL(+) (USA300 strain), a ST8-MRSA-IVb-PVL(−), and a new MLST, ST2562-MRSA-IV-PVL(−), identified in this study. These isolates were thus not transmitted among students. Conclusion. We found a low rate of MRSA carriage among students in a black university. Our finding highlights the need of future study which involves multiinstitutions and other ethnic group to assess the association of black race with MRSA carriage.