Sarah Chapman looks at a Cochrane Review on how useful signs and symptoms are for diagnosing COVID-19 (coronavirus). The blog has been substantially revised to reflect the updated version of the review in February 2021.
There can’t be many of us that haven’t given some thought to the symptoms of COVID-19, the infectious disease caused by a recently discovered coronavirus. I’ve been reporting my symptoms, or lack of them, through the COVID symptom study app, and have seen how the range of symptoms asked about has expanded over the weeks. In the early days of lockdown, I suddenly lost my sense of taste; soon afterwards, this was added to a list of possible symptoms of COVID-19 or coronavirus. After weeks of especially missing being able to taste tea, I now have a renewed appreciation of my favourite drink, but I’m none the wiser about whether I’ve had COVID-19.
According to the NHS website (at the time of writing this) the main symptoms of coronavirus are a high temperature, a new, continuous cough and a loss or change to your sense of smell or taste. It states, “most people with coronavirus have at least 1 of these symptoms.” But do they? In fact, just this week it’s been reported that only 22% of people testing positive for coronavirus say they have symptoms on the day of their test, based on an Office for National Statistics (ONS) survey, though this was based on a small sample, making it hard to draw firm conclusions. Some of these may have had symptoms earlier, or gone on to get symptoms, while others never had symptoms.
It would seem that we can’t assume that if you don’t have one of those listed symptoms, or indeed any other, then you probably haven’t got it. If you do have one or more of those symptoms, do these point to COVID-19? These symptoms, more than others? What about combinations of symptoms too?
Why it’s important to be able to diagnose COVID-19 (coronavirus)
Timely, accurate diagnosis of COVID-19 in people who consult their GP or go to hospital with symptoms is important to ensure that the right things happen to the right people (appropriate treatment and isolation measures, for example) and that resources aren’t wasted. Symptoms, along with signs assessed by clinicians – such as heart rate, provide early clues to what might be wrong with someone. If we can use these reliably to make a diagnosis, that’s helpful, not least because it reduces the need for specialist tests.
New Cochrane evidence on signs and symptoms of COVID-19
A Cochrane Review on the accuracy of any signs and symptoms, either alone or in combination, for diagnosing COVID‐19 has been updated, with studies published from January to July 2020.
Studies could be included if they recruited people with suspected COVID‐19, or known cases with COVID‐19 and controls without COVID‐19, in primary care (GP practices) or in hospital outpatient departments, including emergency departments. Studies of people in hospital were included only if signs and symptoms were recorded when they were admitted to the hospital.
The review authors did a broad and systematic search for studies, both published research studies and those which had not yet been peer-reviewed.
Here’s what they found
The review now includes 44 studies with almost 27,000 people. Most were carried out in hospital and only three in primary care settings. The studies did not distinguish between mild and severe COVID-19 so results are given for all disease severities together. Only one study focused on older adults and none provided separate data on children. All the studies confirmed COVID‐19 diagnosis by the most accurate tests available.
The studies looked at 84 signs and symptoms in all, and just two assessed combinations of signs and symptoms. The symptoms most frequently studied were cough and fever, but this update also added more studies focusing on the diagnostic value of loss of smell or taste.
On average 21% of people in the studies had COVID-19; that’s 210 people with COVID-19 out of every 1000.
Of these, 655 people would have a cough, of whom 142 would have COVID-19. Of the 345 who do not have a cough, 68 would have COVID-19.
In the same 1000 people, around 371 would have a fever, of whom 113 wouldhave COVID-19. Of the 629 people without a fever, 97 would have COVID-19.
Loss of smell or taste
The presence of either or both of these also increase the likelihood that someone has COVID-19.
The bottom line
The review update confirms the previous conclusion that the individual signs and symptoms studied here cannot accurately diagnose COVID-19 and that “neither absence nor presence of signs or symptoms are accurate enough to rule in or rule out disease.”
However, the review authors also now say that the presence of the loss of taste or smell may serve as a red flag for the presence of the disease, and that high temperature or cough may also be useful to identify people who might have COVID-19. They suggest that these symptoms may be useful to prompt further testing when they are present.
This is a ‘living systematic review’ which will be updated as often as is feasible, to take account of new research as it emerges.
There are also big gaps in the evidence. Doctors base diagnosis on a combination of signs and symptoms but the studies, all but two only looking at single signs or symptoms, haven’t reflected that. Let’s hope future studies will do this. Also that they will clearly differentiate between milder COVID‐19 disease and COVID‐19 pneumonia, which the studies included here did not do.
There is a need for studies of children, who may be misdiagnosed with COVID-19, based on “predefined, but not yet evidence-based symptoms”, and required to isolate, with negative impacts associated with that. We also need studies on older adults, a population at high risk of a poor outcome of SARS‐CoV‐2 infection.
Researchers across the world are working incredibly hard to provide evidence to advance our knowledge of COVID-19 and help us manage it, so let’s hope that this living systematic review can soon be updated with more and better studies, with new evidence on signs and symptoms that are more helpful for diagnosis. Meanwhile, we can continue to follow official health advice but keeping in mind that there are many continuing uncertainties.
Join in the conversation on Twitter with @CochraneUK, @Cochrane_IDG, @SarahChapman30 or leave a comment on the blog. Please note, we cannot give medical advice and we will not publish comments that link to commercial sites or appear to endorse commercial products.
Podcast: Struyf T. Can symptoms and medical examination accurately diagnose COVID-19? Cochrane Library, Cochrane Podcasts, 23 February 2021. Web. 24 February 2021.
Sarah Chapman has nothing to disclose.
Page last updated 24 February 2021.