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How doctors can have more confidence in a COVID-19 diagnosis: analysis

27 October 2020
Balancing medical decisions
University of Sydney researchers suggest using the methods of clinical epidemiology to help minimise uncertainty in a COVID-19 diagnosis and help public health decisions during the pandemic.

A 26-year-old man in Sydney visits a clinician with a blocked nose, cough and fever in late March 2020. Could it be COVID-19, or another respiratory disease such as influenza?

Frontline clinicians in the COVID-19 pandemic can use clinical epidemiology methods to be more confident in ruling in, or ruling out, a COVID-19 diagnosis in an individual patient, say researchers.

In a peer-reviewed paper in the Medical Journal of Australia, University of Sydney researchers use COVID-19 as an example to demonstrate how estimating the probability of disease before and after a test result may be used to make clinical decisions based on all the evidence available.

The authors write that tests for COVID-19, similar to tests for other diseases, are not perfect and there is a potential for false positive and false negative results.

The paper emphasises the importance of not relying on a single test result, but rather gaining a clearer picture of the probability of a disease by applying the test result to the clinical context of the particular patient sitting in front of the doctor.

“That is why clinicians need to bring together multiple sources of information and leave no stone unturned making a decision on whether a disease is likely to be present or absent, and the need for management options such as quarantine. Clinicians also need to consider patient symptoms, risk factor information as well as medical test results such as virus and imaging tests,” says Dr Fiona Stanaway from the Faculty of Medicine and Health and School of Public Health.

Lead author Associate Professor Katy Bell from the Faculty of Medicine and Health and School of Public Health said the team hopes that this article will help clinicians to provide evidence-based patient-centred care, while preventing the spread of the pandemic.

“The importance of accurate medical tests has been brought to the fore with the pandemic, where a key strategy to control spread of the infection is through robust testing and contact tracing programs.

“But given the known inaccuracies of the tests developed to diagnose the new disease, clinicians may find it difficult to decide whether or not the patient in front of them actually has COVID-19, whether this possibility has been adequately ruled out, and the safety of releasing them from self-isolation or quarantine.

“By following clinical epidemiology methods for estimating probability of disease in the patient, and then revising this as test results and other information become available, clinicians and public health professionals can make informed decisions about the management of their patients that balance potential benefits against potential harms.”

Using clinical epidemiology helps clinicians to quantify what the chances are of the patient truly having COVID-19 based on both their test results and other risk factors such as close contact with a known case.
Dr Fiona Stanaway

Dr Stanaway said: “Using clinical epidemiology helps clinicians to quantify what the chances are of the patient truly having COVID-19 based on both their test results and other risk factors such as close contact with a known case. This provides clearer guidance to clinicians and public health professionals making decisions about how to manage positive and negative test results in different patients.”

“There is often poor understanding of how imperfect tests can be and that tests can both miss people as well as falsely diagnose people that have nothing wrong.

“The principles outlined in this paper help demonstrate why clinicians need to take into account more than just test results when deciding how likely it is that someone has a disease.”

The article is the second of three journal articles on how to interpret medical tests for diagnosis and screening.

Associate Professor Bell says that the last of the papers to be published in Medical Journal of Australia will be on the principles of screening, and the potential benefits and harms from screening for people who have no symptoms of a condition.


Note: The article is part of a medical education series and it was peer reviewed and has been accepted for publication in an issue and awaiting issue allocation. It has been published online to make it available sooner.

DECLARATION: The authors have no conflicts of interest to declare.

Ivy Shih

Assistant Media and Public Relations Adviser (Health)

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