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Screening-based predictive tools for COVID-19 in ED inferior to PCR test

13th January 2023

Three screening-based predictive tools for COVID-19 infection used in an emergency department were far less sensitive compared to a PCR test

Three screening-based predictive tools for COVID-19 used within an emergency department (ED) have been shown to be inferior to a polymerase chain reaction (PCR) test according to the results of a study by US researchers.

During the early phase of the COVID-19 pandemic, diagnostic testing was not always readily available. Consequently, there was a need for clinical decision-making methods to identify patients most likely to be infected with the virus. Some such methods were developed and one study using a risk score for COVID-19 diagnosis, achieved an area under the receiver operating characteristic curve of 0.85 in a validation dataset, prompting the authors to suggest that it could be used as a supplemental tool to assist in the clinical decision to quarantine patients admitted to hospital from the emergency room. Nevertheless, while there are several available methods, no studies have compared the performance of different methods to predict the likelihood that a patient presenting to an ED has COVID-19.

In the current study, the US team retrospectively assessed three screening-based methods to determine which was better at detecting those who ultimately tested positive for COVID-19. The three methods were a nursing triage screen (NTS), an ED review of systems (ROS) performed by physicians and physician assistants and a standardised COVID-19 probability assessment (PA) by an ED attending (i.e., consultant) physician. The study included all patients aged 18 years or older who were admitted to hospital from the ED and who had a PCR confirmed positive COVID-19 infection. The NTS for example, involved asking about the presence of symptoms including fever, chills, weakness, severe headache, anosmia, dysgeusia, conjunctival injection, sore throat, cough, shortness of breath (SOB), abdominal pain, vomiting, diarrhoea, bruising or bleeding, myalgia, arthralgia and rash. Similarly, the ED review of ROS asked about symptoms, whereas after the initial ROS (but before the COVID-19 test result was available), the attending physician would classify the patient as high, moderate, low or no probability of having COVID-19. The sensitivity, specificity and positive predictive value (PPV) and negative predictive value (NPV) were calculated for each method. and regression analysis used to assessed each tool’s performance.

Screening-based prediction and COVID-19 positivity

A total of 748 patients with mean age of 57.5 years (56.8% male) were included in the analysis. Overall, 21.3% of patients tested positive for COVID-19 following a PCR test.

The attending physician had the highest sensitivity (0.62, 95% CI 0.53 – 0.71), followed by the ED ROS (0.53, 95% CI 0.43 – 0.62) and the least sensitive was the NTS (0.46, 95% CI 0.37 – 0.56). Specificity values were also highest for the attending physician (0.76) though this was similar to the NTS (0.71) and lowest for the ED ROS (0.62). Nevertheless, all three methods had a low positive predictive value, ranging from 26% (ED ROS) to 40% (attending physician).

The authors concluded that none of the three screening-based tools was accurate enough to replace a COVID-19 PCR test, adding that hospitals should not rely symptom screening to identify infected patients and recommended universal COVID-19 testing prior to all admissions.

Dilorenzo MA et al. Performance of three screening tools to predict COVID-19 positivity in emergency department patients. Emerg Med J 2023

Risk assessment tools enhance emergency medical service triage for patients with suspected COVID-19

3rd March 2022

Risk assessment tools improve the sensitivity of emergency medical staff’s assessment in the prehospital setting for patients with COVID-19

Risk assessment tools can be to used to assist emergency medical services personnel in deciding whether to transport a patient with suspected COVID-19 to hospital. This was the conclusion of a study by a team from the School of Health and Related Research, The University of Sheffield, Sheffield, UK.

Emergency medical service (EMS) staff have a vital role in deciding to convey community-based patients with a suspected COVID-19 infection to hospital. Risk factors for adverse outcomes among COVID-19-infected inpatients that can be assessed in a primary care setting include increasing age, decreased oxygen saturation, dyspnoea on presentation and the presence of comorbidities.

However, there is a need for clinical prediction models to be developed and validated to determine outpatient risk scores. While a number of risk assessment tools for those with suspected COVID-19 already exist, these have been validated only in hospitalised patients. If these tools were to be applied to patients before reaching hospital, it might be possible to reduce unnecessary hospital attendance.

For the present study, the UK team retrospectively examined the utility of five risk assessment tools to predict severe illness in adults with suspected COVID-19 before being transferred to hospital. The researchers were also interested in comparing the accuracy of the risk-stratification of each tool with the existing clinical decision-making process employed by EMS clinical staff.

The team considered the following tools: PRIEST tool, NEWS2, the World Health Organization (WHO) algorithm, CRB-65 and PMEWS. The primary outcome of the study was death, renal, respiratory or cardiovascular organ support at 30 days after the first (i.e., index) date of attendance by EMS staff. The secondary outcome was death up to 30 days after the index date.

Each of these tools was retrospectively applied to adult patients to assess their accuracy for the primary and secondary outcomes. Each tool was assessed in terms of the area under the receiver operating characteristics curve (AUC) and both sensitivities and specificities were calculated and compared with the values obtained by the EMS clinical staff’s decision to transfer patients to hospital.

Risk assessment tools and COVID-19 outcomes

A total of 7549 patients with a mean age of 60 years (47.5% male) were included in the analysis, of whom 17.6% experienced the primary outcome and 14.1% the secondary outcome of death.

Among the whole cohort, the decision to transfer to hospital was made by an EMS clinician for 65% of patients and, of whom, 22.9% experienced the primary adverse outcome.

The sensitivities of each of the risk assessment tools were all all above 90%, except for CRB-65 (89%). In comparison, the EMS clinician decision to transfer a patient to hospital had a sensitivity of 84% (95% CI 83 – 85%) and a specificity of 39% (95% CI 39 – 40%) for the primary outcome.

From the five tools, the authors determined that some tools such as the PMEWS, WHO and NEWS, although having a higher sensitivity than the EMS, would actually lead to a 10% increase the conveyance to hospital. In contrast, for the PRIEST tool, while it had a higher sensitivity than the EMS assessment, it would not increase the number of patients transported to the hospital.

The authors concluded that PRIEST would improve the EMS sensitivity of triage but not increase the number of patients transferred to hospital and could therefore be of assistance to staff.

Marincowitz C et al. Prognostic accuracy of triage tools for adults with suspected COVID-19 in a prehospital setting: an observational cohort study. Emerg Med J 2022