Progression to bacteremia in critical care patients colonized with methicillin-resistant Staphylococcus aureus expressing Panton-Valentine leukocidin

Epidemiological and clinical features of Panton-Valentine Leukocidin positive Staphylococcus aureus bacteremia: A case-control study

BACKGROUND

Panton-Valentine Leukocidin (PVL) toxin in Staphylococcus aureus has been associated with both severe pneumonia and skin and soft tissue infections. However, there are only limited data on how this virulence factor may influence the clinical course or complications of bacteremic S. aureus infections.

METHODS

Between September 2016 and March 2018, S. aureus isolates from clinical cultures from hospitals in an academic medical center underwent comprehensive genomic sequencing. Four hundred sixty-nine (29%) of 1681 S. aureus sequenced isolates were identified as containing the genes that encode for PVL. Case patients with one or more positive blood cultures for PVL were randomly matched with control patients having positive blood cultures with lukF/lukS-PV negative (PVL strains from a retrospective chart review).

RESULTS

51 case and 56 control patients were analyzed. Case patients were more likely to have a history of injection drug use, while controls more likely to undergo hemodialysis. Isolates from 78.4% of case patients were methicillin resistant as compared to 28.6% from control patients. Case patients had a higher incidence of pneumonia and skin and soft tissue infection and longer duration of fever without differences in length of bacteremia. Clinical cure or expiration was comparable.

CONCLUSIONS

These results are consistent with prior observations associating the PVL toxin with both community-acquired MRSA strains as well as severe staphylococcal pneumonia. The presence of the PVL toxin does not appear to otherwise influence the natural history of bacteremic S. aureus disease other than in prolonging the duration of fever.

Development of a vaccine against Staphylococcus aureus invasive infections: Evidence based on human immunity, genetics and bacterial evasion mechanisms

Invasive Staphylococcus aureus infections are a leading cause of morbidity and mortality in both hospital and community settings, especially with the widespread emergence of virulent and multi-drug resistant methicillin-resistant S. aureus strains. There is an urgent and unmet clinical need for non-antibiotic immune-based approaches to treat these infections as the increasing antibiotic resistance is creating a serious threat to public health. However, all vaccination attempts aimed at preventing S. aureus invasive infections have failed in human trials, especially all vaccines aimed at generating high titers of opsonic antibodies against S. aureus surface antigens to facilitate antibody-mediated bacterial clearance. In this review, we summarize the data from humans regarding the immune responses that protect against invasive S. aureus infections as well as host genetic factors and bacterial evasion mechanisms, which are important to consider for the future development of effective and successful vaccines and immunotherapies against invasive S. aureus infections in humans. The evidence presented form the basis for a hypothesis that staphylococcal toxins (including superantigens and pore-forming toxins) are important virulence factors, and targeting the neutralization of these toxins are more likely to provide a therapeutic benefit in contrast to prior vaccine attempts to generate antibodies to facilitate opsonophagocytosis.

Host-Pathogen-Treatment Triad: Host Factors Matter Most in Methicillin-Resistant Staphylococcus aureus Bacteremia Outcomes

Previous studies have separately emphasized the importance of host, pathogen, and treatment characteristics in determining short-term or in-hospital mortality rates for patients with methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections. Less is known about the relative importance of these factors and their interactions in determining short-, medium-, and long-term mortality rates. This is an observational cohort study in which data for all patients admitted to the University of New Mexico (UNM) Health Sciences Center (HSC) between July 2002 and August 2013 with MRSA-positive blood cultures were recorded. We collected patients' demographics and treatment data, as well as data on genetic markers of the MRSA isolates. Outcomes of interest were determinants of short-term (within 30 days), medium-term (30 to 90 days), and long-term (>90 days) mortality rates. This study included 273 patients with MRSA bacteremia. Short-, medium-, and long-term mortality rates were 18.7%, 26.4%, and 48%, respectively. Thirty-day mortality rates were influenced by host variables and host-pathogen interaction characteristics. Pitt bacteremia scores, malignancy, and health care exposure contributed to 30- to 90-day mortality rates, while treatment duration of >4 weeks had a protective effect. Age remained a significant risk factor for death at >90 days, while admission leukocytosis was protective. Infection represented the most frequent cause of death for all three time frames; rates varied from 72.6% in the first 30 days and 60% for 30 to 90 days to 35.7% for >90 days (P = 0.003). Host characteristics affect short-, medium-, and long-term mortality rates for MRSA bloodstream infections more than do pathogen genetic markers and treatment factors.

Staphylococcus aureus Colonization and Long-Term Risk for Death, United States

To examine the association of colonization by Staphylococcus aureus and general population mortality, we followed 10,598 adults for 8.5 years on average. Methicillin-susceptible S. aureus colonization was not associated with death. Methicillin-resistant S. aureus carriage predicted death in a crude analysis but not after adjustment for socioeconomic status and co-morbidities.

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

OBJECTIVE

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

DATA SOURCES

MEDLINE and EMBASE and reference lists of all eligible articles.

STUDY SELECTION

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

DATA EXTRACTION

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

DATA SYNTHESIS

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

CONCLUSIONS

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

Clinical significance of methicillin-resistant Staphylococcus aureus colonization on hospital admission: one-year infection risk

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3).

METHODOLOGY/PRINCIPAL FINDINGS

Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively).

CONCLUSIONS/SIGNIFICANCE

MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Association between prehospital vitamin D status and hospital-acquired bloodstream infections

BACKGROUND

Alterations in immune function can predispose patients to nosocomial infections. Few studies have explored potentially modifiable host factors that may improve immune function and decrease risk of hospital-acquired bloodstream infection (HABSI). Vitamin D is a key regulator of innate and adaptive immune systems that may influence host susceptibility to infections.

OBJECTIVE

We investigated the association between prehospital serum 25-hydroxyvitamin D [25(OH)D] concentrations and risk of HABSI.

DESIGN

We performed a retrospective cohort study of 2135 adult patients from 2 Boston teaching hospitals. All patients had 25(OH)D concentrations measured before hospitalization between 1993 and 2010. The main outcome measure was HABSI, which was defined as positive blood cultures from samples drawn 48 h after hospital admission. Coagulase-negative Staphylococcus isolates were not considered to be bloodstream infections. Associations between 25(OH)D groups and HABSI were estimated by using bivariable and multivariable logistic regression models. Adjusted ORs were estimated with the inclusion of covariate terms thought to plausibly interact with both 25(OH)D concentration and HABSI.

RESULTS

Compared with patients with 25(OH)D concentrations ≥30 ng/mL, patients with concentrations <30 ng/mL had higher odds of HABSI. For 25(OH)D concentrations <10 ng/mL, the OR was 2.33 (95% CI: 1.45, 3.74); for 25(OH)D concentrations from 10 to 19.9 ng/mL, the OR was 1.60 (95% CI: 1.04, 2.46); and for 25(OH)D concentrations from 20 to 29.9 ng/mL, the OR was 1.13 (95% CI: 0.69, 1.84). After adjustment for age, sex, race (nonwhite compared with white), patient type (medical compared with surgical), and Deyo-Charlson index, the ORs of HABSI were 1.95 (95% CI: 1.22, 3.12), 1.36 (95% CI: 0.89, 2.07), and 0.98 (95% CI: 0.60, 1.62), respectively.

CONCLUSIONS

The analysis of 2135 adult patients showed that 25(OH)D concentrations <10 ng/mL before hospitalization were associated with significantly increased odds of developing HABSI. These data support the initiation of randomized trials to test the role of vitamin D supplementation in HABSI prevention.

Staphylococcal enterotoxin P predicts bacteremia in hospitalized patients colonized with methicillin-resistant Staphylococcus aureus

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) colonization predicts later infection, with both host and pathogen determinants of invasive disease.

METHODS

This nested case-control study evaluates predictors of MRSA bacteremia in an 8-intensive care unit (ICU) prospective adult cohort from 1 September 2003 through 30 April 2005 with active MRSA surveillance and collection of ICU, post-ICU, and readmission MRSA isolates. We selected MRSA carriers who did (cases) and those who did not (controls) develop MRSA bacteremia. Generating assembled genome sequences, we evaluated 30 MRSA genes potentially associated with virulence and invasion. Using multivariable Cox proportional hazards regression, we assessed the association of these genes with MRSA bacteremia, controlling for host risk factors.

RESULTS

We collected 1578 MRSA isolates from 520 patients. We analyzed host and pathogen factors for 33 cases and 121 controls. Predictors of MRSA bacteremia included a diagnosis of cancer, presence of a central venous catheter, hyperglycemia (glucose level, >200 mg/dL), and infection with a MRSA strain carrying the gene for staphylococcal enterotoxin P (sep). Receipt of an anti-MRSA medication had a significant protective effect.

CONCLUSIONS

In an analysis controlling for host factors, colonization with MRSA carrying sep increased the risk of MRSA bacteremia. Identification of risk-adjusted genetic determinants of virulence may help to improve prediction of invasive disease and suggest new targets for therapeutic intervention.

Community-onset Staphylococcus aureus infections presenting to general practices in South-eastern Australia

Community-acquired Staphylococcus aureus infections are a public health concern, yet little is known about infections that do not present to hospital. We identified community-onset S. aureus infections via specimens submitted to a community-based pathology service. Referring doctors confirmed eligibility and described infection site, severity and treatment. Isolates were characterized on antibiotic resistance, PFGE, MLST/SCCmec, and Panton-Valentine leukocidin (PVL), representing 106 community-onset infections; 34 non-multiresistant methicillin-resistant S. aureus (nmMRSA) (resistant to <3 non-β-lactam antibiotics), 15 multiply antibiotic-resistant MRSA (mMRSA) and 57 methicillin-sensitive S. aureus (MSSA). Most (93%) were skin and soft tissue infections. PVL genes were carried by 42% of nmMRSA isolates [95% confidence interval (CI) 26-61] and 15% of MSSA (95% CI 8-28). PVL was associated with infections of the trunk, head or neck (56·4% vs. 24·3%, P=0·005) in younger patients (23 vs. 52 years, P<0·001), and with boils or abscesses (OR 8·67, 95% CI 2·9-26·2), suggesting underlying differences in exposure and/or pathogenesis.

Staphylococcus aureus colonization before infection is not associated with mortality among S. aureus-infected patients: a meta-analysis

BACKGROUND AND OBJECTIVE

The literature is conflicted as to whether people colonized with Staphylococcus aureus are at an increased risk of mortality. The aim of this meta-analysis was to review and analyze the current literature to determine whether prior history of S. aureus colonization is associated with mortality among S. aureus-infected patients.

METHODS

The PUBMED databases were searched with keywords related to S. aureus colonization and mortality. After reviewing 380 article abstracts and 59 articles in detail, only 7 studies had data on the association between S. aureus colonization and mortality among S. aureus-infected patients. Crude estimates of study odds ratios (ORs) were calculated on the basis of data from subset analyses. We pooled crude ORs from the 7 studies using a random-effects model. Woolf's test for heterogeneity was assessed.

RESULTS

When all studies were pooled in a random-effects model, no association between S. aureus colonization and mortality among S. aureus-infected patients was seen (pooled OR, 1.08 [95% confidence interval (CI), 0.32-3.66]; [Formula: see text]; heterogeneity [Formula: see text]). When the analyses were restricted to infection-attributable mortality, the association between colonization and mortality among S. aureus-infected patients was not statistically significant (pooled OR, 0.42 [95% CI, 0.15-1.21]; [Formula: see text]; heterogeneity [Formula: see text]).

CONCLUSIONS

S. aureus colonization was not associated with mortality among patients who developed an S. aureus infection. Interventions to decolonize S. aureus carriers may prevent S. aureus infections but may not be sufficient to prevent mortality.

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.

Red cell distribution width and all-cause mortality in critically ill patients

OBJECTIVE

Red cell distribution width is a predictor of mortality in the general population. The prevalence of increased red cell distribution width and its significance in the intensive care unit are unknown. The objective of this study was to investigate the association between red cell distribution width at the initiation of critical care and all cause mortality.

DESIGN

Multicenter observational study.

SETTING

Two tertiary academic hospitals in Boston, MA.

PATIENTS

A total of 51,413 patients, aged ≥ 18 yrs, who received critical care between 1997 and 2007.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The exposure of interest was red cell distribution width as a predictor of mortality in the general population. The prevalence of increased red cell distribution width and its significance in the intensive care unit are unknown and categorized a priori in quintiles as ≤ 13.3%, 13.3% to 14.0%, 14.0% to 14.7%, 14.7% to 15.8%, and >15.8%. Logistic regression examined death by days 30, 90, and 365 postcritical care initiation, inhospital mortality, and bloodstream infection. Adjusted odds ratios were estimated by multivariable logistic regression models. Adjustment included age, sex, race, Deyo-Charlson index, coronary artery bypass grafting, myocardial infarction, congestive heart failure, hematocrit, white blood cell count, mean corpuscular volume, blood urea nitrogen, red blood cell transfusion, sepsis, and creatinine. Red cell distribution width was a particularly strong predictor of all-cause mortality 30 days after critical care initiation with a significant risk gradient across red cell distribution width quintiles after multivariable adjustment: red cell distribution width 13.3% to 14.0% (odds ratio [OR], 1.19; 95% confidence interval [CI], 1.08-1.30; p <.001); red cell distribution width 14.0% to 14.7% (OR, 1.28; 95% CI, 1.16-1.42; p <.001); red cell distribution width 14.7% to 15.8% (OR, 1.69; 95% CI, 1.52-1.86; p <.001); red cell distribution width >15.8% (OR, 2.61; 95% CI, 2.37-2.86; p <.001), all relative to patients with red cell distribution width ≤ 13.3%. Similar significant robust associations postmultivariable adjustments are seen with death by days 90 and 365 postcritical care initiation as well as inhospital mortality. In a subanalysis of patients with blood cultures drawn (n = 18,525), red cell distribution width at critical care initiation was associated with the risk of bloodstream infection and remained significant after multivariable adjustment. The adjusted risk of bloodstream infection was 1.40- and 1.44-fold higher in patients with red cell distribution width values in the 14.7% to 15.8% and >15.8% quintiles, respectively, compared with those with red cell distribution width ≤ 13.3%. Estimating the receiver operating characteristic area under the curve shows that red cell distribution width has moderate discriminative power for 30-day mortality (area under the curve = 0.67).

CONCLUSION

Red cell distribution width is a robust predictor of the risk of all-cause patient mortality and bloodstream infection in the critically ill. Red cell distribution width is commonly measured, inexpensive, and widely available and may reflect overall inflammation, oxidative stress, or arterial underfilling in the critically ill.

Elevation of blood urea nitrogen is predictive of long-term mortality in critically ill patients independent of "normal" creatinine

OBJECTIVE

We hypothesized that elevated blood urea nitrogen can be associated with all-cause mortality independent of creatinine in a heterogeneous critically ill population.

DESIGN

Multicenter observational study of patients treated in medical and surgical intensive care units.

SETTING

Twenty intensive care units in two teaching hospitals in Boston, MA.

PATIENTS

A total of 26,288 patients, age ≥ 18 yrs, hospitalized between 1997 and 2007 with creatinine of 0.80-1.30 mg/dL.

INTERVENTIONS

None.

MEASUREMENTS

Blood urea nitrogen at intensive care unit admission was categorized as 10-20, 20-40, and >40 mg/dL. Logistic regression examined death at days 30, 90, and 365 after intensive care unit admission as well as in-hospital mortality. Adjusted odds ratios were estimated by multivariable logistic regression models.

MAIN RESULTS

Blood urea nitrogen at intensive care unit admission was predictive for short- and long-term mortality independent of creatinine. Thirty days following intensive care unit admission, patients with blood urea nitrogen of >40 mg/dL had an odds ratio for mortality of 5.12 (95% confidence interval, 4.30-6.09; p < .0001) relative to patients with blood urea nitrogen of 10-20 mg/dL. Blood urea nitrogen remained a significant predictor of mortality at 30 days after intensive care unit admission following multivariable adjustment for confounders; patients with blood urea nitrogen of >40 mg/dL had an odds ratio for mortality of 2.78 (95% confidence interval, 2.27-3.39; p < .0001) relative to patients with blood urea nitrogen of 10-20 mg/dL. Thirty days following intensive care unit admission, patients with blood urea nitrogen of 20-40 mg/dL had an odds ratio of 2.15 (95% confidence interval, 1.98-2.33; <.0001) and a multivariable odds ratio of 1.53 (95% confidence interval, 1.40-1.68; p < .0001) relative to patients with blood urea nitrogen of 10-20 mg/dL. Results were similar at 90 and 365 days following intensive care unit admission as well as for in-hospital mortality. A subanalysis of patients with blood cultures (n = 7,482) demonstrated that blood urea nitrogen at intensive care unit admission was associated with the risk of blood culture positivity.

CONCLUSION

Among critically ill patients with creatinine of 0.8-1.3 mg/dL, an elevated blood urea nitrogen was associated with increased mortality, independent of serum creatinine.