Staphylococcus aureus bacteriuria as a prognosticator for outcome of Staphylococcus aureus bacteremia: a case-control study

Risk of infective endocarditis and complicated infection in Staphylococcus aureus bacteremia - a retrospective cohort study on the role of bacteriuria

PURPOSE

S. aureus bacteremia (SAB) is a common and severe infection with high mortality and morbidity. The clinical relevance of the finding of concurrent S. aureus bacteriuria (SABU) is debated. The goal of this study was to analyze whether a concurrent SABU is associated with complicated SAB, infective endocarditis (IE) and mortality.

METHODS

We conducted a retrospective cohort study, reviewing medical charts of all episodes of SAB in patients > 18 years in the region of Skåne, Sweden, between 1st of January and 31st of June 2020. Episodes where a concurrent urine culture was performed were included for analysis. An episode was considered as complicated SAB if there was either attributable mortality, recurrent infection, embolic stroke, or occurrence of a complicated focus of infection.

RESULTS

During the study period, there were 279 episodes of SAB. 154 episodes met the eligibility criteria, of whom 37 (24%) had concurrent SABU. In 78 episodes (51%), the patients had a complicated SAB. There was a significantly lower proportion of complicated SAB for episodes with concurrent SABU (32%), compared to episodes without concurrent SABU (56%), p-value 0.014. Moreover, in the cohort there were 11 episodes (7.1%) of IE and a 30 days mortality rate of 16%, with no difference between the groups with or without SABU.

CONCLUSIONS

There is an association between concurrent SABU and a decreased risk for complicated SAB among patients with SAB. This study found no significant association between SABU and neither IE nor mortality for patients with SAB.

Bacteremia From a Presumed Urinary Source in Hospitalized Adults With Asymptomatic Bacteriuria

Importance

Guidelines recommend withholding antibiotics in asymptomatic bacteriuria (ASB), including among patients with altered mental status (AMS) and no systemic signs of infection. However, ASB treatment remains common.

Objectives

To determine prevalence and factors associated with bacteremia from a presumed urinary source in inpatients with ASB with or without AMS and estimate antibiotics avoided if a 2% risk of bacteremia were used as a threshold to prompt empiric antibiotic treatment of ASB.

Design, Setting, and Participants

This cohort study assessed patients hospitalized to nonintensive care with ASB (no immune compromise or concomitant infections) in 68 Michigan hospitals from July 1, 2017, to June 30, 2022. Data were analyzed from August 2022 to January 2023.

Main Outcomes and Measures

The primary outcome was prevalence of bacteremia from a presumed urinary source (ie, positive blood culture with matching organisms within 3 days of urine culture). To determine factors associated with bacteremia, we used multivariable logistic regression models. We estimated each patient's risk of bacteremia and determined what percentage of patients empirically treated with antibiotics had less than 2% estimated risk of bacteremia.

Results

Of 11 590 hospitalized patients with ASB (median [IQR] age, 78.2 [67.7-86.6] years; 8595 female patients [74.2%]; 2235 African American or Black patients [19.3%], 184 Hispanic patients [1.6%], and 8897 White patients [76.8%]), 8364 (72.2%) received antimicrobial treatment for UTI, and 161 (1.4%) had bacteremia from a presumed urinary source. Only 17 of 2126 patients with AMS but no systemic signs of infection (0.7%) developed bacteremia. On multivariable analysis, male sex (adjusted odds ratio [aOR], 1.45; 95% CI, 1.02-2.05), hypotension (aOR, 1.86; 95% CI, 1.18-2.93), 2 or more systemic inflammatory response criteria (aOR, 1.72; 95% CI, 1.21-2.46), urinary retention (aOR, 1.87; 95% CI, 1.18-2.96), fatigue (aOR, 1.53; 95% CI, 1.08-2.17), log of serum leukocytosis (aOR, 3.38; 95% CI, 2.48-4.61), and pyuria (aOR, 3.31; 95% CI, 2.10-5.21) were associated with bacteremia. No single factor was associated with more than 2% risk of bacteremia. If 2% or higher risk of bacteremia were used as a cutoff for empiric antibiotics, antibiotic exposure would have been avoided in 78.4% (6323 of 8064) of empirically treated patients with low risk of bacteremia.

Conclusions and Relevance

In patients with ASB, bacteremia from a presumed urinary source was rare, occurring in less than 1% of patients with AMS. A personalized, risk-based approach to empiric therapy could decrease unnecessary ASB treatment.

Female Sex and Mortality in Patients with Staphylococcus aureus Bacteremia: A Systematic Review and Meta-analysis

Importance

Staphylococcus aureus is the leading cause of death due to bacterial bloodstream infection. Female sex has been identified as a risk factor for mortality in S aureus bacteremia (SAB) in some studies, but not in others.

Objective

To determine whether female sex is associated with increased mortality risk in SAB.

Data Sources

MEDLINE, Embase, and Web of Science were searched from inception to April 26, 2023.

Study Selection

Included studies met the following criteria: (1) randomized or observational studies evaluating adults with SAB, (2) included 200 or more patients, (3) reported mortality at or before 90 days following SAB, and (4) reported mortality stratified by sex. Studies on specific subpopulations (eg, dialysis, intensive care units, cancer patients) and studies that included patients with bacteremia by various microorganisms that did not report SAB-specific data were excluded.

Data Extraction and Synthesis

Data extraction and quality assessment were performed by 1 reviewer and verified by a second reviewer. Risk of bias and quality were assessed with the Newcastle-Ottawa Quality Assessment Scale. Mortality data were combined as odds ratios (ORs).

Main Outcome and Measures

Mortality at or before 90-day following SAB, stratified by sex.

Results

From 5339 studies retrieved, 89 were included (132 582 patients; 50 258 female [37.9%], 82 324 male [62.1%]). Unadjusted mortality data were available from 81 studies (109 828 patients) and showed increased mortality in female patients compared with male patients (pooled OR, 1.12; 95% CI, 1.06-1.18). Adjusted mortality data accounting for additional patient characteristics and treatment variables were available from 32 studies (95 469 patients) and revealed a similarly increased mortality risk in female relative to male patients (pooled adjusted OR, 1.18; 95% CI, 1.11-1.27). No evidence of publication bias was encountered.

Conclusions and Relevance

In this systematic review and meta-analysis, female patients with SAB had higher mortality risk than males in both unadjusted and adjusted analyses. Further research is needed to study the potential underlying mechanisms.

Clinical significance of concomitant bacteriuria in patients with Staphylococcus aureus bacteraemia

This retrospective study, conducted at Lausanne University Hospital (2015-2021), compared Staphylococcus aureus bacteraemia (SABA) patients with or without concomitant bacteriuria (SABU). Among 448 included bacteraemic patients, 62 (13.8%) had S. aureus concurrently isolated from urine. In multivariate analysis, there was a significant difference in the odds of community-onset bacteraemia (P 0.030), malignancy (P 0.002), > 1 pair of positive blood cultures (P 0.037), and persistent bacteraemia for at least 48 h (P 0.045) in patients with concurrent SABU. No difference concerning mortality was found. On the other hand, SABU was associated with higher rates of SABA recurrence after antibiotic cessation.

Implementation of an asymptomatic bacteriuria assessment protocol for patients discharged from the emergency department

Objective

We evaluated the impact of an asymptomatic bacteriuria (ASB) assessment protocol on the number of antibiotics prescribed for ASB after discharge from the emergency department (ED).

Design

Single-center, before-and-after, retrospective cohort study.

Setting

The study was conducted at a large community health system in North Carolina.

Patients

Eligible patients were discharged from an ED without an antibiotic prescription and had a positive urine culture result after discharge from May through July 2021 (preimplementation group) and October through December 2021 (postimplementation group).

Methods

Patient records were reviewed to determine the number of antibiotic prescriptions for ASB on follow-up call before and after implementation of an ASB assessment protocol. Secondary outcomes included 30-day admissions, 30-day ED visits, 30-day UTI-related encounters, and projected antibiotic days of therapy.

Results

The study included 263 patients: 147 in the preimplementation group and 116 in the postimplementation group). There were significantly fewer antibiotic prescriptions for ASB in the postimplementation group (50% vs 87%; P < .0001). There were no differences in the incidence of 30-day admissions (7% vs 8%; P = .9761), 30-day ED visits (14% vs 16%; P = .7805), or 30-day UTI-related encounters (0% vs 0%, NA).

Conclusions

Implementation of an ASB assessment protocol for patients discharged from the ED significantly reduced the number of antibiotic prescriptions for ASB on follow-up call without an increase in 30-day admissions, ED visits, or UTI-related encounters.

Potent, Broad-Spectrum Antimicrobial Effects of S-Nitroso-N-acetylpenicillamine-Impregnated Nitric Oxide-Releasing Latex Urinary Catheters

Although numerous prevention and intervention techniques have been developed to counteract catheter-associated urinary tract infections (CAUTIs), urinary catheters remain one of the most common sources of hospital-acquired infections. Nitric oxide (NO), a gaseous free radical responsible for regulating many physiological functions in the body, has gained immense popularity due to its potent, broad-spectrum antimicrobial activity, which is capable of combating medical device-associated infections. In this work, a straightforward solvent-swelling method was used to load the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) into commercial latex catheters (SNAP-UCs) for the first time. The effects of swelling catheters with different concentrations of SNAP solutions (25-125 mg/mL SNAP in tetrahydrofuran (THF)) were studied by measuring the NO release kinetics, SNAP loading, and SNAP leaching. SNAP-UCs impregnated with a 50 mg/mL SNAP-THF solution were found to maximize the amount of SNAP loaded into the latex (0.115 ± 0.009 mg SNAP/mg catheter) and showed physiological levels of NO release (>2 × 10^-10 mol min^-1 cm^-2) over 7 days and minimal SNAP leaching (<2%). SNAP-UCs showed impressive in vitro contact-based and diffusible antimicrobial efficacy against three CAUTI-associated pathogens, reducing the viability of adhered and planktonic Escherichia coli, Proteus mirabilis, and Staphylococcus aureus by ∼98.0 to 99.1% (adhered) and 86.3-96.3% (planktonic) compared to control latex catheters. In vitro cytotoxicity against 3T3 mouse fibroblasts using a CCK-8 assay showed that SNAP-UCs were noncytotoxic (>90% viability). In summary, SNAP-UCs show stable, noncytotoxic NO release characteristics capable of potent, broad-spectrum antimicrobial activity, demonstrating great potential for reducing the devastating effects associated with CAUTIs.

A Narrative Review on the Role of Staphylococcus aureus Bacteriuria in S. aureus Bacteremia

Staphylococcus aureus bacteriuria (SABU) can occur in patients with S. aureus bacteremia (SAB). However, little is known on the (molecular) pathomechanisms of the renal passage of S. aureus. This review discusses the epidemiology and pathogenesis of SABU in patients with SAB and identifies knowledge gaps. The literature search was restricted to the English language. The prevalence of SABU in patients with SAB is 7.8%-39% depending on the study design. The main risk factor for SABU is urinary tract catheterization. SABU in SAB patients is associated with increased mortality. Given present evidence, hematogenous seeding-as seen in animal models-and the development of micro-abscesses best describe the translocation of S. aureus from blood to urine. Virulence factors that might be involved are adhesion factors, sortase A, and coagulase, among others. Other potential routes of bacterial translocation (eg, transcytosis, paracytosis, translocation via "Trojan horses") were identified as knowledge gaps.

Management of Staphylococcus aureus Bloodstream Infections

Staphylococcus aureus bloodstream infections are associated with a high morbidity and mortality. Nevertheless, significance of a positive blood culture with this pathogen is often underestimated or findings are misinterpreted as contamination, which can result in inadequate diagnostic and therapeutic consequences. We here review and discuss current diagnostic and therapeutic key elements and open questions for the management of Staphylococcus aureus bloodstream infections.

Prevalence and risk factors for bacteremia in patients with Staphylococcus aureus bacteriuria: A retrospective cohort study

OBJECTIVES

Staphylococcus aureus bacteriuria (SABU) is rare but can be an indicator of S. aureus bacteremia (SAB). The objective of this study was to assess the proportion of SAB in patients with SABU and identify risk factors in a hospital-based population.

METHODS

We used electronic databases to identify eligible patients to be enrolled in a retrospective cohort study. Inclusion criteria were (i) SABU, (ii) ≥18 years of age, and (iii) ≥1 blood culture sampled ±3 months of SABU. Patients with missing values for demographic (e.g., age, sex) or clinical characteristics (e.g., comorbidities) and laboratory analyses were excluded.

RESULTS

In total, 245 patients attending the University Hospital Münster, Germany, between 1 January 2012 and 31 December 2019 met the inclusion/exclusion criteria. Of the 245 patients with SABU, 66 had a concomitant SAB (26.9%). Elevated C-reactive protein (CRP) levels were associated with SAB. Other parameters (e.g., leukocytes, comorbidities) were not associated with SAB in a multivariate analysis.

CONCLUSION

The frequency of SAB in patients with SABU was high and warrants active screening for bloodstream infections in hospitalized patients, particularly if CRP levels are elevated.

Staphylococcus Aureus Bacteriuria as a Predictor of In-Hospital Mortality in Patients with Staphylococcus Aureus Bacteremia. Results of a Retrospective Cohort Study

Staphylococcus aureus bloodstream infection (SA-BSI) is an infection with increasing morbidity and mortality. Concomitant Staphylococcus aureus bacteriuria (SABU) frequently occurs in patients with SA-BSI. It is considered as either a sign of exacerbation of SA-BSI or a primary source in terms of urosepsis. The clinical implications are still under investigation. In this study, we investigated the role of SABU in patients with SA-BSI and its effect on the patients' mortality. We performed a retrospective cohort study that included all patients in our university hospital (Charité Universitätsmedizin Berlin) between 1 January 2014 and 31 March 2017. We included all patients with positive blood cultures for Staphylococcus aureus who had a urine culture 48 h before or after the first positive blood culture. We identified cases while using the microbiology database and collected additional demographic and clinical parameters, retrospectively, from patient files and charts. We conducted univariate analyses and multivariable Cox regression analysis to evaluate the risk factors for in-hospital mortality. 202 patients met the eligibility criteria. Overall, 55 patients (27.5%) died during their hospital stay. Cox regression showed SABU (OR 2.3), Pitt Bacteremia Score (OR 1.2), as well as moderate to severe liver disease (OR 2.1) to be independent risk factors for in-hospital mortality. Our data indicates that SABU in patients with concurrent SA-BSI is a prognostic marker for in-hospital death. Further studies are needed for evaluating implications for therapeutic optimization.

[Urosepsis]

Urosepsis is defined as a severe disease due to organ failure caused by a urinary tract infection. An empirical antibiotic therapy should be instigated within the first hour after diagnosis. Urine cultures and blood cultures should be performed before antibiotic treatment. Further diagnostics should be carried out at an early stage to enable an interventional focus control in the case of urinary tract obstruction or abscess formation, if necessary. Gram-negative pathogens are most frequently isolated. Extended spectrum beta-lactamase (ESBL) forming bacteria as a cause of urosepsis are increasing. Carbapenemase-forming Enterobacteriaceae, on the other hand, are still rare. The empirical treatment consists of a broad spectrum beta-lactam antibiotic. While piperacillin/tazobactam, carbapenems and the new cephalosporin/beta-lactamase inhibitor (BLI) combinations are given as monotherapy, cephalosporins should be combined with aminoglycosides (preferred) or fluoroquinolones. If a combination therapy is given, it should be de-escalated to a monotherapy after 48-72 h.

Multimodal Tracking of Controlled Staphylococcus aureus Infections in Mice

There is a need to develop diagnostic and analytical tools that allow noninvasive monitoring of bacterial growth and dissemination in vivo. For such cell-tracking studies to hold translational value to controlled human infections, in which volunteers are experimentally colonized, they should not require genetic modification, and they should allow tracking over a number of replication cycles. To gauge if an antimicrobial peptide tracer, 99mTc-UBI29-41-Cy5, which contains both a fluorescent and a radioactive moiety, could be used for such in vivo bacterial tracking, we performed longitudinal imaging of a thigh-muscle infection with 99mTc-UBI29-41-Cy5-labeled Staphylococcus aureus. Mice were imaged using SPECT and fluorescence-imaging modalities at various intervals during a 28 h period. Biodistribution analyses were performed to quantitate radioactivity in the abscess and other tissues. SPECT and fluorescence imaging in mice showed clear retention of the 99mTc-UBI29-41-Cy5-labeled bacteria following inoculation in the thigh muscle. Despite bacterial replication, the signal intensity in the abscess only modestly decreased within a 28 h period: 52% of the total injected radioactivity per gram of tissue (%ID/g) at 4 h postinfection (pi) versus 44%ID/g at 28 h pi (15% decrease). After inoculation, a portion of the bacteria disseminated from the abscess, and S. aureus cultures were obtained from radioactive urine samples. Bacterial staining with 99mTc-UBI29-41-Cy5 allowed noninvasive bacterial-cell tracking during a 28 h period. Given the versatility of the presented bacterial-tracking method, we believe that this concept could pave the way for precise imaging capabilities during controlled-human-infection studies.

Community-acquired Staphylococcus aureus bacteriuria: a warning microbiological marker for infective endocarditis?

Background

Urinary tract infection (UTI) is frequently diagnosed in the Emergency Department (ED). Staphylococcus aureus (SA) is an uncommon isolate in urine cultures (0.5–6% of positive urine cultures), except in patients with risk factors for urinary tract colonization. In the absence of risk factors, community-acquired SA bacteriuria may be related to deep-seated SA infection including infective endocarditis. We hypothesized that SA bacteriuria could be a warning microbiological marker of unsuspected infective endocarditis in the ED.

Methods

This is a retrospective chart review of consecutive adult patients between December 2005 and February 2018. All patients admitted in the ED with both SA bacteriuria (10⁴ CFU/ml SA isolated from a single urine sample) and SA bacteremia, without risk factors for UT colonization (i.e., < 1 month UT surgery, UT catheterization) were analyzed. Diagnosis of infective endocarditis was based on the Duke criteria.

Results

During the study period, 27 patients (18 men; median age: 61 [IQR: 52–73] years) were diagnosed with community-acquired SA bacteriuria and had subsequently documented bacteremia and SA infective endocarditis. Only 5 patients (18%) had symptoms related to UT infection. Median delay between ED admission and SA bacteriuria identification was significantly shorter than that between ED admission and the diagnosis of infective endocarditis (1.4 ± 0.8 vs. 4.3 ± 4.2 days: p = 0.01). Mitral and aortic valves were most frequently involved by infective endocarditis (93%). Mortality on day 60 reached 56%.

Conclusions

This study suggests that community-acquired SA bacteriuria should warn the emergency physician about a potentially associated left-sided infective endocarditis in ED patients without risk factors for UT colonization.

[Urosepsis]

Urosepsis is defined as a severe disease due to organ failure caused by a urinary tract infection. An empirical antibiotic therapy should be instigated within the first hour after diagnosis. Urine cultures and blood cultures should be performed before antibiotic treatment. Further diagnostics should be carried out at an early stage to enable an interventional focus control in the case of urinary tract obstruction or abscess formation, if necessary. Gram-negative pathogens are most frequently isolated. Extended spectrum beta-lactamase (ESBL) forming bacteria as a cause of urosepsis are increasing. Carbapenemase-forming Enterobacteriaceae, on the other hand, are still rare. The empirical treatment consists of a broad spectrum beta-lactam antibiotic. While piperacillin/tazobactam, carbapenems and the new cephalosporin/beta-lactamase inhibitor (BLI) combinations are given as monotherapy, cephalosporins should be combined with aminoglycosides (preferred) or fluoroquinolones. If a combination therapy is given, it should be de-escalated to a monotherapy after 48-72 h.

Phenazine-1-carboxamide functionalized mesoporous silica nanoparticles as antimicrobial coatings on silicone urethral catheters

Microbial infections due to biofilms on medical implants can be prevented by antimicrobial coatings on biomaterial surfaces. Mesoporous silica nanoparticles (MSNPs) were synthesized via base-catalyzed sol-gel process at room temperature, functionalized with phenazine-1-carboxamide (PCN) and characterized by UV-visible, FT-IR, DLS, XRD spectroscopic techniques, SEM, TEM, TGA and BET analysis. Native MSNPs, PCN and PCN-MSNPs were evaluated for anti-Candida minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), Candida albicans (C. albicans) biofilms and C. albicans-Staphylococcus aureus (S. aureus) polymicrobial biofilm inhibition. PCN-MSNPs were four-fold effective (MIC 3.9 µg mL-1; 17.47 µM) and MFC (7.8 µg mL-1; 34.94 µM) as compared to pure PCN (MIC 15.6 µg mL-1; 69.88 µM) and MFC (31.2 µg mL-1; 139.76 µM). PCN-MSNPs inhibited in vitro C. albicans MTCC 227-S. aureus MTCC 96 biofilms at very low concentration (10 µg mL-1; 44.79 µM) as compared to pure PCN (40 µg mL-1; 179.18 µM). Mechanistic studies revealed that PCN induced intracellular ROS accumulation in C. albicans MTCC 227, S. aureus MTCC 96 and S. aureus MLS-16 MTCC 2940, reduction in total ergosterol content, membrane permeability, disruption of ionic homeostasis followed by Na+, K+ and Ca2+ leakage leading to cell death in C. albicans MTCC 227 as confirmed by confocal laser scanning micrographs. The silicone urethral catheters coated with PCN-MSNPs (500 µg mL-1; 2.23 mM) exhibited no formation of C. albicans MTCC 227 - S. aureus MTCC 96 and C. albicans MTCC 227 - S. aureus MLS -16 MTCC 2940 biofilms. This is the first report on PCN-MSNPs for use as antimicrobial coatings against microbial adhesion and biofilm formation on silicone urethral catheters.

Agreement between Parallel Canine Blood and Urine Cultures: Is Urine Culture the Poor Man's Blood Culture?

Bloodstream infections are a significant cause of morbidity and mortality in critically ill dogs, but due to cost and difficulties in sample acquisition, blood cultures are infrequently obtained. In ill dogs, urine cultures may be recommended as surrogates for blood cultures. In order to determine the outcome agreement between parallel urine and blood cultures, we retrospectively analyzed parallel blood and urine specimens submitted for culture from dogs at the NC State Veterinary Hospital between 2011 and 2016. Positive cultures were reported from 15% of the submitted blood specimens and 23% of the submitted urine specimens. A total of 295 urine and blood samples were submitted in parallel, with positive growth demonstrated in 14 concordant and five discordant pairs. A kappa statistic comparing blood and urine culture outcomes was 0.266 (fair) when all parallel growth was included, including concordant and discordant results, and 0.170 (poor) when restricted to parallel concordant growth. The sensitivity of urine to reflect concordant bloodstream bacterial organisms was 30%, with a specificity of 87%. The positive and negative predictive values were 30% and 88%, respectively. Of dogs with both specimens positive on bacterial culture, 7 of 7 (100%) with suspected urogenital infection sources were concordant. All dogs with discordant bloodstream and urinary infections were immunosuppressed. Urinary coagulase-positive Staphylococcus isolates were most likely to be concordant with bloodstream infections. In conclusion, we found that urine culture is neither a substitute nor a screen for blood culture. Blood cultures should be performed in any potentially septic animal, especially those that are considered immunosuppressed.

The clinical significance of concomitant bacteriuria in patients with Staphylococcus aureus bacteremia. A review and meta-analysis

BACKGROUND

Staphylococcus aureus bacteriuria (SABU) concomitant to S. aureus bacteremia (SAB) has been associated with deep-seated infections and worse prognosis. However, the relevant studies were small and inconsistent. Here, we aim to provide a review of the relevant literature, and a meta-analysis of these studies.

METHODS

We searched PubMed and Scopus for studies comparing patients with SAB and concomitant SABU to patients with SAB without SABU.

RESULTS

Nine relevant studies were identified, involving 1429 patients with SAB, of whom 18.5% (n = 265) had concomitant SABU. Pooling the results of those studies, SABU was significantly associated with endocarditis, bone/joint infection and septic embolism. SABU was also associated with persistent SAB, and higher mortality.

CONCLUSIONS

Although SABU may be a useful marker of complicated SAB, the current literature has several limitations. Larger prospective studies are required to clarify the value of SABU in clinical decision making.

Evaluation and management of Staphylococcus aureus bacteriuria: an updated review

BACKGROUND AND AIMS

There is little guidance regarding the evaluation and management of patients with Staphylococcus aureus bacteriuria (SABU). Here, we aimed to provide an up-to-date review of the literature.

METHODS

We searched PubMed, Scopus, and clinical trial registries for articles evaluating the epidemiology of SABU, risk factors of SABU, the association of SABU with urinary tract infection, bacteremia and invasive S. aureus infections, and the management of patients with SABU.

RESULTS

S. aureus is an uncommon isolate in urine cultures. It is more common among certain patients, e.g., patients with indwelling urinary tract devices or prior urinary tract instrumentation. SABU may represent asymptomatic bacteriuria, primary urinary tract infection, or hematogenous seeding of the urinary tract associated with other foci of infection. SABU may also serve as the focus for subsequent bacteremia and invasive infections. We did not find any clinical trials regarding the management of patients with SABU.

CONCLUSIONS

Based on our review, we suggest an algorithmic approach for the evaluation and management of patients with SABU. However, evidence from clinical trials is lacking and there are several gaps in the current literature. These are discussed in this review.

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.

Methicillin-resistant Staphylococcus aureus as a uropathogen in an Irish setting

Urinary tract infections are one of the most common infectious diseases diagnosed in the community and in the hospital setting. Their treatment is complicated by drug-resistant pathogens and the colonization by microbes of indwelling urinary catheters. This study assessed the occurrence and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) uropathogens isolated for 5 consecutive years at University Hospital Waterford between 2010 and 2014. We created 4 clinically relevant subdivisions, based on urine source: hospital inpatients, patients from the Emergency Department, patients referred from their General Practitioner, and Nursing Home patients. We performed a retrospective review from the hospital's electronic microbiological system and calculated resistance rates for each of the standard antimicrobial agents. During the 5-year study period, we studied 151 urine isolates obtained from 128 patients who had an MRSA cultured in their urine sample. There was 100% resistance of all MRSA isolates to Flucloxacillin and Coamoxiclav. Ninety-eight percent of isolates were resistant to Ciprofloxacin. The resistance rate for Trimethoprim was 7.4% and there was only 2.7% resistance for Nitrofurantoin. For a clinical subset of patients, we also demonstrated 100% sensitivity for samples tested against Teicoplanin and Vancomycin. Urinary MRSA is an infrequently studied phenomenon, but with the rising trend of hospital superbugs nationally, its management is of critical importance. Suitable agents to address this within our population include Nitrofurantoin in the well patient requiring urinary MRSA eradication or Vancomycin/Teicoplanin in the unwell patient requiring intravenous therapy. In all groups, fluoroquinolones should be avoided due to significant resistance rates.

Neonatal Staphylococcus lugdunensis urinary tract infection

Staphylococcus lugdunensis is a known pathogen of infective endocarditis, but not of urinary tract infection. We report a previously healthy neonate without congenital anomalies of the kidney and urinary tract who developed urinary tract infection due to Staphylococcus lugdunensis, illustrating that Staphylococcus lugdunensis can cause urinary tract infection even in those with no urinary tract complications.

Staphylococcus saprophyticus native valve endocarditis in a diabetic patient with neurogenic bladder: A case report

A 61-year-old man was admitted to our hospital with 2-day history of malaise and dyspnea. He had mitral prolapse and type II diabetes mellitus with neurogenic bladder, which was cared for by catheterization on his own. On arrival the patient was in septic condition with hypoxemia, and physical examination revealed systolic murmur at the apex. Transthoracic echocardiography revealed vegetation of the mitral and the aortic valve. The presence of continuous bacteremia was confirmed by multiple sets of blood culture, whereby gram-positive cocci was retrieved and identified as Staphylococcus saprophyticus (S. saprophyticus) both phenotypically and genetically. Because two major criteria of the Modified Duke Criteria were met, the patient was diagnosed with native valve endocarditis due to S. saprophyticus. The urine culture was also positive for gram-positive cocci, phenotypically identified as Staphylococcus warneri, which was subsequently identified as S. saprophyticus with the use of 16S rRNA gene sequence analysis and MALDI-TOF MS (matrix-assisted laser desorption ionization time of flight mass spectrometry), indicating strongly that the intermittent catheterization-associated urinary tract infection resulted in bacteremia that eventually lead to infective endocarditis. This patient was treated with vancomycin and clindamycin. Because of multiple cerebral infarctions, the patient underwent mitral and aortic valve replacement on hospital day 5. Blood culture turned negative at 6th hospital day. Antibiotic therapy was continued for six weeks after surgery. The patient's clinical course was uneventful thereafter, and was discharged home. This is the first case report of native valve endocarditis caused by S. saprophyticus of confirmed urinary origin.

Epidemiology and outcome of Staphylococcus aureus bloodstream infection and sepsis in a Norwegian county 1996-2011: an observational study

Background

Staphylococcus aureus is one of the most common and lethal causes of bloodstream infection and the incidence is increasing. We carried out a prospective observational study of patients with Staphylococcus aureus bloodstream infection and sepsis in Nord-Trøndelag county in Norway from 1996–2011. The main outcome of interest was all-cause mortality within 30 and 90 days.

Methods

Positive blood cultures were registered prospectively by the microbiology laboratory and clinical variables were retrospectively registered from patients’ hospital records. The severity of sepsis was assigned according to the 2001 International Sepsis Definition Conference criteria. The association between clinical characteristics and mortality was studied using logistic regression analysis, and adjusted 30- and 90-day mortality risks were estimated.

Results

Among 373 patients, the median age was 74 years and 60.3% were male. 0.8% of the patients were diagnosed with MRSA. 29.8% of the patients developed severe sepsis and 12.9% developed septic shock. The all-cause mortality was 14.5%, 27.3% and 36.2% at 7, 30 and 90 days, respectively. Compared to patients with sepsis without organ failure (Mortality risk 13.3%, 95% CI 7.5-16.3%), the 30-day mortality risk was 3-fold higher among those with severe sepsis (39.9%, 95% CI 29.5-48.5%) and more than 4-fold higher for those with septic shock (57.3%, 95% CI 42.5-72.2%). The 30-day all-cause mortality varied by focus of infection, with the highest 30-day mortality risk among those with a pulmonary focus (42.4%, 95% CI 26.0-58.5%) and unknown focus of infection (38.7%, 95% CI 27.5-48.2%). The mortality risk did not differ between the first and second halves of the study period with a 30-day mortality risk of 27.3%, (95% CI 18.1-33.1%) for 1996–2003 versus 27.4% (95% CI 19.4-31.4%) for 2004–2011. The same pattern was seen for 90-day mortality risk.

Conclusion

Staphylococcus aureus bloodstream infection carries a high case fatality rate, especially among those with severe sepsis and septic shock and among those with a pulmonary or unknown focus of infection. There was no decrease in 30- or 90-day mortality risk during the study period. This underscores the importance of continuing surveillance and efforts to improve the outcome of this serious disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0849-4) contains supplementary material, which is available to authorized users.

Methicillin-resistant Staphylococcus aureus bloodstream infection surveillance: National Healthcare Safety Network's laboratory-identified event reporting versus traditional laboratory-confirmed bloodstream infection surveillance

Hospitals must report cases of methicillin-resistant Staphylococcus aureus bloodstream infection (BSI) using a new laboratory-identified (LabID) event reporting module. BSI rates obtained using LabID differ from rates of BSI obtained from traditional surveillance (concordance of healthcare facility-onset cases, 61%-76%) because definitions used to report LabID events are inconsistent with traditional BSI definitions.

Unexpected Multidrug Resistance of Methicillin-Resistant Staphylococcus aureus in Urine Samples: A Single-Center Study

PURPOSE

Infections of methicillin-resistant Staphylococcus aureus (MRSA) are becoming an increasingly concerning clinical problem. The aim of this study was to assess the development of MRSA in urine cultures in a major public university-affiliated hospital and the therapeutical and hygiene-related possibilities for reducing resistance.

MATERIALS AND METHODS

This study included 243 samples from patients diagnosed with MRSA infection over a period of 6 years. An agar diffusion test measured the effects of antimicrobial agents against bacteria grown in culture. The analyses were based on the guidelines of the Clinical and Laboratory Standards Institute.

RESULTS

A regression analysis was performed, which showed 100% resistance to the following antibiotics throughout the entire testing period: carbapenem, cephalosporin (1st-4th generation), penicillin G, aminopenicillin, β-lactamase, and isoxazolyl penicillin. However, a significant decrease in resistance was found for amikacin, gentamicin, clindamycin, levofloxacin, erythromycin, and mupirocin.

CONCLUSIONS

MRSA showed a decreasing trend of antimicrobial resistance, except against carbapenem, cephalosporin (1st-4th generation), penicillin G, aminopenicillin, β-lactamase, and isoxazolyl penicillin, for which complete resistance was observed.

Clinical significance of Staphylococcus aureus bacteriuria at a tertiary care hospital

OBJECTIVES

Staphylococcus aureus bacteriuria has been associated with invasive S. aureus disease. The current project describes the clinical significance of S. aureus bacteriuria.

METHODS

We conducted a retrospective chart review of patients who had S. aureus bacteriuria at the Michael E. DeBakey Veterans Affairs Medical Center, 2008-2010.

RESULTS

A total of 326 patients were included. Invasive S. aureus disease was documented within 12 months of bacteriuria in 56 patients (22.3% of methicillin-resistant S. aureus (MRSA) cases and 8.4% of methicillin-sensitive S. aureus (MSSA), p = 0.002). Multiple logistic regression indicated that MRSA bacteriuria (odds ratio (OR) 2.91, p = 0.010), absence of symptoms suggestive of a urinary tract infection (UTI) (OR 3.21, p = 0.019), inpatient status (OR 4.72, p = 0.003), and receipt of antibiotics active against S. aureus (OR 6.41, p < 0.001) were significantly associated with the presence of invasive S. aureus disease. Seventy-seven patients (23.6%) died within 12 months of the documented S. aureus bacteriuria. Age (OR 1.02, p = 0.025), absence of pyuria (OR 2.00, p = 0.029), the presence of invasive S. aureus disease (OR 2.05, p = 0.033), and inpatient status (OR 3.62, p < 0.001) were significantly associated with death.

CONCLUSIONS

S. aureus bacteriuria is associated with significant morbidity and mortality. Patients without UTI symptoms, those with MRSA bacteriuria, and those without pyuria were more to likely to have worse outcomes (invasive S. aureus disease or death). Obtaining blood cultures should be considered in these cases.

Staphylococcus aureus Bacteriuria: Source, Clinical Relevance, and Management

Staphylococcus aureus bacteriuria is a common condition with still largely undetermined clinical relevance. Although S. aureus bacteriuria can be secondary to bacteremia and systemic infection in some patients, it may predispose to bacteremia and invasive disease in others. Whereas most patients with S. aureus bacteriuria do not have symptomatic urinary tract infection, it is reportedly associated with endocarditis and other types of invasive diseases, thereby resulting in major morbidity and occasional mortality. This review summarizes and analyzes the results of previous reports of S. aureus bacteriuria and assesses the clinical relevance and management of this increasingly recognized entity.

Predictors of mortality in Staphylococcus aureus Bacteremia

Staphylococcus aureus bacteremia (SAB) is an important infection with an incidence rate ranging from 20 to 50 cases/100,000 population per year. Between 10% and 30% of these patients will die from SAB. Comparatively, this accounts for a greater number of deaths than for AIDS, tuberculosis, and viral hepatitis combined. Multiple factors influence outcomes for SAB patients. The most consistent predictor of mortality is age, with older patients being twice as likely to die. Except for the presence of comorbidities, the impacts of other host factors, including gender, ethnicity, socioeconomic status, and immune status, are unclear. Pathogen-host interactions, especially the presence of shock and the source of SAB, are strong predictors of outcomes. Although antibiotic resistance may be associated with increased mortality, questions remain as to whether this reflects pathogen-specific factors or poorer responses to antibiotic therapy, namely, vancomycin. Optimal management relies on starting appropriate antibiotics in a timely fashion, resulting in improved outcomes for certain patient subgroups. The roles of surgery and infectious disease consultations require further study. Although the rate of mortality from SAB is declining, it remains high. Future international collaborative studies are required to tease out the relative contributions of various factors to mortality, which would enable the optimization of SAB management and patient outcomes.

Clinical significance of Staphylococcus aureus bacteriuria in a nationwide study of adults with S. aureus bacteraemia

OBJECTIVES

To evaluate the clinical significance of Staphylococcus aureus bacteriuria (SABU) in adults with S. aureus bacteraemia (SAB).

METHODS

All individuals ≥18 years old diagnosed with SAB in Iceland between December 1st 2003 and November 30th 2008 were retrospectively identified. Data was collected from medical records. Concomitant SABU was defined as growth of S. aureus in a urine sample taken within 24 h of the index blood culture.

RESULTS

SABU was seen in 27 of 166 (16.3%) SAB patients having urine cultured before administration of antibiotics, but after excluding those with SAB of urinary tract origin SABU was seen in 16 of 152 (10.5%). In this latter cohort SABU was independently associated with having endocarditis (RR 6.68; 95% CI 1.53-17.3) and admission to intensive-care unit (RR 2.84; 95% CI 1.25-4.44), while for having complicated SAB the RR was 1.56 (95% CI 0.96-1.80). No correlation was seen with mortality or relapse rates.

CONCLUSIONS

SABU appears to be secondary to SAB in some cases while it is the primary infection causing SAB in others. In patients with SAB of non-urinary tract origin SABU should probably be regarded as distant haematogenous seeding and a marker of deep tissue dissemination, thus affecting general management and treatment duration.