A bacteraemia risk prediction model: development and validation in an emergency medicine population

Procalcitonin for safe reduction of unnecessary blood cultures in the emergency department: Development and validation of a prediction model

OBJECTIVES

Blood cultures (BCs) are commonly ordered in emergency departments (EDs), while a minority yields a relevant pathogen. Diagnostic stewardship is needed to safely reduce unnecessary BCs. We aimed to develop and validate a bacteremia prediction model for ED patients, with specific focus on the benefit of incorporating procalcitonin.

METHODS

We included adult patients with suspected bacteremia from a Dutch ED for a one-year period. We defined 23 candidate predictors for a "full model", of which nine were used for an automatable "basic model". Variations of both models with C-reactive protein and procalcitonin were constructed using LASSO regression, with bootstrapping for internal validation. External validation was done in an independent cohort of patients with confirmed infection from 71 Spanish EDs. We assessed discriminative performance using the C-statistic and calibration with calibration curves. Clinical usefulness was evaluated by sensitivity, specificity, saved BCs, and Net Benefit.

RESULTS

Among 2111 patients in the derivation cohort (mean age 63 years, 46% male), 273 (13%) had bacteremia, versus 896 (20%) in the external cohort (n = 4436). Adding procalcitonin substantially improved performance for all models. The basic model with procalcitonin showed most promise, with a C-statistic of 0.87 (0.86-0.88) upon external validation. At a 5% risk threshold, it showed a sensitivity of 99% and could have saved 29% of BCs while only missing 10 out of 896 (1.1%) bacteremia patients.

CONCLUSIONS

Procalcitonin-based bacteremia prediction models can safely reduce unnecessary BCs at the ED. Further validation is needed across a broader range of healthcare settings.

External validation of ID-BactER and Shapiro scores for predicting bacteraemia in the emergency department

Introduction

The blood culture positivity rate in the emergency department (ED) is <20%; however, the mortality associated with Community-acquired bacteraemia (CAB) is as high as 37.8%. For this reason, several models have been developed to predict blood culture positivity for the diagnosis of CAB.

Objective

To validate two bacteraemia prediction models in a high-complexity hospital in Colombia.

Design

External validation study of the ID-BactER and Shapiro scores based on a consecutive cohort of patients who underwent blood culture within 48 h of ED admission.

Methods

Scale calibration was assessed by comparing expected and observed events (calibration belt). Discriminatory ability was assessed by area under the ROC curve (AUC-ROC).

Results

We included 1347 patients, of whom 18.85% were diagnosed with CAB. The most common focus of infection was the respiratory tract (36.23%), and the most common microorganism was Escherichia coli (52.15%). The Shapiro score underestimated the risk in all categories and its discriminatory ability was poor (AUC 0.68 CI 95% 0.64-0.73). In contrast, the ID-BactER score showed an adequate observed/expected event ratio of 1.07 (CI 0.85-1.36; p = 0.018) and adequate calibration when expected events were greater than 20%, in addition to good discriminatory ability (AUC 0.74 95% CI 0.70-0.78).

Conclusion

The Shapiro score is not calibrated, and its discriminatory ability is poor. ID-BactER has an adequate calibration when the expected events are higher than 20%. Limiting blood culture collection to patients with an ID-BactER score ⩾4 could reduce unnecessary blood culture collection and thus health care costs.

Microbiologic Analysis of Hand Infections: A Prospective Study

Background: Hand infections are a common problem in emergency departments. Staphylococcus aureus is the main pathogen of both hand and blood stream infections. Therefore, the aim of the present study was to evaluate the frequency and impact of bacteremia in patients with hand infections to improve the microbiologic diagnostics. Patients and Methods: A prospective study of 90 patients with acute hand infections without antimicrobial pre-treatment was performed. Blood cultures were taken pre-operatively. If positive, transesophageal echocardiography was performed to rule out infectious endocarditis. Tissue samples were microbiologically processed using standardized culture media. If negative, a broad-spectrum bacterial 16S ribosomal RNA (rRNA) gene polymerase chain reaction (PCR) was applied. The etiology and location of the infection, the length of hospital stay, the number of surgical interventions, and the inflammatory parameters were obtained. Results: Six patients with bacteremia (6.6%) were diagnosed, after animal bites (n = 3) and intra-articular empyema (n = 3). Pathogens included Staphylococcus pettenkoferi, Pasteurella multocida, Staphylococcus epidermidis, Staphylococcus aureus, and Bacteroides pyogenes. No case of infective endocarditis was detected. Patients with bacteremia required more surgical interventions (p = 0.002), had a longer hospital stay (p < 0.001), higher plasma C-reactive protein (CRP; p = 0.016), and a higher age (p = 0.002) compared with those without bacteremia. In 14 cases (15.6%) no pathogen was detected by culture, whereas the subsequent broad-spectrum PCR diagnosed three cases (21.4%). Conclusions: Pre-operative blood cultures in patients with hand infections are important to detect bacteremia as an essential marker of clinical severity. Those blood cultures are indicated after deep animal bites and joint empyema. A precise identification of pathogens is fundamental for an effective treatment of hand infections, for which a 16S rRNA gene PCR can contribute in culture-negative tissue samples.

Usefulness of the 5MPB-Toledo model to predict bacteremia in patients with urinary tract infections in the emergency department

OBJECTIVE

To analyze the usefulness of a new predictive model of bacteremia (5MPB-Toledo) in patients treated for urinary tract infection (UTI) in the emergency department (ED).

METHODS

Prospective and multicenter observational cohort study of the blood cultures (BC) ordered for patients with UTIs in 65 Spanish ED from November 1, 2019, to March 31, 2020. The predictive ability of the model was analyzed with the area under the Receiver Operating Characteristic curve (AUC-ROC). The diagnostic performance was calculated with the chosen cut-off point for sensitivity, specificity, positive predictive value, and negative predictive value.

RESULTS

A total of 1,499 blood cultures were evaluated. True cases of bacteremia were confirmed in 277 (18.5%). The remaining 1,222 cultures (81.5%) were negative. Ninety-four (6.3%) were considered contaminated. The model's area under the ROC curve was 0.937 (95% CI, 0.926-0.949). The prognostic performance with a model's cut-off value of ≥5 points achieved 97.47% (95% CI, 94.64-98.89) sensitivity, 76.68% (95% CI, 74.18-79.00) specificity, 48.65% (95% CI, 44.42-52.89) positive predictive value and 99.26% (95% CI, 98.41-99.67) negative predictive value.

CONCLUSION

The 5MPB-Toledo score is useful for predicting bacteremia in patients with UTIs who visit the ED.

Models for bacteraemia risk prediction. Clinical implications

Bacteraemia has important consequences for the patient, as it is associated with worse clinical outcomes. On the other hand, unnecessarily obtaining samples for blood cultures increases costs and the workload in the microbiology laboratory. Its diagnosis implies a time delay, but decisions about start antibiotic treatment, discharge, or admits the patient must be taken during the first attention and, therefore, before known the blood cultures results. This manuscript reviews the different strategies based on clinical scores and biomarkers that are useful for predicting bacteraemia and improving initial decision-making.