Prospective Validation of a Rapid Host Gene Expression Test to Discriminate Bacterial From Viral Respiratory Infection

Importance

Bacterial and viral causes of acute respiratory illness (ARI) are difficult to clinically distinguish, resulting in the inappropriate use of antibacterial therapy. The use of a host gene expression-based test that is able to discriminate bacterial from viral infection in less than 1 hour may improve care and antimicrobial stewardship.

Objective

To validate the host response bacterial/viral (HR-B/V) test and assess its ability to accurately differentiate bacterial from viral infection among patients with ARI.

Design, Setting, and Participants

This prospective multicenter diagnostic study enrolled 755 children and adults with febrile ARI of 7 or fewer days' duration from 10 US emergency departments. Participants were enrolled from October 3, 2014, to September 1, 2019, followed by additional enrollment of patients with COVID-19 from March 20 to December 3, 2020. Clinical adjudication of enrolled participants identified 616 individuals as having bacterial or viral infection. The primary analysis cohort included 334 participants with high-confidence reference adjudications (based on adjudicator concordance and the presence of an identified pathogen confirmed by microbiological testing). A secondary analysis of the entire cohort of 616 participants included cases with low-confidence reference adjudications (based on adjudicator discordance or the absence of an identified pathogen in microbiological testing). Thirty-three participants with COVID-19 were included post hoc.

Interventions

The HR-B/V test quantified the expression of 45 host messenger RNAs in approximately 45 minutes to derive a probability of bacterial infection.

Main Outcomes and Measures

Performance characteristics for the HR-B/V test compared with clinical adjudication were reported as either bacterial or viral infection or categorized into 4 likelihood groups (viral very likely [probability score <0.19], viral likely [probability score of 0.19-0.40], bacterial likely [probability score of 0.41-0.73], and bacterial very likely [probability score >0.73]) and compared with procalcitonin measurement.

Results

Among 755 enrolled participants, the median age was 26 years (IQR, 16-52 years); 360 participants (47.7%) were female, and 395 (52.3%) were male. A total of 13 participants (1.7%) were American Indian, 13 (1.7%) were Asian, 368 (48.7%) were Black, 131 (17.4%) were Hispanic, 3 (0.4%) were Native Hawaiian or Pacific Islander, 297 (39.3%) were White, and 60 (7.9%) were of unspecified race and/or ethnicity. In the primary analysis involving 334 participants, the HR-B/V test had sensitivity of 89.8% (95% CI, 77.8%-96.2%), specificity of 82.1% (95% CI, 77.4%-86.6%), and a negative predictive value (NPV) of 97.9% (95% CI, 95.3%-99.1%) for bacterial infection. In comparison, the sensitivity of procalcitonin measurement was 28.6% (95% CI, 16.2%-40.9%; P < .001), the specificity was 87.0% (95% CI, 82.7%-90.7%; P = .006), and the NPV was 87.6% (95% CI, 85.5%-89.5%; P < .001). When stratified into likelihood groups, the HR-B/V test had an NPV of 98.9% (95% CI, 96.1%-100%) for bacterial infection in the viral very likely group and a positive predictive value of 63.4% (95% CI, 47.2%-77.9%) for bacterial infection in the bacterial very likely group. The HR-B/V test correctly identified 30 of 33 participants (90.9%) with acute COVID-19 as having a viral infection.

Conclusions and Relevance

In this study, the HR-B/V test accurately discriminated bacterial from viral infection among patients with febrile ARI and was superior to procalcitonin measurement. The findings suggest that an accurate point-of-need host response test with high NPV may offer an opportunity to improve antibiotic stewardship and patient outcomes.

Efficacy of Tocilizumab in Patients Hospitalized with Covid-19

BACKGROUND

The efficacy of interleukin-6 receptor blockade in hospitalized patients with coronavirus disease 2019 (Covid-19) who are not receiving mechanical ventilation is unclear.

METHODS

We performed a randomized, double-blind, placebo-controlled trial involving patients with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, hyperinflammatory states, and at least two of the following signs: fever (body temperature >38°C), pulmonary infiltrates, or the need for supplemental oxygen in order to maintain an oxygen saturation greater than 92%. Patients were randomly assigned in a 2:1 ratio to receive standard care plus a single dose of either tocilizumab (8 mg per kilogram of body weight) or placebo. The primary outcome was intubation or death, assessed in a time-to-event analysis. The secondary efficacy outcomes were clinical worsening and discontinuation of supplemental oxygen among patients who had been receiving it at baseline, both assessed in time-to-event analyses.

RESULTS

We enrolled 243 patients; 141 (58%) were men, and 102 (42%) were women. The median age was 59.8 years (range, 21.7 to 85.4), and 45% of the patients were Hispanic or Latino. The hazard ratio for intubation or death in the tocilizumab group as compared with the placebo group was 0.83 (95% confidence interval [CI], 0.38 to 1.81; P = 0.64), and the hazard ratio for disease worsening was 1.11 (95% CI, 0.59 to 2.10; P = 0.73). At 14 days, 18.0% of the patients in the tocilizumab group and 14.9% of the patients in the placebo group had had worsening of disease. The median time to discontinuation of supplemental oxygen was 5.0 days (95% CI, 3.8 to 7.6) in the tocilizumab group and 4.9 days (95% CI, 3.8 to 7.8) in the placebo group (P = 0.69). At 14 days, 24.6% of the patients in the tocilizumab group and 21.2% of the patients in the placebo group were still receiving supplemental oxygen. Patients who received tocilizumab had fewer serious infections than patients who received placebo.

CONCLUSIONS

Tocilizumab was not effective for preventing intubation or death in moderately ill hospitalized patients with Covid-19. Some benefit or harm cannot be ruled out, however, because the confidence intervals for efficacy comparisons were wide. (Funded by Genentech; ClinicalTrials.gov number, NCT04356937.).

Diagnostic accuracy of combined WBC, ANC and CRP in adult emergency department patients suspected of acute appendicitis

OBJECTIVES

To assess the sensitivity, specificity, and negative predictive value (NPV) of normal total white blood cell count (WBC) and normal absolute neutrophil count (ANC) combined with a normal proprietary C-reactive protein (pCRP) level in adult emergency department (ED) patients with abdominal pain suspected of possible acute appendicitis.

METHODS

We prospectively enrolled patients ≥18 years of age at seven U.S. emergency departments with ≤72 h of abdominal pain and other signs and symptoms suggesting possible acute appendicitis. Sensitivity, specificity, and NPV for normal WBC and ANC combined with normal pCRP were correlated with the final diagnosis of acute appendicitis.

RESULTS

We enrolled 422 patients with a prevalence of acute appendicitis of 19.1%. The combination of normal WBC and pCRP exhibited a sensitivity of 97.5% (95% CI, 91.3-99.3%), an NPV of 98.8% (95% CI, 95.9-99.7%) and a specificity of 50.0% (95% CI, 44.7-55.3%) for acute appendicitis. Normal ANC and pCRP resulted in a sensitivity of 100% (95% CI, 95.4-100%), a negative predictive value of 100% (95% CI, 97.5-100%) and a specificity of 44.4% (95% CI, 39.2-49.7%) for acute appendicitis. Normal WBC and pCRP correctly identified 171 of 342 (50.0%) patients who did not have appendicitis with 2 (2.5%) false negatives, while normal ANC and pCRP identified 150 of 338 (44.3%) of patients without appendicitis with no false negatives.

CONCLUSION

The combination of normal WBC and ANC with normal pCRP levels exhibited high sensitivity and negative predictive value for acute appendicitis in this prospective adult patient cohort. Confirmation and validation of these findings with further study using commercially available CRP assays is needed.

Diagnostic performance of a biomarker panel as a negative predictor for acute appendicitis in adult ED patients with abdominal pain

OBJECTIVES

Evaluate the diagnostic accuracy of the APPY1TM biomarker panel, previously described for use in pediatric patients, for identifying adult ED patients with abdominal pain who are at low risk of acute appendicitis.

METHODS

This study prospectively enrolled subjects >18years of age presenting to seven U.S. emergency departments with <72hours of abdominal pain suggesting possible acute appendicitis. The APPY1 panel was performed on blood samples drawn from each patient at the time of initial evaluation and results were correlated with the final diagnosis either positive or negative for acute appendicitis.

RESULTS

431 patients were enrolled with 422 completing all aspects of the study. The APPY1 biomarker panel exhibited a sensitivity of 97.5% (95% CI, 91.3-99.3%), a negative predictive value of 98.4% (95% CI, 94.4-99.6%), a negative likelihood ratio of 0.07 (95% CI, 0.02-0.27), with a specificity of 36.5% (95% CI, 31.6-41.8%) for acute appendicitis. The panel correctly identified 125 of 342 (36.6%) patients who did not have appendicitis with 2 (2.5%) false negatives. The CT utilization rate in this population was 72.7% (307/422). Of 307 CT scans, 232 were done for patients who did not have appendicitis and 79 (34%) of these patients were correctly identified as negative with "low risk" biomarker panel results, representing 26% (79/307) of all CT scans performed.

CONCLUSION

This biomarker panel exhibited high sensitivity and negative predictive value for acute appendicitis in this prospective adult cohort, thereby potentially reducing the dependence on CT for the evaluation of possible acute appendicitis.

Generalizability of a simple approach for predicting hospital admission from an emergency department

OBJECTIVES

The objective was to test the generalizability, across a range of hospital sizes and demographics, of a previously developed method for predicting and aggregating, in real time, the probabilities that emergency department (ED) patients will be admitted to a hospital inpatient unit.

METHODS

Logistic regression models were developed that estimate inpatient admission probabilities of each patient upon entering an ED. The models were based on retrospective development (n = 4,000 to 5,000 ED visits) and validation (n = 1,000 to 2,000 ED visits) data sets from four heterogeneous hospitals. Model performance was evaluated using retrospective test data sets (n = 1,000 to 2,000 ED visits). For one hospital the developed model also was applied prospectively to a test data set (n = 910 ED visits) coded by triage nurses in real time, to compare results to those from the retrospective single investigator-coded test data set.

RESULTS

The prediction models for each hospital performed reasonably well and typically involved just a few simple-to-collect variables, which differed for each hospital. Areas under receiver operating characteristic curves (AUC) ranged from 0.80 to 0.89, R(2) correlation coefficients between predicted and actual daily admissions ranged from 0.58 to 0.90, and Hosmer-Lemeshow goodness-of-fit statistics of model accuracy had p > 0.01 with one exception. Data coded prospectively by triage nurses produced comparable results.

CONCLUSIONS

The accuracy of regression models to predict ED patient admission likelihood was shown to be generalizable across hospitals of different sizes, populations, and administrative structures. Each hospital used a unique combination of predictive factors that may reflect these differences. This approach performed equally well when hospital staff coded patient data in real time versus the research team retrospectively.

Emergency department crowding and risk of preventable medical errors

The objective of the study is to determine the association between emergency department (ED) crowding and preventable medical errors (PME). This was a retrospective cohort study of 533 ED patients enrolled in the National ED Safety Study (NEDSS) in four Massachusetts EDs. Individual patients' average exposure to ED crowding during their ED visit was compared with the occurrence of a PME (yes/no) for the three diagnostic categories in NEDSS: acute myocardial infarction, asthma exacerbation, and dislocation requiring procedural sedation. To accommodate site-to-site differences in available administrative data, ED crowding was measured using one of three previously validated crowding metrics (ED Work Index, ED Workscore, and ED Occupancy). At each site, the continuous measure was placed into site-specific quartiles, and these quartiles then were combined across sites. We found that 46 (8.6%; 95% confidence interval, 6.4-11.3%) of the 533 patients experienced a PME. For those seen during higher levels of ED crowding (quartile 4 vs. quartile 1), the occurrence of PMEs was more than twofold higher, both on unadjusted analysis and adjusting for two potential confounders (diagnosis, site). The association appeared non-linear, with most PMEs occurring at the highest crowding level. We identified a direct association between high levels of ED crowding and risk of preventable medical errors. Further study is needed to determine the generalizability of these results. Should such research confirm our findings, we would suggest that mitigating ED crowding may reduce the occurrence of preventable medical errors.

Diagnostic characteristics of S100A8/A9 in a multicenter study of patients with acute right lower quadrant abdominal pain

OBJECTIVES

Over the past decade, clinicians have become increasingly reliant on computed tomography (CT) for the evaluation of patients with suspected acute appendicitis. To limit the radiation risks and costs of CT, investigators have searched for biomarkers to aid in diagnostic decision-making. We evaluated one such biomarker, calprotectin or S100A8/A9, and determined the diagnostic performance characteristics of a developmental biomarker assay in a multicenter investigation of patients presenting with acute right lower quadrant abdominal pain.

METHODS

This was a prospective, double-blinded, single-arm, multicenter investigation performed in 13 emergency departments (EDs) from August 2009 to April 2010 of patients presenting with acute right lower quadrant abdominal pain. Plasma samples were tested using the investigational S100A8/A9 assay. The primary outcome of acute appendicitis was determined by histopathology for patients undergoing appendectomy or 2-week telephone follow-up for patients discharged without surgery. The sensitivity, specificity, negative likelihood ratio (LR-), and positive likelihood ratio (LR+) of the biomarker assay were calculated using the prespecified cutoff value of 14 units. A post hoc stability study was performed to investigate the potential effect of time and courier transport on the measured value of the S100A8/A9 assay test results.

RESULTS

Of 1,052 enrolled patients, 848 met criteria for analysis. The median age was 24.5 years (interquartile range [IQR] = 16-38 years), 57% were female, and 50% were white. There was a 27.5% prevalence of acute appendicitis. The sensitivity and specificity for the investigational S100A8/A9 assay in diagnosing acute appendicitis were estimated to be 96% (95% confidence interval [CI] = 93% to 98%) and 16% (95% CI = 13% to 19%), respectively. The LR- ratio was 0.24 (95% CI = 0.12 to 0.47), and the LR+ was 1.14 (95% CI = 1.10 to 1.19). The post hoc stability study demonstrated that in the samples that were shipped, the estimated time coefficient was 7.6 × 10(-3) ± 2.0 × 10(-3) log units/hour, representing an average increase of 43% in the measured value over 48 hours; in the samples that were not shipped, the estimated time coefficient was 2.5 × 10(-3) ± 0.4 × 10(-3) log units/hour, representing a 13% increase on average in the measured value over 48 hours, which was the maximum delay allowed by the study protocol. Thus, adjusting the cutoff value of 14 units by the magnitude of systematic inflation observed in the stability study at 48 hours would result in a new cutoff value of 20 units and a "corrected" sensitivity and specificity of 91 and 28%, respectively.

CONCLUSIONS

In patients presenting with acute right lower quadrant abdominal pain, we found the investigational enzyme-linked immunosorbent assay (ELISA) test for S100A8/A9 to perform with high sensitivity but very limited specificity. We found that shipping effect and delay in analysis resulted in a subsequent rise in test values, thereby increasing the sensitivity and decreasing the specificity of the test. Further investigation with hospital-based laboratory analyzers is the next critical step for determining the ultimate clinical utility of the ELISA test for S100A8/A9 in ED patients presenting with acute right lower quadrant abdominal pain.

Utilization and yield of chest computed tomographic angiography associated with low positive D-dimer levels

BACKGROUND

It is unclear to what degree broadly applied D-dimer testing combined with a low threshold for imaging with even minimally positive results may be contributing to the utilization of chest computed tomographic angiography (CTA).

STUDY OBJECTIVES

To determine what proportion of chest CTAs for suspected pulmonary embolism (PE) were performed in the setting of minimally elevated D-dimer levels, and to determine the prevalence of PE in those patients when stratified by clinical risk.

METHODS

Retrospective chart review of all patients who had chest CTA for the evaluation of suspected PE during the years 2002-2006 in a suburban community teaching hospital emergency department.

RESULTS

There were 1136 eligible patient visits, of which 353 (31.1%) were found to have D-dimer levels in the low positive range (0.5-0.99 μg/mL). Of these 353 patients, 9 (2.6%; 95% confidence interval [CI] 0.9-4.2%) were diagnosed with PE. There were also 109 patients (9.6%) who had normal D-dimer levels (<0.5 μg/mL). Two of these 109 (1.8%; 95% CI 0-4.2%) were diagnosed with PE. When stratified by the Pulmonary Embolism Rule-out Criteria, 99 of 353 patients with low positive D-dimer levels (28.0%; 95% CI 23.4-32.7%), and 14 of 109 with normal D-dimer levels (12.8%; 95% CI 6.6-19.1%) were classified as low risk, none of whom had PE.

CONCLUSIONS

Nearly one-third of all chest CTAs were done for patients with minimally elevated D-dimer levels, and another 9.6% for patients with normal D-dimer levels with very low yield. Further research to define clinical criteria identifying patients with minimal risk of PE despite low positive D-dimer levels represents an opportunity to improve both patient safety and utilization efficiency of chest CTA.

Occult splenic rupture presenting as acute scrotal swelling

BACKGROUND

Scrotal pain and swelling is a common complaint encountered in emergency medicine. The differential diagnosis includes testicular, scrotal, and intra-abdominal pathology.

CASE REPORT

We present a case of an 80-year-old man on warfarin therapy presenting with acute atraumatic scrotal pain and swelling initially diagnosed as a hydrocele. The diagnosis was subsequently determined to be a communicating hematocele secondary to occult splenic rupture.

CONCLUSION

Intra-abdominal pathology can result in scrotal pain and swelling due to passage of intra-abdominal contents into the scrotum via a patent processus vaginalis. Therefore, any cause of hemoperitoneum may also cause hematocele and hematocele should be considered in the differential diagnosis of acute scrotal swelling in any patient with risk factors for bleeding. In these patients, both scrotal and abdominal imaging should be considered.