Methicillin-resistant Staphylococcus aureus in the community: a hospital-based study

Modeling Transmission of Methicillin-ResistantStaphylococcus AureusAmong Patients Admitted to a Hospital

Objective:

To determine the impact of the screening test, nursing workload, handwashing rates, and dependence of handwashing on risk level of patient visit on methicillin-resistantStaphylococcus aureus(MRSA) transmission among hospitalized patients.

Setting:

General medical ward.

Methods:

Monte Carlo simulation was used to model MRSA transmission (median rate per 1,000 patient-days). Visits by healthcare workers (HCWs) to patients were simulated, and MRSA was assumed to be transmitted among patients via HCWs.

Results:

The transmission rate was reduced from 0.89 to 0.56 by the combination of increasing the sensitivity of the screening test from 80% to 99% and being able to report results in 1 day instead of 4 days. Reducing the patient-to-nurse ratio from 4.3 in the day and 6.8 at night to 3.8 and 5.7, respectively, reduced the number of nosocomial infections from 0.89 to 0.85; reducing the ratio to 1 and 1, respectively, further reduced the number of nosocomial infections to 0.32. Increases in handwashing rates by 0%, 10%, and 20% for high-risk visits yielded reductions in nosocomial infections similar to those yielded by increases in handwashing rates for all visits (0.89, 0.36, and 0.24, respectively). Screening all patients for MRSA at admission reduced the transmission rate to 0.81 per 1,000 patient-days from 1.37 if no patients were screened.

Conclusion:

Within the ranges of parameters studied, the most effective strategies for reducing the rate of MRSA transmission were increasing the handwashing rates for visits involving contact with skin or bodily fluid and screening patients for MRSA at admission. (Infect Control Hosp Epidemiol 2005;26:607- 615)

Staphylococcus aureus Bacteremia in Older Adults: Predictors of 7-Day Mortality and Infection With a Methicillin-Resistant Strain

Objectives.

To determine the predictors of 7-day mortality in older adult patients with Staphylococcus aureus bacteremia after controlling for comorbidity using the Charlson weighted index of comorbidity (WIC) and to identify the risk factors associated with bacteremia due to methicillin-resistant S. aureus (MRSA).

Design.

Retrospective cohort study from January 2003 until December 2004.

Setting.

Two tertiary care, university-affiliated hospitals.

Methods.

One hundred thirty-five hospitalized patients with S. aureus bacteremia were included in the study. All patients who were 60 years or older and had 1 or more blood cultures positive for S. aureus were included in the study. The primary outcome was death 7 days after the onset of S. aureus bacteremia.

Results.

Twenty-one patients (15.6%) died within 7 days after the onset of S. aureus bacteremia. Seventy-four patients (56.1%) had MRSA bacteremia. Multivariate analysis identified 3 independent determinants of 7-day mortality: Charlson WIC score greater than 5 (odds ratio [OR], 3.6 [95% confidence interval {CI}, 1.1-11.2]; P = .03), previous hospitalization in the past 3 months (OR, 5.0 [95% CI, 1.1-25.1]; P = .04), and altered mental status at the onset of S. aureus bacteremia (OR, 13.6 [95% CI, 2.9-64.6]; P = .001). Multivariate analysis identified .previous hospitalization in the past 3 months (OR, 2.6 [95% CI, 1.1-5.9]; P = .02), residence in a long-term care facility (OR, 4.5 [95% CI, 1.7-12.3]; P = .003), and altered mental status at the onset of S. aureus bacteremia (OR, 2.5 [95% CI, 1.5-5.6]; P = .02) to be independently associated with the presence of MRSA.

Conclusions.

The Charlson WIC is significantly associated with increased mortality of S. aureus bacteremia in older adults. Previous hospitalization in the past 3 months, residence in a long-term care facility, and altered mental status should be used as a guidance for empirical vancomycin therapy and application of infection control measures in older adults with suspected S. aureus bacteremia.

Incidence of community-acquired methicillin-resistant Staphylococcus aureus carrying Pantone-Valentine leucocidin gene at a referral hospital in United Arab Emirates

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging pathogen in hospitalized patients worldwide. The present study was undertaken to identify CA-MRSA in hospitalized patients in a 350-bed tertiary care hospital in Sharjah, UAE over a 2-year period from January 2011 to December 2012. CA-MRSA was defined based on identification within first 48 h of admission in the hospital. Staphylococcal cassette chromosome (SCC) mec typing of the CA-MRSA isolates was carried out by multiplex polymerase chain reaction (PCR). Detection of PVL and mecA genes was done by PCR using the GenoType(®) MRSA test system (Hain Lifescience). Patient's clinical data and antimicrobial susceptibility pattern of the CA-MRSA isolates were also evaluated. Fifty seven of the 187 MRSA isolates were identified as CA-MRSA. All the CA-MRSA strains in our study belonged to SCCmecIV type and were positive for both PVL and mecA genes. The patients with CA-MRSA infections were young (median age, 32 years) and the majority of infections involved the skin and soft tissue (36%). Antimicrobial susceptibility pattern of the CA-MRSA isolates showed a better susceptibility profile to the non-beta-lactam antimicrobials with the exception of ciprofloxacin having 28% resistance. This study evidently strengthens the recent observation of an increase in CA-MRSA emergence among hospitalized patients in the UAE.

Community-acquired disseminated methicillin-resistantStaphylococcus aureusinfection: case report and clinical implications

A 6-year-old girl with community-acquired disseminated infection caused by methicillin-resistant Staphylococcus aureus (MRSA) is described. She had sepsis, meningo-encephalitis, pyomyositis, osteomyelitis, pericarditis and pulmonary embolisation caused by a multi-resistant strain of MRSA. Vancomycin is not routinely recommended as the first-line antimicrobial agent for suspected Staphylococcus aureus infection; however, it should be considered pending susceptibility results in patients presenting with severe sepsis in areas where the prevalence of MRSA is high.

Staphylococcus aureus adherence to Candida albicans hyphae is mediated by the hyphal adhesin Als3p

The bacterium Staphylococcus (St.) aureus and the opportunistic fungus Candida albicans are currently among the leading nosocomial pathogens, often co-infecting critically ill patients, with high morbidity and mortality. Previous investigations have demonstrated preferential adherence of St. aureus to C. albicans hyphae during mixed biofilm growth. In this study, we aimed to characterize the mechanism behind this observed interaction. C. albicans adhesin-deficient mutant strains were screened by microscopy to identify the specific receptor on C. albicans hyphae recognized by St. aureus. Furthermore, an immunoassay was developed to validate and quantify staphylococcal binding to fungal biofilms. The findings from these experiments implicated the C. albicans adhesin agglutinin-like sequence 3 (Als3p) in playing a major role in the adherence process. This association was quantitatively established using atomic force microscopy, in which the adhesion force between single cells of the two species was significantly reduced for a C. albicans mutant strain lacking als3. Confocal microscopy further confirmed these observations, as St. aureus overlaid with a purified recombinant Als3 N-terminal domain fragment (rAls3p) exhibited robust binding. Importantly, a strain of Saccharomyces cerevisiae heterologously expressing Als3p was utilized to further confirm this adhesin as a receptor for St. aureus. Although the parental strain does not bind bacteria, expression of Als3p on the cell surface conferred upon the yeast the ability to strongly bind St. aureus. To elucidate the implications of these in vitro findings in a clinically relevant setting, an ex vivo murine model of co-infection was designed using murine tongue explants. Fluorescent microscopic images revealed extensive hyphal penetration of the epithelium typical of C. albicans mucosal infection. Interestingly, St. aureus bacterial cells were only seen within the epithelial tissue when associated with the invasive hyphae. This differed from tongues infected with St. aureus alone or in conjunction with the als3 mutant strain of C. albicans, where bacterial presence was limited to the outer layers of the oral tissue. Collectively, the findings generated from this study identified a key role for C. albicans Als3p in mediating this clinically relevant fungal-bacterial interaction.

Validation study of artificial neural network models for prediction of methicillin-resistant Staphylococcus aureus carriage

OBJECTIVE

Use of active surveillance cultures for methicillin-resistant Staphylococcus aureus (MRSA) for all patients admitted to the intensive care unit has been shown to reduce nosocomial transmission. However, the cost-effectiveness and the utility of implementing use of active surveillance cultures nationwide remain controversial. We sought to develop an artificial neural network (ANN) model that would predict the likelihood of MRSA colonization.

SETTING

Two acute care hospitals, one in Pittsburgh (hospital A) and one in Kaohsiung, Taiwan (hospital B).

METHODS

Nasal cultures were performed for all patients admitted to the hospitals. A total of 46 potential risk factors in hospital A and 86 potential risk factors in hospital B associated with MRSA colonization were assessed. Culture results were obtained; 75% of the data were used for training our ANN model, and the remaining 25% were used for validating our ANN model. The culture results were the "gold standard" for determining the accuracy of the model predictions.

RESULTS

The ANN model predictions were accurate 95.2% of the time for hospital A (sensitivity, 94.3%; specificity, 96.0%) and 94.2% of the time for hospital B (sensitivity, 96.6%; specificity, 91.8%), integrating all potential risk factors into the model. Only 17 potential risk factors were needed for the hospital A ANN model (accuracy, 90.9%; sensitivity, 98.5%; specificity, 83.4%), and only 20 potential risk factors were needed for the hospital B ANN model (accuracy, 90.5%; sensitivity, 96.6%; specificity, 84.3%), if the minimal risk factor method was used. Cross-validation analysis showed an average accuracy of 85.6% (sensitivity, 91.3%; specificity, 80.0%).

CONCLUSION

Our ANN model can be used to predict with an accuracy of more than 90% which patients carry MRSA. The false-negative rates were significantly lower than the false-positive rates in the ANN predictions, which can serve as a safety buffer in case of patient misclassification.

Staphylococcus aureus clumping factor A binds to complement regulator factor I and increases factor I cleavage of C3b

The human complement system plays an important role in the control of Staphylococcus aureus infection. For instance, we previously demonstrated that the central complement component deposited on the organism's surface, C3b, can be cleaved by the host complement control protein, factor I, resulting in diminished phagocytosis of S. aureus. In the present study, we have identified clumping factor A (ClfA) from cell wall proteins of S. aureus as a specific protein bound by factor I. Recombinant ClfA (rClfA) containing the full-length A region (peptides 40-559) also bound factor I. We identified an 50-kDa fragment of ClfA that is shed by S. aureus into growth medium. The shed ClfA fragment was derived from the A region of ClfA and bound factor I. rClfA and the shed ClfA fragment increased factor I cleavage of C3b into inactive C3b. Our findings describe a new S. aureus mechanism for modification of host complement activities.

Health-care workers: source, vector, or victim of MRSA?

There is ongoing controversy about the role of health-care workers in transmission of meticillin-resistant Staphylococcus aureus (MRSA). We did a search of the literature from January, 1980, to March, 2006, to determine the likelihood of MRSA colonisation and infection in health-care workers and to assess their role in MRSA transmission. In 127 investigations, the average MRSA carriage rate among 33 318 screened health-care workers was 4.6%; 5.1% had clinical infections. Risk factors included chronic skin diseases, poor hygiene practices, and having worked in countries with endemic MRSA. Both transiently and persistently colonised health-care workers were responsible for several MRSA clusters. Transmission from personnel to patients was likely in 63 (93%) of 68 studies that undertook genotyping. MRSA eradication was achieved in 449 (88%) of 510 health-care workers. Subclinical infections and colonisation of extranasal sites were associated with persistent carriage. We discuss advantages and disadvantages of screening and eradication policies for MRSA control and give recommendations for the management of colonised health-care workers in different settings.

Analysis of methicillin resistance among Staphylococcus aureus blood isolates in an emergency department

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) has become of great concern in both hospital and community settings. To evaluate the prevalence and risk factors for methicillin resistance among Staphylococcus aureus, blood isolates in our Emergency Department (ED) were collected. All patients with S. aureus bacteremia (SAB) who presented to the ED from January 2000 to August 2005 were included, and a retrospective study was performed. A total of 231 patients with SAB were enrolled (median age, 59 yr; M:F, 125:106). Among these patients, methicillin-resistant strains accounted for 27.3% (63 patients). Catheter-related infection was the most frequent primary site of SAB (39.0%), followed by skin and soft tissue infection (16.5%). In multivariate analysis, recent surgery (OR, 3.41; 95% CI, 1.48-7.85), recent hospitalization (2.17; 1.06-4.62), and older age (> or =61 yr) (2.39; 1.25-4.57) were independently associated with the acquisition of methicillin-resistant strains. When antimicrobial therapy is considered for the treatment of a patient with suspected SAB, clinicians should consider obtaining cultures and modifying empirical therapy to provide MRSA coverage for patients with risk factors: older age, recent hospitalization, and recent surgery.

Clinical outcome and costs of nosocomial and community-acquired Staphylococcus aureus bloodstream infection in haemodialysis patients

The main aim of this study was to evaluate the clinical outcome and costs of nosocomial and community-acquired methicillin-susceptible Staphylococcus aureus (MSSA) or methicillin-resistant S. aureus (MRSA) bloodstream infection (BSI) in patients undergoing haemodialysis. A multicentre retrospective study was conducted that included 109 patients with end-stage renal disease and S. aureus BSI who were hospitalised in three German centres between 1999 and 2005. Nosocomial and community-acquired infections were analysed separately with regard to costs and outcome. Forty-nine (45%) patients had nosocomial infection. Compared to patients with community-acquired infection, these patients were more likely to have had BSI caused by MRSA (40.8% vs. 13.3%, p <0.05). BSI was the initial reason for admission for 33 (55%) patients who had community-acquired infection. The mean length of hospitalisation was 24 days for patients with community-acquired infection and 51 days for patients with nosocomial infection (p <0.05). Costs per treatment episode were 20,024 Euros for nosocomial infection vs. 9554 Euros for community-acquired infection (p <0.05). The average treatment costs for patients with MSSA BSI were <50% of those for patients with MRSA BSI (10,573 vs. 24,931 Euros, p <0.05). S. aureus BSI is an underlying cause of substantial health risk and high morbidity among the haemodialysis-dependent population, who are already at high-risk for other reasons. This study also highlighted differences according to the source of BSI, including costs arising from hospitalisation and treatment.

Use of stochastic epidemic modeling to quantify transmission rates of colonization with methicillin-resistant Staphylococcus aureus in an intensive care unit

OBJECTIVE

To consider statistical methods for estimating transmission rates for colonization of patients with methicillin-resistant Staphylococcus aureus (MRSA) in an intensive care unit (ICU) from three different sources: background contamination, non-isolated patients, and isolated patients.

METHODS

We developed statistical methods that allowed for the analysis of interval-censored, routine surveillance data and extended the general epidemic model for the flow of patients through the ICU.

RESULTS

Within this ICU, the rate of transmission to susceptible patients from a background source of MRSA (0.0092 case per day; 95% confidence interval [CI95], 0.0062-0.0126) is approximately double the rate of transmission from a non-isolated patient (0.0052 case per day; CI95, 0.0013-0.0096) and six times the rate of transmission from an isolated patient (0.0015 case per day; CI95, 0.0001-0.0043). We used the methodology to investigate whether transmission rates vary with workload.

CONCLUSION

Our methodology has general application to infection by and transmission of pathogens in a hospital setting and is appropriate for quantifying the effect of infection control interventions.

Serum complement factor I decreases Staphylococcus aureus phagocytosis

Complement-mediated opsonization of Staphylococcus aureus is a critical host defense in animal models. Specifically, C3b and CD35 play important roles in effective opsonophagocytosis of S. aureus. We have shown that complement control protein factor I mediates cleavage of the complement opsonin C3b bound to the S. aureus surface. In this study, we examined the physiologic relevance of this observation by determining whether factor I-mediated cleavage of S. aureus-bound C3b decreased phagocytosis of S. aureus by neutrophils. Compared with controls, anti-factor I antibody inhibited C3b-cleavage on the S. aureus surface by >83% (as measured by iC3b generation) and increased phagocytosis of S. aureus by >100%. Treatment of C3b-coated S. aureus with factor I increased generation of iC3b (75%), decreased the total amount of C3-fragments bound to the S. aureus surface (58%), and decreased the number of bacteria phagocytosed (40%). Testing specifically for C3-fragments shed from the S. aureus surface, we found that factor I increased shedding (43%). Notably, these factor I-mediated effects were of the same magnitude regardless of whether factor H, a known cofactor for factor I, was present. These findings indicate that S. aureus benefits from, and possibly manipulates, the normally host-protective activity of factor I cleavage of C3b, which results in bacterial escape from complement-mediated opsonophagocytosis. Because escaping opsonophagocytosis-mediated destruction is a necessary mechanism for bacterial survival resulting in human disease, preventing cleavage of C3b on the S. aureus surface, and thereby enhancing opsonophagocytosis, is a promising potential target for therapeutic intervention.

MRSA bacteraemia in patients on arrival in hospital: a cohort study in Oxfordshire 1997-2003

OBJECTIVE

To describe the incidence and determinants of methicillin resistant and methicillin sensitive Staphylococcus aureus (MRSA and MSSA) bacteraemia in patients presenting to acute hospitals.

DESIGN

Anonymised record linkage study with information from hospital information systems and microbiology databases.

SETTING

One teaching hospital and one district general hospital in Oxfordshire.

PARTICIPANTS

All patients admitted to a teaching hospital 1 April 1997 to 31 March 2003 and to a district general hospital 1 April 1999 to 31 March 2003.

MAIN OUTCOME MEASURES

Detection of MRSA and MSSA from blood cultures taken during the first two days of admission to hospital.

RESULTS

In the teaching hospital, there were 479 patients with MSSA and 116 with MRSA bacteraemia admitted from the community. Among this group, which comprised 24% of all hospital MRSA cases, 31% (36 cases) of patients had been admitted to renal, oncology, or haematology services for intensive day case therapy. The 69% remaining were most commonly patients admitted as medical or surgical emergencies. At least 91% had been in hospital previously; the median time since discharge was 46 days. About half of cases were in patients in whom MRSA had not been isolated before. Similar epidemiology was observed in the district general hospital.

CONCLUSION

Diagnostic algorithms and policies on use of antibiotics need to reflect the fact that a quarter of hospital MRSA cases occur in patients who have previously been in hospital and are subsequently readmitted.

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.

Safety and immunogenicity of a booster dose of Staphylococcus aureus types 5 and 8 capsular polysaccharide conjugate vaccine (StaphVAX®) in hemodialysis patients

StaphVAX, an unadjuvanted, bivalent vaccine composed of Staphylococcus aureus (S. aureus) capsular polysaccharides (CPS) types 5 and 8 bound to the mutant non-toxic recombinant Pseudomonas aeruginosa exotoxin A (rEPA) conferred approximately 60% protection for 10 months against bacteremia caused by this pathogen in hemodialysis patients. A protective level of 80 microg/ml was estimated based upon geometric mean (GM) antibody levels at the end of the efficacy period. To extend the duration of protection conferred by StaphVAX in hemodialysis patients, recipients of the vaccine were reinjected in a randomized double-blinded, placebo-controlled study. Vaccinees received StaphVAX and a saline placebo injection 14 days apart according to the randomization schedule. The booster dose of StaphVAX was administered an average of 958 days (753-1167 days) after the first injection. There were no serious adverse reactions. Antibody levels at day 14, 28, 92, and 182 post-injection were measured by ELISA. Maximal levels of IgG anti-CPS were observed at the 28-day interval. For type 5, GM antibody levels increased from 73 microg/ml at day 0 to 162 microg/ml (P < 0.001) and for type 8 from 59 microg/ml to 133 microg/ml (P < 0.001). Anti-CPS antibody levels of approximately 80 microg/ml to type 5 and type 8 were achieved in 72.4 and 74.3% of vaccinees, respectively. There was excellent correlation between the level of anti-CPS and opsonic titer (r = 0.93). Moreover, the decline of anti-CPS antibody levels at six months was significantly less rapid than that observed from the first immunization (P < 0.001). We conclude that a booster immunization to maintain protective levels of specific antibodies for an extended period of time is feasible for patients at continuous risk for S. aureus bacteremia.

Epidemiological Typing of Community-Acquired Methicillin-Resistant Staphylococcus aureus Isolates from Children in Taiwan

BACKGROUND

A 1400-bed tertiary medical center in northern Taiwan was used to conduct an epidemiological study of children hospitalized with community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection during a 5-year period.

METHODS

Nineteen previously healthy children with predominantly skin and soft-tissue CA-MRSA infections were enrolled into the study. Seventeen CA-MRSA isolates were examined for antimicrobial susceptibility and molecular typing.

RESULTS

A comparison of our results with the reported resistance rates among CA-MRSA isolates from other countries showed uniformly high macrolide resistance (100%). Of the 17 MRSA isolates in our study, all had the macrolide-lincosamide-streptogramin-constitutive phenotype and the ermB gene. Moreover, on the basis of molecular typing results, 11 (65%) of 17 CA-MRSA isolates were genetically related (as determined by pulsed-field gel electrophoresis), and multilocus sequence typing revealed a sequence type of 59 in all isolates. Staphylococcal toxin genes lukS-PV and lukF-PV were detected in all isolates. However, staphylococcal cassette chromosome mec type IV was only detected in 3 (17.6%) of 17 isolates; the remaining 14 isolates were untypeable.

CONCLUSIONS

Analysis of our data suggests the predominance of a single endemic CA-MRSA strain with high macrolide resistance in our community. Clinical improvement with incision and drainage was noted for most patients, despite treatment with an ineffective antibiotic, so the need for a change in treatment guidelines should be addressed.

Cleavage of complement C3b to iC3b on the surface of Staphylococcus aureus is mediated by serum complement factor I

Complement-mediated opsonization of Staphylococcus aureus bearing the dominant capsule serotypes, serotypes 5 and 8, remains incompletely understood. We have previously shown that complement plays a vital role in the efficient phagocytosis of a serotype 5 S. aureus strain and that the opsonic fragments of the central complement protein C3, C3b and iC3b, were present on the bacterial surface after incubation in human serum. In the present studies, C3b and iC3b were found on several serotype 5 and 8 S. aureus strains after incubation in human serum. Using purified classical activation pathway complement proteins and the Western blot assay, we showed that when C3b was generated on the S. aureus surface no iC3b fragments were found, suggesting that other serum proteins may be required for cleaving C3b to iC3b. When C3b-coated S. aureus was incubated with serum factor I, a complement regulatory protein, iC3b was generated. Purified factor H, a serum protein cofactor for factor I, did not enhance factor I-mediated cleavage of C3b. These findings suggest that C3b cleavage to iC3b on S. aureus is mediated by serum factor I and does not require factor H.

Methicillin-Resistant Staphylococcus aureus Infections in Vascular Surgery: Increasing Prevalence

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a virulent organism that causes substantial infection-related morbidity and mortality in hospitalized patients. For example, MRSA infection of prosthetic vascular grafts can be limb- and life-threatening in surgical patients. We investigated the incidence of MRSA infection in vascular surgical patients who developed postoperative infectious complications.

METHODS

Prospective data (including procedure, nature of complication, and outcome) were collected on all vascular surgery patients (n = 772) over a two-year period from January, 2000, to December, 2001. The study cohort included all patients who developed postoperative complications (n = 119, 15.4%), including infection, unplanned or prolonged intubation, metabolic abnormalities, and myocardial ischemia. Bacteriologic data of all clinical cultures were reviewed and infection-related outcomes were examined.

RESULTS

Hospital-acquired infection occurred in 79 (66.4%) of 119 patients who developed postoperative complications. Review of microbiology data (total, 197 bacterial isolates) confirmed that gram-positive organisms were the leading cause of infections, with 120 gram-positive isolates (60.9%). Of the gram-positive isolates, S. aureus was the most common pathogen, isolated in 73 (60.8%) cultures. The single most prevalent organism was MRSA, identified in 42 of 73 (57.5%) of cultures. The site of MRSA infection was confirmed to be the surgical site (54.8%), sputum (17.0%), blood (14.3%), urine (9.5%), peritoneal fluid (2.4%), or catheter insertion site (2.4%). Only four patients had prior MRSA infection or colonization. Prosthetic vascular grafts were placed in 51 (42.9%) of the 119 vascular patients, and 26 patients (51.6%) acquired MRSA infection. Graft removal was required in three patients due to infection (MRSA infection in two patients, Pseudomonas aeruginosa in one patient). Forty percent of patients with MRSA infection required an amputation as their surgical procedure. No patient died of MRSA bacteremia during the study period. Mean hospital length of stay (LOS) was longer in patients with MRSA infection (29.6 d vs. 22.7 days, range 2-174 days, p < 0.05) compared to the total study cohort of vascular patients with postoperative infections.

CONCLUSIONS

Methicillin-resistant S. aureus has emerged as the leading cause of postoperative infection in vascular surgery patients, and is associated with substantial morbidity, increased hospital LOS, and higher incidences of amputation and graft removal. Greater emphasis on preoperative screening protocols for MRSA colonization is warranted, in conjunction with aggressive infection control measures, alteration of preoperative prophylactic antimicrobial use in MRSA-colonized patients, and meticulous postoperative surveillance for MRSA infection. Furthermore, antimicrobial treatment of postoperative infectious complications in vascular surgery patients should include empiric coverage for MRSA in institutions where MRSA is endemic.

Role of complement receptors 1 and 2 (CD35 and CD21), C3, C4, and C5 in survival by mice of staphylococcus aureus bacteremia

Complement-mediated opsonization and phagocytosis of encapsulated serotype 5 Staphylococcus aureus are essential to host defense. We describe the effects of complement depletion and deficiencies of C4, C5, and complement receptors 1 and 2 on mouse survival after intravenous exposure to S aureus. Depletion of complement proteins in C57BL/6 mice with the use of cobra-venom factor decreased survival compared with that of controls after the induction of bacteremia with mucoid (90% mortality), encapsulated (73%), and unencapsulated (59%) S aureus strains. In this model complement is even more important in the control of infection with encapsulated S aureus (80% of clinical isolates) than in the control of infection by unencapsulated strains. C4-deficient mice demonstrated similar mortality from bacteremia caused by encapsulated S aureus compared with controls, suggesting that in the unimmunized animal the alternative complement pathway contributes more to control of bacteremia caused by encapsulated S aureus than the classical complement pathway or mannan-binding lectin pathway. C5-deficient mice (B10.D2-H2(d) H2-T18(c) Hc(0)/oSnJ) showed similar mortality when subjected to bacteremia caused by encapsulated S aureus compared with C5-sufficient (B10.D2-Hc(1) H2(d) H2-T18(c)/nSnJ) mice, suggesting that in this model the anaphylatoxin C5a and the late complement cascade are not critical to survival of bacteremia induced with the use of these strains. However, C5-deficient mice depleted of C3 with the use of cobra-venom factor had 60% decreased survival compared with untreated C5-deficient mice with bacteremia induced by encapsulated S aureus, suggesting that in this model C3 is more critical than C5 in controlling S aureus bacteremia. Complement receptor 1 (CD35) is the primary receptor for the opsonin C3b. Mice deficient in CD35/CD21 showed a 67% decrease in survival compared with normal mice, suggesting that CD35/CD21 is of major importance in the control of S aureus-induced bacteremia.

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.

Nasal carriage of methicillin-resistant Staphylococcus aureus among hospital staff and outpatients

This study sought to determine the rate of nasal methicillin-resistant Staphylococcus aureus (MRSA) carriage among hospital staff and outpatients. Nasal swabs were obtained from 500 outpatients and 500 hospital staff. Hospital staff were 2.3-fold more likely to carry MRSA than were outpatients (6% vs 2.6%, P = .013).

Methicillin-resistant Staphylococcus aureus: impact on dermatology practice

Methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) emerged in the 1960s and is now commonly seen in hospitals, clinics and, since the mid-1990s, the community. Risk factors for the acquisition of MRSA include chronic dermatoses, underlying medical illnesses, attending healthcare facilities, use of prescription antibacterials, surgery, intravenous lines, hospitalization in an intensive care unit, and proximity to patients colonized with MRSA. Recent community-associated strains often occur in patients without these risk factors. Staphylococci are readily spread from person to person and readily contaminate the environment. Infection control measures thus involve identifying the infected patients, separating them from other non-infected patients, cleaning of the environment and, most important of all, scrupulous attention to hand hygiene. Alcoholic antiseptic hand rubs offer an alternative to antiseptic hand washes and increase compliance. Treatment of MRSA skin infections is challenging. Topical agents such as mupirocin or fusidic acid can be used, but the organisms often become resistant. Systemic therapy involves non-beta-lactams. Parenteral treatment is generally with glycopeptides such as vancomycin; oral therapy is more complex. Monotherapy with quinolones, rifampin (rifampicin), and fusidic acid often results in the development of resistance and so, if any of these agents are chosen it should be in combination. There are no data on combination therapy, although rifampin-containing combinations are often chosen. Fourth-generation quinolones and linezolid are expensive but promising alternatives.

Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and methicillin-resistant isolates

We investigated the genetic relatedness of 5 community-acquired (CA) Staphylococcus aureus isolates obtained from 4 consecutive pediatric patients presenting with sepsis syndrome and severe pneumonia during a 3-week period in 2000. Two patients were infected with methicillin-susceptible S. aureus (MSSA), and 2 were infected with methicillin-resistant S. aureus (MRSA). The pulsed-field gel electrophoresis patterns for the 2 CA-MRSA isolates were identical to each other, as were the patterns for the 3 CA-MSSA isolates. A 2-band difference reflecting the presence of a staphylococcal cassette chromosome mec (SCCmec) element distinguished the CA-MRSA isolates from the CA-MSSA isolates. The small, mobile type IV SCCmec element was present in the CA-MRSA isolates. These data suggest that an insertion or, less likely, a deletion of the SCCmec type IV element occurred in a highly virulent S. aureus background. Staphylococcal toxin genes sea, seh, lukS-PV, and lukF-PV were detected in all isolates. Also, in all isolates, was a partial homolog of seo (seo'). The relationship among these patient isolates strengthens the assumption that CA-MRSA infections may be caused by isolates closely related to MSSA isolates.

Linezolid for the treatment of complicated skin and skin structure infections in children

BACKGROUND

Gram-positive pathogens are a major cause of complicated skin and skin structure infections (CSSSIs) in children. Many pathogens are developing decreased susceptibility to currently used antibiotics, increasing the need for new therapies. Linezolid is well-tolerated and effective in the treatment of these infections in adults.

OBJECTIVE

To evaluate the clinical efficacy and safety of iv/oral linezolid and iv vancomycin in children with Gram-positive CSSSIs.

METHODS

Hospitalized children <12 years of age were randomized (2:1 ratio) to receive either linezolid 10 mg/kg iv every 8 h (with the option to change treatment to oral linezolid suspension 10 mg/kg every 8 h) or iv vancomycin 10 to 15 mg/kg every 6 to 24 h (according to age). Clinical response, tolerance and safety were evaluated at follow-up. The results of a subset analysis of patients with CSSSIs are presented here.

RESULTS

One hundred twenty intent-to-treat patients (linezolid 80, vancomycin 40) with CSSSI were included in this analysis. Clinical cure rates for clinically evaluable patients with CSSSI did not differ between treatment groups (linezolid, 93.2% vs. vancomycin, 90.0%; P = 0.594). Significantly fewer linezolid-treated patients experienced drug-related adverse events than did vancomycin-treated patients (23% vs. 48%; P = 0.006). The percentages of patients with laboratory abnormalities, including selected hematologic parameters, were generally low and similar between the treatment groups.

CONCLUSIONS

Linezolid given iv or orally was well-tolerated and safe. It was as effective as vancomycin in treating children with Gram-positive CSSSIs.

Prevalence of and risk factors for colonization with methicillin-resistant Staphylococcus aureus at the time of hospital admission

OBJECTIVES

To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization among patients presenting for hospital admission and to identify risk factors for MRSA colonization.

DESIGN

Surveillance cultures were performed at the time of hospital admission to identify patients colonized with S. aureus. A case-control study was performed to identify risk factors for MRSA colonization.

SETTING

A tertiary-care academic medical center.

PATIENTS

Adults presenting for hospital admission (N = 974).

RESULTS

S. aureus was isolated from 205 (21%) of the patients for whom cultures were performed. Methicillin-sensitive S. aureus was isolated from 179 (18.4%) of the patients, and MRSA was isolated from 26 (2.7%) of the patients. All 26 MRSA-colonized patients had been admitted to a healthcare facility in the preceding year, had at least one chronic illness, or both. In multivariate analyses comparing MRSA-colonized patients with control-patients, admission to a nursing home (odds ratio [OR], 16.5; 95% confidence interval [CI95], 1.4 to 192.1; P = .025) or a hospitalization of 5 days or longer during the preceding year (OR, 3.91; CI95, 1.1 to 13.9; P = .035) were independent predictors of MRSA colonization.

CONCLUSIONS

Patients colonized with MRSA admitted to this hospital likely acquired the organism during previous encounters with healthcare facilities. There was no evidence that MRSA colonization occurs commonly among low-risk individuals in this community. These data suggest that evaluation of recent healthcare exposures is essential if true community acquisition of MRSA is to be confirmed.

Rates of carriage of methicillin-resistant and methicillin-susceptible Staphylococcus aureus in an outpatient population

OBJECTIVES

To assess the prevalence of and the clinical features associated with asymptomatic Staphylococcus aureus colonization in a healthy outpatient population, and to compare the characteristics of colonizing methicillin-resistant S. aureus (MRSA) strains with those of strains causing infection in our community and hospital.

SETTING

Outpatient military clinics.

METHODS

Specimens were obtained from the nares, pharynx, and axillae of 404 outpatients, and a questionnaire was administered to obtain demographic and risk factor information. MRSA strains were typed by pulsed-field gel electrophoresis (PFGE) and evaluated for antibiotic susceptibility. Antibiograms of study MRSA strains were compared with those of MRSA strains causing clinical illness during the same time period.

RESULTS

Methicillin-susceptible S. aureus (MSSA) colonization was present in 153 (38%) of the 404 asymptomatic outpatients, and MRSA colonization was present in 8 (2%). Detection of colonization was highest from the nares. No clinical risk factor was significantly associated with MRSA colonization; however, a tendency was noted for MRSA to be more common in men and in those who were older or who had been recently hospitalized. All colonizing MRSA strains had unique patterns on PFGE. In contrast to strains responsible for hospital infections, most colonizing isolates of MRSA were susceptible to oral antibiotics.

CONCLUSIONS

MRSA and MSSA colonization is common in our outpatient population. Colonization is best detected by nares cultures and most carriers of MRSA are without apparent predisposing risk factors for acquisition. Colonizing isolates of MRSA are heterogeneous and, unlike nosocomial isolates, often retain susceptibility to other non-beta-lactam antibiotics.

Prevalence of and risk factors for colonization with methicillin-resistant Staphylococcus aureus in an outpatient clinic population

OBJECTIVES

To determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization in an outpatient population and to identify risk factors for MRSA colonization.

DESIGN

Surveillance cultures were performed during outpatient visits to identify S. aureus colonization. A case-control study was performed to identify risk factors for MRSA colonization.

SETTING

Primary care internal medicine clinic.

PATIENTS

Adults presenting for non-acute primary care (N = 494).

RESULTS

S. aureus was isolated from 122 (24.7%) of the patients for whom cultures were performed. Methicillin-susceptible S. aureus was isolated from 107 (21.7%) of the patients, whereas MRSA was isolated from 15 (3.0%) of the patients. All MRSA isolates were resistant to multiple non-beta-lactam antimicrobial agents. In multivariate analyses, MRSA colonization was independently associated with admission to a nursing home (adjusted odds ratio [OR], 103; 95% confidence interval [CI95], 7 to 999) or hospital in the previous year, although the association with hospital admission was observed only among those without chronic illness (adjusted OR, 7.1; CI95, 1.3 to 38.1). In addition, MRSA colonization was associated with the presence of at least one underlying chronic illness, although this association was observed only among those who had not been hospitalized in the previous year (adjusted OR, 5.1; CI95, 1.2 to 21.9).

CONCLUSIONS

We found a low prevalence of MRSA colonization in an adult outpatient population. MRSA carriers most likely acquired the organism through contact with healthcare facilities rather than in the community. These data show that care must be taken when attributing MRSA colonization to the community if detected in outpatients or during the first 24 to 48 hours of hospitalization.

Microbial flora of hands of homemakers

OBJECTIVES AND METHODS

Because of increasing concern about antimicrobial resistance in the community, aerobic flora of hands of 224 healthy homemakers in northern Manhattan, New York, were examined.

RESULTS

Mean log colony-forming unit counts before and after handwashing were 5.72 and 5.69, respectively, P =.60; mean number of species identified/sample was 3.6 before washing and 3.3 after (P =.02). After handwashing gram-negative bacteria were isolated from 75.1% of subjects; yeast from 32.9%; and Staphylococcus aureus from 18.5%, 1 of which (2.4%) was oxacillin-resistant. Generally, these community isolates were more sensitive than isolates from inpatients in the local hospital, although community isolates of Pseudomonas aeruginosa were significantly more resistant than inpatient isolates for 4/10 agents tested.

CONCLUSIONS

Hands of healthy persons in the community were usually colonized with gram-negative bacteria, a single handwash had little impact on microbial counts, and hands of healthy adults may increasingly become one reservoir for antimicrobial resistance.

Availability of complement bound to Staphylococcus aureus to interact with membrane complement receptors influences efficiency of phagocytosis

Complement-mediated opsonization of encapsulated Staphylococcus aureus (CP+) of the predominant capsule types, 5 and 8, remains poorly understood. Our previous work showed that complement is important for mouse survival of CP+ type 5 bacteremia and that the type 5 capsule inhibits the binding of opsonic C3 fragments to the organism. The importance of complement-mediated opsonization of CP+ was tested by neutrophil phagocytosis assays. Complement-mediated opsonization of CP+ increased phagocytosis by 57% compared to opsonization in complement-inhibited serum. Agar-grown CP+, enhancing capsule expression, was phagocytosed only one-tenth as well as the capsule-negative organisms (CP-), supporting the belief that staphylococcal polysaccharide capsules impair phagocytosis. Despite relatively poor phagocytosis of CP+ compared to CP-, complement activation increased the phagocytosis of CP+ by 103%. Thus, complement in normal human serum may have an important role in opsonizing CP+, even when capsule expression is strong. The ability of bound C3 fragments to interact with complement receptor 1 (CD35) on the membrane of human erythrocytes was tested in an immune adherence assay. S. aureus capsule was able to mask C3 fragments on the organism from binding to complement receptor 1. The inhibition of C3 binding to CP+ and the masking of deposited C3 fragments caused by the presence of capsule was associated with markedly decreased phagocytosis. The addition of anti-capsule antibodies to normal human serum was found to markedly improve the recognition of deposited C3 fragments by complement receptor 1 even when the absolute number of C3 molecules bound to S. aureus was not increased.

Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors

Reports suggest that carriage of methicillin-resistant Staphylococcus aureus (MRSA) among persons without health care-associated risks has increased. A meta-analysis of studies reporting the prevalence of community-acquired MRSA (CA-MRSA) among MRSA isolates from hospitalized patients or the prevalence of MRSA colonization among community members was conducted. The CA-MRSA prevalence among hospital MRSA was 30.2% in 27 retrospective studies and 37.3% in 5 prospective studies; 85% of all patients with CA-MRSA had > or =1 health care-associated risk. The pooled MRSA colonization rate among community members was 1.3% (95% confidence interval [CI], 1.04%-1.53%), but there was significant heterogeneity among study populations. Community members from whom samples were obtained in health care facilities were more likely to be carrying MRSA than were community members from whom samples were obtained outside of the health care setting (relative risk, 2.35; 95% CI, 1.56-3.53). Among studies that excluded persons with health care contacts, the MRSA prevalence was 0.2%. Moreover, most persons with CA-MRSA had > or =1 health care-associated risk, which suggests that the prevalence of MRSA among persons without risks remains low (< or =0.24%). Effective control of dissemination of MRSA throughout the community likely will require effective control of nosocomial MRSA transmission.

Prevalence of methicillin-resistant Staphyloccocus aureus and associated risk factors on admission to a specialist care eye hospital

BACKGROUND

Staphylococcus aureus is known to be a frequent pathogen in hospital settings, with its well-known and resistant forms to the anti-staphylococcal penicillins. Reports on community carriage outside hospital settings have been feared to be on the increase due to the frequency of reported cases on admission to hospitals. We undertook this study to determine the prevalence of, and to establish predictors for, nasal carriage of methicillin-resistant S. aureus (MRSA) at the time of admission to a specialist care eye hospital.

MATERIALS AND METHODS

A prospective survey was conducted at King Khaled Eye Specialist Hospital (KKESH), Riyadh, during three differing weeks randomly selected from the year 1999. The first 100 patients admitted during those three weeks were selected according to inclusion criteria. The hospital is a 220-bed tertiary ophthalmic care facility, with an average 7,500 admissions per year. Nasal bacterial swabs were taken within 48 hours of admission and tested for all strains of S. aureus and sensitivity to methicillin. Detailed interviews were conducted about medical history and habitual environment.

RESULTS

Of 306 nasal cultures tested, none was isolated for MRSA and 102 (33%) were sensitive to methicillin (MSSA). We found 0% nasal carriage rate for MRSA. Respondents had difficulty with questions related to antibiotic administration. No identifiable medical or environmental risk factors could be found.

CONCLUSION

Nasal swabs of patients admitted to KKESH did not reveal MRSA colonization, indicating that MRSA may not be prevalent in the community at present.

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

The study objective was to determine the prevalence and risk factors for nasal colonization with Staphylococcus aureus and methicillin resistance among the urban poor and to compare antibiotic resistance and genetic similarity to concurrently collected clinical isolates of methicillin-resistant S. aureus (MRSA). A population-based community sample of 833 homeless and marginally housed adults were cultured and compared with 363 clinical isolates of MRSA; 22.8% of the urban poor were colonized with S. aureus. Of S. aureus isolates, 12.0% were methicillin resistant. Overall prevalence of MRSA was 2.8%. Significant multivariate risk factors for MRSA were injection drug use (odds ratio [OR], 9.7), prior endocarditis (OR, 4.1), and prior hospitalization within 1 year (OR, 2.4). Resistance to antimicrobials other than beta-lactams was uncommon. Only 2 individuals (0.24%) with MRSA had no known risk factors. A total of 22 of 23 community MRSA genotypically matched clinical MRSA isolates, with 15 of 23 isolates identical to MRSA clones endemic among hospitalized patients.

Use of a Staphylococcus aureus conjugate vaccine in patients receiving hemodialysis

BACKGROUND

In patients with decreased resistance to infection, Staphylococcus aureus is a major cause of bacteremia and its complications. The capsular polysaccharides are essential for the pathogenesis of and immunity to S. aureus infection and are targets for vaccines.

METHODS

In a double-blind trial involving patients with end-stage renal disease who were receiving hemodialysis, we evaluated the safety, immunogenicity, and efficacy of a vaccine with S. aureus type 5 and 8 capsular polysaccharides conjugated to nontoxic recombinant Pseudomonas aeruginosa exotoxin A. Between April 1998 and August 1999, 1804 adult patients at 73 hemodialysis centers were randomly assigned to receive a single intramuscular injection of either vaccine or saline. IgG antibodies to S. aureus type 5 and 8 capsular polysaccharides were measured for up to two years, and episodes of S. aureus bacteremia were recorded. Efficacy was estimated by comparing the incidence of S. aureus bacteremia in the patients who received the vaccine with the incidence in the control patients.

RESULTS

Reactions to the vaccine were generally mild to moderate, and most resolved within two days. The capsular polysaccharides elicited an antibody response of at least 80 microg per milliliter (the estimated minimal level conferring protection) in 80 percent of patients for type 5 and in 75 percent of patients for type 8. The efficacy during weeks 3 to 54 was only 26 percent (P=0.23). However, between weeks 3 and 40 after vaccination, S. aureus bacteremia developed in 11 of 892 patients in the vaccine group who could be evaluated for bacteremia, as compared with 26 of 906 patients in the control group (estimate of efficacy, 57 percent; 95 percent confidence interval, 10 to 81 percent; nominal P=0.02).

CONCLUSIONS

In patients receiving hemodialysis, a conjugate vaccine can confer partial immunity against S. aureus bacteremia for approximately 40 weeks, after which protection wanes as antibody levels decrease.

Antibiotic resistance patterns of bacterial isolates from blood in San Francisco County, California, 1996-1999

Countywide antibiotic resistance patterns may provide additional information from that obtained from national sampling or individual hospitals. We reviewed susceptibility patterns of selected bacterial strains isolated from blood in San Francisco County from January 1996 to March 1999. We found substantial hospital-to-hospital variability in proportional resistance to antibiotics in multiple organisms. This variability was not correlated with hospital indices such as number of intensive care unit or total beds, annual admissions, or average length of stay. We also found a significant increase in methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, and proportional resistance to multiple antipseudomonal antibiotics. We describe the utility, difficulties, and limitations of countywide surveillance.

Methicillin-resistant Staphylococcus aureus sepsis associated with the transfusion of contaminated platelets: a case report

BACKGROUND

Platelet transfusion-associated sepsis is usually due to donor skin flora introduced into the unit during phlebotomy. An unusual case of a platelet component contaminated with methicillin-resistant Staphylococcus aureus (MRSA) is reported.

CASE REPORT

A 54-year-old man, terminally ill with progressive non-Hodgkin's lymphoma, developed fever and hypotension during a platelet transfusion. He was receiving multiple antibiotics, including vancomycin. Blood cultures taken soon after transfusion were negative. An aliquot taken from the platelet pool grew MRSA at a count of 1.6 x 10(8) CFUs per mL. One of the individual bags constituting the pool showed MRSA at a count of 5.1 x 10(8) CFUs per mL. The patient died soon after the platelet transfusion. This case was reported to the FDA and submitted to the BaCon Study. The identity of the isolate and its methicillin resistance were confirmed by the CDC as part of the BaCon Study protocol. The source of contamination of the implicated unit could not be established with certainty.

CONCLUSION

The emergence of antimicrobial-resistant organisms poses additional challenges for the diagnosis and treatment of transfusion-associated sepsis. Measures to prevent or intercept the transfusion of contaminated platelets should be developed.

Excessive antibiotic use for acute respiratory infections in the United States

Estimating the amount and cost of excess antibiotic use in ambulatory practice and identifying the conditions that account for most excess use are necessary to guide intervention and policy decisions. Data from the 1998 National Ambulatory Medical Care Survey, a sample survey of United States ambulatory physician practices, was used to estimate primary care office visits and antibiotic prescription rates for acute respiratory infections. Weight-averaged antibiotic costs were calculated with use of 1996 prescription marketing data and adjusted for inflation. In 1998, an estimated 76 million primary care office visits for acute respiratory infections resulted in 41 million antibiotic prescriptions. Antibiotic prescriptions in excess of the number expected to treat bacterial infections amounted to 55% (22.6 million) of all antibiotics prescribed for acute respiratory infections, at a cost of approximately $726 million. Upper respiratory tract infections (not otherwise specified), pharyngitis, and bronchitis were the conditions associated with the greatest amount of excess use. This study documents that the amount and cost of excessive antibiotic use for acute respiratory infections by primary care physicians are substantial and establishes potential target rates for antibiotic treatment of selected conditions.

Community-acquired methicillin-resistant Staphylococcus aureus colonization in healthy children attending an outpatient pediatric clinic

BACKGROUND

We previously showed that children attending an inner city pediatric emergency department were sometimes asymptomatically colonized with clindamycin-susceptible community-acquired methicillin-resistant Staphylococcus aureus (MRSA) and borderline methicillin-resistant S. aureus (BRSA) as well. We wished to ascertain whether healthy children attending an outpatient clinic were colonized with these organisms. Therefore to estimate the prevalence of community-acquired MRSA and BRSA nasal colonization in a well child population, we cultured children attending an inner city pediatric outpatient clinic.

STUDY DESIGN

This was a prospective cross-sectional study conducted from January to August, 1999, at a primary care outpatient facility at the University of Chicago. The target population was 500 healthy children < or = 16 years of age who attended this facility to receive well child care.

RESULTS

One hundred twenty-two (24.4%) children were colonized with S. aureus. Three of the 122 (2.5%) S. aureus isolates were MRSA; they came from children who lacked predisposing risk factors and were susceptible to clindamycin, gentamicin, trimethoprim-sulfamethoxazole, rifampin and ciprofloxacin. Two (1.6%) additional S. aureus isolates were BRSA; both children had predisposing risk factors for MRSA colonization. The mecA gene was present in the 3 MRSA isolates and absent in both BRSA isolates.

CONCLUSIONS

These data document that a reservoir of asymptomatic MRSA colonization exists among healthy children who lack traditional risk factors for MRSA infections.

Duration of colonization by methicillin-resistant Staphylococcus aureus after hospital discharge and risk factors for prolonged carriage

To investigate persistent carriage of methicillin-resistant Staphylococcus aureus (MRSA), we conducted a prospective 10-month study of MRSA carriage in previous carriers who were readmitted to our hospital. Four screening specimens, 2 from the skin and 2 from the nares, were obtained within 3 days after admission, in addition to diagnostic specimens requested by physicians. Of the 78 patients included in our study, 31 (40%) were persistent carriers of MRSA, with an estimated median time of 8.5 months to MRSA clearance. In the multivariate analysis, the only factor significantly associated with persistent carriage was the presence of a break in the skin at readmission (odds ratio, 4.34; P=.004); however, a trend was found for admission from a chronic-care institution (odds ratio, 3.65; P=.06). Our data confirm that prolonged carriage of MRSA can occur after hospital discharge, support routine screening for MRSA at readmission of previously MRSA-positive patients, and suggest that a particularly high index of suspicion for MRSA carriage should be maintained if these patients have a break in the skin.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains: state of affairs and tomorrow' s possibilities

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have posed a clinical threat for nearly 40 years. During these years, an array of additional technologies suited for identification of MRSA below the species level has become available. The technologies, whether they assess phenotype or genotype, provide data that can be used for elucidation of the routes of dissemination of individual MRSA types. This review summarizes the current state of affairs with respect to the quality of the various laboratory techniques and includes descriptions of novel strategies such as binary typing and multilocus sequence typing (MLST). Drawbacks of procedures will be compared, and the value of molecular typing in the elucidation of complex biological phenomena, such as epidemicity, carriage, and reduced vancomycin susceptibility, will be indicated. Means for integrated assessment of bacterial biology, epidemiology, and population structure will be discussed.

Evolving antimicrobial chemotherapy for Staphylococcus aureus infections: Our backs to the wall

Staphylococcus aureus is responsible for many nosocomial and community-acquired infections. Its evolving resistance to traditional antimicrobial chemotherapy and emerging prevalence outside of the healthcare environment are serious concerns. This review of the changing epidemiology of methicillin-resistant S. aureus, the emergence of vancomycin (glycopeptide)-resistant isolates, and the mechanisms of resistance to beta-lactams and glycopeptides provides an update for clinicians regarding effective strategies for treatment.

Current trends in community-acquired methicillin-resistant Staphylococcus aureus at a tertiary care pediatric facility

BACKGROUND

The prevalence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections increased at the University of Chicago Children's Hospital (UCCH) from 10 per 100,000 admissions from 1988 to 1990 to 259 per 100,000 admissions from 1993 to 1995. Because this increase may have represented a one time occurrence or a limited disease outbreak, we updated our previous observations at UCCH in 1998 and 1999 to see whether this trend had continued.

DESIGN

Prospective observational study.

RESULTS

Twenty-three hospitalized children had an MRSA isolate during the 1-year study period. Ten were community-acquired, equally distributed between children with predisposing risk factors and those without. The overall prevalence of community-acquired MRSA was 208 per 100,000 admissions. Seven of the 10 community-acquired MRSA isolates were susceptible to clindamycin. Skin and soft tissue infections predominated among the children with a community-acquired MRSA isolate. Pulsed field gel electrophoresis of the 10 community-acquired MRSA isolates revealed 8 distinct patterns; these data suggest that multiple clones were circulating at UCCH.

CONCLUSION

MRSA are no longer confined to children with established risk factors. The prevalence of community-acquired MRSA among children without identified risk factors is high in our institution.

Prevalence of nasal colonization with methicillin-resistant Staphylococcus aureus in selected patient populations

Methicillin-resistant Staphylococcus aureus nasal colonization was investigated in patients arriving for elective cardiovascular surgery, renal patients admitted for arteriovenous graft surgery, and patients transferred to our hospital from other institutions. Renal patients were significantly more likely to be colonized and represent a potential source of MRSA to our institution.

Methicillin-resistant Staphylococcus aureus in the community: new battlefronts, or are the battles lost?

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections worldwide. Interpretation of community MRSA trends is problematical, in that the term is ill-defined, and related data are difficult to put into context. There are four relevant battlefronts, all of interest to risk assessment and prevention. These comprise the following: the issues relating to an increasing pool of patients with MRSA discharged from hospitals into the community; MRSA spreading to patients in nursing and residential homes; and MRSA spreading from patients and healthcare workers to others in the community. There are often difficulties in determining whether the fourth issue, MRSA arising apparently de novo in the community, is in fact due to one of these other fronts. All these battlefronts are important and not yet lost. However, we must agree on definitions and design-appropriate surveillance strategies, so that we can best inform prevention and control activities to contain these emerged or emerging problems.