Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

The Comparative Risks of Bacterial Contamination between a Venturi Atomizer and a Positive Displacement Atomizer

Introduction

This laboratory study determined the incidence of internal contamination of Venturi principle atomizers and positive displacement atomizers exposed to high external concentrations of Staphylococcal aureus (Staph).

Methods

Atomizer device nozzle tips were immersed into a Staph solution and 1 ml of spray was atomized via compressed wall air (Venturi) or hydraulic pump (positive displacement). The Venturi nozzle was then wiped with 70% isopropyl alcohol while the disposable positive displacement nozzle was replaced. After 30 minutes, 1 ml of atomized fluid was collected and cultured and the process was repeated. After sixteen uses the fluid remaining in the bottles was cultured. The Venturi atomizer also was subjected to a single use trial to determine the location of device contamination.

Results

Venturi atomizers sprays grew Staph in every case (144/144), while positive displacement atomizer sprays never grew contaminants (0/144; p < 0.0001). At the end of 16 uses, 7/9 of Venturi atomizers had Staph within their medication reservoirs while none (0/9; p = 0.002) existed in the positive displacement atomizers. After a single use of the Venturi atomizer, the medication reservoir, the air lumen and the medication lumen of the nozzle were all contaminated with Staph.

Conclusions

External bacterial contamination of the atomizer nozzle tip results in internal bacterial contamination of Venturi devices in as little as one use but not of positive displacement devices. These results warrant further investigation to determine whether a risk of cross-contamination exists in a clinical setting.

Neomycin Sulfate Improves the Antimicrobial Activity of Mupirocin-Based Antibacterial Ointments

In the midst of the current antimicrobial pipeline void, alternative approaches are needed to reduce the incidence of infection and decrease reliance on last-resort antibiotics for the therapeutic intervention of bacterial pathogens. In that regard, mupirocin ointment-based decolonization and wound maintenance practices have proven effective in reducing Staphylococcus aureus transmission and mitigating invasive disease. However, the emergence of mupirocin-resistant strains has compromised the agent's efficacy, necessitating new strategies for the prevention of staphylococcal infections. Herein, we set out to improve the performance of mupirocin-based ointments. A screen of a Food and Drug Administration (FDA)-approved drug library revealed that the antibiotic neomycin sulfate potentiates the antimicrobial activity of mupirocin, whereas other library antibiotics did not. Preliminary mechanism of action studies indicate that neomycin's potentiating activity may be mediated by inhibition of the organism's RNase P function, an enzyme that is believed to participate in the tRNA processing pathway immediately upstream of the primary target of mupirocin. The improved antimicrobial activity of neomycin and mupirocin was maintained in ointment formulations and reduced S. aureus bacterial burden in murine models of nasal colonization and wound site infections. Combination therapy improved upon the effects of either agent alone and was effective in the treatment of contemporary methicillin-susceptible, methicillin-resistant, and high-level mupirocin-resistant S. aureus strains. From these perspectives, combination mupirocin-and-neomycin ointments appear to be superior to that of mupirocin alone and warrant further development.

Polymerase chain reaction-based active surveillance of MRSA in emergency department patients

Conventional culture methods to detect methicillin-resistant Staphylococcus aureus (MRSA) take a few days, and their sensitivity and usefulness also need to be improved. In this study, active screening was performed using the polymerase chain reaction (PCR) for colonization with MRSA on admission and follow-up surveillance after admission to an emergency department between June 2012 and August 2012, and the backgrounds of PCR and/or culture-method-positive patients were compared. Among 95 patients, 15 (15.8%) patients were positive for MRSA on PCR and/or culture; 6.3% (6/95) of patients were positive on admission, and 9.5% (9/95) became positive during the stay after admission. The major primary diagnoses in MRSA-positive patients were trauma and cerebrovascular diseases. Nine (60%) of 15 patients were MRSA-positive on both PCR and culture, compared with three (20%) of 15 who were PCR-positive but culture-negative. The other three (20%) of 15 patients were PCR-negative but culture-positive. Furthermore, there was a tendency for younger age and shorter stay to be associated with PCR-positive but culture-negative results. These findings suggest that active surveillance with PCR may be highly sensitive and useful for the early diagnosis of MRSA colonization to prevent nosocomial transmission from the emergency department to the regular inpatient wards of the hospital.

The prevalence and significance of methicillin-resistant Staphylococcus aureus colonization at admission in the general ICU Setting: a meta-analysis of published studies

OBJECTIVE

To estimate the prevalence and significance of nasal methicillin-resistant Staphylococcus aureus colonization in the ICU and its predictive value for development of methicillin-resistant S. aureus infection.

DATA SOURCES

MEDLINE and EMBASE and reference lists of all eligible articles.

STUDY SELECTION

Studies providing raw data on nasal methicillin-resistant S. aureus colonization at ICU admission, published up to February 2013. Analyses were restricted in the general ICU setting. Medical, surgical, and interdisciplinary ICUs were eligible. ICU studies referring solely on highly specialized ICUs populations and reports on methicillin-resistant S. aureus outbreaks were excluded.

DATA EXTRACTION

Two authors independently assessed study eligibility and extrapolated data in a blinded fashion. The two outcomes of interest were the prevalence estimate of methicillin-resistant S. aureus nasal colonization at admission in the ICU and the sensitivity/specificity of colonization in predicting methicillin-resistant S. aureus-associated infections.

DATA SYNTHESIS

Meta-analysis, using a random-effect model, and meta-regression were performed. Pooled data extracted from 63,740 evaluable ICU patients provided an estimated prevalence of methicillin-resistant S. aureus nasal colonization at admission of 7.0% (95% CI, 5.8-8.3). Prevalence was higher for North American studies (8.9%; 95% CI, 7.1-10.7) and for patients screened using polymerase chain reaction (14.0%; 95% CI, 9.6-19). A significant per year increase in methicillin-resistant S. aureus colonization was also noted. In 17,738 evaluable patients, methicillin-resistant S. aureus infections (4.1%; 95% CI, 2.0-6.8) developed in 589 patients. The relative risk for colonized patients was 8.33 (95% CI, 3.61-19.20). Methicillin-resistant S. aureus nasal carriage had a high specificity (0.96; 95% CI, 0.90-0.98) but low sensitivity (0.32; 95% CI, 0.20-0.48) to predict methicillin-resistant S. aureus-associated infections, with corresponding positive and negative predictive values at 0.25 (95% CI, 0.11-0.39) and 0.97 (95% CI, 0.83-1.00), respectively.

CONCLUSIONS

Among ICU patients, 5.8-8.3% of patients are colonized by methicillin-resistant S. aureus at admission, with a significant upward trend. Methicillin-resistant S. aureus colonization is associated with a more than eight-fold increase in the risk of associated infections during ICU stay, and methicillin-resistant S. aureus infection develops in one fourth of patients who are colonized with methicillin-resistant S. aureus at admission to the ICU.

The role of broth enrichment in Staphylococcus aureus cultivation and transmission from the throat to newborn infants: results from the Swedish hygiene intervention and transmission of S. aureus study

Staphylococcus aureus is detected by direct plating, whereas incubation in enrichment broth prior to plating to increase the proportion of positive samples has not been fully evaluated. S. aureus throat colonization has been suggested to be more common than colonization of the anterior nares, but no data are available on the transmission of S. aureus from the throat. Swab samples were collected from the anterior nares and umbilicus from newborn infants (n = 168), anterior nares, throat, skin lesions, and vagina from parents (n = 332), and anterior nares, throat, and skin lesions from healthcare workers (n = 231) at three maternity wards. spa typing was used to elucidate the transmission routes of S. aureus. The use of enrichment broth prior to plating increased the proportion of positive samples by 46 %. The prevalence of S. aureus colonization in adults was 58 %. Throat colonization (47 %) was significantly more common than colonization in any of the other screened sites (p < 0.001). In total, 103 out of 168 (61 %) newborn infants were colonized during their hospital stay. Overall, 124 S. aureus transmissions to newborn infants were detected. Although we detected an increased risk of transmission from the nares as compared to the throat, with an odds ratio of 4.8 [95 % confidence interval (CI) 1.8–12.7], we detected a transmission rate of 7 % from the throat. We show that S. aureus throat colonization is more common than colonization in any of the other sites among the parents and staff. We also show evidence of transmission from the throat.

Prevalence of methicillin-resistant Staphylococcus aureus based on culture and PCR in inpatients at a tertiary care center in Tokyo, Japan

We investigated active screening for colonization with methicillin-resistant Staphylococcus aureus (MRSA) on admission and weekly follow-up surveillance after admission to a tertiary care center (TCC) between June 2007 and 31 December 2007. Eleven percent (30/267) of patients were found to be positive for MRSA by polymerase chain reaction (PCR) and/or culture on admission; 5% (12/267) became positive during the TCC stay. The major primary diagnoses in MRSA-positive patients were pneumonia and cerebrovascular diseases. Twenty-two (52%) of 42 patients were found to be MRSA positive by both PCR and culture, compared with 19 (45%) of 42 who were PCR positive and culture negative. These findings suggest that active surveillance with PCR is highly sensitive and useful for the detection of MRSA colonization. To our knowledge, this is the first report of active surveillance of MRSA by PCR and bacterial culture in critically ill inpatients in Japan.

Structural and biochemical characterization of Staphylococcus aureus clumping factor B/ligand interactions

Clumping factor B (ClfB) from Staphylococcus aureus is a bifunctional protein that binds to human cytokeratin 10 (K10) and fibrinogen (Fg). ClfB has been implicated in S. aureus colonization of nasal epithelium and is therefore a key virulence factor. People colonized with S. aureus are at an increased risk for invasive staphylococcal disease. In this study, we have determined the crystal structures of the ligand-binding region of ClfB in an apo-form and in complex with human K10 and Fg α-chain-derived peptides, respectively. We have determined the structures of MSCRAMM binding to two ligands with different sequences in the same site showing the versatile nature of the ligand recognition mode of microbial surface components recognizing adhesive matrix molecules. Both ligands bind ClfB by parallel β-sheet complementation as observed for the clumping factor A·γ-chain peptide complex. The β-sheet complementation is shorter in the ClfB·Fg α-chain peptide complex. The structures show that several residues in ClfB are important for binding to both ligands, whereas others only make contact with one of the ligands. A common motif GSSGXG found in both ligands is part of the ClfB-binding site. This motif is found in many human proteins thus raising the possibility that ClfB recognizes additional ligands.

[Methicillin-resistant Staphylococcus (MRSA, MRSE) in the nose, paranasal sinuses and sputum]

Detection of Staphylococcus in humans can be of extremely varying importance ranging from commensal to pathogens of fatal infections. MRSAs in particular are iatrogenic and nosocomial infective pathogens, which are a threat to the success of medical treatment. In this review the causes for occurrence and the spread of MRSA are presented and the heterogeneity of MRSA due to the presence of additional resistant pathogens (VISA, VRSA) and pathogenetic forms (cMRSA) will be discussed. The current diagnostic and therapeutic procedures in various situations for MRSA in the nasal and paranasal sinuses and sputum will be discussed exemplified by an actual case. The danger of colonization by MRSA will be discussed with reference to the literature as nasal colonization can be accompanied by a greatly increased risk of an invasive infection and transmission of the pathogen to other persons.

Acquisition and cross-transmission of Staphylococcus aureus in European intensive care units

OBJECTIVE

To study the acquisition and cross-transmission of Staphylococcus aureus in different intensive care units (ICUs).

METHODS

We performed a multicenter cohort study. Six ICUs in 6 countries participated. During a 3-month period at each ICU, all patients had nasal and perineal swab specimens obtained at ICU admission and during their stay. All S. aureus isolates that were collected were genotyped by spa typing and multilocus variable-number tandem-repeat analysis typing for cross-transmission analysis. A total of 629 patients were admitted to ICUs, and 224 of these patients were found to be colonized with S. aureus at least once during ICU stay (22% were found to be colonized with methicillin-resistant S. aureus [MRSA]). A total of 316 patients who had test results negative for S. aureus at ICU admission and had at least 1 follow-up swab sample obtained for culture were eligible for acquisition analysis.

RESULTS

A total of 45 patients acquired S. aureus during ICU stay (31 acquired methicillin-susceptible S. aureus [MSSA], and 14 acquired MRSA). Several factors that were believed to affect the rate of acquisition of S. aureus were analyzed in univariate and multivariate analyses, including the amount of hand disinfectant used, colonization pressure, number of beds per nurse, antibiotic use, length of stay, and ICU setting (private room versus open ICU treatment). Greater colonization pressure and a greater number of beds per nurse correlated with a higher rate of acquisition for both MSSA and MRSA. The type of ICU setting was related to MRSA acquisition only, and the amount of hand disinfectant used was related to MSSA acquisition only. In 18 (40%) of the cases of S. aureus acquisition, cross-transmission from another patient was possible.

CONCLUSIONS

Colonization pressure, the number of beds per nurse, and the treatment of all patients in private rooms correlated with the number of S. aureus acquisitions on an ICU. The amount of hand disinfectant used was correlated with the number of cases of MSSA acquisition but not with the number of cases of MRSA acquisition. The number of cases of patient-to-patient cross-transmission was comparable for MSSA and MRSA.

Screening for multidrug-resistant bacteria as a predictive test for subsequent onset of nosocomial infection

OBJECTIVE

To investigate whether carriage of multidrug-resistant bacteria is a risk factor for nosocomial infection and whether detection of carriage is predictive of subsequent onset of nosocomial infection.

METHODS

In this observational cohort (study period, June 1998 through October 2002), nasal and rectal swab specimens from 412 consecutive patients admitted to the intensive care unit were tested for carriage of multidrug-resistant bacteria. Concomitantly, the bacteria responsible for any subsequent nosocomial infection, the date of infection, and some of the known clinical risk factors for nosocomial infection were noted. These factors were adjusted for potential confounders, using a Cox model stratified on the propensity score of multidrug-resistant bacteria carriage. The diagnostic characteristics of a carriage test, including the positive and negative diagnostic likelihood ratios, were calculated for all strata of the propensity score.

RESULTS

Forty-two patients were carrying multidrug-resistant bacteria. Nosocomial infection occurred in 95 patients, of whom 16 (38%) were carriers, and 79 (83%) were noncarriers (P=.01). After adjustment for potential confounders, statistical analysis revealed that carriage remained a risk factor for nosocomial infection (relative risk, 2.08 [95% confidence interval {CI}, 1.13-3.81]). Receipt of antibiotic treatment at the time of intensive care unit admission was found to be protective against nosocomial infection. A positive result of test for detection of carriage seemed to be an efficient predictor of subsequent nosocomial infection (positive diagnostic likelihood ratio, 2.05 [95% CI, 1.15-3.66]), although a negative test result was not a predictor of subsequent nosocomial infection (negative likelihood ratio, 0.91 [95% CI, 0.73-1.11]).

CONCLUSION

Carriage proved to be a risk factor for subsequent nosocomial infection. However, the carriage test was useful as a predictive tool only for patients with a positive test result.

Methicillin-resistant Staphylococcus aureus in elderly care facilities

Among multidrug-resistant bacteria, methicillin-resistant Staphylococcus aureus (MRSA) is of immediate concern, given its potential for pathogenicity and widespread presence in geriatric hospitals. Epidemiological surveys indicate that rates of MRSA cross-transmission are increasing in elderly care facilities. MRSA carriage is far more frequent than MRSA-positive clinical specimens in this setting, and the consequences of these epidemics in terms of morbidity, remain limited within these facilities. However, given that patients are continually transferred between long-term and acute-care facilities, it is reasonable to consider these units together with all other care units and to measure the effect of MRSA on a regional healthcare network, rather than on the scale of a given ward or hospital. With regard to the worldwide increase in morbidity associated with MRSA, the emergence of a community-based disease linked to these strains and the emergence of glycopeptide-resistant strains, the application of a voluntary strategy including screening, isolation and eventually, topical decolonization in elderly care facilities, appears to be an urgent matter of priority, even if this strategy will be expensive.

Molecular evidence that nasal carriage of Staphylococcus aureus plays a role in respiratory tract infections of critically ill patients

The relationship between nasal Staphylococcus aureus carriage and lower respiratory tract infections was studied in 16 critically ill patients. S. aureus strains from nasal and bronchial samples were characterized by pulsed-field gel electrophoresis. In all but one case, nasal and bronchial strains were genetically identical in the same patients.

[Methicillin-resistant Staphylococcus aureus (MRSA) in rehabilitation and chronic-care-facilities: what is the best strategy?]

BACKGROUND

The risk associated with methicillin-resistant Staphylococcus aureus (MRSA) has been decreasing for several years in intensive care departments, but is now increasing in rehabilitation and chronic-care-facilities (R-CCF). The aim of this study was to use published data and our own experience to discuss the roles of screening for MRSA carriers, the type of isolation to be implemented and the efficiency of chemical decontamination.

DISCUSSION

Screening identifies over 90% of patients colonized with MRSA upon admission to R-CCF versus only 50% for intensive care units. Only totally dependent patients acquire MRSA. Thus, strict geographical isolation, as opposed to "social reinsertion", is clearly of no value. However, this should not lead to the abandoning of isolation, which remains essential during the administration of care. The use of chemicals to decolonize the nose and healthy skin appeared to be of some value and the application of this procedure could make technical isolation unnecessary in a non-negligible proportion of cases.

SUMMARY

Given the increase in morbidity associated with MRSA observed in numerous hospitals, the emergence of a community-acquired disease associated with these strains and the evolution of glycopeptide-resistant strains, the voluntary application of a strategy combining screening, technical isolation and chemical decolonization in R-CCF appears to be an urgent matter of priority.

Isolation measures in the hospital management of methicillin resistant Staphylococcus aureus (MRSA): systematic review of the literature

OBJECTIVE

To evaluate the evidence for the effectiveness of isolation measures in reducing the incidence of methicillin resistant Staphylococcus aureus (MRSA) colonisation and infection in hospital inpatients.

DESIGN

Systematic review of published articles.

DATA SOURCES

Medline, Embase, CINAHL, Cochrane Library, System for Information on Grey Literature in Europe (SIGLE), and citation lists (1966-2000).

REVIEW METHODS

Articles reporting MRSA related outcomes and describing an isolation policy were selected. No quality restrictions were imposed on studies using isolation wards or nurse cohorting. Other studies were included if they were prospective or employed planned comparisons of retrospective data.

RESULTS

46 studies were accepted; 18 used isolation wards, nine used nurse cohorting, and 19 used other isolation policies. Most were interrupted time series, with few planned formal prospective studies. All but one reported multiple interventions. Consideration of potential confounders, measures to prevent bias, and appropriate statistical analysis were mostly lacking. No conclusions could be drawn in a third of studies. Most others provided evidence consistent with a reduction of MRSA acquisition. Six long interrupted time series provided the strongest evidence. Four of these provided evidence that intensive control measures including patient isolation were effective in controlling MRSA. In two others, isolation wards failed to prevent endemic MRSA.

CONCLUSION

Major methodological weaknesses and inadequate reporting in published research mean that many plausible alternative explanations for reductions in MRSA acquisition associated with interventions cannot be excluded. No well designed studies exist that allow the role of isolation measures alone to be assessed. None the less, there is evidence that concerted efforts that include isolation can reduce MRSA even in endemic settings. Current isolation measures recommended in national guidelines should continue to be applied until further research establishes otherwise.

Control of endemic MRSA-what is the evidence? A personal view

Although there is extensive literature on the control of MRSA, when that concerning epidemics is excluded, only a limited amount remains regarding the control of endemic MRSA. Several guidelines have been recently published recommending stringent control measures, which are often suggested based on their success in controlling MRSA outbreaks in hospitals with few MRSA or in containing MRSA cases introduced into a hospital with no MRSA. In these settings, multiple measures are usually introduced with apparently successful results. However, results may not be generalizable to other settings and we do not know the minimum effective measures required for MRSA containment. This paper aims critically to review the literature to determine whether evidence exists for the value of the infection control measures that are widely recommended in the endemic setting. Much of this literature is based on observational studies, with few randomized, controlled trials having been conducted. More well-designed studies are required before many of the principles on which we build infection control programmes can be regarded as evidence based.

Surveillance régionale de l'évolution de Staphylococcus aureus résistant à la méticilline (SARM) : quels résultats pour quels enseignements ?

OBJECTIVE

The aim of this study was to describe the evolution of MRSA within hospitals located in Franche-Comté from 1999 to 2003 and to establish the MRSA risk according to the type of hospitalization.

METHODS

Surveillance of multidrug resistant bacteria was carried out according to the French national guidelines for the prevention of nosocomial infections.

RESULTS

The global incidence of MRSA colonized/infected patients (screened by clinical samples) per 1000 patient-days had decreased from 0.73 in 1999 to 0.58 in 2003 (P < 0.004). However, analyzing the results according to each type of hospitalization revealed great heterogeneity. In 2003, the increase of MRSA incidence in short-term public hospitalization was indeed alarming whereas MRSA risk had regularly decreased in the other hospitalization types (rehabilitation and long-term care-facilities) since 1999. The number of potentially serious colonizations/infections caused by MRSA (bacteremia, deep infections, and pulmonary infections) accounted for 12.8% of all colonizations/infections.

CONCLUSION

MRSA, in spite of improved prevention in our region, remains responsible for numerous infections.

Methicillin-resistant Staphylococcus aureus (MRSA) in rehabilitation and chronic-care-facilities: what is the best strategy?

Background

The risk associated with methicillin-resistant Staphylococcus aureus (MRSA) has been decreasing for several years in intensive care departments, but is now increasing in rehabilitation and chronic-care-facilities (R-CCF). The aim of this study was to use published data and our own experience to discuss the roles of screening for MRSA carriers, the type of isolation to be implemented and the efficiency of chemical decolonization.

Discussion

Screening identifies over 90% of patients colonised with MRSA upon admission to R-CCF versus only 50% for intensive care units. Only totally dependent patients acquire MRSA. Thus, strict geographical isolation, as opposed to "social reinsertion", is clearly of no value. However, this should not lead to the abandoning of isolation, which remains essential during the administration of care. The use of chemicals to decolonize the nose and healthy skin appeared to be of some value and the application of this procedure could make technical isolation unnecessary in a non-negligible proportion of cases.

Summary

Given the increase in morbidity associated with MRSA observed in numerous hospitals, the emergence of a community-acquired disease associated with these strains and the evolution of glycopeptide-resistant strains, the voluntary application of a strategy combining screening, technical isolation and chemical decolonization in R-CCF appears to be an urgent matter of priority.

Enterocolitis caused by methicillin-resistant Staphylococcus aureus: molecular characterization of respiratory and digestive tract isolates

We investigated the mechanism of outbreak of enterocolitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Five epidemiological markers [coagulase type, enterotoxin type, toxic shock syndrome toxin-1 (TSST-1) production, beta-lactamase production and pulsed-field gel electrophoresis (PFGE)] of 45 strains of MRSA isolated simultaneously from the respiratory tract (nasal cavity and/or pharynx and/or sputum) and stool (plus one sample of gastric juice) in 13 patients (8 males and 5 females, mean age, 77.1 years) were compared retrospectively. Forty-four of the 45 isolates of MRSA were positive for enterotoxin C and TSST-1 production, and the remaining isolate was positive for enterotoxin A and negative for TSST-1 production. All isolates were coagulase type II, and 27 showed beta-lactamase production. The patterns of coagulase type, enterotoxin type, TSST-1 and beta-lactamase production of MRSA isolated from the respiratory tract were similar to those of MRSA isolated from the intestine in 12 of 13 patients. Molecular typing by PFGE demonstrated that the pattern of respiratory tract isolates was identical to those of stool isolates in 9 (69.2%), similar in 3 (23.1 %), and different in 1 (7.7%). The data suggested that enterocolitis might be caused by the MRSA colonized in the respiratory tract and incorporated into the digestive tracts. Therefore, we propose that early eradication of MRSA in the respiratory tract is important for protection of patients against the development of enterocolitis, particularly in susceptible patients, e.g., immunocompromised or pre-operated patients with digestive diseases, especially malignant disease.

[The importance of detecting methicillin-resistant Staphylococcus aureus in an intensive care setting]

In recent years, the fight against nosocomial infections has constituted a major public health challenge. Measures aimed at preventing the spread of multiresistant bacteria (MRB) through carriage combine the more or less systematic detection of carriers and precautions concerning isolation. In the light of published data, elements for the evaluation of a cost-efficiency ratio for measures concerning detection and isolation in intensive care are presented. The high levels of methicillin-resistant Staphylococcus aureus (MRSA) observed in hospitals constitute the principal target. Although isolation precautions appear to be effective, the value of detecting MRSA remains a subject of debate. Such detection has several objectives: the identification of carriers, assistance in the implementation of isolation precautions, the eradication of carriage and the evaluation of strategy. These different objectives are discussed.

Simultaneous detection of the mecA and ileS-2 genes in coagulase-negative staphylococci isolated from Brazilian hospitals by multiplex PCR

Coagulase-negative Staphylococcus spp. (CNS) has been associated with primary bloodstream infections and implanted medical devices. Its importance is increasing due to the acquisition of resistance to oxacillin (Oxa) and, recently, resistance to mupirocin (Mup). Mupirocin, a topical antimicrobial, has been used in the prevention of staphylococci catheter colonization. Susceptibility to Oxa and Mup was analyzed by different testing methods in clinical CNS isolates. Among 112 CNS strains, 69 (61.6%) were Oxa(R) by the disk diffusion (DD) method and 72 (64.2%) grew on the oxacillin agar screen plate. S. epidermidis and S. haemolyticus presented high rates of oxacillin resistance, 75.4% and 96.1%, respectively. Twenty four (21.4%) strains were Mup(R) by the DD test and 21 of them (87.5%) were identified as S. epidermidis. The detection of the mecA and ileS-2 genes, determined by multiplex-PCR, showed that 72 (64.2%) CNS strains possessed the mecA gene, while 16 (14.3%) possessed the ileS-2 gene. Fifteen of these strains presented the two resistance genes simultaneously. The isolates containing the ileS-2 gene presented a minimum inhibitory concentration (MIC) >1024 microg/mL in the E-test, while low-level mupirocin resistance (MICs of 12-16 microg/mL) was observed in those strains without ileS-2. The resistances to high and low levels of mupirocin could not be distinguished when the DD test was used. The analysis of the Mup(R) S. epidermidis strains by Pulsed Field Gel Electrophoresis showed that 17 (80.9%) strains belonged to one of two patterns (A and B), which have been shown to be prevalent in hospitals in Rio de Janeiro. This report showed that the PCR method for detection of oxacillin and mupirocin resistance in CNS is necessary to determine accurate rates of these resistance, and will can help in the staphylococcal infections prevention and control policies in Brazil.

Low concentrations of mupirocin in the pharynx following intranasal application may contribute to mupirocin resistance in methicillin-resistant Staphylococcus aureus

We describe a patient with methicillin-resistant Staphylococcus aureus (MRSA) colonizing the pharynx. The MIC of mupirocin was 0.25 microg/ml before treatment and increased after treatment to 8 microg/ml. Using pulsed-field gel electrophoresis, we confirmed that the genotypes of MRSA that colonized the pharynx before and after the use of mupirocin were identical. We measured the delivery of mupirocin to the pharynx in three normal volunteers and two patients. Low concentrations of mupirocin were present in the pharynx in all cases 10 min to 3 days after intranasal application. Our data suggested that low concentrations of the drug in the pharynx after intranasal application of mupirocin ointment might explain the selection of mupirocin resistance in MRSA.

MRSA patients: proven methods to treat colonization and infection

Methicillin-resistant Staphylococcus aureus (MRSA) infections continue to cause serious nosocomial infections in many hospitals. Measures used to control the spread of these infections include ongoing laboratory-based surveillance, placing colonized and infected patients in isolation, use of barrier precautions and handwashing and hand antisepsis. Culturing hospitalized patients at high risk of acquiring MRSA can facilitate detection and isolation of colonized patients. Eradicating MRSA nasal colonization among affected patients and healthcare personnel has also been as a control measure, with variable success. Eradicating MRSA nasal carriage from epidemiologically-implicated healthcare workers has been used on a number of occasions to control outbreaks. Attempts to eradicate MRSA colonization among affected patients has proven difficult. Of more than 40 different decolonization regimens that have been tested during the last 60 years, topical intranasal application of mupirocin ointment has proven to be the most effective. However, intranasal application of mupirocin has limited effectiveness in eradicating colonization in patients who carry the organism at multiple body sites. Furthermore, because decolonization of patients has virtually always been used in combination with other control measures, its efficacy has been difficult to determine. Because MRSA is transmitted primarily on the hands of healthcare workers, greater emphasis should be given to improving hand hygiene practices among health personnel. For patients infected with MRSA, vancomycin remains a drug of choice.

Emergence and spread of low-level mupirocin resistance in methicillin-resistant Staphylococcus aureus isolated from a community hospital in Japan

The objective of this study was to investigate the state of mupirocin resistance in methicillin-resistant Staphylococcus aureus (MRSA) in a community hospital in Japan. Ninety strains of MRSA were isolated from the respiratory tract of 56 patients (group I, Jun 1990-Aug 1996) before introduction of mupirocin in Japan, which were compared with 168 strains from 48 patients (group II, Sept 1996-Jan 1998) and 146 strains from 85 patients (group III, Feb 1999-Dec 1999) isolated after introduction of mupirocin. Comparisons were made by determining the minimum inhibitory concentrations (MIC) against nine antibiotics. Fifty-five MRSA isolates from 27 patients [13 (27.1%) of 48 in group II and 14 (16.5%) of 85 in group III] after introduction of mupirocin showed low-level resistance to mupirocin (MIC, 6.25 to 50 microg/ml) but the remaining isolates were sensitive to mupirocin (MIC < or =3.13 microg/ml). Most patients colonized with low-level mupirocin-resistant MRSA were elderly (> or =65 years of age), on total parenteral nutrition or nasal feeding and had other underlying diseases. The proportion of patients colonized with low-level mupirocin-resistant MRSA following repeated use of mupirocin was higher in patients of group II than those of group III. Molecular typing by pulsed-field gel electrophoresis (PFGE) demonstrated that the pattern of 13 MRSA isolates from 13 patients of group II consisted of three patterns (A, B, C) with predominance of pattern A, while the pattern of 13 MRSA isolates from 13 patients of group III consisted of three patterns (A, C, D) with predominance of patterns A and D. Our results indicated that resistance of MRSA to mupirocin remains at a low level at present in Japan. However, we should be aware of the possible emergence of MRSA highly resistant to mupirocin in the future.

Infection control measures to limit antimicrobial resistance

Increasing antimicrobial resistance has resulted in a rapidly decreasing array of therapeutic options for infections in the critical care setting. Reports of reduced susceptibility to vancomycin in Staphylococcus aureus raise the possibility of patients being infected with a virulent pathogen for which most antibiotics are ineffective. Infection control methods to contain resistance, exclusive of antimicrobial restrictions, focus on surveillance to identify carriers of resistant organisms, prevention of nosocomial infections, adequate hand hygiene, isolation of patients who harbor resistant organisms, and the use of barrier techniques such as gowns and gloves. Surveillance using clinical isolates alone is inadequate for the identification of the majority of patients who carry resistant organisms. However, it is unclear what intensity of surveillance is needed to control the spread of these organisms in the intensive care unit in nonoutbreak situations. Attempts at eradicating carriage are often unsuccessful when there is extranasal colonization with methicillin-resistant S. aureus. Transmission of resistant organisms is primarily the result of transient contamination of healthcare workers' hands. Adequate handwashing, isolation of carriers, and barrier techniques are all necessary for containing resistance within the intensive care unit, however, compliance with these measures can be compromised by high staff turnover and heavy workload.

Molecular analysis of methicillin-resistant Staphylococcus aureus as a causative agent of bronchopulmonary infection: relation to colonization in the upper respiratory tract

Using five diagnostic markers, we compared the types of 72 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated simultaneously from the nasal cavity, pharynx, and sputum from 24 patients. Almost identical MRSA types had colonized the nasal cavity and sputum from the same patient for 21 (88%) of the patients. We speculate that most MRSA organisms isolated in sputum are derived from the nasal cavity, while a few are derived from the pharynx.

Methicillin-resistant Staphylococcus aureus as a causative agent of postoperative intra-abdominal infection: relation to nasal colonization

In the surgical intensive care unit of a university hospital, we investigated the frequency of and the risk factors for acquisition of methicillin-resistant Staphylococcus aureus (MRSA) during postoperative intra-abdominal infection (pIAI). We conducted a prospective MRSA nasal screening and case evaluation for 17 months among 73 consecutive patients with having pIAI. MRSA pIAI was diagnosed when MRSA was obtained from culture of intraperitoneal fluids. The identity of nasal and peritoneal MRSA strains was assessed by genomic analysis. Twelve patients had MRSA pIAI, representing 21% of all MRSA infections acquired by the 73 patients. An organ system failure score of >/=1 and MRSA nasal carriage prior to pIAI were the independent risk factors for acquisition of MRSA pIAI. Patients with MRSA pIAI had a longer intensive care unit stay and more reoperations than did those free of MRSA pIAI. We conclude that MRSA may be a causative pathogen in pIAI and may be related to nasal colonization.

Staphylococcus aureus nasal carriage in 104 cirrhotic and control patients. A prospective study

BACKGROUND/AIMS

Bacterial infections, specially Staphylococcus aureus (S. aureus) septicemia, remain a leading cause of death following liver transplantation. It has been demonstrated that nasal carriage of S. aureus is associated with invasive infections in patients undergoing hemodialysis and could be decreased by use of antibiotic nasal ointment. However, in cirrhotic patients, the frequency of nasal carriage is unknown. The aims of this study were to determine the prevalence of S. aureus nasal carriage in cirrhotic patients and to assess nosocomial contamination.

METHODS

One hundred and four patients were included in a prospective study, 52 cirrhotic and 52 control (hospitalized patients without cirrhosis or disease which might increase the rate of nasal carriage of S. aureus). On admission and after a few days of hospitalization, nasal specimens from each anterior naris were obtained for culture. S. aureus was identified by the gram strain, positive catalase and coagulase reactions; antibiotic susceptibility was determined using a disk-diffusion test.

RESULTS

Both groups were similar with regard to age and sex. The prevalence of nasal colonization on hospital admission was 56% in cirrhotic patients and 13% in control patients (p = 0.001). After an average of 4 days, 42% of cirrhotics and 8% of control patients were colonized (p = 0.001), without any nosocomial contamination. Three strains out of 29 were oxacillin-resistant in cirrhotic patients, and none in controls (p>0.05). There was no statistical difference in carriage rate according to sex, age, cause of cirrhosis and Child-Pugh score. Previous hospitalization (OR, 6.3; 95% CI, 2.3 to 19.9; p = 0.0006) and cirrhosis (OR, 4.4; 95% CI, 1.5 to 13.4; p = 0.0048) were independent predictors of colonization.

CONCLUSION

Cirrhotic patients had a higher S. aureus nasal carriage rate than control subjects. Previous hospitalization and cirrhosis diagnosis were correlated to nasal colonization. Further studies are necessary to determine if nasal decontamination could reduce S. aureus infections after liver transplantation.

Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.

Sternal wound infection after heart operations in pediatric patients associated with nasal carriage of Staphylococcus aureus

A cluster of six pediatric cases of deep-seated Staphylococcus aureus infection after heart operations prompted us to perform molecular typing of the S. aureus isolates by pulsed-field gel electrophoresis. This revealed the presence of genotypically distinct isolates in four of the six patients. Isolates of two patients were genotypically identical. All patients carried S. aureus in the anterior nares. In each patient, the banding pattern of deoxyribonucleic acid in these isolates was indistinguishable from that in strains isolated from blood or wound cultures. Molecular typing with pulsed-field gel electrophoresis ruled out nosocomial transmission of S. aureus between four patients; at the same time, it provided evidence for an association between nasal colonization and postoperative wound infection. Epidemiologic investigation of potential links between two patients with identical isolates did not provide any evidence for nosocomial transmission of S. aureus between these patients. Because nasal colonization with S. aureus may be a risk factor for surgical wound infection in pediatric patients undergoing heart operations, preoperative decolonization appears to be warranted.