Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Cochrane is preparing a special series of reviews to help decision makers deal with the COVID-19 pandemic and its impact, and we are keeping these up to date as new evidence becomes available. One of these reviews examines the accuracy of using signs and symptoms to diagnose whether someone has the disease. It was first published in June 2020 and has been updated in February 2021. Here's the lead author, Thomas Struyf from the Katholieke Universiteit Leuven in Belgium, to tell us about the latest findings.

Thomas: The accurate diagnosis of COVID-19 disease is important to identify individuals who need treatment or to isolate themselves to prevent spread of the infection. It's also important not to label someone as having COVID-19 when they don't, because this might lead to unnecessary further testing, treatment, isolation (of them and their close contacts), and false reassurance about having immunity in the future.
Our review examines some of the evidence on this. We wanted to find out how accurate symptoms (such as cough, fever, or loss of smell or taste) and signs from medical examination (such as an increased heart rate) are for diagnosing COVID-19. We had hoped to separate out the diagnosis of mild disease and COVID-19 pneumonia, but the studies did not clearly distinguish between the two, so we present the findings for both of these combined.
We searched for studies published from January 2020 to July 2020 and were able to include 44, with a total of just under 27,000 patients. These had investigated 84 different individual symptoms and signs. 
The accuracy of individual symptoms and signs varied widely across studies. In all but two studies, the diagnosis of COVID-19 was confirmed by the most accurate laboratory test available. Most studies were conducted in hospital outpatient settings, which means that the results may not be entirely representative of what would happen in primary care settings. The studies also selected participants in a way that meant the accuracy of tests based on symptoms and signs may be uncertain.
Two of the most commonly studied symptoms were cough and fever. The results from these showed that for every 1000 adults with one or both of these, approximately 210 would have COVID-19. On average, 655 of the 1000 would have a cough, of whom 142 would actually have COVID-19. Conversely, of the 345 patients without a cough, 68 would have COVID-19.
In the same group of 1000 adults, 371 patients would have fever and on average, 113 of these would have COVID-19, meaning that 97 of the 629 patients without fever would actually have COVID-19.
In summary, our review of the research up to July 2020 suggests that no single symptom or sign is good at detecting whether someone has COVID-19. However, the presence of a cough or high temperature may be useful to identify people who might have COVID-19 and we also found that loss of taste or smell may serve as a red flag for the presence of the disease. We did not find any studies investigating the accuracy of multiple symptoms and signs used together, which is what happens in usual practice; but we will continue to update this review regularly to capture any such studies and to keep this summary of the evidence as up to date as possible.

Monaz: If you would like to read this latest version of the review and to watch for future updates, it's available free online at Cochrane Library dot com. Just go to the website and search 'Signs and symptoms of COVID-19'.