April 1, 2020

expert reaction to unpublished preprint on loss of smell and taste as symptoms of COVID-19

A preprint, posted on Medrxiv, reports on loss of smell and taste as symptoms of COVID-19.

Dr Jane Parker, Associate Professor, Flavour Chemistry, University of Reading, said:

“This paper shows good preliminary (non peer-reviewed) evidence that loss of smell and taste is likely to be a symptom of Covid-19, but its role as an early warning signal has not been confirmed.  There is no evidence that those with loss of smell and taste are infectious.  However, given the severity of the pandemic, the data are convincing enough that precautionary self-isolation on sudden loss of smell or taste should be considered.  It is important, however, that any public health message should come with the caveat that post viral smell loss may also be caused by viruses other than Covid-19.

“Note that “taste” is used in the colloquial sense, and the App does not attempt to distinguish between loss of olfaction (aroma perceived in the nose) or gustation (sweet, salty, sour, bitter etc. as perceived by the tongue).  This doesn’t affect the conclusion, as the general population do not distinguish these terms.

Is this a peer-reviewed, published paper?

“Seems to be non-peer reviewed.

Does the press release accurately reflect the science?

“I agree that smell loss should lead to self-isolation.  The opening sentence is misleading.  It IS a good way to tell whether you may develop the disease but it doesn’t necessarily mean you will.  Note that of the people with symptoms who tested negative for COVID-19, 18% self-reported loss of smell and taste.  This is very high but these were undoubtedly suffering from other viral infections, so the smell loss is a good indicator, but there are other viruses going around which also have a similar effect on smell.  This is important for any public health message. Whereas smell loss is a good indicator of Covid 19, and reason to self-isolate, it does not follow necessarily that you will develop, or have developed CV19 – it does not mean you are “immune”.

Is this good quality research?  Are the conclusions backed up by solid data?

“Yes, I believe so, although it relies on self-reported data.  The questionnaire asks widely about all symptoms, and is not biased by the smell loss question which appears half way down the list of 12 different symptoms.

How does this work fit with the existing evidence?

“We know that loss of smell is often post-viral, particularly from upper respiratory tract infection, which is consistent with findings in this paper.

Have the authors accounted for confounders?  Are there important limitations to be aware of?

“Authors discuss the limitations.  They have done a marvellous job in getting this out so fast, but probably the most relevant limitation is the fact that they haven’t reported whether the anosmia was acquired prior to other COVID symptoms, during the illness or afterwards.  The App actually tracks over time, so maybe the data will be released at a later date.

What are the implications in the real world?  Is there any overspeculation?

“The advice to isolate if you have a sudden loss of smell and taste should be considered.  The authors show a good correlation between anosmia and COVID-19.

An author says in the press release “When combined with other symptoms, people with loss of smell and taste appear to be 3 times more likely to have contracted COVID-19 according to our data, and should therefore self-isolate for seven days to reduce the spread of the disease”; is that justified?

“Yes, given the severity of the pandemic.

Do we know whether people can transmit the virus if the only symptom they have is loss of taste and smell?

“No, we don’t know.”

Prof Trish Greenhalgh, Professor of Primary Care Health Sciences, Nuffield Department of Primary Care Health Sciences, University of Oxford, said:

“This is an important study because it is the first to demonstrate scientifically and in a large population sample that loss of smell is a characteristic feature of COVID.  The researchers also showed that loss of smell occasionally occurs in people who do not have COVID, and that not everyone with COVID loses their sense of smell.

“A very recent review of the literature by my group found no proper studies on this topic (https://www.cebm.net/covid-19/what-is-the-evidence-for-anosmia-loss-of-smell-as-a-clinical-feature-of-covid-19/), so this is a novel finding.

“Some people might criticise the scientists for using self-reports (i.e. asking patients to report their own test results rather than obtaining the report from their doctor), but my own view is that most respondents would give an accurate report.”

Preprint (not a paper): ‘Loss of smell and taste in combination with other symptoms is a strong predictor of COVID-19 infection’ by Cristina Menni et al. will be posted on medRxiv.  This work is not peer-reviewed.

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19/

Declared interests

None received.