Methicillin-sensitive S. Aureus Infection Research Articles

Machine learning to predict risk for community-onset Staphylococcus aureus infections in children living in southeastern United States.

Staphylococcus aureus (S. aureus) is known to cause human infections and since the late 1990s, community-onset antibiotic resistant infections (methicillin resistant S. aureus (MRSA)) continue to cause significant infections in the United States. Skin and soft tissue infections (SSTIs) still account for the majority of these in the outpatient setting. Machine learning can predict the location-based risks for community-level S. aureus infections. Multi-year (2002-2016) electronic health records of children <19 years old with S. aureus infections were queried for patient level data for demographic, clinical, and laboratory information. Area level data (Block group) was abstracted from U.S. Census data. A machine learning ecological niche model, maximum entropy (MaxEnt), was applied to assess model performance of specific place-based factors (determined a priori) associated with S. aureus infections; analyses were structured to compare methicillin resistant (MRSA) against methicillin sensitive S. aureus (MSSA) infections. Differences in rates of MRSA and MSSA infections were determined by comparing those which occurred in the early phase (2002-2005) and those in the later phase (2006-2016). Multi-level modeling was applied to identify risks factors for S. aureus infections. Among 16,124 unique patients with community-onset MRSA and MSSA, majority occurred in the most densely populated neighborhoods of Atlanta's metropolitan area. MaxEnt model performance showed the training AUC ranged from 0.771 to 0.824, while the testing AUC ranged from 0.769 to 0.839. Population density was the area variable which contributed the most in predicting S. aureus disease (stratified by CO-MRSA and CO-MSSA) across early and late periods. Race contributed more to CO-MRSA prediction models during the early and late periods than for CO-MSSA. Machine learning accurately predicts which densely populated areas are at highest and lowest risk for community-onset S. aureus infections over a 14-year time span.

Risk factors for non-invasive (skin and soft tissue) and invasive Staphylococcus aureus infections among children and adults living in southeastern USA: a retrospective cohort study

ObjectiveTo characterise individual and area-level risks associated with invasive or skin and soft tissue (SSTIs) Staphylococcus aureus infections comparing methicillin-resistant S. aureus (MRSA) with methicillin-sensitive S. aureus (MSSA); and highlight...

Positive nasal Staphylococcus aureus polymerase chain reaction assay is not sensitive in predicting concurrent or subsequent Staphylococcus aureus infection in critically ill patients.

Staphylococcal infection is associated with significant morbidity and mortality in critically ill patients. Using data from 16,681 patients who had a nasal Staphylococcus aureus polymerase chain reaction (PCR) assay on admission to the intensive care unit (ICU) of Royal Perth Hospital between March 2006 and September 2016, this retrospective cohort study assessed whether nasal S. aureus colonisation on admission to an ICU was predictive of concurrent or subsequent S. aureus infections. Culture-proven S. aureus infections were identified using the hospital microbiology database. Of the 16,681 patients included, 565 (3.4%) had a positive methicillin-resistant S. aureus (MRSA) assay, 146 (0.9%) had a positive methicillin-sensitive S. aureus (MSSA) assay and eight (0.05%) had both positive MRSA and MSSA assays. Of those 565 patients with a positive MRSA PCR assay, 79 (13.8%) had concurrent or subsequent MRSA infections. Of those 146 patients with a positive MSSA PCR assay, only 5 (3.4%) had MSSA infection. The sensitivity and specificity for the MRSA PCR assay in predicting concurrent or subsequent MRSA infection were 72.7% (95% confidence intervals (CI) 63.4%-80.8%) and 97.0% (95% CI 96.8%-97.3%), respectively. The sensitivity and specificity for the MSSA PCR assay in predicting concurrent or subsequent MSSA infection were 3.3% (95% CI 1.1%-7.6%) and 99.1% (95% CI 98.9%-99.2%), respectively. Both nasal MRSA and MSSA PCR assays had a high specificity and negative predictive value in predicting MRSA and MSSA infections, respectively, suggesting that in centres without endemic S. aureus infections, a negative nasal MRSA or MSSA PCR assay may be useful to reduce unnecessary empirical antibiotic therapy against S. aureus.

In Vitro Synergistic Effect of Vancomycin and Some Antibacterial Agents Against Clinical Methicillin-Resistant and Sensitive Staphylococcus aureus Isolates.

Methicillin-resistant Staphylococcus aureus (MRSA) can be responsible for serious long-term infections. Sometimes monotherapy can be ineffective for the treatment of these infections; hence, it is hypothesized that combined drug treatment can be more potent in these cases. The aim of this study was to investigate the synergistic effect of vancomycin and eight other antibacterial agents to identify the best combination pattern in the management of MRSA. Ameri-Ziaee double synergism test (AZDAST), double-disc, checkerboard, and time-kill methods were used to assess the synergistic effect in 24 isolates of S. aureus, including 22 MRSA and two methicillin-sensitive S. aureus (MSSA). Furthermore, based on the results, handmade combined antibiotic discs were prepared to evaluate the results of the checkerboard and time-kill methods at the plate level. All the isolates were sensitive to vancomycin, linezolid, and daptomycin. Furthermore, penicillin had the highest resistance (100%) in all isolates. The synergistic activities were observed, when the vancomycin was combined with the imipenem, using three double-disc, checkerboard, and time-kill methods. The sub-minimum inhibitory concentration (MIC) amount of the combined discs could increase the diameter of the inhibition zone, confirming the results. The data obtained from this study suggested that vancomycin and imipenem together, even at sub-MIC, could be effective against MRSA and MSSA infections.

Twice daily cefazolin is effective for treatment of serious methicillin-sensitive Staphylococcus aureus infection in an outpatient parenteral antimicrobial therapy program.

Background:The use of cefazolin for infections caused by Staphylococcus aureus has been demonstrated to be effective, and associated with fewer adverse effects compared with anti-staphylocccal penicillins; however, use of cefazolin on outpatient parenteral antimicrobial therapy (OPAT) programs often requires the use of continuous infusions. We report the outcomes of patients with serious infections caused by methicillin-sensitive S. aureus (MSSA) treated using twice daily cefazolin by a large tertiary hospital OPAT program. The aim of this study was to evaluate the safety, efficacy and outcomes after 90 days of follow up for patients with serious infections caused by MSSA treated with twice daily cefazolin by our OPAT program.Methods:A retrospective analysis of clinical outcomes of cases treated for a serious infection proven to be caused by MSSA treated with cefazolin monotherapy on the OPAT program at a tertiary hospital between January 2010 and July 2016 (6.5 years). Outcome measures included readmission rate, adverse drug reactions and clinical cure.Results:A total of 111 cases of serious MSSA infection were treated with cefazolin in the OPAT service during the study period, including 52 with peripheral or vertebral osteomyelitis and 13 with infective endocarditis; 56 patients had bacteraemia. Median duration of intravenous antibiotic therapy was 41 days, and the median proportion of intravenous therapy administered via OPAT was 69%. Two patients had recurrence of infection within 90 days, but were in the setting of retained prosthetic material. A total of 4% of patients experienced an adverse drug reaction. No cases of antibiotic failure were identified.Conclusions:The use of twice daily cefazolin for serious MSSA infection on an OPAT program is safe and effective. Further study is needed to assess for noninferiority to conventional treatment regimes.

Is methicillin-resistant Staphylococcus Aureus infection associated with higher mortality and morbidity in hospitalized patients? A cohort study of 551 patients from South Western India.

PurposeTo determine morbidity and mortality of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) infections in a tertiary health care facility.MethodsA cohort study among hospitalized adult patients with culture proven MRSA or MSSA monoinfection were recruited in a tertiary referral center in South India from November 2011 to December 2012.ResultsOf total 551 subjects, 284 (52%) had MRSA and 267 (48%) MSSA infection. A total of 184 (65%) subjects had health care-associated MRSA (HA-MRSA) and 100 (35%) community-associated MRSA (CA-MRSA). Chronic kidney disease and recent antibiotic use had significant association with MRSA. MRSA patients had significant respiratory infection (OR 2.24 [1.04, 5.16]) and bacteremia (OR 2.24 [10.40, 5.16]), relative to MSSA. MSSA group had better survival function compared to MRSA group (P=0.028). Median duration of ICU stays were 5 days (IQR 4, 8) and 2 days (IQR 2, 2) in MRSA and MSSA, respectively. Complications such as acute kidney injury, sepsis, multiorgan dysfunction, need for supportive measures were more in the MRSA group.ConclusionMRSA imposes a huge burden in Indian scenario and HA-MRSA remains the main culprit. Patients with history of chronic kidney disease and recent use of antibiotics were found to be at a higher risk. Patients with MRSA infections tend to have poorer outcomes in terms of longer hospital stay, greater complications, and mortality.

Spinal epidural abscess with a rapid course in young healthy infantry recruits with multiple skin lacerations

In recent years, there has been high prevalence of Staphylococcus aureus (S. aureus) infection among soldiers in the Israeli military, with devastating sequelae in several cases. Emergency department physicians have developed a high level of suspicion for spinal epidural abscess (SEA) in patients presenting known risk factors; however, SEA is a particularly elusive diagnosis in young healthy adults with no history of drug abuse. We review three cases of SEA secondary to methicillin-sensitive S. aureus (MSSA) infection in young healthy soldiers without known risk factors. We retrospectively reviewed clinical files of soldiers treated at our Medical Center from 2004–2015 to identify patients diagnosed with SEA. Those aged less than 30years with no history of intravenous drug use, spine surgery or spine trauma were included in the study. Three young army recruits met the inclusion criteria. These young men developed SEA through extension of MSSA infection to proximal skin and soft tissue from impetigo secondary to skin scratches sustained during “basic” training. All presented with mild nuchal rigidity and severe persistent unremitting lancinating radicular pain. Although healthy at baseline, they had a severe, rapidly progressive course. Following urgent surgery, two patients recovered after rehabilitation; one remained with paraparesis at late follow-up. Neurological deficits and systemic evidence of S. aureus infection progressed rapidly in these young healthy SEA patients with no history of drug abuse, emphasizing the critical role of timely MRI, diagnosis, and surgery.

Antibiotic susceptibility and genomic variations in Staphylococcus aureus associated with Skin and Soft Tissue Infection (SSTI) disease groups.

BackgroundStaphylococcus aureus is associated with human skin and soft tissue infections (SSTIs); however, the involvement of virulence factors in different clinical presentations is unclear.MethodsWe analyzed methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains from Taiwan to determine correlations among the clinical characteristics of SSTIs, antimicrobial susceptibility and virulence factors of S. aureus with specific genetic backgrounds.ResultsWe identified 177 MRSA isolates and 130 MSSA isolates among the 307 SSTI-associated S. aureus isolates. Hospital-acquired (HA)- and community-acquired (CA)-MRSA isolates accounted for 61.6 % and 38.4 % of the isolates, respectively. Clinical presentations in SSTI patients differed significantly for the disease groups. Deep-seated MRSA infections presented with higher amputation rate than MSSA infections. MRSA isolates were all susceptible to linezolid, teicoplanin, and vancomycin, and >94 % of isolates were erythromycin- and clindamycin-resistant. Staphylococcal cassette chromosome (SCCmec) types IV, V, and VII were the most frequent in the CA-MRSA group (n = 68); types III, IV and V were the most frequent in the HA-MRSA group (n = 109). Panton-Valentine leukocidin (PVL) genes were significantly more frequent in CA-MRSA strains (75.0 %) than in HA-MRSA (33.0 %) and MSSA (24.6 %) and were found in 66.7 % (74/111) strains isolated from the abscess group. Exfoliatin A genes were more common in catheter-related exit-site MSSA infections (37.5 %) compared with other MSSA disease groups (P < 0.05). Exfoliatin B and superantigen exotoxin genes were uncommon in all SSTI disease types. Pulsotypes A (ST239), C, and D (ST59) were the predominant MRSA genotypes in deep-seated infections.ConclusionsIf not treated appropriately, deep-seated MRSA-associated infections present with higher amputation rates than deep-seated MSSA-associated infections. PVL-positive MRSA strains caused more frequently pus-forming lesions and less bacteremia and invasive diseases. Methods for discriminating CA-MRSA from HA-MRSA strains are now unreliable due to circulation of both ST 239 and ST 59 strains in the community and nosocomial settings. Initial antibiotic treatments should consider MRSA for patients with SSTIs in areas where MRSA is prevalent.

Risk factors associated with methicillin-resistant Staphylococcus aureus infection in children.

To identify the clinical variables that differentiate MRSA (Methicillin-resistant Staphylococcus aureus) from MSSA (Methicillin-sensitive S. aureus) infection. Cases having culture isolates of Staphylococcus species were recruited. Baseline and other laboratory parameters were compared between MSSA and MRSA sub-groups to identify the predictors for MRSA. Out of 98 isolates of S.aureus, 46 (47%) were MRSA. Significant leukocytosis was found in cases with MRSA (P <t0.03). None of the other clinical variables could differentiate MRSA from MSSA infection. Presence of leukocytosis was twice more likely to predict MRSA than MSSA at admission. Empiric therapy must be guided by antimicrobial sensitivity pattern of regional culture isolates.

Socio-economic profile of patients with community-acquired skin and soft tissue infections in Delhi

Aim:To study the socio-demographic and clinical profile of patients with community-acquired skin and soft tissue infections (CA-SSTIs).Methods:This study was a cross sectional, observational study. Patients with CA-SSTIs (ICD-10 L00-L08) were enrolled from February to August 2013. Clinical and microbiological data of all patients were recorded. Socioeconomic status (SES) of each patient was calculated using the Modified Kuppuswamy Scale.Results:Seventy-three patients were studied, of whom 45 had SSTIs caused by Staphylococcus aureus. Of the 45, 11 (24%) were methicillin-resistant S. aureus (MRSA) and 34 (76%) were methicillin-sensitive S. aureus (MSSA). Patients with MRSA infections had significantly lower monthly income and lower educational status than those with MSSA infections. However, SES was not significantly different in the two groups.Conclusion:S. aureus was the most common cause of CA-SSTIs, of which, MRSA was isolated in 24% of the cases. Patients with MRSA SSTIs had significantly lesser family income and lower education levels compared to patients with MSSA SSTIs.

Metabolic Profiling for Detection of Staphylococcus aureus Infection and Antibiotic Resistance

Due to slow diagnostics, physicians must optimize antibiotic therapies based on clinical evaluation of patients without specific information on causative bacteria. We have investigated metabolomic analysis of blood for the detection of acute bacterial infection and early differentiation between ineffective and effective antibiotic treatment. A vital and timely therapeutic difficulty was thereby addressed: the ability to rapidly detect treatment failures because of antibiotic-resistant bacteria. Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) were used in vitro and for infecting mice, while natural MSSA infection was studied in humans. Samples of bacterial growth media, the blood of infected mice and of humans were analyzed with combined Gas Chromatography/Mass Spectrometry. Multivariate data analysis was used to reveal the metabolic profiles of infection and the responses to different antibiotic treatments. In vitro experiments resulted in the detection of 256 putative metabolites and mice infection experiments resulted in the detection of 474 putative metabolites. Importantly, ineffective and effective antibiotic treatments were differentiated already two hours after treatment start in both experimental systems. That is, the ineffective treatment of MRSA using cloxacillin and untreated controls produced one metabolic profile while all effective treatment combinations using cloxacillin or vancomycin for MSSA or MRSA produced another profile. For further evaluation of the concept, blood samples of humans admitted to intensive care with severe sepsis were analyzed. One hundred thirty-three putative metabolites differentiated severe MSSA sepsis (n = 6) from severe Escherichia coli sepsis (n = 10) and identified treatment responses over time. Combined analysis of human, in vitro, and mice samples identified 25 metabolites indicative of effective treatment of S. aureus sepsis. Taken together, this study provides a proof of concept of the utility of analyzing metabolite patterns in blood for early differentiation between ineffective and effective antibiotic treatment in acute S. aureus infections.

Crafting a system-wide response to healthcare-associated infections.

According to the US Centers for Disease Control and Prevention, 1 in 20 Americans admitted to hospitals is infected while receiving treatment for another condition. More than 48,000 people die each year of infections that are acquired in healthcare settings (1). And each year, 18,650 deaths follow infection with methicillin-resistant Staphylococcus aureus (MRSA), a pathogen that is now easily transmitted in both community and healthcare settings (2). MRSA bacteremia significantly increases the length of hospital stays, the charges per patient, and hospital costs per case (3). According to a large-cohort study at Duke University Medical Center (Durham, NC), MRSA in surgical wounds resulted in more than a 12-fold increase in mortality vs. that in uninfected patients and more than a 3-fold increase vs. that in patients infected with methicillin-sensitive S. aureus (MSSA). The average total cost of treatment for a patient with an MRSA infection was ∼$40,000 more than for a patient with an MSSA infection and ∼$84,000 more than for an uninfected patient (4).

Spinal epidural abscess in adults caused by Staphylococcus aureus: Clinical characteristics and prognostic factors

ObjectiveSpinal epidural abscess (SEA) is a devastating infectious disease, which may result in neurologic sequelae. Staphylococcus (S.) aureus is a common pathogen of SEA. Here, we analyzed the clinical characteristics and laboratory data of adult patients with S. aureus SEA and compared the clinical characteristics of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) infections. MethodsBetween 2003 and 2008, we collected data regarding 29 adult cases of S. aureus SEA and analyzed the clinical presentations, magnetic resonance (MR) imaging features, therapeutic outcome, and prognostic factors. Antibiotic susceptibility test results of 11 implicated MRSA strains were also further analyzed. ResultsWe identified 17 MSSA strains and 12 MRSA strains. Lumbar and lumbosacral spine segments were the most commonly involved segments. All 29 patients had back pain. Other findings included sensory abnormalities (25), motor weakness (21), fever (16), bladder dysfunction (16), and altered consciousness (3). Disease onset at admission was acute in 6 cases and chronic in 23. The stages of disease severity were early stage in 9 and late stage in 20. After therapy, 21 patients had a good prognosis and 8 had a poor prognosis. Significant prognostic factors included older age (>70years), presence of diabetes mellitus, adrenal insufficiency, and MRSA infection. The prognosis alone was clinically different between patients with MSSA and MRSA infections. ConclusionsPatients with localized back pain, particularly those with a fever and compromised immune system, should undergo MR imaging to ensure an early diagnosis and management.

The effectiveness of an improved combination therapy for experimental Staphylococcus aureus keratitis

antibiotic and steroid combination therapies, such as tobramycin with dexamethasone, are often used in ophthalmology to treat or prevent infection and inflammation. The purpose of this study was to use a model of Staphylococcus aureus keratitis to quantify and compare the effectiveness of a standard tobramycin and dexamethasone combined therapy, with each drug individually, and with a new formulation of the two drugs in a xanthan gum vehicle. rabbit corneas were intrastromally injected with a methicillin-sensitive S. aureus (MSSA) or a methicillin-resistant S. aureus (MRSA) strain. Rabbit eyes were treated every hour from 10 to 15 hours postinfection (PI) with 0.1% dexamethasone, 0.3% tobramycin, 0.3% tobramycin with 0.1% dexamethasone, or 0.3% tobramycin with 0.05% dexamethasone in a xanthan gum vehicle (ST). Slit lamp examinations (SLE) were performed on infected eyes and pathology scored at 15 hours PI. At 16 hours PI, colony forming units (CFUs) per cornea were quantified. the CFUs in eyes treated with dexamethasone alone were similar to untreated control eyes for MSSA or MRSA infections. All other treatment groups had significantly less CFUs per cornea than untreated eyes. The eyes treated with the ST formulation had significantly fewer CFUs per cornea than all other treatment groups when infected with MSSA or MRSA. The SLE scores of MSSA or MRSA infected eyes treated with tobramycin alone were similar to untreated control eyes. All other treatment groups had significantly lower SLE scores than untreated controls eyes, but were not significantly different from each other. the results of this study demonstrated that the tobramycin and dexamethasone combination therapy with a xanthan gum vehicle has an improved bactericidal effectiveness compared to the commercially available formulation, and maintains a similar anti-inflammatory effect while containing half the amount of steroid.

Staphylococcus Aureus colonization and bacteremia in children with cancer.

Abstract 3666Poster Board III-602 BackgroundStaphylococcus aureus is an important cause of blood stream infections in children and adults. In recent years, new strains of methicillin-resistant S. aureus (MRSA), also known as community-acquired (CA)-MRSA have been isolated from otherwise healthy individuals. These strains frequently carry the Panton-Valentine Leukocidin (PVL) leukotoxin and belong to spa type 8; USA300 genotype, which is the most common strain causing CA-MRSA infections in the U.S. The clinical course of infections with PVL-positive S.aureus strains appears to be more severe than infection from PVL-negative strains. Bacteremia due to these strains has been reported in children, adolescents and adults. It is not known if methcillin-resistance or infection with CA-MRSA strains adversely affects outcome in children with cancer. Colonization of MRSA in healthy children has increased significantly since 2001 and has shown to be a risk factor for subsequent infection. However the prevalence of nasal and rectal colonization with MRSA; in particular with PVL-positive strains and the relationship between colonization and infection is not known in children or adults with cancer. MethodsThe epidemiology of MRSA and methicillin-sensitive S.aureus (MSSA) bacteremia and prevalence of MRSA nasal and rectal colonization in children with cancer was retrospectively studied from 2000 to 2007. Medical record review included patient demographics, underlying disease and antimicrobial susceptibility patterns of the MRSA and MSSA bacteremia isolates. Molecular typing was performed by polymerase chain reaction (PCR) on all isolates for detection of the PVL genes. Staphylococcus cassette chromosome (SCC) mec and spa typing was performed on all PVL-positive MRSA and MSSA bacteremia isolates and MRSA isolates causing colonization and infection. Demographic and treatment variables were compared between patients with MRSA and MSSA bacteremia and patients with PVL-positive and PVL-negative MRSA and MSSA bacteremia using exact two-sample Wilcoxon rank sum test or robust rank sum test for unequal variances and Fisher's exact chi-square test. The trend of MRSA/MSSA bacteremia and MRSA colonization was evaluated by logistic regression models. ResultsTen (19%) MRSA and 42 (81%) MSSA isolates from clinically distinct infectious bacteremic episodes were collected from 52 patients with cancer during the eight year study period. The proportion of cancer patients with MRSA, or MSSA bacteremia did not change significantly over the duration of the study. A third of the patients, 17 (33%), had complications. Thirty-eight (73%) of the bacteremic episodes were catheter-related. Catheters were removed significantly more often for MRSA infections than for MSSA infections for persistently positive blood cultures or complications (p=0.003). Subcutaneous ports was removed significantly more often than Hickman catheters (p= 0.005). The number of patients with persistently positive MRSA bacteremia were higher as compared to MSSA bacteremia (p= 0.004). Methicillin resistance was associated with decreased susceptibility to erythromycin (p=0.0003) and gentamicin (p=0.03). The difference in PVL positivity between MRSA and MSSA was statistically significant (P=0.01). None of the other variables studied including complications were significantly different between patients with MRSA or MSSA bacteremia or between patients with PVL-positive and PVL-negative S.aureus bacteremia. The number of patients colonized with MRSA compared to the total number of samples tested increased significantly between 2000-2001 and 2006-2007 (p=0.0007). PVL-positivity was associated both with increased colonization (p=0.004) and with an increased risk of infection (p=0.0005). There was a discordance in the spa types between the colonization and infection isolates. ConclusionsThis report represents the first description of the epidemiology of S.aureus bacteremia and colonization including analysis of PVL-positive strains in children with cancer. Methicillin-resistance or PVL-positivity did not appear to be associated with a worse outcome in our patient population. The number of patients colonized with MRSA increased significantly during this time period. PVL-positivity was associated with an increased risk of colonization and infection. Further studies are needed to confirm these observations in patients with cancer. Disclosures:No relevant conflicts of interest to declare.

Prevalence of cutaneous bacterial infections and nasal carriage ofStaphylococcus aureusin recipients of renal transplants

Renal transplant recipients (RTRs) often develop bacterial infections as a result of their long-term immunosuppressive treatment. However, there is no published case-control study of cutaneous bacterial infections in this population, and the prevalence of nasal Staphyloccus aureus carriage and its role in cutaneous bacterial infections in RTRs are not known. To determine whether the prevalence of cutaneous bacterial infections and nasal S. aureus carriage are increased in RTRs and to investigate the association between nasal S. aureus carriage and cutaneous staphylococcal infections. In total, 66 outpatient RTRs and 67 controls were investigated for the presence of cutaneous bacterial infections. Bacterial cultures were taken from clinically suspicious cutaneous lesions, and three nasal swabs were collected to detect nasal S. aureus colonization. Cutaneous bacterial infection was suspected in 42.4% of RTRs, and in 14.2% of controls. However, of the lesions that could be cultured, microbiologically proven cutaneous bacterial [methicillin-sensitive S. aureus (MSSA)] infections were confirmed in only two RTRs and one control subject. Nasal S. aureus carriage was found in 10.6% of RTRs and 29.9% of controls (P < 0.05). Both RTRs with MSSA infection were nasal carriers, whereas nasal S. aureus carriage was not detected in the only control subject with MSSA infection. All S. aureus isolates were oxacillin-sensitive. Screening for nasal S. aureus carriage does not seem to assist in preventing staphylococcal bacterial infections in outpatient RTRs.

Future strategies for treating Staphylococcus aureus bloodstream infections

Bloodstream infections are potentially life-threatening diseases. They can cause serious secondary infections, such as infective endocarditis and osteomyelitis, and may result in severe sepsis. One of the most critical determinants of survival is the induction of timely and effective antibiotic therapy. One of the leading causes of bloodstream infections is Staphylococcus aureus, with an increasing proportion of isolates being resistant to methicillin. Methicillin-resistant S. aureus (MRSA) is associated with greater morbidity and mortality rates than methicillin-sensitive S. aureus (MSSA). Standard-of-care antibiotic treatments for S. aureus bloodstream infections are limited by toxicity and/or differential efficacy against MRSA and MSSA, which makes the choice of empirical therapy difficult. New management strategies are required to address the challenges raised by S. aureus bloodstream infections and MRSA in particular. These may include the use of techniques that allow the early identification of complications arising from S. aureus bacteraemia, rapid pathogen identification to enable the administration of appropriate antibiotic therapy, and the identification of new drugs with novel modes of action that may circumvent antibiotic resistance and enable effective empirical treatment of both MSSA and MRSA infections.

Hospital Mortality for Patients With Bacteremia Due to Staphylococcus aureus or Pseudomonas aeruginosa

To evaluate the relationship between hospital mortality and bloodstream infections due to Staphylococcus aureus or Pseudomonas aeruginosa. Prospective cohort study. A 1,400-bed, university-affiliated urban teaching hospital. Between December 2001 and September 2002, 314 patients with bacteremia due to S aureus or P aeruginosa were prospectively evaluated. Prospective patient surveillance and data collection. Thirteen patients (4.1%) received inadequate initial antibiotic treatment. Fifty-four patients (17.2%) died during hospitalization. Hospital mortality was statistically greater for patients with bloodstream infections due to P aeruginosa (n = 49) compared to methicillin-sensitive S aureus (MSSA) [n = 117; 30.6% vs 16.2%, p = 0.036] and methicillin-resistant S aureus (MRSA) [n = 148; 30.6% vs 13.5%, p = 0.007]. Multiple logistic regression analysis identified the lack of response to initial medical treatment (adjusted odds ratio [AOR], 2.69; 95% confidence interval [CI], 1.83 to 3.94; p = 0.010) and endocarditis (AOR, 4.62; 95% CI, 2.45 to 8.73; p = 0.016) as independent determinants of hospital mortality. Patients with bloodstream infections due to P aeruginosa were statistically more likely to be nonresponders to early medical treatment compared to patients with MSSA (73.5% vs 11.1%, p < 0.001) and MRSA (73.5% vs 16.9%, p < 0.001) bloodstream infections. These data suggest that bloodstream infections due to P aeruginosa have a greater risk of hospital mortality compared to bloodstream infections due to S aureus despite adequate antibiotic treatment.

Staphylococcal bacteraemia: the hospital or the home? A review of Staphylococcus aureus bacteraemia at Concord Hospital in 1993.

To examine the risk factors for, and the complications and mortality of, Staphylococcus aureus bacteraemia. A retrospective case review of patients with S. aureus bacteraemia in 1993 diagnosed at the Concord Repatriation General Hospital, Sydney. Of 104 cases reviewed, 32 were due to methicillin resistant S. aureus (MRSA), 73 were due to methicillin sensitive S. aureus (MSSA) and one was a dual infection. Twenty-eight of the bacteraemias were community-acquired, including one case of MRSA, and 76 were hospital-acquired; 38% had an implanted prosthetic device or graft. The average age (68 years), incidence of underlying diseases and hospitalisation in the past month (26%) did not differ between MRSA and MSSA groups. MRSA was more likely in patients with recent broad-spectrum antibiotic use (53% vs 0, p < .01). Vascular access was the commonest source of sepsis (61%) but in community-acquired cases the source was unknown in 50%. Use of central line access was more predictive of MRSA infection (75% vs 49%, p = .018). In hospital-acquired infection, MRSA sepsis occurred later in the course of the admission (26 days vs eight days, p < .01). Directly attributable mortality was highest in MRSA and community-acquired MSSA infection (9% and 11%) compared with hospital-acquired MSSA infection (1%). Nosocomial S. aureus bacteraemia, particularly MRSA, is a major source of preventable morbidity, which could be addressed by improved infection control of MRSA, antibiotic use and attention to central line catheter use.

Ventilator-associated pneumonia by Staphylococcus aureus. Comparison of methicillin-resistant and methicillin-sensitive episodes.

All episodes of ventilator-associated pneumonia (VAP) caused by Staphylococcus aureus were prospectively analyzed for a 30-mo period. Methicillin-sensitive S. aureus (MSSA) was isolated in 38 episodes and methicillin-resistant S. aureus (MRSA) in 11 others. The two groups were similar regarding sex, severity of underlying diseases, prior surgery, and presence of renal failure, diabetes, cardiopathy, and coma. MRSA-infected persons were more likely to have received steroids before developing infection (relative risk [RR] = 3.45, 95% confidence interval [CI] = 1.38-8.59), to have been ventilated > 6 d (RR = 2.03, 95% CI = 1.36-3.03), to have been older than 25 yr (RR = 1.50, 95% CI = 1.09-2.06), and to have had preceding chronic obstructive pulmonary disease (RR = 2.76, 95% CI = 0.89-8.56) than MSSA-infected patients. MSSA-infected persons were more likely than MRSA-infected patients to have cranioencephalic trauma (RR = 1.94, 95% CI = 1.22-3.09). All patients with MRSA VAP had previously received antibiotics, compared with only 21.1% of those with MSSA infection (p < 0.000001). The incidence of empyema was similar in both groups; nevertheless, the presence of bacteremia and septic shock was more frequent in the MRSA group. Finally, mortality directly related to pneumonia was significantly higher among patients with MRSA episodes (RR = 20.72, 95% CI = 2.78-154.35). This analysis was repeated for monomicrobial episodes, and the difference remained statistically significant. We conclude that MRSA and MSSA strains infect patients with different demographic profiles; previous antibiotic therapy is the most important risk factor for developing MRSA infection.(ABSTRACT TRUNCATED AT 250 WORDS)