Simple, at-home test helps screen COVID-19-related anosmia, ageusia

A quick, objective testing kit for daily self-assessment of olfactory and gustatory function can effectively measure smell and taste losses associated with COVID-19, as shown in a study.

Anosmia and accompanying ageusia have emerged as important warning signs of COVID-19, and experts believe that monitoring sudden changes in smell and taste can prompt early self-isolation and, in turn, minimize the community transmission of COVID-19.

Self-report questionnaire measures are commonly used to measure changes in smell and/or taste. While cost-effective and easy to implement at a large scale, these measures can be subjective and disposed to biases and inaccuracies. To address this problem, a team of Singapore-based researchers developed the ‘Singapore Smell and Taste Test’ (SSTT)—a quick smell and taste test kit to objectively measure smell and taste losses related to COVID-19.

Easily administered at home with minimal cost and burden, SSTT includes two separate tests. The smell test involves two odour pens: food (mango) and nonfood (detergent). The self-administered taste test, on the other hand, includes four food-grade taste stimuli in powder form. Each stimulus represents a standardized supra-threshold example of the four prototypical basic tastes, namely sweet (table sugar), salty (table salt), bitter (granulated coffee powder), and sour (lime powder).

On a scale of ‘not strong’ to ‘extremely strong’

To test the performance of SSTT, the researchers recruited 99 individuals (mean age 34.93, 75 men), of which 72 were confirmed COVID-19 positive and 27 were confirmed COVID-19 negative. All of them completed questionnaires to record recent changes in smell and taste ability at baseline.

They were also asked to complete the self-administered SSTT daily for up to 28 days at their place of residence. This was in addition to a self-reported rating of their sense of smell and taste using one of the six predefined list of household items commonly found in Singapore—an approach based on a previously reported self-assessment measure of smell sensitivity. [Chem Senses 2020;45:449-456]

To perform the SSTT smell test, the pen lid had to be removed and the odour pen placed 3 inches from the participants’ nose while breathing normally. For the taste test, a small amount of each powder had to be taken in a sequential monadic order on the tip of the participants’ tongue using a spoon. The participants had to identify and rate the perceived intensity of the smell and taste on a visual analogue scale, from “not strong at all” to “extremely strong.”

Out of the 65 participants completed the SSTT at home, 22 exhibited smell and/or taste loss at baseline, of whom only one was COVID-19 negative and had objectively measured taste loss only. Of the 21 COVID-19 positive patients, 17 exhibited both smell and taste loss, two had smell loss only, and another two had taste loss only.

The SSTT measures of smell and taste function were positively associated with the participants’ self-reported smell and taste acuity as well as with the rated smell intensity of six common household items. [Food Qual Prefer 2022;97:104482]

A useful early diagnostic tool

“We found that smell and taste losses were typically exhibited together, as opposed to smell or taste loss alone. It may be that COVID-19 only impacts smell function, and the observed changes in taste sensitivity reflect smell-referred taste loss as opposed to impaired gustatory function,” the team pointed out. [Int Forum Allergy Rhinol 2020;10:1105-1107]

Along with other home testing procedures that measure changes in the senses of smell and taste, SSTT enables remote and self-administered assessment, which according to the researchers is particularly valuable in times of social distancing and self-isolation, where in-person data collection is difficult.

Furthermore, SSTT does not require participants to source or prepare their own test stimuli. This minimizes the risks of introducing unwanted stimuli variation or problems for comparability of smell and taste loss across individuals that can occur when participants are required to source and prepare their own test stimuli, the researchers explained.

Another advantage of the SSTT kit is that it is cost-effective as compared with conventional clinical tests, such as Sniffin’ Stix. The researchers pointed out that despite being effective at measuring changes in olfactory sensitivity and identification, the latter can be impractical when administering a to a large population of COVID-19–infected participants, due to the high cost of each testing kit and the inability to share or re-use test kits due to the risk of contamination and the increased spread of the virus.

“In the early stages of self-diagnosis, the SSTT could be extremely useful in initiating prompt self-isolation and the seeking of a formal medical consultation, especially in lower-middle income countries where rapid, widespread access to formal PCR swab testing is not always available,” the team said.

“The SSTT also has applications in monitoring smell and taste recovery in individuals suffering long-term effects of COVID-19, commonly referred to as ‘long COVID’, and could assist in identifying individuals that need to seek further medical advice to manage chronic smell and taste losses or disorders,” they added.

The odour pens and stimuli powders of the SSTT have a shelf life of 1 year, so it is possible to keep a testing kit in the household for use if individuals suspect sudden loss, or slow recovery, of sensory acuity.