Staphylococcus aureus Bacteremia: Compliance with Standard Treatment, Long-term Outcome and Predictors of Relapse

Short-term versus usual-term antibiotic treatment for uncomplicated Staphylococcus aureus bacteremia: a systematic review and meta-analysis

Introduction

Uncomplicated Staphylococcus aureus bacteremia remains a leading cause of morbidity and mortality in hospitalized patients. Current guidelines recommend a minimum of 14 days of treatment.

Objective

To evaluate the efficacy and safety of short versus usual antibiotic therapy in adults with uncomplicated S. aureus bacteremia (SAB).

Methods

We developed a search strategy to identify systematic review and meta-analysis of non-randomized studies (NRS), comparing short versus usual or long antibiotic regimens for uncomplicated SAB in MEDLINE, Embase, and the Cochrane Register up to June 2023. The risk of bias was assessed using the ROBINS I tool. The meta-analysis was performed using Review Manager software with a random effect model.

Results

Six NRS with a total of 1700 patients were included. No significant differences were found when comparing short versus prolonged antibiotic therapy as defined by the authors for 90-day mortality [odds ratio (OR): 1.09; 95% confidence interval (CI): 0.82-1.46, p: 0.55; I2 = 0%] or 90-day recurrence or relapse of bacteremia [OR: 0.72; 95% CI: 0.31-1.68, p: 0.45; I2 = 26%]. Sensitivity analysis showed similar results when comparing a predefined duration of <14 days versus ⩾14 days and when excluding the only study with a high risk of bias.

Conclusion

Shorter-duration regimens could be considered as an alternative option for uncomplicated SAB in low-risk cases. However, based on a small number of studies with significant methodological limitations and risk of bias, the benefits and harms of shorter regimens should be analyzed with caution. Randomized clinical trials are needed to determine the best approach regarding the optimal duration of therapy.

Longer-term Mortality and Kidney Outcomes of Participants in the Combination Antibiotics for Methicillin-Resistant Staphylococcus aureus (CAMERA2) Trial: A Post Hoc Analysis

Background

The Combination Antibiotic Therapy for Methicillin-Resistant Staphylococcus aureus (CAMERA2) trial ceased recruitment in July 2018, noting that a higher proportion of patients in the intervention arm (combination therapy) developed acute kidney injury (AKI) compared to the standard therapy (monotherapy) arm. We analyzed the long-term outcomes of participants in CAMERA2 to understand the impact of combination antibiotic therapy and AKI.

Methods

Trial sites obtained additional follow-up data. The primary outcome was all-cause mortality, censored at death or the date of last known follow-up. Secondary outcomes included kidney failure or a reduction in kidney function (a 40% reduction in estimated glomerular filtration rate to <60 mL/minute/1.73 m²). To determine independent predictors of mortality in this cohort, adjusted hazard ratios were calculated using a Cox proportional hazards regression model.

Results

This post hoc analysis included extended follow-up data for 260 patients. Overall, 123 of 260 (47%) of participants died, with a median population survival estimate of 3.4 years (235 deaths per 1000 person-years). Fifty-five patients died within 90 days after CAMERA2 trial randomization; another 68 deaths occurred after day 90. Using univariable Cox proportional hazards regression, mortality was not associated with either the assigned treatment arm in CAMERA2 (hazard ratio [HR], 0.84 [95% confidence interval [CI], .59-1.19]; P = .33) or experiencing an AKI (HR at 1 year, 1.04 [95% CI, .64-1.68]; P = .88).

Conclusions

In this cohort of patients hospitalized with methicillin-resistant S aureus bacteremia, we found no association between either treatment arm of the CAMERA2 trial or AKI (using CAMERA2 trial definition) and longer-term mortality.

Teicoplanin versus β-lactam for febrile patients with Staphylococcus-like bacteremia: focus on methicillin-susceptible Staphylococcus aureus bacteremia

Background

Many studies have shown that vancomycin is inferior to β-lactam antibiotics in terms of effectiveness in the treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. However, limited data are available regarding the comparison of clinical outcomes between patients receiving initial teicoplanin and those receiving β-lactam antibiotics for MSSA bacteremia.

Methods

Eighty-four adults with MSSA bacteremia were included: initial teicoplanin treatment group (n = 28) and β-lactam treatment group (n = 56). The two groups were further stratified based on propensity score matching according to the outcome analysis using a logistic regression model. We investigated the clinical outcomes between the groups before and after propensity score matching after treatment completion.

Results

Pittsburgh bacteremia score ≥ 4 (odds ratio, 60.6; 95%CI, 7.4–496.8) was an independent risk factor for unfavorable outcome. After propensity score matching, the initial teicoplanin treatment group and the β-lactam treatment group consisted of 28 patients each. No statistically significant differences were observed in the proportions of patients with favorable outcomes and 30-day overall mortality rates between the groups before and after propensity score matching after the completion of teicoplanin or β-lactam treatment. The Kaplan-Meier 30-day survival curve also showed no significant difference between the patients receiving initial teicoplanin treatment and those receiving β-lactam treatment before and after matching (hazard ratio, 1.84, 95%CI, 0.60–5.64; and 3.12, 95%CI, 0.98–9.99, respectively).

Conclusions

There were no significant difference in clinical outcomes between initial teicoplanin treatment and β-lactam treatment among patients with MSSA bacteremia. Pittsburgh bacteremia score ≥ 4 was a significant risk factor for mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06111-w.

Do written diagnosis-treatment recommendations on microbiological test reports improve the management of Staphylococcus aureus bacteremia? A single-center, retrospective, observational study

The objective of this study was to assess the impact of microbiological test reports that provide specific written recommendations on the appropriate management of Staphylococcus aureus bacteremia (SAB). We performed a retrospective analysis of laboratory and clinical data of all SAB patients treated at one German University hospital, 2012-2015. Among 467 included patients, methicillin-resistant S. aureus (MRSA) accounted for 15.2% of all SAB cases. All-cause in-hospital mortality was 25.2%, and was significantly elevated in individuals aged >55 years, in MRSA bacteremia and if the source of infection remained unidentified. Focus identification was achieved in 71.1%, with the most prevalent foci being catheter-associated bloodstream infection (23.1%), soft tissue infection (15.4%), osteomyelitis (5.1%) and endocarditis (4.9%). Standardized written recommendations on microbiological test reports led to a significant increase of transesophageal echocardiography, additional imaging studies for focus identification and more frequent follow-up blood cultures, but no significant effect on mortality was observed.

Management of Staphylococcus aureus bacteraemia (SAB) in the oncology patient: Further evidence supports prompt removal of central venous catheters and shorter duration of intravenous antimicrobial therapy

Background

Staphylococcus aureus bacteraemia (SAB) is associated with relatively high risk of complications and high levels of mortality. Internationally, SAB management guidelines lack consensus and especially so regarding oncology patients. This is likely a reflection of insufficient randomised control trials (RCT) and the diversity of SAB patient populations. However, there are 2011 guidelines recommending a minimum of 14 days of appropriate IV antibiotic therapy for SAB.

Objective

We wished to determine whether our practice of shortened duration of intravenous antimicrobial therapy in favour of oral administration proved as effective as recommended guidelines in a mixed oncology patient cohort.

Methods

Retrospective review of patient records that included any SAB episode among oncology patients from January 2002 to December 2015. Medical chart reviews were undertaken to determine patient demographics, clinical management & antimicrobial therapy, duration of stay, presence of a central venous catheter (CVC) and outcome.

Results

Our CVC removal rate was just 73% in SAB where CVC was the identified source of infection, with an attributable mortality rate (<4%) far lower than would be expected. Antimicrobial therapy durations were considerably lower (10 days) than current recommendations of 14 days IV therapy. The recurrence rate of 15% was also significantly lower than has been reported previously.

Conclusions

Our observations contribute new insights concerning the management of SAB in oncology patients. Our findings suggest that therapeutic approaches should perhaps remain individualised and reflective of patient characteristics taking into consideration the complex nature of oncology patients.

Antibiotic Resistance Profile and Methicillin-Resistant Encoding Genes of Staphylococcus aureus Strains Isolated from Bloodstream Infection Patients in Northern Vietnam

BACKGROUND:

Evaluating the antibiotic susceptibility and resistance genes is essential in the clinical management of bloodstream infections (BSIs). Nevertheless, there are still limited studies in Northern Vietnam. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0)

AIM:

This study aimed to determine the antibiotic resistance profile and methicillin-resistant encoding genes of Staphylococcus aureus (S. aureus) causing BSIs in Northern Vietnam.

METHODS:

The cross-sectional study was done from December 2012 to June 2014 in two tertiary hospitals in Northern Vietnam. Tests performed at the lab of the hospital.

RESULTS:

In 43 S. aureus strains isolating, 53.5 % were MRSA. Distribution of gene for overall, MRSA, and MSSA strains were following mecA gene (58.1 %; 95.7%, and 15%), femA gene (48.8%, 47.8%, and 50%), femB gene (88.4%, 82.6%, and 95%). Antibiotic resistance was highest in penicillin (100%), followed by erythromycin (65.1%) and clindamycin (60.5%). Several antibiotics were susceptible (100%), including vancomycin, tigecycline, linezolid, quinupristin/dalfopristin. Quinolone group was highly sensitive, include ciprofloxacin (83.7%), levofloxacin (86%) and moxifloxacin (86%).

CONCLUSION:

In S. aureus causing BSIs, antibiotic resistance was higher in penicillin, erythromycin, and clindamycin. All strains were utterly susceptible to vancomycin, tigecycline, linezolid, quinupristin/dalfopristin.

Real-Time Monitoring of Bacteria Clearance From Blood in a Murine Model

Bloodstream infections, especially those that are antibiotic resistant, pose a significant challenge to health care leading to increased hospitalization time and patient mortality. There are different facets to this problem that make these diseases difficult to treat, such as the difficulty to detect bacteria in the blood and the poorly understood mechanism of bacterial invasion into and out of the circulatory system. However, little progress has been made in developing techniques to study bacteria dynamics in the bloodstream. Here, we present a new approach using an in vivo flow cytometry platform for real-time, noninvasive, label-free, and quantitative monitoring of the lifespan of green fluorescent protein-expressing Staphylococcus aureus and Pseudomonas aeruginosa in a murine model. We report a relatively fast average rate of clearance for S. aureus (k = 0.37 ± 0.09 min^-1 , half-life ~1.9 min) and a slower rate for P. aeruginosa (k = 0.07 ± 0.02 min^-1 , half-life ~9.6 min). We also observed what appears to be two stages of clearance for S. aureus, while P. aeruginosa appeared only to have a single stage of clearance. Our results demonstrate that an advanced research tool can be used for studying the dynamics of bacteria cells directly in the bloodstream, providing insight into the progression of infectious diseases in circulation. © 2019 International Society for Advancement of Cytometry.

Formal Infectious Diseases Specialist Consultation Improves Long-term Outcome of Methicillin-Sensitive Staphylococcus aureus Bacteremia

Background

Formal infectious diseases specialist (IDS) consultation has been shown to improve short-term outcomes in Staphylococcus aureus bacteremia (SAB), but its effect on long-term outcomes lacks evaluation.

Methods

This retrospective study followed 367 methicillin-sensitive (MS) SAB patients for 10 years. The impact of formal IDS consultation on risk for new bacteremia and outcome during long-term follow-up was evaluated. Patients who died within 90 days were excluded to avoid interference from early deceased patients.

Results

Three hundred four (83%) patients had formal IDS consultation, whereas 63 (17%) received informal or no IDS consultation. Formal consultation, compared with informal or lack of consultation, was associated with a reduced risk of new bacteremia caused by any pathogen within 1 year (odds ratio [OR], 0.39; 95% confidence interval [CI], 0.18–0.84; P = .014; 8% vs 17%) and within 3 years (OR, 0.39; 95% CI, 0.19–0.80; P = .010; 9% vs 21%), whereas a trend toward lower risk was observed within 10 years (OR, 0.56; 95% CI, 0.29–1.08; P = .079; 16% vs 25%). Formal consultation, compared with informal or lack of consultation, improved outcomes at 1 year (OR, 0.16; 95% CI, 0.06–0.44; P < .001; 3% vs 14%), at 3 years (OR, 0.19; 95% CI, 0.09–0.42; P < .001; 5% vs 22%), and at 10 years (OR, 0.43; 95% CI, 0.24–0.74; P = .002; 27% vs 46%). Considering all prognostic parameters, formal consultation improved outcomes (HR, 0.42; 95% CI, 0.27–0.65; P < .001) and lowered risk for any new bacteremia (OR, 0.45; 95% CI, 0.23–0.88; P = .02) during 10 years of follow-up.

Conclusions

MS-SAB management by formal IDS consultation, compared with informal or lack of IDS consultation, reduces risk for new bacteremia episodes and improves long-term prognosis up to 10 years.

A Phase 1, Randomized, Single-Ascending-Dose Study To Investigate the Safety, Tolerability, and Pharmacokinetics of DSTA4637S, an Anti-Staphylococcus aureus Thiomab Antibody-Antibiotic Conjugate, in Healthy Volunteers

Staphylococcus aureus causes serious bacterial infections with high morbidity and mortality, necessitating the discovery of new antibiotics. DSTA4637S is a novel antibody-antibiotic conjugate designed to target intracellular S. aureus that is not adequately eliminated by current standard-of-care antibiotics. DSTA4637S is composed of an anti-S. aureus Thiomab human immunoglobulin G1 (IgG1) monoclonal antibody linked to a novel rifamycin-class antibiotic (4-dimethylaminopiperidino-hydroxybenzoxazino rifamycin [dmDNA31]) via a protease-cleavable linker. Phagocytic cells ingest DSTA4637S-bound S. aureus, and intracellular cathepsins cleave the linker, releasing dmDNA31and killing intracellular S. aureus This first-in-human, randomized, double-blind, placebo-controlled, single-ascending-dose phase 1 trial analyzed the safety, pharmacokinetics, and immunogenicity of DSTA4637S in healthy volunteers. Thirty healthy male and female volunteers, 18-65 years old, were randomized into five cohorts receiving single intravenous (i.v.) doses of 5, 15, 50, 100, and 150 mg/kg of DSTA4637S or placebo (4 active:2 placebo). Subjects were followed for 85 days after dosing. No subject withdrew from the study, and no serious or severe adverse events occurred. One moderate infusion-related reaction (150 mg/kg DSTA4637S) occurred. No clinically meaningful or dose-related changes in laboratory parameters or vital signs occurred. Pharmacokinetics of plasma DSTA4637S conjugate and serum DSTA4637S total antibody were dose proportional. Systemic exposure of unconjugated dmDNA31 was low. No DSTA4637S-induced anti-drug antibody responses were observed. DSTA4637S was generally safe and well tolerated as a single i.v. dose in healthy volunteers. DSTA4637S has a favorable safety and pharmacokinetic profile that supports future development as a novel therapeutic for S. aureus infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02596399.).

Effect of Clinically Uninfected Orthopedic Implants and Pacemakers/AICDs in Low-Risk Staphylococcus aureus Bloodstream Infection on Crude Mortality Rate: A Post Hoc Analysis of a Large Cohort Study

Background

The standard treatment duration in low-risk Staphylococcus aureus bloodstream (SAB) is 14 days. However, it is unclear whether an extended course of antimicrobial therapy is necessary in patients with clinically uninfected prosthetic joints/osteosyntheses or pacemakers/automated implanted cardioverter-defibrillators (AICDs). Thus, we compared the duration of antimicrobial therapy and outcomes in patients with and those without clinically uninfected foreign bodies.

Methods

We conducted a post hoc analysis of data from the prospective Invasive Staphylococcus aureus Infection Cohort (INSTINCT) study. Adult low-risk patients who survived ≥4 days were assessed for duration of treatment, SAB-related events (attributable death, relapse, or new deep-seated infection), and survival.

Results

Of the 1288 patients enrolled, 292 satisfied criteria for low-risk SAB. Forty-three patients (15%) had a clinically uninfected pacemaker/AICD or orthopedic implant. Patients with foreign bodies were significantly older (mean age, 72 vs 62 years for those without; P < .001; P = .9) and had a higher Charlson score (median, 3 vs 2; P = .06). The total duration of antimicrobial therapy (median, 18 vs 17 days, respectively; P = .7), all-cause mortality rate (16% vs 14%; P = .7), and prevalence of SAB-related events within 90 days were similar (2% vs 2%) in the 2 groups. At 1-year follow-up, SAB-related events were more frequent in patients with foreign bodies (7% vs 4% in those without; P = .4) (hazard ratio, 1.41; 95% confidence interval, .35–5.69; in a multivariable Cox model), but this difference was not statistically significant.

Conclusions

Low-risk patients with clinically uninfected foreign bodies received a similar duration of antimicrobial therapy without a significant impact on mortality rate. The observed higher hazard ratio of SAB-related events within 1 year necessitates additional studies before recommendations concerning treatment duration in this patient subgroup can be adapted or modified.

Infectious diseases consultation improves key performance metrics in the management of Staphylococcus aureus bacteremia: A multicentre cohort study

BACKGROUND

Staphylococcus aureus bacteremia (SAB) is associated with significant morbidity and mortality. We sought to identify factors associated with infectious diseases consultation (IDC) and understand how IDC associates with SAB patient management and outcomes.

METHODS

A multicentre retrospective study was performed between 2012 and 2014 in a large Canadian Health Zone in order to determine factors associated with IDC and performance of key quality of care determinants in SAB management and clinical outcomes. Factors subject to quality of care determinants were established a priori and studied for associations with IDC and 30-day all-cause mortality using multivariable analysis.

RESULTS

Of 961 SAB episodes experienced by 892 adult patients, 605 episodes received an IDC. Patients receiving IDC were more likely to have prosthetic valves and joints and to have community-acquired and known sources of SAB, but increasing age decreased IDC occurrence. IDC was the strongest independent predictor for quality of care performance metrics, including repeat blood cultures and echocardiography. Mortality at 30 days was 20% in the cohort, and protective factors included IDC, achievement of source control, targeted therapy within 48 hours, and follow-up blood cultures but not the performance of echocardiography.

CONCLUSIONS

There were significant gaps between the treatments and investigations that patients actually received for SAB and what is considered the optimal management of their condition. IDC is associated with improved attainment of targeted SAB quality of care determinants and reduced mortality rates. Based on our findings, we propose a policy of mandatory IDC for all cases of SAB to improve patient management and outcomes.

Implementing a hospital-wide protocol for Staphylococcus aureus bacteremia

Staphylococcus aureus bacteraemia (SAB) is associated with high-mortality and complication rates. A multidisciplinary approach is needed to predict, detect and treat complications. In this pre- and post-intervention study, we investigated the effects of a hospital-wide protocol for diagnosis, classification and treatment of SAB. It was hypothesized that complications and endocarditis would be better identified and treated. Medical records of SAB patients admitted in 2011 and 2012 (pre) were analysed. In 2013, a protocol, describing risk factors, diagnostic classification and recommended treatment, was implemented. In 2014 and 2015 (post), SAB patients were followed prospectively. Transthoracic (TTE) or transoesophageal cardiac ultrasound (TEE) was chosen following a decision tree. A resident internal medicine acted as contact person. Pre-intervention, 98 patients were eligible for analysis compared to 85 patients post-intervention. Age and number of risk factors were slightly higher post-intervention; other baseline characteristics were similar. Most SAB-patients were classified as complicated (89 and 82% pre- and post-intervention, respectively). Follow-up blood cultures drawn within 2 days after initiating treatment increased from 51 to 85%. Cardiac ultrasounds increased from 44 to 83% for TTE and 13 to 24% for TEE. Endocarditis was more frequently diagnosed (4 vs. 12%). Additionally, duration of antibiotic therapy increased. The 3-month mortality did not change significantly (33% pre-intervention vs. 35% post-intervention; p > 0.05). Introduction of a hospital-wide protocol for SAB management increased standard of care, created awareness among clinicians to properly classify SAB, search for endocarditis and adapt duration of antibiotic treatment. Mortality did not decrease.

Staphylococcus aureus bacteraemia and endocarditis - epidemiology and outcome: a review

PURPOSE

To review the epidemiology of Staphylococcus aureus bacteraemia (SAB) and endocarditis (SAE), and discuss the short- and long-term outcome.  Materials and methods: A literature review of the epidemiology of SAB and SAE.

RESULTS

The reported incidence of SAB in Western countries is 16-41/100,000 person-years. Increasing incidence has been observed in many regions, in Iceland by 27% during 1995-2008. The increase is believed to depend on changes in population risk factors and possibly better and more frequent utilization of diagnostic procedures. S. aureus is now the leading causes of infective endocarditis (IE) in many regions of the world. It accounts for 15-40% of all IE cases, and the majority of cases in people who inject drugs (PWID). Recently, the incidence of SAE in PWID in Stockholm, Sweden, was found to be 2.5/1000 person-years, with an in-hospital mortality of 2.5% in PWID as compared to 15% in non-drug users. The 30-day mortality associated with SAB amounts to 15-25% among adults in Western countries, but is lower in children (0-9%). Mortality associated with SAE is high (generally 20-30% in-hospital mortality), and symptomatic cerebral embolizations are common (12-35%). The 1-year mortality reported after SAB and SAE is 19-62% and reflects deaths from underlying diseases and complications caused by the infection. In a subset of SAE cases, valvular heart surgery is needed (15-45%), but active intravenous drug use seems to be a reason to refrain from surgery. Despite its importance, there are insufficient data on the optimal management of SAB and SAE, especially on the required duration of antibiotic therapy.  Conclusions: The epidemiology of SAB and SAE has been changing in the past decades. They still carry a substantial morbidity and mortality. Intensified studies on treatment are warranted for improving patient outcome.

Predictive Value of C-Reactive Protein (CRP) in Identifying Fatal Outcome and Deep Infections in Staphylococcus aureus Bacteremia

Introduction

Clear cut-off levels could aid clinicians in identifying patients with a risk of fatal outcomes or complications such as deep infection foci in Staphylococcus aureus bacteremia (SAB). Cut-off levels for widely used clinical follow-up parameters including serum C-reactive protein (CRP) levels and white blood cell counts (WBC) have not been previously studied.

Methods

430 adult SAB patients in Finland took part in prospective multicentre study in which their CRP levels and WBC counts were measured on the day of the positive blood culture, every other day during the first week, twice a week during hospitalization and at 30 days. Receiver operating characteristic (ROC) analysis was used to evaluate the prognostic value of CRP and WBC on the day of the positive blood culture and at days 4, 7, and 14 in predicting mortality and the presence of deep infections at 30 days. Adjusted hazard ratios (HR) for CRP level and WBC count cut-off values for mortality were calculated by the Cox regression analysis and adjusted odds ratios (OR) for cut-off values to predict the presence of deep infection by the binary logistic regression analysis.

Results

The succumbing patients could be distinguished from the survivors, starting on day 4 after the positive blood culture, by higher CRP levels. Cut-off values of CRP for day 30 mortality in adjusted analysis, that significantly predicted fatal outcome were at day 4 CRP >103 mg/L with sensitivity of 77%, specificity of 55%, and HR of 3.5 (95% CI, 1.2–10.3; p = 0.024), at day 14 CRP >61 mg/L with a sensitivity of 82%, specificity of 80% and HR of 3.6 (95% CI, 1.1–10.3; p<0.039) and cut-off value of WBC at day 14 >8.6 x10⁹/L was prognostic with sensitivity of 77%, specificity of 78% and HR of 8.2 (95% CI, 2.9–23.1; p<0.0001). Cut-off values for deep infection in adjusted analysis were on the day of the positive blood culture CRP >108 mg/L with sensitivity of 77%, specificity of 60%, and HR of 2.6 (95% CI, 1.3–4.9; p = 0.005) and at day 14 CRP >22 mg/L with sensitivity of 59%, specificity of 68%, and HR of 3.9 (95% CI, 1.6–9.5; p = 0.003). The lack of decline of CRP in 14 days or during the second week were neither prognostic nor markers of deep infection focus.

Conclusions

CRP levels have potential for the early identification of SAB patients with a greater risk for death and deep infections.

Novel antibody-antibiotic conjugate eliminates intracellular S. aureus

Staphylococcus aureus is considered to be an extracellular pathogen. However, survival of S. aureus within host cells may provide a reservoir relatively protected from antibiotics, thus enabling long-term colonization of the host and explaining clinical failures and relapses after antibiotic therapy. Here we confirm that intracellular reservoirs of S. aureus in mice comprise a virulent subset of bacteria that can establish infection even in the presence of vancomycin, and we introduce a novel therapeutic that effectively kills intracellular S. aureus. This antibody-antibiotic conjugate consists of an anti-S. aureus antibody conjugated to a highly efficacious antibiotic that is activated only after it is released in the proteolytic environment of the phagolysosome. The antibody-antibiotic conjugate is superior to vancomycin for treatment of bacteraemia and provides direct evidence that intracellular S. aureus represents an important component of invasive infections.

Novel antibody-antibiotic conjugate eliminates intracellular S. aureus

Staphylococcus aureus is considered to be an extracellular pathogen. However, survival of S. aureus within host cells may provide a reservoir relatively protected from antibiotics, thus enabling long-term colonization of the host and explaining clinical failures and relapses after antibiotic therapy. Here we confirm that intracellular reservoirs of S. aureus in mice comprise a virulent subset of bacteria that can establish infection even in the presence of vancomycin, and we introduce a novel therapeutic that effectively kills intracellular S. aureus. This antibody-antibiotic conjugate consists of an anti-S. aureus antibody conjugated to a highly efficacious antibiotic that is activated only after it is released in the proteolytic environment of the phagolysosome. The antibody-antibiotic conjugate is superior to vancomycin for treatment of bacteraemia and provides direct evidence that intracellular S. aureus represents an important component of invasive infections.

Determination of risk factors for recurrent methicillin-resistant Staphylococcus aureus bacteremia in a Veterans Affairs healthcare system population

OBJECTIVE

To identify important risk factors for recurrent methicillin-resistant Staphylococcus aureus (MRSA) to assist clinicians in identifying high-risk patients for continued surveillance and follow-up.

METHODS

In this retrospective cohort study, we examined patients with MRSA bacteremia at 122 Veterans Affairs medical facilities from January 1, 2003, through December 31, 2010. Recurrent MRSA bacteremia was identified by a positive blood culture result from 2 to 180 days after index hospitalization discharge. Subset analyses were performed to evaluate risk factors for early-onset (2-60 days after discharge) and late-onset (61-180 days after discharge) recurrence. Risk factors were evaluated using Cox proportional hazards regression.

RESULTS

Of 18,425 patients, 1,159 (6.3%) had recurrent MRSA bacteremia. The median time to recurrence was 63 days. Longer duration of index bacteremia, increased severity of illness, receipt of only vancomycin, community-acquired infection, and several comorbidities were risk factors for recurrence. Congestive heart failure, hypertension, and rheumatoid arthritis/collagen disease were risk factors for early-onset but not late-onset recurrence. Geographic region and cardiac arrhythmias were risk factors for late-onset but not early-onset recurrence.

CONCLUSIONS

Risk factors for recurrent MRSA bacteremia included comorbidities, severity of illness, duration of bacteremia, and receipt of only vancomycin. Awareness of risk factors may be important at patient discharge for implementation of quality improvement initiatives including surveillance, follow-up, and education for high-risk patients.

Improved understanding of factors driving methicillin-resistant Staphylococcus aureus epidemic waves

Methicillin-resistant Staphylococcus aureus (MRSA) remains one of the most important causes of nosocomial infections worldwide. Since the global spread of MRSA in the 1960s, MRSA strains have evolved with increased pathogenic potential. Notably, some strains are now capable of causing persistent infections not only in hospitalized patients but also in healthy individuals in the community. Furthermore, MRSA is increasingly associated with infections among livestock-associated workers, primarily because of transmission from animals to humans. Moreover, many MRSA strains have gained resistance to most available antibiotics. In this review, we will present current knowledge on MRSA epidemiology and discuss new endeavors being undertaken to understand better the molecular and epidemiological underpinnings of MRSA outbreaks.

Timing of initiating glycopeptide therapy for methicillin-Resistant Staphylococcus aureus bacteremia: the impact on clinical outcome

When a Staphylococcus-like organism (SLO) is microscopically found in Gram staining of blood culture (BC) specimen, it seems reasonable to administrate a glycopeptide (GP) for empirical therapy. The paper investigates the risk factors for 14-day mortality in patients with methicillin-resistance Staphylococcus aureus bacteremia (MRSAB) and clarifies the impact of the timing for initiating GP therapy. A retrospective study identifies patients with MRSAB (endocarditis was excluded) between 2006 and 2009. Patients were categorized as receiving GP at the interval before a preliminary BC report indicating the growth of SLO and the onward 24 hours or receiving GP 24 h after a preliminary BC report indicating the growth of SLO. Total 339 patients were enrolled. There was no difference on the 14-day overall or infection-related mortality rates at the time to administer GP. Multivariate analysis disclosed pneumonia (OR = 4.47; of 95% CI; of 2.09–9.58; P < 0.01) and high APACHE II score (OR, 2.81, with 95% CI, 1.19–6.65; P = 0.02) were independent risk factors for infection-related mortality. The mortality rate did not decrease following administrating GP immediately after a preliminary BC indicating SLO growth. An additional research for the optimal timing for initiating GP treatment is warranted.

Cationic antimicrobial peptide LL-37 is effective against both extra- and intracellular Staphylococcus aureus

The increasing resistance of bacteria to conventional antibiotics and the challenges posed by intracellular bacteria, which may be responsible for chronic and recurrent infections, have driven the need for advanced antimicrobial drugs for effective elimination of both extra- and intracellular pathogens. The purpose of this study was to determine the killing efficacy of cationic antimicrobial peptide LL-37 compared to conventional antibiotics against extra- and intracellular Staphylococcus aureus. Bacterial killing assays and an infection model of osteoblasts and S. aureus were studied to determine the bacterial killing efficacy of LL-37 and conventional antibiotics against extra- and intracellular S. aureus. We found that LL-37 was effective in killing extracellular S. aureus at nanomolar concentrations, while lactoferricin B was effective at micromolar concentrations and doxycycline and cefazolin at millimolar concentrations. LL-37 was surprisingly more effective in killing the clinical strain than in killing an ATCC strain of S. aureus. Moreover, LL-37 was superior to conventional antibiotics in eliminating intracellular S. aureus. The kinetic studies further revealed that LL-37 was fast in eliminating both extra- and intracellular S. aureus. Therefore, LL-37 was shown to be very potent and prompt in eliminating both extra- and intracellular S. aureus and was more effective in killing extra- and intracellular S. aureus than commonly used conventional antibiotics. LL-37 could potentially be used to treat chronic and recurrent infections due to its effectiveness in eliminating not only extracellular but also intracellular pathogens.

Treatment duration for uncomplicated Staphylococcus aureus bacteremia to prevent relapse: analysis of a prospective observational cohort study

Practice guidelines recommend at least 14 days of antibiotic therapy for uncomplicated Staphylococcus aureus bacteremia (SAB). However, these recommendations have not been formally evaluated in clinical studies. To evaluate the duration of therapy for uncomplicated SAB, we analyzed data from our prospective cohort of patients with SAB. A prospective observational cohort study was performed in patients with SAB at a tertiary-care hospital in Korea between August 2008 and September 2010. All adult patients with SAB were prospectively enrolled and observed over a 12-week period. Uncomplicated SAB was defined as follows: negative results of follow-up blood cultures at 2 to 4 days, defervescence within 72 h of therapy, no evidence of metastatic infection, and catheter-related bloodstream infection or primary bacteremia without evidence of endocarditis on echocardiography. Of 483 patients with SAB, 111 met the study criteria for uncomplicated SAB. Fifty-three (47.7%) had methicillin-resistant SAB. When short-course therapy (<14 days) and intermediate-course therapy (≥14 days) were compared, the treatment failure rates (10/38 [26.3%] versus 16/73 [21.9%]) and crude mortality (7/38 [18.4%] versus 16/73 [21.9%]) did not differ significantly between the two groups. However, short-course therapy was significantly associated with relapse (3/38 [7.9%] versus 0/73; P = 0.036). In multivariate analysis, primary bacteremia was associated with a trend toward increased treatment failure (P = 0.06). Therefore, in the treatment of uncomplicated SAB, it seems reasonable to consider at least 14 days of antibiotic therapy to prevent relapse, as practice guidelines recommend. Because of its poor prognosis, primary bacteremia, even with a low risk of complication, should not be treated with short-course therapy.

Combination therapy with an aminoglycoside for Staphylococcus aureus endocarditis and/or persistent bacteremia is associated with a decreased rate of recurrent bacteremia: a cohort study

PURPOSE

Although limited data exist on the efficacy and potential risk of synergistic aminoglycoside therapy for persistent Staphylococcus aureus bacteremia and endocarditis, aminoglycosides are frequently used in clinical practice.

METHODS

As our study population, we included subjects fulfilling the modified Duke criteria for S. aureus endocarditis and/or having greater than 72 h of S. aureus bacteremia. Among these subjects, we compared patients who did and did not receive aminoglycoside therapy for their S. aureus bloodstream infection. These groups were compared for the primary outcome of recurrent bacteremia, as well as for the duration of bacteremia, mortality, complication rate, and incident renal failure.

RESULTS

Eighty-seven subjects fulfilled the inclusion criteria. Of these, 49 received aminoglycoside therapy, whereas 38 did not. There were no significant differences in the baseline characteristics when comparing groups who did or did not receive aminoglycoside therapy. Four (8.2%) subjects treated with aminoglycoside therapy experienced recurrent bacteremia versus nine (23.7%) who did not receive aminoglycoside therapy [relative risk and 95% confidence interval [RR (95%CI)] = 0.51 (0.22-1.17), p = 0.04]. In multivariable analyses, aminoglycoside use remained significantly associated with a decrease in recurrent bacteremia [adjusted odds ratio (OR) (95%CI) = 0.26 (0.07-0.98), p = 0.046]. No significant differences were seen between groups treated with and without an aminoglycoside in terms of the 6-month all-cause mortality (51.0 vs. 42.1%, p = 0.41), complication rate (71.4 vs. 73.7%, p = 0.82), or incident renal failure (54.5 vs. 46.9%, p = 0.54).

CONCLUSIONS

The use of combination therapy with an aminoglycoside in persistent S. aureus bacteremia and/or endocarditis may be associated with a lower rate of recurrent bacteremia without significant differences in the incident renal failure.

Clinical management of Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia is one of the most common serious bacterial infections worldwide. In the UK alone, around 12,500 cases each year are reported, with an associated mortality of about 30%, yet the evidence guiding optimum management is poor. To date, fewer than 1500 patients with S aureus bacteraemia have been recruited to 16 controlled trials of antimicrobial therapy. Consequently, clinical practice is driven by the results of observational studies and anecdote. Here, we propose and review ten unanswered clinical questions commonly posed by those managing S aureus bacteraemia. Our findings define the major areas of uncertainty in the management of S aureus bacteraemia and highlight just two key principles. First, all infective foci must be identified and removed as soon as possible. Second, long-term antimicrobial therapy is required for those with persistent bacteraemia or a deep, irremovable focus. Beyond this, the best drugs, dose, mode of delivery, and duration of therapy are uncertain, a situation compounded by emerging S aureus strains that are resistant to old and new antibiotics. We discuss the consequences on clinical practice, and how these findings define the agenda for future clinical research.

Staphylococcus aureus bacteraemia--Nationwide assessment of treatment adequacy and outcome

OBJECTIVES

To assess the treatment adequacy for Staphylococcus aureus bacteraemia (SAB) and its association with outcome on a whole population basis.

METHODS

All individuals ≥18 years old diagnosed with SAB in Iceland between December 1 2003 and November 30 2008 were retrospectively identified. Clinical data was collected from medical records and adequacy of antibiotic treatment based on antibiotic choice, dose, administration route and treatment duration.

RESULTS

Empirical therapy was considered adequate in 262 of 325 (81%) SAB episodes, with no correlation to outcome. The complete antibiotic treatment was deemed adequate in 147 of 279 (53%) episodes. Among patients with complicated SAB median duration of active intravenous therapy was 14 days in those experiencing relapse compared to 30 days in patients without relapse (p = 0.03). No patient died after completing adequate treatment compared to 4 (3.0%) following inadequate therapy (p = 0.01). Despite no overall change being seen in antibiotic treatment, 30-day mortality decreased from 25.0 to 6.8% from first to last year of study (p = 0.001).

CONCLUSION

Appropriate antibiotic therapy for SAB was associated with lower relapse rates and mortality. Although treatment adequacy was regarded as insufficient in half of cases, mortality of SAB in Iceland is amongst the lowest recorded.

SUMMARY

In a national study of S. aureus bacteraemia the antibiotic treatment was judged inadequate in 53% of episodes, while appropriate treatment was associated with lower relapse rate and mortality. Despite this, the mortality in Iceland is among the lowest reported.

Intra- and extracellular activities of dicloxacillin and linezolid against a clinical Staphylococcus aureus strain with a small-colony-variant phenotype in an in vitro model of THP-1 macrophages and an in vivo mouse peritonitis model

The small-colony-variant (SCV) phenotype of Staphylococcus aureus has been associated with difficult-to-treat infections, reduced antimicrobial susceptibility, and intracellular persistence. This study represents a detailed intra- and extracellular investigation of a clinical wild-type (WT) S. aureus strain and its counterpart with an SCV phenotype both in vitro and in vivo, using the THP-1 cell line model and the mouse peritonitis model, respectively. Bacteria of both phenotypes infected the mouse peritoneum intra- and extracellularly. The SCV phenotype was less virulent and showed distinct bacterial clearance, a reduced multiplication capacity, and a reduced internalization ability. However, some of the SCV-infected mice were still culture positive up to 96 h postinfection, and bacteria of this phenotype could spread to the mouse kidney and furthermore revert to the more virulent WT phenotype in both the mouse peritoneum and kidney. The SCV phenotype is therefore, despite reduced virulence, an important player in S. aureus pathogenesis. In the THP-1 cell line model, both dicloxacillin (DCX) and linezolid (LZD) reduced the intracellular inocula of bacteria of both phenotypes by approximately 1 to 1.5 log(10) in vitro, while DCX was considerably more effective against extracellular bacteria. In the mouse peritonitis model, DCX and LZD were also able to control both intra- and extracellular infections caused by either phenotype. Treatment with a single dose of DCX and LZD was, however, insufficient to clear the SCVs in the kidneys, and the risk of recurrent infection remained. This stresses the importance of an optimal dosing of the antibiotic when SCVs are present.

A matched prospective cohort study on Staphylococcus aureus and Escherichia coli bloodstream infections: extended perspectives beyond resistance

BACKGROUND

Bacteremias caused by Staphylococcus aureus and Escherichia coli are among the most common bloodstream infections (BSIs) in adults. The aim of the study was to investigate risk factors for infection and clinical outcomes of bacteremias caused by S aureus or E coli.

METHODS

We conducted a 1-year matched prospective cohort study including 150 patients with BSI caused by susceptible or resistant S aureus or E coli and 300 controls without BSI caused by these organisms.

RESULTS

Of the 150 episodes of bacteremia, 37% were caused by S aureus (including 5 cases of methicillin-resistant S aureus [MRSA]) and 63% were caused by E coli (including 9 cases of extended-spectrum beta lactamase [ESBL]-producing E coli). We identified 4 independent risk factors for acquisition of S aureus bacteremia (emergency, peripheral or central vascular catheter, renal disease) and 6 risk factors for E coli bacteremia (emergency, peripheral or central vascular catheter, malignancy, cytoreductive or immunosuppressive therapy). Both types of bacteremia were associated with an increased length of hospital stay compared with controls. We observed a 5-fold increase in the 30-day mortality rate for bacteremias due to S aureus, and a 2-fold increase in BSI caused by E coli. The in-hospital mortality rate was increased by 6-fold for S aureus and by 3-fold for E coli.

CONCLUSION

Longer hospitalization periods and increased mortality of bacteremias caused by S aureus or E coli, irrespective of susceptibility, implicate controlling for risk factors at an early stage.

Safety and immunogenicity of a novel Staphylococcus aureus vaccine: results from the first study of the vaccine dose range in humans

Merck V710 is a novel vaccine containing the conserved Staphylococcus aureus iron surface determinant B shown to be protective in animal models. A phase I, multicenter, double-blind study of the dose range was conducted to assess the immunogenicity and safety of an adjuvanted liquid formulation of V710. A total of 124 adults (18 to 55 years of age) were randomized 1:1:1:1 to receive one 0.5-ml intramuscular injection of V710 (5 μg, 30 μg, or 90 μg) or saline placebo. A positive immune response was defined as at least a 2-fold increase in IsdB-specific IgG levels from baseline levels. Local and systemic adverse events were assessed for 5 and 14 days, respectively, following vaccination. Positive immune responses were detected in 12 (67%) of the 18 subjects in the groups receiving 30 and 90 μg V710 tested at day 10. At day 14, a significantly greater proportion of subjects manifested a positive immune response with higher geometric mean concentrations in the V710 30-μg (86%; geometric mean concentration of 116 μg/ml) and 90-μg (87%; geometric mean concentration of 131 μg/ml) dose groups than in the V710 5-μg (29%; geometric mean concentration of 51 μg/ml) or placebo (4%; geometric mean concentration of 23 μg/ml) groups. Immune responses were durable through day 84. Subjects <40 and ≥40 years of age had comparable immune responses. The most common adverse events were injection-site pain, nausea, fatigue, and headache, usually of mild intensity. No immediate reactions or serious adverse events were reported. In this first study of V710 in humans, a single 30-μg or 90-μg dose was more immunogenic than the 5-μg dose or placebo. Immune responses were evident by 10 to 14 days after vaccination in most responders.

Risk factors associated with long-term prognosis of patients with Staphylococcus aureus bacteremia

OBJECTIVE

To estimate risk factors associated with long-term outcome (i.e., 1-year survival) in patients with Staphylococcus aureus bacteremia (SAB).

METHODS AND MATERIALS

This was a retrospective study in which the microbiological laboratory data records of patients admitted to the University Hospital of Regensburg between January 2004 and June 2005 were examined to identify those patients with blood cultures positive for S. aureus. Corresponding clinical records for all patients were reviewed using a standardized questionnaire. Of the 119 patients identified with SAB, 80 were available for the >1-year follow-up.

RESULTS

Crude 1-year mortality was 47.5; 30- and 90-day mortality was 28.8 and 37.5%, respectively. In-hospital mortality was 28.8%. There were no significant differences in 1-year survival in terms of age, gender, antibiotic resistance, and mode of acquisition (nosocomial vs. community-acquired). A significantly better survival was observed with an identifiable focus present, if the chosen empiric antibiotic therapy was adequate or if the body mass index of the patient was >24.

CONCLUSION

In summary, in this patient cohort, considerable additional mortality due to SAB beyond 30 or 90 days was present. Our results suggest that long-term survival data should be taken into account in outcome studies involving patients with S. aureus bacteremia.

Intra- and extracellular activities of dicloxacillin against Staphylococcus aureus in vivo and in vitro

Antibiotic treatment of Staphylococcus aureus infections is often problematic due to the slow response and recurrences. The intracellular persistence of the staphylococci offers a plausible explanation for the treatment difficulties because of the impaired intracellular efficacies of the antibiotics. The intra- and extracellular time- and concentration-kill relationships were examined in vitro with THP-1 cells and in vivo by use of a mouse peritonitis model. The in vivo model was further used to estimate the most predictive pharmacokinetic/pharmacodynamic (PK/PD) indices (the ratio of the maximum concentration of drug in plasma/MIC, the ratio of the area under the concentration-time curve/MIC, or the cumulative percentage of a 24-h period that the free [f] drug concentration exceeded the MIC under steady-state pharmacokinetic conditions [fT(MIC)]) for dicloxacillin (DCX) intra- and extracellularly. In general, DCX was found to have similar intracellular activities, regardless of the model used. Both models showed (i) the relative maximal efficacy (1-log-unit reduction in the numbers of CFU) of DCX intracellularly and (ii) the equal relative potency of DCX intra- and extracellularly, with the MIC being a good indicator of the overall response in both situations. Discordant results, based on data obtained different times after dosing, were obtained from the two models when the extracellular activity of DCX was measured, in which the in vitro model showed a considerable reduction in the number of CFU from that in the original inoculum (3-log-unit decrease in the number of CFU after 24 h), whereas the extracellular CFU reduction achieved in vivo after 4 h did not exceed 1 log unit. Multiple dosing of DCX in vivo revealed increased extra- and intracellular efficacies (2.5 log and 2 log units of reduction in the numbers of CFU after 24 h, respectively), confirming that DCX is a highly active antistaphylococcal antibiotic. PK/PD analysis revealed that fT(MIC) is the index that is the most predictive of the outcome of infection both intra- and extracellularly.

Intra- and extracellular activity of linezolid against Staphylococcus aureus in vivo and in vitro

BACKGROUND AND AIMS

Treatment of Staphylococcus aureus infections remains problematic (slow responses and frequent recurrences). Intracellular persistence of the S. aureus could explain those difficulties because of impaired intracellular efficacy of antibiotics. Our aim was to study linezolid for its intracellular activity.

METHODS

(i) Pharmacodynamic (PD) analysis of intracellular activity using in vitro (THP-1 macrophages) and in vivo (mouse peritonitis) models with determination of key dose-response parameters [maximal relative efficacy (E(max)), relative potency (EC(50)) and static concentration (C(static))] towards methicillin-susceptible S. aureus (ATCC 25923; clinical isolate) with linezolid MICs of 4 mg/L; (ii) pharmacokinetic (PK) analysis in uninfected mice for determination of C(max), AUC and half-life for total and free drug; and (iii) determination of the predictive PK/PD parameter (fT > MIC, fAUC(24)/MIC or fC(max)/MIC) for therapeutic outcome.

RESULTS

In vitro, linezolid showed an E(max) of approximately 1 log(10) cfu reduction compared with initial inoculum both intra- and extracellularly and an approximately 3-fold increased relative potency (lower EC(50) and C(static)) intracellularly. In vivo, the efficacy of linezolid was impaired (<0.5 log(10) reduction extracellularly; failure to reduce the cfu to less than the initial load intracellularly) with, however, an increased intracellular potency (lower EC(50)). Infection outcome correlated better with the fAUC(24)/MIC (R(2) = 55%) than with the fT > MIC parameter (R(2) = 51%) for the extracellular compartment, but no parameter emerged as significant for the intracellular compartment.

CONCLUSIONS

Linezolid exerts only a weak intracellular activity against the strains of S. aureus tested, even though, in contrast to most other antibiotics, its potency does not appear impaired in comparison with the extracellular activity.

Mortality of S. aureus bacteremia and infectious diseases specialist consultation--a study of 521 patients in Germany

OBJECTIVES

To evaluate the relationship between mortality of bloodstream infection due to Staphylococcus aureus and infectious diseases specialist consultation and other factors potentially associated with outcomes.

METHODS

A 6-year cohort study was conducted at a 1600-bed university hospital. Consecutive adult patients with S. aureus bacteremia were assessed using a standardised data collection and review form. A new infectious diseases service increased its consultations for S. aureus bacteremia from 33% of cases in 2002 to >80% in 2007. Infectious disease consultation and other factors potentially associated with in-hospital mortality were analysed by multivariate logistic regression.

RESULTS

A total of 521 patients were studied. All-cause in-hospital mortality was 22%, 90-day mortality was 32%. Factors significantly associated with in-hospital mortality in multivariate analysis were ICU admission (OR 5.8, CI 3.5-9.7), MRSA (OR 2.6, CI 1.4-4.9), age >/=60 years (OR 2.4, CI 1.4-4.2), a diagnosis of endocarditis (OR 2.8, CI 1.4-5.7), a non-fatal underlying disease/comorbidity according to the McCabe classification (OR 0.2, CI 0.1-0.4), and infectious disease specialist consultation (OR 0.6, CI 0.4-1.0).

CONCLUSIONS

These data suggest that outcome of S. aureus bacteremia may be improved by an expert consultation service.

The role of vancomycin in the persistence or recurrence of Staphylococcus aureus bacteraemia

Persistence and recurrence of Staphylococcus aureus bacteraemia (SAB) have been linked primarily with difficult-to-eradicate foci of infection such as endocarditis, osteomyelitis or abscess formation. Although vancomycin therapy has been suggested as a predictor of relapse of SAB, it has never been shown to be associated with persistent SAB. The purpose of this study was to examine the possible association of vancomycin therapy and persistence of SAB. Two groups of patients were retrospectively studied. One group consisted of 124 patients who completed > or =10 d of appropriate anti-staphylococcal therapy (from among a total of 284 patients with SAB during 2 y, 1997-8). In this group, persistence of SAB (methicillin resistant and susceptible combined) for >3 d while on therapy, occurred in 11 (22%) of 55 vancomycin recipients and in none of 52 cloxacillin recipients (p = 0.002). When calculated for methicillin susceptible SAB alone, the numbers were 3 of 13 vs 0 of 52, respectively (p = 0.007). The second study group included all patients with persistence and/or relapse of SAB while on appropriate anti-staphylococcal therapy during 4 y (1997-2000). In this group, the persistence occurred while on vancomycin therapy, in 32 (94%) of 34 patients with >3 d of persistence of SAB. In the majority of these patients a secondary focus of infection serving as the site of persistence was identified in addition to the primary focus (or portal of entry). It was concluded that vancomycin is inferior to cloxacillin therapy in terminating SAB and therefore may predispose to prolonged bacteraemia and secondary seeding of infection during therapy.

Intracellular activity of antibiotics against Staphylococcus aureus in a mouse peritonitis model

Antibiotic treatment of Staphylococcus aureus infections is often problematic due to the slow response to therapy and the high frequency of infection recurrence. The intracellular persistence of staphylococci has been recognized and could offer a good explanation for these treatment difficulties. Knowledge of the interplay between intracellular antibiotic activity and the overall outcome of infection is therefore important. Several intracellular in vitro models have been developed, but few experimental animal models have been published. The mouse peritonitis/sepsis model was used as the basic in vivo model exploring a quantitative ex vivo extra- and intracellular differentiation assay. The intracellular presence of S. aureus was documented by electron microscopy. Five antibiotics, dicloxacillin, cefuroxime, gentamicin, azithromycin, and rifampin (rifampicin), were tested in the new in vivo model; and the model was able to distinguish between their extra- and intracellular effects. The intracellular effects of the five antibiotics could be ranked as follows as the mean change in the log(10) number of CFU/ml (Delta log(10) CFU/ml) between treated and untreated mice after 4 h of treatment: dicloxacillin (3.70 Delta log(10) CFU/ml) > cefuroxime (3.56 Delta log(10) CFU/ml) > rifampin (1.86 Delta log(10) CFU/ml) > gentamicin (0.61 Delta log(10) CFU/ml) > azithromycin (0.21 Delta log(10) CFU/ml). We could also show that the important factors during testing of intracellular activity in vivo are the size, number, and frequency of doses; the time of exposure; and the timing between the start of infection and treatment. A poor correlation between the intracellular accumulation of the antibiotics and the actual intracellular effect was found. This stresses the importance of performing experimental studies, like those with the new in vivo model described here, to measure actual intracellular activity instead of making predictions based on cellular pharmacokinetic and MICs.

Antibiotic allergies in the medical record: effect on drug selection and assessment of validity

STUDY OBJECTIVES

To determine the frequency with which reported antibiotic allergies alter drug selection and to assess the validity of these allergies.

DESIGN

Retrospective medical record review, with concurrent interviews conducted in a selected subgroup of patients.

SETTING

Tertiary care academic medical center.

PATIENTS

Three hundred patients with at least one documented antibiotic allergy and who received an antibiotic while hospitalized.

MEASUREMENTS AND MAIN RESULTS

Data were collected to determine the patients' allergies documented in the medical record. The first antibiotic regimen that each patient received while hospitalized was evaluated for deviation from the standard of care as determined from institutional protocols, recommendations in the literature, and expert opinion. A total of 416 allergies to antibiotics were reported. Penicillins were the agents most commonly reported (198 reports), followed by sulfonamides, cephalosporins, macrolides, and fluoroquinolones. The reported allergies altered antibiotic therapy in 91 (30.3%) patients. Report of a penicillin or cephalosporin allergy and use of antibiotics for prophylaxis were strong predictors of altered therapy. The subgroup consisted of 100 patients who were interviewed to determine the specific details of their reported allergic reactions. For 22 of the 100 patients, major discrepancies were found between their verbal reports and medical record documentation. The Naranjo adverse drug reaction probability scale was used to determine the validity of their reactions. Among these 100 patients, 109 (78.4%) of 139 reported reactions to antibiotics were deemed to be allergic in nature. For 55 (50.5%) of the 109 allergic reactions, the Naranjo score was 5 or greater, which correlates with probable to definite validity.

CONCLUSION

Discrepancies between the medical record and in-depth allergy histories are common, and the validity of reported allergic reactions is frequently questionable. Because documentation of an antibiotic allergy frequently alters therapy, increased effort to verify these reactions may be beneficial.

Development, impact and outcomes of the Hull Bacteraemia Service

BACKGROUND

Bacteraemia is a significant cause of mortality and healthcare expenditure. Evidence suggests that consultation by an infection specialist may improve outcomes.

AIM

To review the characteristics and outcomes of patients seen by a newly implemented bacteraemia service.

METHODS

Retrospective review of data collected at time of consultation. Economic analyses and benchmarking of outcomes were also performed.

RESULTS

One hundred and fifty-one patients were seen by the service over an 18-month period. Staphylococcus aureus was the most common isolate and central venous lines the most common source. Antibiotics were changed and additional investigations suggested in 62% and 61% of patients, respectively. The 30-day mortality was 19%. Implementation and delivery of the service over the 18-month study period cost pound 22,663 (pound 15,109 per year). The cost per change in antibiotic prescription was pound 244. The cost per 'near-miss' detected was pound 1193. Overall mortality was no higher and possibly lower than in published studies.

CONCLUSION

We believe that this model of care may be suitable for the management of patients with bacteraemia. A study assessing the cost-effectiveness of this approach is required.

Outcome for invasive Staphylococcus aureus infections

We report a survey of invasive Staphylococcus aureus (ISA) infections concerning outcome variables such as mortality, recurrence and residual symptoms. A prospective, population-based study of all cases of ISA was conducted in the catchment area of Skaraborg Hospital (population 255,109) in western Sweden during the period from 1st March 2003 to 28th February 2005. One hundred and fifty-seven patients were included. Recurrences were seen in 13 cases (9.3%). Thirty patients (19.1%) died during the first 28 days. Mortality rates for complicated bacteraemia and severe sepsis were 32% and 54%, respectively. Older patients (>65 years of age), patients with concomitant heart disease and patients with endovascular infections all suffered higher mortality. Line-associated infections had a higher recurrence rate. Residual symptoms were common, with 34% of the living patients reporting incomplete recovery. Accessory gene regulator (agr) type within the bacteria did not affect disease presentation. We conclude that ISA infections are of major medical importance, with high rates of mortality (19.1%), recurrence (9.3%) and residual functional impairment (34%).

Impact of initial antibiotic choice and delayed appropriate treatment on the outcome of Staphylococcus aureus bacteremia

The study presented here investigated the impact of initial antibiotic choice (beta-lactams vs vancomycin) on the outcome of 342 patients with Staphylococcus aureus bacteremia (50.9% with methicillin-resistant isolates) encountered between 1 January 2002 and 30 June 2003. Initial antibiotics were inappropriate (beta-lactams) in 60 (34.5%) methicillin-resistant cases and suboptimal (vancomycin) in 62 (36.9%) methicillin-susceptible cases. Time to effective antibiotic therapy was longer in methicillin-resistant cases (25.5+/-28.6 vs 9.6+/-16.6 h; p<0.0005). All-cause in-hospital mortality was higher with inappropriate therapy (35.0 vs 20.9%; p=0.02). Initial vancomycin treatment was associated with a higher incidence of delayed clearance (>or=3 days) of methicillin-susceptible bacteremia (56.3 vs 37.0%; p=0.03). The results indicate inappropriate initial therapy is associated with higher in-hospital mortality and initial vancomycin may delay clearance.

Risk factors for recurrence in patients with Staphylococcus aureus infections complicated by bacteremia

Recurrence is a common complication of Staphylococcus aureus infections. A shorter duration of antibiotic treatment for a S. aureus infection has been previously suggested as a possible risk factor for recurrence. We conducted a retrospective cohort study of patients with S. aureus infection complicated by bacteremia who survived their initial treatment (N = 397) at the VA Maryland Health Care System from 1995 to 2004 to determine if 2 weeks or less of antibiotic therapy is significantly associated with a higher rate of recurrence. Recurrence was defined as recurrence of infection because of S. aureus with the same susceptibility to methicillin within 1 year of treatment of the initial bacteremia. Seventeen percent of patients who survived their initial infection had a recurrence of infection. Mean duration of antibiotic therapy in those who recurred was longer than in those who did not recur (21 versus 18 days, P = .18). No evidence was found to support an association between a duration of therapy of 14 days or less and an increased risk for recurrence (RR, 0.68; 95% CI, 0.44-1.04). However, being HIV infected (OR, 4.59; 95% CI, 1.61-13.10), having diabetes (OR, 2.02; 95% CI, 1.13-3.61) and having an infection due to a methicillin-resistant S. aureus (MRSA) (OR, 2.11; 95% CI, 1.17-3.80) were independent risk factors for recurrence. In conclusion, 2 weeks or less of antibiotic therapy was not associated with an increased risk for recurrence. However, patients with diabetes or HIV infection and patients with MRSA infections are at an increased risk for recurrence and should be followed more closely.