Molecular epidemiology of antimicrobial resistant microorganisms in the 21th century: a review of the literature

Healthcare-associated infections (HAIs) are the most frequent and severe complication acquired in healthcare settings with high impact in terms of morbidity, mortality and costs. Many bacteria could be implicated in these infections, but, expecially multidrug resistance bacteria could play an important role. Many microbial typing technologies have been developed until to the the bacterial whole-genome sequencing and the choice of a molecular typing method therefore will depend on the skill level and resources of the laboratory and the aim and scale of the investigation. In several studies the molecular investigation of pathogens involved in HAIs was performed with many microorganisms identified as causative agents such as Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Clostridium difficile, Acinetobacter spp., Enterobacter spp., Enterococcus spp., Staphylococcus aureus and several more minor species. Here, we will describe the most and least frequently reported clonal complex, sequence types and ribotypes with their worldwide geographic distribution for the most important species involved in HAIs.

Staphylococcus aureus carriage in older populations in community residential care homes: Prevalence and molecular characterization of MRSA isolates

INTRODUCTION

The epidemiology of S. aureus depends on conditions in specific populations. Few studies of S. aureus colonization in the older population have been performed in Spain. The aim of this study was to determine the prevalence of methicillin-resistant S. aureus (MRSA) colonization and its molecular epidemiological characteristics in an institutionalized population in community residential care homes in Cadiz, Spain.

METHODS

A cross-sectional epidemiological study was conducted in three residential care homes for older people. Axilla and nostril samples were tested. Identification of S. aureus and antimicrobial susceptibility testing were by MALDI-TOF and MicroScan panels. MRSA strains were subjected to SCCmec typing, multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). The presence of Panton-Valentine leukocidin (PVL) genes was determined by PCR in all S. aureus strains.

RESULTS

A total of 293 residents were included. Fifty-one residents (17.4%) were colonized with methicillin-sensitive S. aureus (MSSA) and 11 (3.8%) with MRSA. Resistance to at least two aminoglycosides was observed in 25.4% of MSSA and 90.9% and of MRSA isolates, and resistance to levofloxacin in 80.3% of MSSA and 100% of MRSA isolates. SCCmecIV was detected in all isolates and all except one (ST-125) were ST-8. None of the S. aureus isolates were positive for PVL.

CONCLUSIONS

A low rate of S. aureus carriage was detected and the prevalence of MRSA was very low. ST8-MRSA-IVc was the dominant clone, and only one strain belonged to ST125-MRSA-IVc. We found MRSA transmission within the residential care homes and a very high rate of quinolone resistance in MSSA and MRSA.

Vancomycin heteroresistant community associated methicillin-resistant Staphylococcus aureus ST72-SCCmecIVa strain colonizing the nostrils of a five-year-old Spanish girl

BACKGROUND AND OBJECTIVES

During a community methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization study, an MRSA strain with vancomycin hetero-resistance (h-VISA) was isolated from a five year-old girl with tetralogy of Fallot without previous exposure to vancomycin. An extended nasal colonization study was performed on all her close relatives.

RESULTS

Only the patient and her sister were colonized by an h-VISA MRSA strain (clone USA 700, ST72, t148, agr 1 and SCCmec IVa). Mupirocin decolonisation was effective in the elder sister. A new nasal decolonisation in the younger girl using fusidic acid was also successful. However, after decolonisation both sisters were colonized by a methicillin-susceptible S. aureus (ST30, t012 and agr 3) previously isolated from their mother's nostrils.

CONCLUSION

As S. aureus have a great capacity to spread among people in close contact, knowledge of a patients' colonization status, tracing contacts, and a correct management are critical issues for the successful containment of multiresistant staphylococci.

An economic evaluation of two interventions for the prevention of post-surgical infections in cardiac surgery

OBJECTIVE

To conduct a cost-effectiveness analysis that compares two prophylactic protocols for treating post-surgical infections in cardiac surgery.

METHODS

A cost effectiveness analysis was done by using a decision tree to compare two protocols for prophylaxis of post-surgical infections (Protocol A: Those patient with positive test to methicillin-resistant Staphylococcus aureus (MRSA) colonization received muripocin (twice a day during a two-week period), with no follow-up verification. Those who tested negative did not receive the prophylaxis treatment; Protocol B: all patients received the mupirocin treatment). The number of post-surgical infections averted was the measure of effectiveness from the health system's perspective, 30 days following the surgery. The incidence of infections and complications was obtained from two cohorts of patients who underwent cardiac surgery Hospital. The times for applying the two protocols were validated by experts. They cost were calculated from the hospital's analytical accounting management system and Pharmaceutical Service. Only direct costs were taken into account, no discount rates were applied. Incremental cost-effectiveness ratio (ICER) was calculated. A probabilistic sensitivity analysis was performed.

RESULTS

A total of 1118 patients were included (721 in Protocol A and 397 in Protocol B). No statistically significant differences were found in age, sex, diabetes, exitus or length of hospital stay between the two protocols. In the control group the rate of infection was 15.3%, compared with 11.3% in the intervention group. Protocol B proves to be more effective and at a lower cost, yielding an ICER of €32,506.

CONCLUSION

Universal mupirocin prophylaxis against surgical site infections (SSI) in cardiac surgery as a dominant strategy, because it shows a lower incidence of infections and cost savings, versus the strategy to treat selectively patients according to their test results prior screening.

Population-based epidemiology and microbiology of community-onset bloodstream infections

Bloodstream infection (BSI) is a major cause of infectious disease morbidity and mortality worldwide. While a positive blood culture is mandatory for establishment of the presence of a BSI, there are a number of determinants that must be considered for establishment of this entity. Community-onset BSIs are those that occur in outpatients or are first identified <48 h after admission to hospital, and they may be subclassified further as health care associated, when they occur in patients with significant prior health care exposure, or community associated, in other cases. The most common causes of community-onset BSI include Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. Antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus and extended-spectrum β-lactamase/metallo-β-lactamase/carbapenemase-producing Enterobacteriaceae, have emerged as important etiologies of community-onset BSI.

Long-Term Control of Endemic Hospital-Wide Methicillin-ResistantStaphylococcus aureus(MRSA): The Impact of Targeted Active Surveillance for MRSA in Patients and Healthcare Workers

Objective.

To evaluate the long-term impact of successive interventions on rates of methicillin-resistantStaphylococcus aureus(MRSA) colonization or infection and MRSA bacteremia in an endemic hospital-wide situation.

Design.

Quasi-experimental, interrupted time-series analysis. The impact of the interventions was analyzed by use of segmented regression. Representative MRSA isolates were typed by use of pulsed-field gel electrophoresis.

Setting.

A 950-bed teaching hospital in Seville, Spain.

Patients.

All patients admitted to the hospital during the period from 1995 through 2008.

Methods.

Three successive interventions were studied: (1) contact precautions, with no active surveillance for MRSA; (2) targeted active surveillance for MRSA in patients and healthcare workers in specific wards, prioritized according to clinical epidemiology data; and (3) targeted active surveillance for MRSA in patients admitted from other medical centers.

Results.

Neither the preintervention rate of MRSA colonization or infection (0.56 cases per 1,000 patient-days [95% confidence interval {CI}, 0.49-0.62 cases per 1,000 patient-days]) nor the slope for the rate of MRSA colonization or infection changed significantly after the first intervention. The rate decreased significantly to 0.28 cases per 1,000 patient-days (95% CI, 0.17-0.40 cases per 1,000 patient-days) after the second intervention and to 0.07 cases per 1,000 patient-days (95% CI, 0.06-0.08 cases per 1,000 patient-days) after the third intervention, and the rate remained at a similar level for 8 years. The MRSA bacteremia rate decreased by 80%, whereas the rate of bacteremia due to methicillin-susceptibleS. aureusdid not change. Eighty-three percent of the MRSA isolates identified were clonally related. All MRSA isolates obtained from healthcare workers were clonally related to those recovered from patients who were in their care.

Conclusion.

Our data indicate that long-term control of endemic MRSA is feasible in tertiary care centers. The use of targeted active surveillance for MRSA in patients and healthcare workers in specific wards (identified by means of analysis of clinical epidemiology data) and the use of decolonization were key to the success of the program.

Antimicrobial resistance and molecular analysis of methicillin-resistant Staphylococcus aureus collected in a Spanish hospital

Clonal distribution of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals may differ according to the geographic location and time period. Knowledge of MRSA clonal epidemiology in hospital settings involves much more than the study of healthcare-associated MRSA (HA-MRSA) clones. In recent years, investigators have documented the introduction of both community-associated MRSA (CA-MRSA) and livestock-associated MRSA (LA-MRSA) clones, the emergence of clones carrying Staphylococcal cassette chromosome mec (SCCmec) XI, and the genetic diversity among sporadic MRSA isolates. The allocation of certain antibiotypes to dominant MRSA clones in an institution allows their use as phenotypic markers for a preliminary search for new clones, early detection of clonal shift, and as a guide for better empirical therapy, infection control, and treatment within a particular institution. For these reasons, we identified 938 strains detected in a System of Universal Active Surveillance of MRSA in clinical samples during the period 2009-2010, obtaining the clonal distribution of MRSA at the Hospital Universitario de Canarias (Tenerife, Spain) and the relationship between antimicrobial susceptibility and three major clones present. The antibiotypes that best defined the ST5-MRSA-IV (Pediatric) clone showed resistance to tobramycin and susceptibility to clindamycin, erythromycin, gentamicin, rifampin, trimethoprim-sulfamethoxazole, vancomycin, quinupristin/dalfopristin, and linezolid, whereas the ST22-MRSA-IV clone (EMRSA-15) showed susceptibility to these antibiotics, and finally, the ST36-MRSA-II clone (EMRSA-16) was resistant to clindamycin, erythromycin, and tobramycin and susceptible to the remaining antimicrobials. Similar observations would allow the early detection of changes in clonal epidemiology by analysis of antimicrobial susceptibility of the isolates within a single institution.

Risk factors for intensive care unit acquired nasal colonization of MRSA and its impact on MRSA infection

OBJECTIVE

We aimed to determine the risk factors of methicillin-resistant Staphylococcus aureus (MRSA) colonization, and the impact of colonization on MRSA infection to evaluate the necessity of MRSA survey program in intensive care units (ICUs) in Turkey.

METHODS

The patients hospitalized in medical and neurosurgical ICUs longer than 24 hr were included into the study. To determine anterior nares MRSA colonization, swabs were taken from each patient in the first 48 hr, and followed by once a week till discharge from ICUs.

RESULTS

During the one-year follow-up period, the number of the hospitalized patients who spent more than 24 hr in ICUs was 195 of 372 and 85 of 619 in medical and neurosurgical ICUs, respectively. Totally, 23 out of 280 patients (14 from medical ICU, 9 from neurosurgical ICU) were colonized with MRSA, and 11 out of 23 colonized patients were accepted as ICU-acquired infection. The duration of ICU hospitalization in patients with ICU-acquired MRSA colonization was found to be longer than the noncolonized patients (18 days vs. 8 days, P value < 0.001). The presence of gastrostomy and femoral catheter were determined as risk factors for ICU-acquired MRSA colonization. The percentages of MRSA infection in patients with and without MRSA colonized were 8.6% and 1.1%, respectively (P value: 0.009).

CONCLUSION

The presence of gastrostomy and femoral catheter, and the duration of ICU hospitalization were found to be related with ICU-acquired MRSA colonization. Also, MRSA nares colonization increased the rates of both MRSA infection and ICU hospitalization.

A comparison of clinical outcomes between healthcare-associated infections due to community-associated methicillin-resistant Staphylococcus aureus strains and healthcare-associated methicillin-resistant S. aureus strains

There are limited data examining whether outcomes of methicillin-resistant Staphylococcus aureus (MRSA) healthcare-associated infections (HAIs) are worse when caused by community-associated (CA) strains compared to HA strains. We reviewed all patients' charts at our institution from 1999 to 2009 that had MRSA first isolated only after 72 h of hospitalization (n=724). Of these, 384 patients had a MRSA-HAI according to CDC criteria. Treatment failure was similar in those infected with a phenotypically CA-MRSA strain compared to a phenotypically HA-MRSA strain (23% vs. 15%, P=0.10) as was 30-day mortality (16% vs. 19%, P=0.57). Independent risk factors associated with (P<0.05) treatment failure were higher Charlson Comorbidity Index, higher APACHE II score, and no anti-MRSA treatment. These factors were also associated with 30-day mortality, as were female gender, older age, MRSA bloodstream infection, MRSA pneumonia, and HIV. Our findings suggest that clinical and host factors, not MRSA strain type, predict treatment failure and death in hospitalized patients with MRSA-HAIs.

Clinical and molecular epidemiology of meticillin-resistant Staphylococcus aureus causing bacteraemia in Southern Spain

BACKGROUND

Some molecular features of meticillin-resistant Staphylococcus aureus (MRSA) isolates causing invasive infections have been shown to have clinical implications. There is a need to monitor the situation using a combination of molecular and clinical data because, although MRSA clones tend to predominate over wide geographical areas, clonal shifts may take place.

AIM

To study the epidemiological features and perform molecular characterization of a retrospective cohort of 98 cases of nosocomial and healthcare-associated MRSA bacteraemia in 10 hospitals in Andalusia, Spain.

METHODS

Relatedness of isolates was investigated using pulsed-field gel electrophoresis (PFGE), S. aureus protein A (spa) typing and clonal complex (CC) assignment. Staphylococcal chromosomal cassette mec (SCCmec) type and accessory gene regulator (agr) group were studied by polymerase chain reaction. agr function was assessed.

RESULTS

Most isolates were CC5, SCCmec type IV and agr group II. The most common spa type was t067. Six major clusters were identified by PFGE. Six small clusters of epidemiologically related cases sharing isolates from the same PFGE subtype were identified. Five percent of isolates had a vancomycin minimum inhibitory concentration (MIC) of 2 μg/mL on broth microdilution, although 44% had an MIC >1 μg/mL on E-test. Variables independently associated with MIC >1 mg/L on E-test were surgery during present admission and Charlson index ≥2.

CONCLUSION

A specific CC that has been predominant in Spain over the last decade caused most of the cases in this study. PFGE was more discriminatory than spa typing in showing clusters of epidemiologically related cases. Some patient features were associated with vancomycin MIC >1 mg/L on E-test.

Risk factors and mortality of healthcare-associated and community-acquired Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia (SAB) is a leading cause of mortality and morbidity in both nosocomial and community settings. The objective of the study is to explore epidemiological characteristics and predisposing risk factors associated with healthcare-associated (HCA) and community-acquired (CA) SAB, and to evaluate any differences in mortality and efficacy of initial antimicrobial therapy on treatment outcome. We conducted a two-part analysis. First, a triple case-control study in which groups of HCA SAB with onset ≥ 48 h after hospital admission (HCA ≥ 48 h), HCA SAB with onset <48 h of hospital admission (HCA <48 h), and CA SAB were compared with controls. Second, a cohort study including all patients with SAB was performed to identify factors associated with in-hospital mortality. SAB was diagnosed in 165 patients over the study period (January 2007 to December 2007). Five variables were independently associated with HCA ≥ 48 h SAB: presence of central venous catheter, solid tumour, chronic renal failure, previous hospitalization and previous antibiotic therapy. Significant risk factors for HCA <48 h SAB were: Charlson Comorbidity Index ≥ 3, previous hospitalization, living in long-term care facilities and corticosteroid therapy. Factors independently associated with CA SAB were: diabetes mellitus, HIV infection and chronic live disease. Patients with HCA <48 h SAB were significantly more likely to receive initial inadequate antimicrobial treatment than patients with CA or HCA ≥ 48 h SAB (44.8% versus 33.3% and 31.5%, respectively). Logistic-regression analysis identified three variables as independent predictors of mortality: presentation with septic shock, infection with methicillin-resistant S. aureus, and initial inadequate antimicrobial treatment. More than half of patients with SAB have MRSA strains and presentation with septic shock, and inappropriate empirical therapy was associated with increased mortality.

Epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection: secular trends over 19 years at a university hospital

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) is a cause of concern in health systems all over the world, due to the high incidence rates and the associated undesirable outcomes. In our tertiary 900-bed university hospital, all episodes of MRSA-BSI have been prospectively followed up since the identification of the first episode in 1990. We conducted the current study to report changes in the epidemiology of MRSA-BSI over the 19-year period between 1990 and 2008, comparing 4 periods (1990-1994, 1995-1999, 2000-2004, and 2005-2008). Overall, 524 patients developed MRSA-BSI. Cumulative incidence was 10.0 episodes/100,000 patient days (range, 1.3-17.4). Although no trend in the incidence rate was observed between the 4 consecutive periods, significant upward trends in patient age and comorbidities, health care acquisition, and non-intravascular catheter source were all identified (p < 0.05). While the Iberian clone (ST247/SCCmecI) was dominant during the first and second periods, almost all the strains isolated in the subsequent periods belonged to Clonal Complex 5 (ST125/SCCmecIV and ST228/SCCmecI). A significant downward trend in vancomycin geometric minimum inhibitory concentration (MIC) was also observed from 2.04 mg/L to 0.88 mg/L, coinciding with the clonal replacement and the reduction in the hospital vancomycin prescription. Therefore, no MRSA vancomycin MIC creep was observed since higher MICs were associated with strains belonging to the Iberian clone. Glycopeptides were the most frequently used antibiotics for MRSA-BSI during all 4 periods. No differences in MRSA-BSI outcomes were found, and the mortality rate at 30 days was close to 29% in each of the 4 periods. In conclusion, we identified significant changes in demographic and clinical characteristics and in the molecular epidemiology of MRSA-BSI during the study period, but found no significant trends in cumulative incidence or in overall mortality rate.

Methicillin-resistant Staphylococcus aureus: the European landscape

Pan-European surveillance of bacteraemia caused by methicillin-resistant Staphylococcus aureus (MRSA) shows it to be a problem affecting all European countries, although there is marked geographical variation in prevalence. Although the proportion of S. aureus bacteraemia due to MRSA is declining in many countries, data from the European Antimicrobial Resistance Surveillance System (EARSS) for 2008 showed that in more than one-third of countries the proportion remained >25%. In contrast to bacteraemia, community-associated MRSA infection in Europe remains relatively uncommon. However, there appears to be an increasing problem involving transmission of MRSA (particularly sequence type 398) from colonized livestock, particularly pigs, to farm workers, abattoir workers and veterinarians who are in contact with such animals. Molecular analysis of isolates of MRSA has shown that there has been spread of only a limited number of MRSA clones in Europe and that many of these clones show geographical clustering due to dissemination through regional healthcare networks. Despite our increasing understanding of the epidemiology of MRSA in Europe, MRSA infections continue to pose a significant public health challenge.

Clinical significance of methicillin-resistantStaphylococcus aureuscolonization in residents in community long-term-care facilities in Spain

Methicillin-resistantStaphylococcus aureus(MRSA) is highly prevalent in Spanish hospitals and community long-term-care facilities (LTCFs). This longitudinal study was performed in community LTCFs to determine whether MRSA colonization is associated with MRSA infections and overall mortality. Nasal and decubitus ulcer cultures were performed every 6 months for an 18-month period on 178 MRSA-colonized residents (86 490 patient-days) and 196 non-MRSA carriers (97 470 patient-days). Fourteen residents developed MRSA infections and 10 of these were skin and soft tissue infections. Two patients with respiratory infections required hospitalization. The incidence rate of MRSA infection was 0·12/1000 patient-days in MRSA carriers and 0·05/1000 patient-days in non-carriers (P=0·46). No difference in MRSA infection rate was found according to the duration of MRSA colonization (P=0·69). The mortality rate was 20·8% in colonized residents and 16·8% in non-carriers; four residents with MRSA infection died. Overall mortality was statistically similar in both cohorts. Our results suggest that despite a high prevalence of MRSA colonization in LTCFs, MRSA infections are neither frequent nor severe while colonized residents remain at the facility. The epidemiological impact of an MRSA reservoir is more relevant than the clinical impact of this colonization for an individual resident and supports current recommendations to control MRSA spread in community LTCFs.

Non-hospital-associated methicillin-resistant Staphylococcus aureus and MRSA chronic carrier patients in infection control

This study reports research on methicillin-resistant Staphylococcus aureus (MRSA) colonized-infected patients who were admitted to a 320-bed hospital. Specifically, we report on the difficulties related to MRSA infection control as a consequence of the increasing incidence of non-hospital-associated MRSA acquisition and patients as chronic carriers who are frequently readmitted to the hospital.

Natural history of meticillin-resistant Staphylococcus aureus colonisation among residents in community long term care facilities in Spain

The spread of meticillin-resistant Staphylococcus aureus (MRSA) is a major problem for both acute care hospitals and among residents in long term care facilities (LTCFs). We performed a cohort study to assess the natural history of MRSA colonisation in LTCF residents. Two cohorts of residents (231 MRSA carriers and 196 non-carriers) were followed up for an 18 month period, with cultures of nasal and decubitus ulcers performed every six months. In the MRSA carrier cohort, 110 (47.8%) residents had persistent MRSA colonisation for six months or longer, 44 (19.0%) had transient colonisation and nine (3.9%) were intermittently colonised. No risk factors for persistent MRSA colonisation could be determined. The annual incidence of MRSA acquisition was around 20% [95% confidence interval (CI): 14.3-25.5]. Antibiotic treatment was independently associated with MRSA acquisition (odds ratio: 2.27; 95% CI: 1.05-4.88; P=0.03). Just two clones were distinguishable by pulsed-field gel electrophoresis and multilocus sequence typing: CC5-MRSA IV, which is widely disseminated in Spanish hospitals, and ST22-MRSA IV. This study adds to the knowledge of the epidemiology of MRSA in community LTCFs, which are important components of long term care in Spain.

[Community-onset and nosocomial bacteremia due to methicillin-resistant Staphylococcus aureus in Spanish hospitals]

INTRODUCTION

Community-onset infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are increasing. However, there is little information about community-onset bacteremia (CB) due to MRSA in Spain. The objectives of this study were to evaluate the prevalence, clinical and molecular epidemiology, clinical features, and prognosis of CB due to MRSA in comparison with nosocomial bacteremia (NB).

METHODS

Prospective multicenter cohort study; all new cases of bacteremia due to MRSA occurring during June 2003 in 59 Spanish hospitals were included. Episodes diagnosed during the first 48 hours of admission were considered CB, and otherwise, NB. Isolates were typed by pulsed field electrophoresis and multilocus sequence typing. Staphylococcal cassete chromosome mec types and Panton-Valentine leukocidin genes were studied by polymerase chain reaction.

RESULTS

Sixty-four cases were included; 21 (33%) were classified as CB. In all CB cases, a relation was found with health care, or the isolate proved to be clonally related to nosocomial isolates. There were no significant differences between the groups in terms of demographic data, underlying conditions, prognosis, or characteristics of the isolates. Regarding the source of bacteremia, catheter-related cases were more frequent in NB than CB (39.5% vs 5%, P=0.005), whereas a urinary source was more frequent in CB than NB (25% vs 0%, P=0.001). Most isolates belonged to 2 clones related to the pandemic "pediatric" clone.

CONCLUSION

MRSA should be considered in empiric treatment for certain infectious syndromes in patients with healthcare-associated community-onset sepsis.

Variable-number tandem repeat analysis and multilocus sequence typing data confirm the epidemiological changes observed with Staphylococcus aureus strains isolated from bloodstream infections

Since 2000, our geographical region in France systematically surveys bloodstream infections (BSI) due to Staphylococcus aureus. This survey involves 39 health care institutions (HCIs) encompassing 6,888 short-stay beds and was performed during two 3-month periods during 2007 and 2008. The study periods of this survey identified 292 S. aureus isolates causing BSI. Extensive molecular characterization, including genotyping as well as toxin, agr, and staphylococcal cassette chromosome content determinations, allowed us to describe epidemiological evolution in comparison to that discussed in our previous study. Our main epidemiological observation shows that the incidence of BSI remained constant but that methicillin (meticillin)-resistant S. aureus strains with a wider variety of genetic backgrounds now harbor pyl, as has already been reported in different European countries. We noticed stable numbers of BSI episodes involving community-acquired methicillin-sensitive S. aureus (MSSA), whereas a drastic increase in the number of strains harboring the tst gene was recorded. The increase in the number of tst gene-harboring strains is related to known hospital-acquired MSSA isolates and appears related to epidemic episodes in specific HCIs. Monitoring the increase in prevalence of specific strains helps us understand where the standard precautions are not satisfactorily applied or do not efficiently prevent the spread of epidemic MSSA strains in these HCIs. The recent increases in incidence of these strains call for particular vigilance to avoid the spread of potentially virulent MSSA strains harboring the tst gene and for continuance of this strategy of BSI surveillance.

Impact of inappropriate empirical therapy for sepsis due to health care-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

We investigated the influence of empirical therapy on the mortality of patients with health care-associated (HCA) sepsis caused by methicillin-resistant Staphylococcus aureus (MRSA) infections in a multicenter cohort, and the variables associated with inappropriate empirical therapy.

METHODS

All new cases of infection caused by HCA-MRSA presenting with sepsis syndrome in 59 Spanish hospitals during June 2003 were prospectively followed. The main outcome variable was mortality at day 30. Predictors of mortality and of inappropriate empirical therapy were studied using multivariate logistic regression.

RESULTS

We included 209 cases. Crude mortality was 23%. After controlling for severity of the underlying condition, ICU stay, presentation with severe sepsis or shock, and site of infection, inappropriate empirical therapy was associated with an increased odds of mortality (OR=3.0; 95% CI: 1.01-9.0; p=0.04). Only 21.1% of the patients received appropriate empirical therapy. Variables independently associated with appropriate therapy were recent surgery, central venous catheter and certain sites of infection (primary bacteraemia, intraabdominal infections, and respiratory tract infections). Cancer patients were at an increased risk of receiving inappropriate therapy.

CONCLUSIONS

Inappropriate empirical therapy was independently associated with increased mortality in this multicenter cohort. Clinicians should be aware of the need to consider coverage against MRSA more frequently.