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Diagnostic Algorithm Supports Evaluation of Hospitalized COVID-19 Patients After Initial Negative Test

Key findings

  • The COvid Risk cALculator (CORAL) is a diagnostic algorithm and clinical decision support system for evaluating hospitalized adults with COVID-19 symptoms or risk factors who have had at least one negative SARS-CoV-2 nucleic acid amplification test (NAAT)
  • This study compared key metrics recorded for inpatient encounters before (n=2,443) and after (n=2,411) CORAL was embedded into the Massachusetts General Hospital electronic health record system on May 20, 2020
  • After implementation of CORAL, repeat NAAT testing was recommended 47% less often for hospitalized persons under investigation; additional diagnostics were recommended 58% less often, after adjustment for COVID-19 incidence (P<0.01 for both comparisons)
  • After implementation of CORAL, this patient population spent an average of 20 fewer hours in isolation, and the relevant workload for infectious disease physicians was reduced by 57 person-hours/day (P<0.01 for both)
  • The CORAL platform can be modified easily to account for different population prevalence of COVID-19. Individual clinicians can also use the scoring system independently of an electronic health record system

Hospitals and other care facilities, including Massachusetts General Hospital, often rely on infectious disease (ID) physicians, hospital epidemiologists and infection preventionists to make case-by-case determinations about whether isolation can be discontinued for patients who are suspected of having COVID-19, after a single negative SARS-CoV-2 nucleic acid amplification test (NAAT).

These individualized evaluations require considerable time from clinicians, which is particularly challenging during COVID-19 surges. To increase the efficiency and accessibility of the diagnostic evaluations, researchers at Mass General created the COvid Risk cALculator (CORAL), a diagnostic algorithm and clinical decision support system.

Caitlin M. Dugdale, MDinfectious diseases physician at Massachusetts General Hospital, and David M. Rubins, MD, physician in the Department of Medicine at Brigham & Women's Hospital and Mass General Brigham Clinical Informatics are lead authors; Emily P. Hyle, MD, MSC, infectious diseases physician, and Erica S. Shenoy, MD, PhD, associate chief of the Infection Control Unit, both of the Division of Infectious Diseases at Mass General are senior authors of the report, which was written in collaboration with colleagues and is now published in Clinical Infectious Diseases.

Background on CORAL

The team created CORAL using a modified Delphi method informed by >4,500 person-hours of ID physician-led, case-by-case evaluation of patients with suspected COVID-19. The tool was designed to be embedded into the Epic electronic health record (EHR) system. Eligible patients are ≥19 years old, have had at least one negative SARS-CoV-2 NAAT and have had chest X-ray or CT within the past three days. The scoring system also incorporates symptoms and epidemiologic risk factors. CORAL offers the following:

  • If the score is below a preset threshold, CORAL recommends discontinuing isolation precautions
  • If the score is at or above the threshold, CORAL displays orders for recommended diagnostics
  • If additional workup cannot be obtained or if clinical/radiographic features remain highly concerning for COVID-19 despite two negative NAATs, CORAL triages the patient to an ID physician for personalized review

CORAL can be used repeatedly as the diagnostic evaluation progresses and creates a summary note that is entered into the electronic medical record.

Study Methods

The researchers compared key metrics before and after the implementation of CORAL:

  • Pre-implementation: March 18 to May 19, 2020—2,443 inpatient encounters in which the initial NAAT was negative
  • Launch: May 20 to May 27, 2020—CORAL was implemented and a hospital-wide education campaign began
  • Post-implementation: May 27 to July 28, 2020—2,411 inpatient encounters in which the initial NAAT was negative; CORAL was used after 2,303 of those encounters (96%)


Repeat NAAT recommended after one initial negative NAAT:

  • Pre-implementation: 67%
  • Post-implementation: 54% (OR adjusted for COVID-19 incidence, 0.53; P<0.01)

Additional diagnostics needed (beyond a second NAAT):

  • Pre: 30%
  • Post: 19% (aOR, 0.42; P<0.01)

Average total duration of isolation:

  • Pre: 36 hours
  • Post: 19 hours (adjusted difference, −20 hours; P<0.01)

Average ID physician workload spent diagnosing the population of interest:

  • Pre: 69 person-hours/day
  • Post: 3 person-hours/day (adjusted difference, −57 person-hours/day (P<0.01)

No patient had a positive NAAT within seven days after discontinuing isolation per CORAL.

Application Outside Mass General

The CORAL platform can be modified easily to conform to expert consensus in other regions or countries, to account for different population prevalence of COVID-19, or to incorporate emerging laboratory testing modalities that help assess the risk of transmission.

Since the time this study was conducted, CORAL has been implemented in eight other affiliated facilities. Supplemental material to the article explains how individual clinicians can use CORAL independently of an EHR system.

lower odds that hospitalized patients with an initial negative NAAT undergo repeat testing

58% lower odds that hospitalized patients with an initial negative NAAT would undergo diagnostics other than a second NAAT

fewer hours in isolation for hospitalized patients with an initial negative NAAT

fewer person-hours/day that ID physicians spent evaluating patients with suspected COVID-19 who initially tested negative

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Learn more about research in the Division of Infectious Diseases at Mass General

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