Population-based community prevalence of methicillin-resistant Staphylococcus aureus in the urban poor of San Francisco

Predictors of hospitalization for injection drug users seeking care for soft tissue infections

BACKGROUND

Soft tissue infections (STIs) from injection drug use are a common cause of Emergency Department visits, hospitalizations, and operating room procedures, yet little is known about factors that may predict the need for these costly medical services.

OBJECTIVE

To describe a cohort of injection drug users seeking Emergency Department care for STIs and to identify risk factors associated with hospitalization. We hypothesized that participants who delayed seeking care would be hospitalized more often than those who did not.

DESIGN

Cohort study using in-person structured interviews and medical record review. Logistic regression assessed the association between hospital admission and delay in seeking care as well as other demographic, clinical, and psychosocial factors.

PARTICIPANTS

Injection drug users who sought Emergency Department care for STIs from May 2001 to March 2002.

RESULTS

Of the 136 participants, 55 (40%) were admitted to the hospital. Delay in seeking care was not associated with hospital admission. Participants admitted for their infection were significantly more likely to be living in a shelter (P = .01) and to report being hospitalized 2 or more times in the past year (P < .01).

CONCLUSIONS

We identified a subpopulation of injection drug users, mostly living in shelters, who were hospitalized frequently in the past year and who were more likely to be hospitalized for their current infections compared to others. As members of this subpopulation can be easily identified and located, they may benefit from interventions to reduce the health care utilization resulting from these infections.

The molecular evolution of methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a potentially pathogenic bacterium that causes a broad spectrum of diseases. S. aureus can adapt rapidly to the selective pressure of antibiotics, and this has resulted in the emergence and spread of methicillin-resistant S. aureus (MRSA). Resistance to methicillin and other beta-lactam antibiotics is caused by the mecA gene, which is situated on a mobile genetic element, the Staphylococcal Cassette Chromosome mec (SCCmec). To date, five SCCmec types (I-V) have been distinguished, and several variants of these SCCmec types have been described. All SCCmec elements carry genes for resistance to beta-lactam antibiotics, as well as genes for the regulation of expression of mecA. Additionally, SCCmec types II and III carry non-beta-lactam antibiotic resistance genes on integrated plasmids and a transposon. The epidemiology of MRSA has been investigated by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), spa typing and SCCmec typing. Numerous MRSA clones have emerged and disseminated worldwide. SCCmec has been acquired on at least 20 occasions by different lineages of methicillin-sensitive S. aureus. Although most MRSA strains are hospital-acquired (HA-MRSA), community-acquired MRSA (CA-MRSA) strains have now been recognised. CA-MRSA is both phenotypically and genotypically different from HA-MRSA. CA-MRSA harbours SCCmec types IV or V, and is associated with the genes encoding Panton-Valentine leukocidin. The prevalence of MRSA ranges from 0.6% in The Netherlands to 66.8% in Japan. This review describes the latest developments in knowledge concerning the structure of SCCmec, the molecular evolution of MRSA, the methods used to investigate the epidemiology of MRSA, and the risk-factors associated with CA-MRSA and HA-MRSA.

Rapid detection of Panton–Valentine leukocidin-positive Staphylococcus aureus by real-time PCR targeting the lukS-PV gene

In order to assess the speed and accuracy of a real-time PCR assay targeting the lukS-PV gene of Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus, 700 S. aureus strains were tested and the results were compared to those achieved with block cycler PCR. Cross-reactivity was tested with 166 other bacterial species. Using this homogeneous real-time PCR assay format, the presence or absence of genetic information for PVL, which is also found in community-associated methicillin-resistant S. aureus, was correctly identified from pure culture and directly in various types of clinical specimens.

Clinical and epidemiologic characteristics cannot distinguish community-associated methicillin-resistant Staphylococcus aureus infection from methicillin-susceptible S. aureus infection: a prospective investigation

BACKGROUND

Community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) infection has become common worldwide. Some researchers have argued that empirical therapy for MRSA should be given only to patients with suspected CA S. aureus infections who have risk factors for acquisition of MRSA. However, there are no prospective data examining this approach.

METHODS

We prospectively enrolled consecutive patients who were hospitalized with S. aureus infection, administered a detailed questionnaire, and collected clinical and microbiological information.

RESULTS

Of the 280 consenting patients, 180 were adults with CA S. aureus infection. Among these subjects, 108 (60%) had MRSA infection, and 78 (40%) had methicillin-susceptible S. aureus (MSSA) infection. MRSA infection was associated with younger age (P<.0001); skin/soft-tissue infection (P=.015); snorting/smoking illegal drugs (P=.01); recent incarceration (P=.03); lower comorbidity index (P=.01); more frequent visits to bars, raves, and/or clubs (P=.03); and higher frequency of laundering clothes in hot water (P=.05). However, the sensitivity, specificity, and predictive values for these factors for discriminating CA-MRSA infection from CA-MSSA infection were relatively poor. Post-hoc modeling revealed that, even in a 10% (i.e., low) MRSA prevalence population, patients lacking the 3 strongest MRSA risk factors would still have a 7% posttest probability of MRSA. Most MRSA strains belonged to the ST-8/USA300 genotype, contained SCCmec type IV, and shared virulence factors commonly found in the ST1:USA400 clone. MSSA strains were genotypically heterogeneous.

CONCLUSIONS

We found that clinical and epidemiological risk factors in persons hospitalized for CA S. aureus infection cannot reliably distinguish between MRSA and MSSA. Our findings have important implications for the choice of empirical antibiotic therapy for suspected S. aureus infections and for infection control.

A prospective investigation of outcomes after hospital discharge for endemic, community-acquired methicillin-resistant and -susceptible Staphylococcus aureus skin infection

BACKGROUND

Although community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has become increasingly common, prospective data on outcomes of patients with skin infection remain poorly defined.

METHODS

We prospectively observed a cohort of 201 patients discharged after hospitalization for CA-MRSA infection or community-acquired methicillin-susceptible S. aureus (CA-MSSA) infection. Patients were interviewed 30 and 120 days after they received a diagnosis. Our primary outcome was clinical response, defined as no relapse, new S. aureus infection, or need for antibiotics at day 30.

RESULTS

Among 117 patients with skin infection, the nonresponse rate at day 30 was similar among patients with CA-MRSA infection and those with CA-MSSA infection (23 [33%] of 70 vs. 13 [28%] of 47 patients; P=.55). Lack of incision and drainage was associated with nonresponse at day 30 (P=.005), but other clinical factors, including receipt of antibiotics inactive against the infecting strain, were not. Patients with CA-MSSA infection were more likely to be rehospitalized (P=.003) and to believe subjectively that they had not been cured (P=.002) at day 30. At day 30, there was a trend for close contacts of CA-MRSA-infected patients to develop a similar infection (13% vs. 4%; odds ratio, 3.3; 95% confidence interval, 0.7-15.8; P=.2).

CONCLUSION

Although it is believed patients with CA-MRSA skin infection may have more serious outcomes than those with CA-MSSA skin infection, we found similar outcomes in these 2 groups after hospital discharge. Clinical nonresponse at day 30 was associated with a lack of receipt of incision and drainage. Our data also suggest that close contacts of persons with CA-MRSA skin infection may have a higher likelihood of acquiring an infection.

Heterosexual transmission of community-associated methicillin-resistant Staphylococcus aureus

Heterosexual transmission of community-associated methicillin-resistant Staphylococcus aureus has not been documented. As part of a survey conducted in northern Manhattan, we encountered 3 households in which heterosexual transmission was responsible for new community-associated methicillin-resistant S. aureus infection. The vaginal and inguinal isolates obtained from the sexual partners were USA 300. This report documents an important and previously unrecognized means of community-associated methicillin-resistant S. aureus colonization and transmission for these potentially invasive strains.

A population-based study examining the emergence of community-associated methicillin-resistant Staphylococcus aureus USA300 in New York City

Background

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is a serious pathogen in several regions in the United States. It is unclear which populations are at high risk for the emergence of these strains.

Methods

All unique patient isolates of S. aureus were collected from hospitals in Brooklyn, NY over a three-month period. Isolates of MRSA that were susceptible to clindamycin underwent SCCmec typing. Isolates with the SCCmec type IV (characteristic of CA-MRSA strains) underwent ribotyping. Demographic information involving the neighborhoods of Brooklyn was also gathered and correlated with the prevalence of CA-MRSA strains.

Results

Of 1316 isolates collected during the surveillance, 217 were MRSA susceptible to clindamycin. A total of 125 isolates possessed SCCmec type IV; 72 belonged to the USA300 strain and five belonged to the USA400 strain. Hospitals in the eastern part of the city had the highest prevalence of USA300 strain. Individuals in the eastern region, when compared to the western region, were more likely to be Black, Hispanic, female, and < 18 years of age, and to have households of ≥ 3 persons. In addition, the median household income was lower, and the proportion of individuals on public assistance was higher, for the population in the eastern region.

Conclusion

The USA300 strain of CA-MRSA is emerging in New York City. In this population-based study, urban regions of lower socioeconomic status and with evidence of overcrowding appear to be at higher risk for the emergence of this pathogen.

New Staphylococcus aureus genotyping method based on exotoxin (set) genes

A variety of methods for genotyping Staphylococcus aureus isolates exists: the two most widely used methods are pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Here, we describe a sequence-based genotyping method based on genes encoding S. aureus superantigen-like proteins, which belong to a family of exotoxins called staphylococcal exotoxins. The sequences of PCR-amplified internal fragments of three different set genes (set2, set5, and set7) of 61 well-characterized clinical methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates and reference strains were compared. Phylogenetic analysis was performed based on single-nucleotide polymorphisms (SNP). The SNP dendrograms of the set gene sequences differentiated the 61 isolates into 22 distinct subgroups, designated exotoxin sequence types (ETST), while the standard seven-gene MLST profiles differentiated the same 61 isolates into 19 subgroups. Of the 19 different MLST subgroups, 16 corresponded to 16 distinct ETST groups. However, three MLST subgroups, ST1, ST30, and ST36, were each further separated into more than one ETST subgroup. The exotoxin-based genotyping method was able to discriminate MRSA and MSSA isolates according to their specific epidemiological characteristics. This SNP analysis of the three set genes is thus equally or more discriminatory than the seven-gene MLST method, providing a good alternative typing tool for a laboratory that has sequencing capability.

Comparisons of community-associated methicillin-resistant Staphylococcus aureus (MRSA) and hospital-associated MSRA infections in Sacramento, California

Methicillin-resistant Staphylococcus aureus (MRSA) has long been a common pathogen in healthcare facilities, but in the past decade, it has emerged as a problematic pathogen in the community setting as well. A retrospective case series study of patients from whom MRSA was isolated from December 1, 2003, through May 31, 2004, was conducted at the University of California, Davis, Medical Center. Patient data were collected from electronic medical records and traditional chart reviews to determine whether MRSA acquisition was likely to have been in the community or in the hospital. Antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) were performed for all confirmed isolates. Skin and soft tissue were the most common infection sites for all MRSA patients. Among the 283 MRSA infections, 127 (44.9%) were defined as community-associated (CA)-MRSA. Ninety-six percent of the CA-MRSA isolates were susceptible to clindamycin. Double-disk diffusion tests were performed to examine inducible clindamycin resistance by erythromycin induction on both CA and hospital-associated (HA) clindamycin-susceptible and erythromycin-resistant isolates. Ten percent (17 of 183) were positive. Most CA-MRSA isolates were identified by PFGE as a unique strain, genotype USA300, which was not genetically related to the predominant genotype, USA100, in the HA-MRSA isolates. Injecting drug users accounted for 49% of CA-MRSA infections but only 19% of the HA-MRSA infections (odds ratio, 4.2; 95% confidence interval, 2.4 to 7.4). Our study shows that a single clone of CA-MRSA accounts for the majority of infections. This strain originated in the community and is not related to MRSA strains from healthcare settings. Injecting drug users could be a major reservoir for CA-MRSA transmission.

Ophthalmic Manifestations of Infections Caused by the USA300 Clone of Community-Associated Methicillin-Resistant Staphylococcus aureus

PURPOSE

To report the microbiological, clinical, and pathological characteristics of community-associated methicillin-resistant Staphylococcus aureus (CAMRSA) infections of the eye and orbit.

DESIGN

Prospective case series.

PARTICIPANTS

Nine patients with CAMRSA infections of the eye and orbit were identified during a 6-month period at 2 tertiary care hospitals in San Francisco.

METHODS

Case identification was by prospective case selection and retrospective laboratory review of 549 MRSA cultures collected in the 2 hospitals. Ophthalmic microbial isolates were analyzed by pulsed-field gel electrophoresis and compared with a control CAMRSA clone (USA300). Clinical characteristics of patients infected with CAMRSA were reviewed, and all surgical specimens underwent pathological examination.

MAIN OUTCOME MEASURES

Pulsed-field gel electrophoresis banding patterns of MRSA isolates, antibiotic sensitivity profiles, patient demographics, systemic and ocular complications of infection, and posttreatment visual acuities.

RESULTS

Nine ophthalmic isolates were CAMRSA clone USA300. The infections included orbital cellulitis, endogenous endophthalmitis, panophthalmitis, lid abscesses, and septic venous thrombosis. Patients were treated with trimethoprim-sulfamethoxazole, rifampin, clindamycin, or vancomycin based on microbial sensitivity studies and severity of infection. Eight of the 9 patients had no history of hospitalization. Seven patients required hospitalization, 3 required surgery, and an additional 4 required invasive procedures. Eight patients had good visual outcomes, but 1 deteriorated to no light perception. Pathological analyses showed extensive necrosis in eyelid and orbital specimens, and disorganized atrophy bulbi in an enucleated eye.

CONCLUSION

The USA300 CAMRSA clone, which carries Panton-Valentine leukocidin genes, can cause aggressive infections of the eye and orbit in hospital-naive patients. Treatment of infections often required debridement of necrotic tissues in addition to non-beta-lactam class antibiotics. In communities where CAMRSA is prevalent, ophthalmologists should obtain microbial cultures and sensitivity studies to help guide antibiotic therapy for severe ophthalmic infections.

Contrasting pediatric and adult methicillin-resistant Staphylococcus aureus isolates

Children may share a reservoir of MRSA strains that have an antimicrobial drug resistance profile distinct from that of adults.

We performed a prospective study of all inpatient and outpatient methicillin-resistant Staphylococcus aureus (MRSA) isolates identified at the University of Chicago Hospitals from November 2003 through November 2004. Differences in resistance to non–β-lactam antimicrobial drugs were determined after stratification of the 578 MRSA isolates into 4 groups by patient age (pediatric vs. adult) and onset location (community vs. hospital). Non–β-lactam resistance was significantly greater among the 288 adult than the 177 pediatric community-associated isolates for erythromycin (93.2 vs. 87.0%, p = 0.03), clindamycin (51.8 vs. 7.3%, p<0.001), ciprofloxacin (62.1 vs. 10.7%, p<0.001), gentamicin (11.1 vs. 1.1%, p<0.001), and tetracycline (19.9 vs. 6.4%, p<0.001). In contrast, hospital-associated MRSA isolates from children and adults had similar rates of non–β-lactam antimicrobial drug resistance. In our region, clindamycin is an appropriate empiric therapy of community-associated MRSA infection in children but should be used with caution in adults.

Prevalence and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus isolates from Trinidad & Tobago

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has become increasingly prevalent worldwide since it was first reported in a British hospital. The prevalence however, varies markedly in hospitals in the same country, and from one country to another. We therefore sought to document comprehensively the prevalence and antimicrobial susceptibility pattern of MRSA isolates in Trinidad and Tobago.

METHODS

All Staphylococcus aureus isolates encountered in routine clinical specimens received at major hospitals in the country between 2000 and 2001 were identified morphologically and biochemically by standard laboratory procedures including latex agglutination test (Staphaurex Plus; Murex Diagnostics Ltd; Dartford, England); tube coagulase test with rabbit plasma (Becton, Dickinson & Co; Sparks, MD, USA), and DNase test using DNase agar (Oxoid Ltd; Basingstoke, Hampshire, England). MRSA screening was performed using Mueller-Hinton agar containing 6 mug oxacillin and 4% NaCl, latex agglutination test (Denka Seiken Co. Ltd, Tokyo, Japan) and E-test system (AB Biodisk, Solna, Sweden). Susceptibility to antimicrobial agents was determined by the modified Kirby Bauer disc diffusion method while methicillin MICs were determined with E-test system.

RESULTS

Of 1,912 S. aureus isolates received, 12.8% were methicillin (oxacillin) resistant. Majority of the isolates were recovered from wound swabs (86.9%) and the least in urine (0.4%) specimens. Highest number of isolates was encountered in the surgical (62.3%) and the least from obstetrics and gynaecology (1.6%) facilities respectively. Large proportions of methicillin sensitive isolates are >85% sensitive to commonly used and available antimicrobials in the country. All MRSA isolates were resistant to ceftriaxone, erythromycin, gentamicin and penicillin but were 100% sensitive to vancomycin, rifampin and chloramphenicol.

CONCLUSION

There is a progressive increase in MRSA prevalence in the country but the present rate is still low in comparison to values in some other countries. Vancomycin is still the drug of choice for treating multidrug resistant MRSA infections. Further use of molecular studies to monitor the epidemiology of MRSA in these hospitals in the country is highly recommended too.

Outbreak in Alberta of community-acquired (USA300) methicillin-resistant Staphylococcus aureus in people with a history of drug use, homelessness or incarceration

BACKGROUND

The USA300 strain of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) can cause severe infection and is increasingly recognized as a cause of community outbreaks. In 2004, an outbreak was identified in the Calgary Health Region (CHR).

METHODS

MRSA isolates were identified with standard methods at a central regional laboratory and typed via pulsed-field gel electrophoresis (PFGE). Isolates were tested by PCR for mecA, Panton-Valentine leukocidin (PVL), SCCmec, and spa genes. Cases were defined as such if a clinical isolate of the USA300 strain was noted between January 1 and September 30, 2004, and the patient had lived or traveled in CHR within 2 years before symptom onset. Demographic, clinical and risk data on all such cases were collected from several sources for statistical analysis. A case was defined as high-risk if the patient had a history of drug use, homelessness or incarceration.

RESULTS

Of 40 isolates with the USA300 PFGE pattern, all tested positive for PVL, SCCmec type IVa and spa type 008. Almost all infections (39/40, 98%) involved skin and soft tissues, except for 1 death from necrotizing hemorrhagic pneumonia; a notable proportion (38%) required hospital admission or intravenous antimicrobial therapy. The outbreak centred on the high-risk population in CHR (70%; risk ratio 169.4, 95% confidence interval 86.1-333.0).

INTERPRETATION

People with histories of illicit drug use, homelessness or recent incarceration were at highest risk for infection with CA-MRSA. The emergence and spread of this virulent strain has important implications for treatment and public health in Canada.

Meticillin-resistant Staphylococcus aureus among US prisoners and military personnel: review and recommendations for future studies

We reviewed published work examining the prevalence and risk factors for meticillin-resistant Staphylococcus aureus (MRSA) infection in two high-risk groups: prisoners and military enlistees. Significant risk factors for infection included prison occupation, gender, comorbidities, prior skin infection, and previous antibiotic use. Although characteristics such as hygiene, physical contact, and crowding were postulated as risk factors for MRSA infection, there were few epidemiological studies supporting these factors. Most studies identified were retrospective in design and only one study used prospective surveillance for MRSA colonisation among all individuals residing within a single military setting. Our results suggest that there is a high incidence of MRSA infection among individuals in prisons and military settings, but surveys that quantify the prevalence of MRSA colonisation among individuals living within these specialised settings are needed. A thorough examination of MRSA acquisition and transmission patterns in prisons and military settings could help elucidate preventive strategies in other crowded and closed settings.

[Prevalence of community-acquired methicillin-résistant Staphylococcus aureus]

OBJECTIVE

The authors had for aim to assess the prevalence of community-acquired methicillin-resistant Staphylococcus aureus in France.

METHOD

Two hundred fifty-four strains identified in 1,079 nasal samples from voluntary individuals were analyzed in 2002. An antibiogram (especially measuring the inhibition diameter of cefoxitine) and screening by oxacillin (6 mug/ml) allowed the identification of strains resistant to betalactams. The resistant phenotype was confirmed by amplification of the mecA gene by PCR. The distribution of strains was compared to the resistance to various antibiotics and especially to cotrimoxazole, macrolides, aminosides, and the mechanisms of resistance were determined.

RESULTS

Eleven methicillin-resistant strains were detected in 254 carriers (4.33%), or 1% of the total population studied.

CONCLUSION

Complementary tests (detection of the Panton-Valentine toxin, pulsed field electrophoresis) will be necessary to finish strain characterization. It can already be stated that compared to previous studies, community-acquired MRSA carriage is weak in France.

Novel PCR-restriction fragment length polymorphism analysis for rapid typing of staphylococcal cassette chromosome mec elements

We developed a novel PCR-restriction fragment length polymorphism test for the ccrB gene by using HinfI and BsmI for rapid typing of staphylococcal cassette chromosome mec (SCCmec). When tested with reference strains and methicillin-resistant Staphylococcus aureus isolates, the method proved to be valid and useful for rapid identification of four SCCmec types, especially type IV.

Community-associated methicillin-resistant Staphylococcus aureus: reconsideration of therapeutic options

Methicillin resistance, long recognized as characteristic of nosocomial Staphylococcus aureus, has increasingly been identified in community-acquired strains in the past 15 years. The genotypes of community-associated methicillin-resistant S. aureus (MRSA) are different from nosocomial strains, and unlike nosocomial strains, they have a distinctive methicillin-resistance chromosomal cassette (designated type IV), are usually susceptible to multiple classes of antimicrobials other than beta-lactams, carry a distinctive virulence factor (the Panton-Valentine leukocidin), cause mainly skin and soft tissue infection and less frequently, necrotizing pneumonia, and involve predominantly children and young adults. Outbreaks have been reported in certain segments of the population (eg, football players, wrestlers, prison inmates, and native people) that often do not have the established risk factors for MRSA. However, these strains have also caused infections likely acquired in an institutional health care setting. Delay in starting appropriate antibiotic therapy for severe infections caused by MRSA can be life-threatening. This requires a reconsideration of the empiric choice of an anti-staphylococcal beta-lactam for seriously ill patients with suspected community-associated S. aureus infections.

New strategies to identify patients harbouring antibiotic-resistant bacteria at hospital admission

Nosocomial infections caused by antibiotic-resistant bacteria are associated with high morbidity and mortality worldwide. Most prevention strategies focus on cross-transmission, but the endemic state inside the hospital is also maintained through the influx of patients colonised or infected with antibiotic-resistant bacteria, balanced by the efflux of colonised patients following discharge. Epidemiological research has demonstrated that eradication can be achieved by preventing the influx of resistant bacteria. The presence of a central venous catheter and a history of methicillin-resistant Staphylococcus aureus (MRSA) infection or colonisation are associated significantly with methicillin-resistant staphylococcal bacteraemia at admission. Previous antibiotic therapy and transfer from long-term care facilities or nursing homes are associated with bacteraemia caused by methicillin-resistant coagulase-negative staphylococci, while skin ulcer and cellulites are independent risk-factors for MRSA bacteraemia. A scoring system using point values has been developed and validated to identify patients positive for vancomycin-resistant enterococci at admission. Six variables were identified: age > 60 years (2 points); hospitalisation in the previous year (3); use of two or more antibiotics during the previous 30 days (3); transfer from another hospital or long-term care facility (3); a requirement for chronic haemodialysis (2); and a previous history of MRSA infection (4). With a point score cut-off of > or = 10, the specificity of this prediction rule is 98%. Knowledge of variables identifying patients at high risk for being colonised or infected with antibiotic-resistant bacteria may assist clinicians in targeting preventive measures and streamlining the use of vancomycin. Current studies are analysing risk-factors for harbouring multiresistant Gram-negative bacteria at hospital admission.

Antimicrobial-resistant bacteria in the community setting

Over the past decade, antimicrobial resistance has emerged as a major public-health crisis. Common bacterial pathogens in the community such as Streptococcus pneumoniae have become progressively more resistant to traditional antibiotics. Salmonella strains are beginning to show resistance to crucial fluoroquinolone drugs. Community outbreaks caused by a resistant form of Staphylococcus aureus, known as community-associated meticillin (formerly methicillin)-resistant Staphylococcus aureus, have caused serious morbidity and even deaths in previously healthy children and adults. To decrease the spread of such antimicrobial-resistant pathogens in the community, a greater understanding of their means of emergence and survival is needed.

Characterization of a strain of community-associated methicillin-resistant Staphylococcus aureus widely disseminated in the United States

A highly stable strain of Staphylococcus aureus with a pulsed-field gel electrophoresis type of USA300 and multilocus sequence type 8 has been isolated from patients residing in diverse geographic regions of the United States. This strain, designated USA300-0114, is a major cause of skin and soft tissue infections among persons in community settings, including day care centers and correctional facilities, and among sports teams, Native Americans, men who have sex with men, and military recruits. The organism is typically resistant to penicillin, oxacillin, and erythromycin (the latter mediated by msrA) and carries SCCmec type IVa. This strain is variably resistant to tetracycline [mediated by tet(K)]; several recent isolates have decreased susceptibility to fluoroquinolones. S. aureus USA300-0114 harbors the genes encoding the Panton-Valentine leucocidin toxin. DNA sequence analysis of the direct repeat units within the mec determinant of 30 USA300-0114 isolates revealed differences in only a single isolate. Plasmid analysis identified a common 30-kb plasmid that hybridized with blaZ and msrA probes and a 3.1-kb cryptic plasmid. A 4.3-kb plasmid encoding tet(K) and a 2.6-kb plasmid encoding ermC were observed in a few isolates. DNA microarray analysis was used to determine the genetic loci for a series of virulence factors and genes associated with antimicrobial resistance. Comparative genomics between USA300-0114 and three other S. aureus lineages (USA100, USA400, and USA500) defined a set of USA300-0114-specific genes, which may facilitate the strain's pathogenesis within diverse environments.

Community-acquired methicillin-resistant Staphylococcus aureus pyomyositis in an intravenous drug user

Pyomyositis is a disease of abscess formation deep within large striated muscles. Outside of the tropics it is a rare disease which occurs mainly in certain patient populations such as the immunosuppressed or intravenous drug users (IDUs). A case of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) pyomyositis in an IDU is described. The incidence of both CA-MRSA and pyomyositis is currently increasing. To the authors' knowledge this is the first reported case of CA-MRSA pyomyositis in the UK. Cases of CA-MRSA pyomyositis are likely to increase and it may be necessary to empirically treat certain patients with glycopeptides.

Widespread Emergence of Methicillin Resistance in Community-acquired Staphylococcus aureus Infections in Denver

BACKGROUND

Increasing rates of methicillin resistance among out-patient Staphylococcus aureus infections led us to assess the epidemiology and outcome of a local outbreak.

METHODS

A retrospective cohort study of outpatient skin and soft tissue infections due to S aureus in 2003.

RESULTS

From 2002 to mid-2004, the percentage of outpatient S aureus isolates resistant to methicillin increased from 6 to 45%. In multivariate analysis, only male sex and age greater than 18 years were associated with methicillin resistance. Methicillin resistance was common (>15%) among isolates from patients in nearly all subgroups evaluated. Pulsed field gel electrophoresis showed isolates related to USA 300, but methicillin-resistant strains had unusually high rates of quinolone resistance.

CONCLUSIONS

A single strain of methicillin-resistant S aureus is responsible for the increase in skin infections in outpatients without traditional risk factors for infection with an antibiotic-resistant strain. In areas with high rates of methicillin-resistant S aureus outpatient infections, we recommend non-beta-lactam antibiotics for initial treatment of skin and soft tissue infections.

Emergence of two populations of methicillin-resistant Staphylococcus aureus with distinct epidemiological, clinical and biological features, isolated from patients with community-acquired skin infections

BACKGROUND

Community-acquired skin and soft-tissue infections due to methicillin-resistant Staphylococcus aureus (MRSA) are an emerging clinical and epidemiological problem.

OBJECTIVES

To characterize community-acquired skin infections caused by S. aureus, and especially MRSA.

METHODS

From November 1999 to December 2003, we conducted in a French hospital a prospective epidemiological, clinical and bacteriological study of skin infections acquired in the community, applying strict criteria for true community-acquired MRSA (CA-MRSA) and health-care-associated MRSA (HCA-MRSA).

RESULTS

One hundred and ninety-seven patients had 207 skin infections (154 primary and 53 secondary infections). Twenty-two (11%) patients had skin infections caused by MRSA. The incidence of MRSA skin infections acquired in the community rose from 4% in 2000 to 17% in 2003, but the increase was not statistically significant. Six patients (3%) were infected by CA-MRSA and 15 (8%) by HCA-MRSA; one patient was lost to follow-up and could not be classified. CA-MRSA and HCA-MRSA had different epidemiological, clinical and biological characteristics. CA-MRSA infections were more severe than HCA-MRSA infections: all the CA-MRSA infections (six of six, 100%) required surgical treatment, compared with only two (15%) of 13 with HCA-MRSA infection (P < 0.001). CA-MRSA all belonged to the same clonal strain, harbouring an agr type 3 allele and the Panton-Valentine leucocidin genes (not detected in HCA-MRSA) and possessing a specific antibiotype.

CONCLUSIONS

Two populations of MRSA causing skin infections are emerging in the French community, with distinct epidemiological, clinical and biological characteristics.

Prevalence of methicillin-resistant and methicillin-sensitive Staphylococcus aureus nasal colonization among patients at the time of admission to the hospital

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is an important agent of hospital-acquired infection. The mode of entry of MRSA in the hospital might be on admission of patients with MRSA infection or nasal colonization. The present study was undertaken to determine the prevalence of MRSA nasal colonization among patients on admission to hospital.

METHODS

Six hundred patients were screened for nasal colonization of MRSA on admission to hospital. Nasal swabs were cultured on salt mannitol agar and blood agar. Age, sex, previous admission to hospital and antibiotic therapy were recorded.

RESULTS

S. aureus was isolated from the nasal swabs of 122 patients (20.2%) on admission to hospital. MRSA was isolated from 7 patients (1.1%) and methicillin-sensitive S. aureus (MSSA) from 115 patients (19.1%). Nasal colonization of S. aureus was higher in younger and elderly patients and significantly higher colonization was observed among females. The MRSA strains isolated from nasal swabs had a different antibiotic susceptibility pattern than those isolated from patients having hospital-acquired MRSA infection. Previous admissions to hospital, underlying disease antibiotic therapy were not risk factors for MRSA nasal colonization.

CONCLUSION

MRSA nasal colonization of patients on admission to hospital is low in this region. The screening of every new admission would not be cost effective, but patients transferred form other institutions should be screened for MRSA. Standard infection control precautions should be strictly implemented to prevent the spread and control of MRSA infections.

Community-acquired meticillin-resistant Staphylococcus aureus: an emerging threat

Community-acquired meticillin-resistant Staphylococcus aureus (MRSA) is becoming an important public-health problem. New strains of S aureus displaying unique combinations of virulence factors and resistance traits have been associated with high morbidity and mortality in the community. Outbreaks of epidemic furunculosis and cases of severe invasive pulmonary infections in young, otherwise healthy people have been particularly noteworthy. We review the characteristics of these new strains of community-acquired MRSA that have contributed to their pathogenicity and discuss new approaches to the diagnosis and management of suspected and confirmed community-acquired MRSA infections.

Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles

BACKGROUND

Necrotizing fasciitis is a life-threatening infection requiring urgent surgical and medical therapy. Staphylococcus aureus has been a very uncommon cause of necrotizing fasciitis, but we have recently noted an alarming number of these infections caused by community-associated methicillin-resistant S. aureus (MRSA).

METHODS

We reviewed the records of 843 patients whose wound cultures grew MRSA at our center from January 15, 2003, to April 15, 2004. Among this cohort, 14 were identified as patients presenting from the community with clinical and intraoperative findings of necrotizing fasciitis, necrotizing myositis, or both.

RESULTS

The median age of the patients was 46 years (range, 28 to 68), and 71 percent were men. Coexisting conditions or risk factors included current or past injection-drug use (43 percent); previous MRSA infection, diabetes, and chronic hepatitis C (21 percent each); and cancer and human immunodeficiency virus infection or the acquired immunodeficiency syndrome (7 percent each). Four patients (29 percent) had no serious coexisting conditions or risk factors. All patients received combined medical and surgical therapy, and none died, but they had serious complications, including the need for reconstructive surgery and prolonged stay in the intensive care unit. Wound cultures were monomicrobial for MRSA in 86 percent, and 40 percent of patients (4 of 10) for whom blood cultures were obtained had positive results. All MRSA isolates were susceptible in vitro to clindamycin, trimethoprim-sulfamethoxazole, and rifampin. All recovered isolates belonged to the same genotype (multilocus sequence type ST8, pulsed-field type USA300, and staphylococcal cassette chromosome mec type IV [SCCmecIV]) and carried the Panton-Valentine leukocidin (pvl), lukD, and lukE genes, but no other toxin genes were detected.

CONCLUSIONS

Necrotizing fasciitis caused by community-associated MRSA is an emerging clinical entity. In areas in which community-associated MRSA infection is endemic, empirical treatment of suspected necrotizing fasciitis should include antibiotics predictably active against this pathogen.

A molecular epidemiological analysis of 2 Staphylococcus aureus clonal types colonizing and infecting patients with AIDS

BACKGROUND

Persons with acquired immune deficiency syndrome (AIDS) who use drugs appear to be at increased risk for colonization and infection with Staphylococcus aureus. Little is known about the nature of and risk factors responsible for this association. This study is among the first to prospectively follow carriage and infection in this uniquely high-risk population.

METHODS

We prospectively followed the cases of 75 patients with AIDS in a residential drug treatment facility and screened for S. aureus nasal colonization and infection.

RESULTS

Thirty-seven baseline cultures (49%) were positive for S. aureus, and 81% of subjects were colonized at least once during the study. Thirteen subjects experienced 17 infections. Pulsed-field gel electrophoresis and sequence-based typing methods revealed that 244 (92%) of the isolates belonged to either clonal type A or B. Clonal type A was methicillin-susceptible. Clonal type B consisted of 3 main subtypes (B1, B2, and B3), all with the same allelic profile (ST8) and staphylococcal protein A gene (spa) type (7). Of note, subtype B1 was methicillin-susceptible (ST8 and spa type 7), lacking mecA, whereas the other B clones were methicillin-resistant. Both clones were resistant to trimethoprim-sulfamethoxazole. Clonal type B isolates were relatively resistant, suggesting prior exposure to the health care setting.

CONCLUSIONS

This study demonstrates a sustained high rate of S. aureus carriage and infection. It demonstrates the capacity of unique methicillin-resistant S. aureus clones with an established linkage to earlier outbreaks of methicillin-resistant S. aureus, as well as to human immunodeficiency virus--infected subjects, to persist in this residential setting. It also illustrates the apparent genetic instability or transmissibility of the staphylococcal chromosomal cassette mec type IV element.

Risk factors and molecular analysis of community methicillin-resistant Staphylococcus aureus carriage

A total of 1,838 subjects from the community and 393 subjects from health care-related facilities in Taiwan were evaluated for the prevalence of nasal Staphylococcus aureus colonization and to identify risk factors associated with S. aureus and methicillin-resistant S. aureus (MRSA) colonization. Among the community subjects, 3.5% had nasal MRSA colonization. Subjects from health care-related facilities had a lower S. aureus colonization rate (19.1%) than community subjects (25.2%) but had a significantly higher rate of colonization with MRSA (7.63%). Age (P < 0.001) was a significant risk factor for S. aureus colonization, with subjects under age 20 years or between 71 and 80 years showing higher rates of colonization. Recent gastrointestinal disease (P = 0.011) and hospital admission (P = 0.026) were risk factors for nasal MRSA colonization. Comparison of hospital MRSA isolates with the colonization strains by staphylococcal cassette chromosome mec (SCCmec) gene typing and pulsed-field gel electrophoresis (PFGE) typing revealed that most MRSA strains carried in the community were SCCmec type IV and that most clinical hospital isolates were type III, while health care facility-related carriage isolates were mainly SCCmec type III and type IV. Two new variant SCCmec types were identified. Six clusters of PFGE patterns were distinguished: two mainly comprised health care facility-related MRSA strains, three mainly comprised community MRSA strains, and one comprised mixed community and health care facility-related MRSA strains. In conclusion, a high prevalence of MRSA colonization was observed among people with no relationship to the hospital setting. The high level of multiple-drug resistance among community MRSA strains in association with the previously reported excessive use of antibiotics in Taiwan highlights the importance of the problem of antibiotic selective pressure. Our results indicate that both the clonal spread of MRSA and the transmission of hospital isolates contribute to the high MRSA burden in the community.

Impact of screening for MRSA carriers at hospital admission on risk-adjusted indicators according to the imported MRSA colonization pressure

We evaluated the impact of the different components of a screening programme of methicillin-resistant Staphylococcus aureus (MRSA) carriers at hospital admission on the value of two risk-adjusted rates: the proportion of imported MRSA and an indicator of the MRSA colonization pressure (ICP), and the incidence of MRSA acquired and detected in our hospital. Indicators were calculated: (1) with no screening programme; (2) with a programme limited to the intensive care unit (ICU); (3) with a programme extended to patients with risk factors for MRSA carriage hospitalized in non-ICU wards. The programme included an automatic alert. Systematic sampling of patients with risk factors hospitalized in non-ICU settings detected nearly 50% of carriers at admission. The proportion of MRSA imported into our hospital varied from 35.4% without any screening programme to 71.8% when all components of our screening programme were considered (P<10(-4)). The ICP varied from 3.1% (31/985) with the complete programme to 10.4% (31/297) without any screening programme (P<10(-6)). Screening patients with risk factors for MRSA carriage hospitalized in non-ICU wards resulted in a 51% increase of the calculated proportion of imported strains and a 58% decrease of the ICP. The two studied indicators were strongly dependent on the screening strategy for MRSA carriers implemented at admission. The screening strategy for patients admitted to non-ICU wards who have risk factors for MRSA carriage seems to be the determinant for the interpretation of certain risk-adjusted indicators of MRSA cross-transmission. Comparisons of these indicators must consider the setting in which the screening programmes are implemented.

High Prevalence of Methicillin-Resistant Staphylococcus aureus in Emergency Department Skin and Soft Tissue Infections

STUDY OBJECTIVE

We sought to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) among emergency department (ED) patients with skin and soft tissue infections, identify demographic and clinical variables associated with MRSA, and characterize MRSA by antimicrobial susceptibility and genotype.

METHODS

This was a prospective observational study involving a convenience sample of patients who presented with skin and soft tissue infections to a single urban public hospital ED in California. Nares and infection site cultures were obtained. A health and lifestyle questionnaire was administered, and predictor variables independently associated with MRSA were determined by multivariate logistic regression. All S aureus isolates underwent antibiotic susceptibility testing. Eighty-five MRSA isolates underwent genotyping by pulsed field gel electrophoresis, staphylococcal chromosomal cassette mec (SCC mec ) typing, and testing for Panton-Valentine leukocidin genes.

RESULTS

Of 137 subjects, 18% were homeless, 28% injected illicit drugs, 63% presented with a deep or superficial abscess, and 26% required admission for the infection. MRSA was present in 51% of infection site cultures. Of 119 S aureus isolates (from infection site and nares), 89 (75%) were MRSA. Antimicrobial susceptibility among MRSA isolates was trimethoprim/sulfamethoxazole 100%, clindamycin 94%, tetracycline 86%, and levofloxacin 57%. Among predictor variables independently associated with MRSA infection, the strongest was infection type being furuncle (odds ratio 28.6). Seventy-six percent of MRSA cases fit the clinical definition of community associated. Ninety-nine percent of MRSA isolates possessed the SCC mec IV allele (typical of community-associated MRSA), 94.1% possessed Panton-Valentine leukocidin genes, and 87.1% belonged to a single clonal group (ST8:S).

CONCLUSION

In this urban ED population, MRSA is a major pathogen in skin and soft tissue infections. Although studies from other practice settings are needed, MRSA should be considered when empiric antibiotic therapy is selected for such infections.

Emergence and spread of community-associated methicillin-resistant Staphylococcus aureus in rural Wisconsin, 1989 to 1999

We investigated the emergence and spread of community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) in central and northern Wisconsin by determining the temporal and clonal relationships and geographic expansion among 581 of 956 clinical isolates of MRSA collected between 1989 and 1999. Based on EcoRI plasmid profiles (PP), two types, PP-11 and PP-13, were highly stable over time and were consistently associated with multidrug-sensitive strains recovered from outpatients treated at Native American community clinics. Pulsed-field gel electrophoresis (PFGE) yielded six major clonal groups (MCGs) and 19 minor clonal groups. The six MCGs represented 82% of the isolates. All strains with either PP-11 or -13 were present in MCG-2. Eighty-nine percent of the isolates in MCG-2 originated from Native American clinics, and 90% belonged to two PFGE types (19 and 20), the types associated with an outbreak of MRSA in a Native American community in 1992. MCG-2 isolates were multidrug sensitive, harbored type IVa staphylococcal cassette chromosome mec, and were very closely related by PFGE to the Midwestern CA-MRSA strain MW2. MCG-2 strains were mostly obtained from skin infections and affected patients with a mean age of 24 (+/-18.0) years. MCG-2 strains spread to four additional Native American communities and 20 other communities. Our findings suggest that CA-MRSA in Wisconsin likely originated in Native American communities in the early 1990s and since has become widespread throughout the state. Two early CA-MRSA strains (WI-33 and WI-34) in Wisconsin represent progenitors of the MW2 strain, based on their almost indistinguishable genotypic characteristics.

Natural history of community-acquired methicillin-resistant Staphylococcus aureus colonization and infection in soldiers

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging pathogen for which the prevalence, risk factors, and natural history are incompletely understood.

METHODS

In this prospective observational study, we evaluated 812 US Army soldiers to determine the prevalence of and risk factors for CA-MRSA colonization and the changes in colonization rate over time, as well as to determine the clinical significance of CA-MRSA colonization. Demographic data and swab samples from the nares for S. aureus cultures were obtained from participants at the start of their training and 8-10 weeks later. Over this time period, participants were observed prospectively to monitor for soft-tissue infections. S. aureus isolates were characterized by in vitro examination of antibiotic susceptibilities, mecA confirmation, pulsed-field gel electrophoresis, and Panton-Valentine leukocidin (PVL) gene testing.

RESULTS

At the initial sampling, 24 of the participants (3%) were colonized with CA-MRSA, 9 of whom (38%) developed soft-tissue infections during the study period. In contrast, 229 participants (28%) were colonized with methicillin-susceptible S. aureus (MSSA), 8 (3%) of whom developed clinical infections during the same period (relative risk, 10.7; 95% confidence interval, 4.6-25.2; P<.001). At follow-up culture, the CA-MRSA colonization rate dropped to 1.6% without eradication efforts. Previous antibiotic use was a risk factor for CA-MRSA colonization at the initial sampling (P=.03). PVL genes were detected in 66% of 45 recovered CA-MRSA isolates, including all 9 clinical isolates available for analysis. Of subjects hospitalized, 5 of 6 had PVL-positive CA-MRSA infections.

CONCLUSIONS

CA-MRSA colonization with PVL-positive strains was associated with a significant risk of soft-tissue infection, suggesting that CA-MRSA may be more virulent than MSSA. Previous antibiotic use may play a role in CA-MRSA colonization.

Widespread skin and soft-tissue infections due to two methicillin-resistant Staphylococcus aureus strains harboring the genes for Panton-Valentine leucocidin

Infections caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are emerging as a major public health problem. CA-MRSA has been associated previously with skin and soft-tissue infection (SSTI) and with carriage of staphylococcal cassette chromosome mec (SCCmec) type IV and the Panton-Valentine leucocidin (PVL) virulence factor. To assess the clonal distribution of PVL-carrying strains and the association with SSTI in the San Francisco Bay area, we surveyed six collections of S. aureus isolates-671 isolates in all-collected between 1997 and 2002 originating from inpatient and outpatient clinical specimens and from a community-based sampling. Isolates were genotyped by pulsed-field gel electrophoresis, multilocus restriction fragment typing, and multilocus sequence typing and assayed for the PVL virulence factor. The S. aureus populations showed a high proportion of PVL-carrying strains, with frequencies ranging up to 70% in MRSA isolated from jail inmate patients and 69% in MRSA from patients receiving surgical treatment at an outpatient clinic specializing in treating SSTIs. PVL-carrying isolates were identified in nine clonal groups, but 88.5% of the PVL-carrying MRSA isolates belonged to only two clonal groups. These two clonal groups carried the SCCmec type IV resistance determinant and were more likely than other clonal groups to be recovered from SSTI sites than from other sites (P < 0.0001). There is evidence of clonal replacement over the period from 1999 to 2002, with one of these two clonal groups being supplanted by the other.

Availability of antibiotics without prescription in New York City

Misuse of antibiotics in the community has been associated with emergence of increasingly antibiotic-resistant bacterial strains. Although antibiotics in the United States are to be prescribed by a health care provider, the extent to which they are obtained by other means is not known. The purpose of this article is to describe a survey of the availability of nonprescription antibiotics in neighborhood independent businesses in several Manhattan, New York, neighborhoods. A survey was conducted of 101 stores in three neighborhoods--one primarily Hispanic; one primarily black, non-Hispanic; and one primarily white, non-Hispanic. Antibiotics were available in all stores in the Hispanic neighborhood (n = 34), but in none of the others (P < .001). If efforts to rationalize the use of antibiotics are to be successful, the beliefs and cultural norms of subpopulations must be considered, and interventions must be culturally relevant.

Diversity among community isolates of methicillin-resistant Staphylococcus aureus in Australia

Community methicillin-resistant Staphylococcus aureus (CMRSA) strains are being isolated with increasing frequency around the world. In Western Australia CMRSA are endemic in geographically remote communities and have been found to belong to five different contour-clamped homogeneous electric field (CHEF) electrophoretic patterns. Representatives of each of these CHEF patterns have been compared to CMRSA representative of CHEF patterns from other Australian states and New Zealand. With one exception, all of the isolates were nonmultiresistant and were not resistant to many antimicrobial agents other than the beta-lactams. With one exception, which is not believed to be a CMRSA, all of the isolates harbored a beta-lactamase plasmid. Erythromycin resistance was associated with a 2-kb plasmid. One of the beta-lactamase plasmids was found to be able to acquire additional resistance determinants to become a multiple resistance plasmid. There were 10 multilocus sequence types belonging to eight distantly related clonal complexes of S. aureus. One new sequence type was found. Although most of the CMRSA harbored the type IVa SCCmec, a type IV structural variant was found and two new SCCmec types were identified. Protein A gene (spa) typing revealed two new spa types and, with two exceptions, corresponded to multilocus sequence typing. In contrast to other reports on CMRSA, most of the CMRSA strains studied here did not contain the Panton-Valentine leukocidin genes. The results also demonstrate that nonmultiresistant hospital strains such as UK EMRSA-15 may be able to circulate in the community and could be mistaken for CMRSA based on their resistance profiles.

Prevalence of and risk factors for nasal colonization with Staphylococcus aureus among human immunodeficiency virus-positive outpatients in Singapore

We studied the prevalence of and risk factors for Staphylococcus aureus nasal colonization in HIV-positive outpatients in Singapore. Overall prevalence was 23% (45 of 195), with 3% (6 of 195) being MRSA. Recent antibiotic use and hospitalization were independent predictors of MRSA colonization. Isolates were genotypically identical to our hospital's inpatient circulating strain.

Community-acquired methicillin-resistant Staphylococcus aureus infections

Staphylococcus aureus causes a variety of minor diseases but also is responsible for staphylococcal pneumonia and sepsis, both of which can be fatal. It is thought to be responsible for many of the pneumonia deaths associated with the influenza pandemics of the 20th century. The introduction of penicillin in the 1940s greatly improved the prognosis for patients with severe staphylococcal infections. However, after a few years of clinical use, most staphylococcal strains were able to hydrolyze penicillin by producing b-lactamases, making penicillin a useless antibiotic to treat staphylococcal infections caused by b-lactamase-producing S aureus. Methicillin, a semisynthetic penicillin introduced in 1959, was specifically designed to be resistant to b-lactamase degradation, but resistance developed soon after its introduction into clinical practice. Methicillin-resistant S aureus (MRSA) was first reported in the United Kingdom in 1961, followed by reports from other European countries, Japan, and Australia. The first reported case of MRSA in the United States was in 1968. Currently, MRSA is an important pathogen in nosocomial infections and is a problem in hospitals worldwide, and it is increasingly recovered from nursing home residents with established risk factors. More recently, community acquired MRSA infections have been documented among healthy individuals with no recognizable risk factors, and it seems clear that community-acquired MRSA (CA-MRSA) strains are epidemiologically and clonally unrelated to hospital-acquired strains. This review focuses on the epidemiology, clinical significance, and virulence markers of CA-MRSA infections.

Are the new quinolones appropriate treatment for community-acquired methicillin-resistant Staphylococcus aureus?

The use of quinolones in the treatment of non-serious community-acquired methicillin-resistant Staphylococcus aureus is discussed. The new C8-modified quinolones may be suitable for such treatment but controlled trials should be carried out to ensure that the pharmacokinetics are such that there is little risk of resistance developing.

Origins of community strains of methicillin-resistant Staphylococcus aureus

To characterize methicillin-resistant Staphylococcus aureus (MRSA) strains circulating in the community, we identified predictors of isolating community MRSA and genotyped a sample of MRSA collected from a community-based, high-risk population. Computerized databases of the Community Health Network of San Francisco and the Clinical Microbiology Laboratory were searched electronically for the years 1992-1999 to identify community-onset infections caused by MRSA. Sequential analyses were performed to identify predictors of MRSA strains. The majority (58%) of infections were caused by strains traceable to the hospital or to long-term care facilities. Injection drug use was associated with infections that were not associated with health care settings. Genotypes for 20 of 35 MRSA isolates recovered from injection drug users did not match any of >600 genotypes of clinical isolates. In a nonoutbreak setting, the hospital was the main source of community MRSA; however, the presence of genetically distinct and diverse MRSA strains indicates MRSA strains now also originate from the community.

Nasal carriage of methicillin-resistant Staphylococcus aureus in an American Indian population

BACKGROUND AND OBJECTIVE

Although reports of methicillin-resistant Staphylococcus aureus (MRSA) infections without healthcare exposure are increasing, population-based data regarding nasal colonization are lacking. We assessed the prevalence of and risk factors for community-associated MRSA nasal carriage in patients of a rural outpatient clinic.

DESIGN

A cross-sectional population survey was conducted through random sample and stratification by community of residence. Recent healthcare exposure (ie, hospitalization, dialysis, or healthcare occupation) and other risk factors for MRSA carriage were assessed. Cultures of the nares were performed. Community-associated MRSA was defined as MRSA carriage without healthcare exposure.

SETTING

A predominantly American Indian community in Washington.

PATIENTS

Those receiving healthcare from an Indian Health Service clinic.

RESULTS

Of 1,311 individuals identified for study, 475 (36%) participated. Unsatisfactory culture specimens resulted in exclusion of 6 participants. In all, 128 (27.3%) of 469 participants had S. aureus. Nine (1.9%) of 469 had MRSA carriage; of these, 5 had community-associated MRSA (5 of 469; overall community-associated MRSA carriage rate, 1.1%). MRSA carriage was associated with antimicrobial use in the previous year (risk ratio [RR], 7.2; P = .04) and residence in a household of more than 7 individuals (RR, 4.5; P = .03). Pulsed-field gel electrophoresis indicated that 5 (55%) of 9 MRSA carriage isolates were closely related, including 3 (60%) of 5 that were community associated.

CONCLUSIONS

Prevalence of community-associated MRSA colonization was approximately 1% in this rural, American Indian population. Community-associated MRSA colonization was associated with recent antimicrobial use and larger household.

Clinical, Epidemiologic, and Molecular Evaluation of a Clonal Outbreak of Methicillin‐ResistantStaphylococcus aureusInfection

San Francisco General Hospital (San Francisco, CA) experienced an overall increase in the recovery of methicillin-resistant Staphylococcus aureus (MRSA) isolates that were shown by pulsed-field gel electrophoresis to have a genotype (genotype A1) that was new to this institution. We performed a case-control study to identify risk factors for acquiring genotype A1 MRSA infection from 1 October 2001 to 19 July 2002. Patients with genotype A1 MRSA infection were compared with 2 control groups: MRSA-infected control patients (i.e., patients with infection due to non-genotype A1 MRSA) and non-MRSA infected control patients (i.e., hospitalized patients without MRSA infection). There were 41 case patients infected with genotype A1 MRSA, 99 control patients infected with MRSA, and 41 control patients without MRSA infection. Pneumonia, surgical wound infections, and line infections occurred more frequently among case patients. Intensive care unit exposure and invasive procedures conferred the greatest risk for genotype A1 MRSA infection in multivariate models. Case patients were not associated with increased mortality, after adjusting for age, comorbidities, and intensive care unit exposure. Genotype A1 MRSA caused a large nosocomial outbreak of infection that was associated with distinct risk factors and clinical manifestations.

Carriage of methicillin-resistant Staphylococcus aureus among hospital employees: prevalence, duration, and transmission to households

OBJECTIVE

To assess the prevalence and duration of methicillin-resistant Staphylococcus aureus (MRSA) carriage among hospital employees and transmission to their households.

DESIGN

A point-prevalence survey of MRSA carriage (nasal swabbing) of staff and patients throughout the hospital; a prevalence survey of MRSA carriage in 2 medical wards, with carriers observed to estimate carriage duration; and evaluation of transmission to MRSA-positive workers' families. All MRSA isolates were analyzed by pulsed-field gel electrophoresis. During the study, no MRSA outbreak was detected among hospitalized patients.

SETTING

A 600-bed, public tertiary-care teaching hospital near Paris.

RESULTS

Sixty MRSA carriers were identified among 965 healthcare providers (prevalence, 6.2%; CI95, 4.7%-7.7%). Prevalence was higher in staff from clinical wards than from elsewhere (9.0% vs 2.1%; P < .0001). Identity of isolates from employees and patients varied from 25% in medical wards to 100% in the long-term-care facility. MRSA carriage was identified in 14 employees from 2 medical wards (prevalence, 19.4%; CI95, 10.3%-28.5%). Prevalence depended on the length of service in these wards. Transmission to households was investigated in 10 MRSA-positive workers' families and was found in 4. All isolates from each family were identical.

CONCLUSIONS

Few data are available concerning the prevalence of MRSA carriers among hospital employees in the absence of an outbreak among patients. MRSA transmission between patients and employees likely depends on the frequency and duration of exposure to MRSA-positive patients and infection control measures employed. Frequent transmission of MRSA from colonized healthcare workers to their households was documented.

Antimicrobial resistance among gram-positive organisms in the intensive care unit

PURPOSE OF REVIEW

The epidemiology of gram-positive pathogens in the intensive care unit are reviewed, recent trends in antimicrobial resistance among these organisms are discussed, and the significance of these data with respect to treatment are considered.

RECENT FINDINGS

Results of surveillance studies published in 2001 and 2002 have demonstrated that gram-positive organisms such as Staphylococcus aureus, coagulase-negative staphylococci, and enterococci are among the most common bacteria infecting patients in intensive care units. Furthermore, these organisms are becoming increasingly resistant to available antimicrobial agents, and 2002 has ushered in worrisome developments such as the appearance of vancomycin-resistant S. aureus. Community-acquired methicillin-resistant S. aureus and the rise in incidence of vancomycin-resistant enterococci are other problems of great concern. Novel antibiotics such as quinupristin/dalfopristin and linezolid have activity against these agents, but resistance may develop to these agents as well. Studies have shown that infections caused by antibiotic-resistant organisms may be associated with increased morbidity, mortality, and costs. Exposure to antibiotics is a major risk factor for producing antibiotic resistance in patients, and methods to limit the spread of these organisms include restriction of antibiotic use, infection control, surveillance programs, and isolation procedures.

SUMMARY

An awareness of the prevalence and patterns of resistance among gram-positive nosocomial pathogens is vital for the appropriate treatment of hospitalized patients. In addition, efforts must be made to minimize the selection and spread of these organisms.

Pulsed-field gel electrophoresis typing of oxacillin-resistant Staphylococcus aureus isolates from the United States: establishing a national database

Oxacillin-resistant Staphylococcus aureus (ORSA) is a virulent pathogen responsible for both health care-associated and community onset disease. We used SmaI-digested genomic DNA separated by pulsed-field gel electrophoresis (PFGE) to characterize 957 S. aureus isolates and establish a database of PFGE patterns. In addition to PFGE patterns of U.S. strains, the database contains patterns of representative epidemic-type strains from the United Kingdom, Canada, and Australia; previously described ORSA clonal-type isolates; 13 vancomycin-intermediate S. aureus (VISA) isolates, and two high-level vancomycin-resistant, vanA-positive strains (VRSA). Among the isolates from the United States, we identified eight lineages, designated as pulsed-field types (PFTs) USA100 through USA800, seven of which included both ORSA and oxacillin-susceptible S. aureus isolates. With the exception of the PFT pairs USA100 and USA800, and USA300 and USA500, each of the PFTs had a unique multilocus sequence type and spa type motif. The USA100 PFT, previously designated as the New York/Tokyo clone, was the most common PFT in the database, representing 44% of the ORSA isolates. USA100 isolates were typically multiresistant and included all but one of the U.S. VISA strains and both VRSA isolates. Multiresistant ORSA isolates from the USA200, -500, and -600 PFTs have PFGE patterns similar to those of previously described epidemic strains from Europe and Australia. The USA300 and -400 PFTs contained community isolates resistant only to beta-lactam drugs and erythromycin. Noticeably absent from the U.S. database were isolates with the previously described Brazilian and EMRSA15 PFGE patterns. These data suggest that there are a limited number of ORSA genotypes present in the United States.

Clonal characterization of Staphylococcus aureus by multilocus restriction fragment typing, a rapid screening approach for molecular epidemiology

We have developed a rapid and simplified approach for the strain characterization of Staphylococcus aureus on the basis of multilocus sequence typing (MLST) in which sequence variations in the MLST housekeeping gene loci are detected by restriction fragment pattern analysis rather than sequencing; we refer to this approach as multilocus restriction fragment typing (MLRFT). Briefly, MLRFT for S. aureus involves the PCR amplification of each of the seven MLST housekeeping gene loci by using the same primer pairs used in MLST. The amplicons are then digested directly with one or two restriction enzymes and the restriction fragments are resolved by agarose gel electrophoresis. Projection from published MLST data shows that MLRFT captures about 95% of the genetic diversity detected by MLST. The MLRFT approach was validated with a set of 59 methicillin-susceptible and 44 methicillin-resistant S. aureus isolates from community-acquired and nosocomial sources which had previously been characterized by pulsed-field gel electrophoresis (PFGE). MLRFT resolved the 103 isolates into 15 restriction fragment types, giving a discrimination index of 89.0%. Clonal groupings established by MLRFT correlated well with those established by PFGE. In short, MLRFT provides a convenient alternative to MLST and PFGE because it requires minimal laboratory facilities and is relatively simple and inexpensive to perform.

Community-acquired Methicillin-resistant Staphylococcus aureus: Epidemiology and Potential Virulence Factors

Methicillin-resistant Staphylococcus aureus (MRSA) has been isolated from patients in the community. Some of these strains may have origins in the hospital, but others appear to be novel and unrelated to known hospital strains. Community MRSA strains have several distinguishing characteristics that may enable them to more readily colonize and infect otherwise healthy individuals. This article reviews recent publications addressing the epidemiology of MRSA in the community, risk factors associated with carriage, potentially associated virulence factors, and concepts of strain fitness as they pertain to MRSA. MRSA likely will be an increasingly important pathogen in the community.

Spider Bites Presenting with Methicillin-ResistantStaphylococcus aureusSoft Tissue Infection Require Early Aggressive Treatment

BACKGROUND

Occasionally, spider bites result in necrotizing soft tissue infections that require aggressive surgical debridement and treatment with intravenous antibiotics. With the rise of microbial resistance in the community, management with standard gram-positive intravenous antibiotic coverage may be ineffective. Our objective was to determine the infectious organisms cultured following wide local excision of soft tissue infections caused by spider bites. We hypothesized that the majority of isolated organisms would be sensitive to penicillin based antibiotics.

METHODS

From March 2000 to November 2001, the medical records were reviewed of patients who presented to a tertiary care hospital with serious soft tissue infections secondary to spider bites that required surgical treatment. For each patient, demographics, symptoms, size, time to surgical evaluation (TTSE), temperature, white blood cell (WBC) count, surgical procedure, and culture data were collected. Data are presented as mean +/- SEM.

RESULTS

Thirty-eight patients presented with serious soft tissue infections secondary to spider bites that required surgical debridement and treatment with intravenous antibiotics. Twenty-nine percent (11 of 38) of these patients had failed initial outpatient therapy with penicillin-based oral antibiotics. The mean TTSE was 5.0 +/- 0.5 days (range = 2-14 days; median = 4.5 days). The most common presenting symptoms were pain and erythema surrounding the bite site. The mean temperature was 98.8 +/- 0.6 degrees F (range = 97.2-102.2 degrees F; median = 99.2 degrees F). The mean WBC count was 12.6 +/- 0.8 mm3. All patients required wide surgical debridement of the infected area. The mean size of the excised tissue was 26 +/- 4 cm2 (range = 4-120 cm2; median = 16 cm2). Every patient had cultures that grew Staphylococcus aureus. In 86.8% of patients, S. aureus was found to be methicillin-resistant (MRSA). All isolated organisms were sensitive to trimethoprim-sulfamethoxazole.

CONCLUSIONS

In our experience, patients who presented with soft tissue infections as result of spider bites predominantly had methicillin-resistant S. aureus infections, corresponding to the increased incidence of MRSA reported in the community. Therefore, a more aggressive approach to the management of spider bites presenting with severe cellulitis is warranted. Routine treatment should include aggressive surgical debridement, intraoperative wound cultures, the empiric use of antibiotics with activity against MRSA, and adjustment of antimicrobial therapy based on culture and sensitivity data.