Smell abnormalities more common among long-COVID Patients

The coronavirus disease 2019 (COVID-19) pandemic has caused worldwide restrictions on ordinary business, public gatherings, travel, and leisure activities.  Other than the immediate severity of disease associated with these infections, persistent disease which involves the lingering of symptoms for weeks after the virus has been cleared from the body, has been a concern with its potential for long-term debility. Concerning COVID-19, persistent disease has become known as long-COVID. A new study available on the preprint server medRxiv* investigates the rising prevalence of abnormalities in the sense of smell persisting in patients who had a loss of smell during their acute infections.

Study: Increasing incidence of parosmia and phantosmia in patients recovering from COVID-19 smell loss. Image Credit: Nenad Cavoski/Shutterstock

Background

COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and presents a wide spectrum of clinical manifestations, ranging from asymptomatic to fatal disease. The loss of smell and taste has been among the more distinctive features of COVID-19, affecting 40-75% of patients.

Anosmia has been used to help distinguish COVID-19 from other respiratory illnesses and screen large groups of people for confirmatory testing. Anosmia is thus a common and useful diagnostic feature of COVID-19, at least for the viral variants circulating in 2020 and up to the present.

The classic presentation is of a sudden loss of smell in the absence of a stuffy nose, accompanied by a loss of taste unrelated to the loss of odor. This is different from the loss of smell found with a blocked nose, which is due to the inability of volatile odor molecules to reach the olfactory mucosa at the top of the nasal cavity.

In about 75-80% of COVID-19 patients who complain of taste and smell loss, these are recovered within a few months. The period varies, with up to 40% still reporting impairment at 1-2 months.

The current study followed up approximately 1,500 people who reported a loss of smell and taste during the acute phase of infection. The scientists focused on recovering this sensation over the 11 or more months following the onset of COVID-19. The aim was to assess smell and taste recovery using a visual analog scale while asking about distortions of smell, parosmia, unexplained smells, or phantosmia.

What are the findings?

The study found that over a median follow-up period of 200 days, approximately half the men, and 60% of women, had regained less than 80% of their original smell acuity compared to before they contracted the infection.

About 60% were finally classified as having smell impairments at follow-up, with about 40% also having an impairment of taste. Conversely, a fifth said they had recovered taste but not smell. Only 3% reported the inverse pattern. This indicates that these sensations are not linked in their impairment and recover separately, with the subjects being able to distinguish them separately.

The researchers found that while most participants who had varying extents of anosmia or ageusia during the acute phase reported improvement at follow-up, the final number of subjects who said they had persistent smell abnormalities was higher at this time point than during acute infection.

About a tenth of patients had parosmia or phantosmia at the beginning of the study, but at follow-up, this percentage went up to 47% and 25%, respectively. These abnormalities were reported more commonly by those who had persistent impairment of smell.

Parosmia was present in almost two-thirds of those with long-COVID smell symptoms, compared to a quarter of those who recovered their sense of smell. Similarly, phantosmia was reported in a third of those with long-haulers compared to 13% of those who recovered smell. This was described as feeling that some things now had a different or unpleasant smell (parosmia), or in some cases, getting a whiff of something burning (phantosmia).

In general, a persistently impaired sense of smell seemed to link to a greater number of chronic symptoms, indicating that this might serve as a marker of long-COVID. At follow-up, these patients were more than seven times more likely to report changes in taste but ten times more likely to have an altered sense of smell. They were almost twice as likely to report tiredness and headache and six times more likely to have a loss of appetite. In addition, loss of hair, brain fog, and hallucinations were more common among those with persistent smell alterations.

The recovery of normal taste sensation appeared to occur more rapidly than that of smell. Very few patients who reported getting back their pre-COVID level of smell had residual disturbances of taste.

Study: Increasing incidence of parosmia and phantosmia in patients recovering from COVID-19 smell loss. Image Credit: graphical abstract from original preprint.

What are the implications?

Parosmia is a major symptom of long-COVID among those who had initial anosmia. This means that millions of people the world over may eventually suffer from smell impairments.

While earlier research suggested that olfactory disturbances might be a sign of milder illness, the current study indicates the opposite is true. The scientists point out that the lower reporting rate of anosmia among severely ill COVID-19 patients could have been due to the failure to detect and report such symptoms and the inability to test critically ill COVID-19 patients for taste and smell abnormalities.

Disturbances of smell have been associated with depression and loss of appetite, indicating the need for medical professionals to note these common effects, which may last for months after resolution of the acute infection, in COVID-19 patients.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.