**3. Diagnosis of olfactory and taste disorders in COVID-19**

In many studies on the transmission method of the SARS-CoV-2 virus, it has been shown that this virus is transmitted by droplets. Objective olfactory tests may pose a risk of contamination and therefore require extra precaution.

*Loss of Smell and Taste as Clinical Onset of COVID-19 DOI: http://dx.doi.org/10.5772/intechopen.99087*

Commonly used objective olfactory tests are the Connecticut Chemosensory Clinical Research Center (CCCRC) test, University of Pennsylvania Smell Identification test (UPSIT), the Sniffin' Sticks method and the Odor Stick Identification test (OSIT). The UPSIT has four "scratch and sniff" booklets that each contain 10 microcapsule fragrances. After people open the capsule, they smell the page in the booklet [25, 26]. In the CCCRC test, fragrances are offered in bottles that are not transparent [27]. Sniffin' Sticks are felt tip pens impregnated with scents that are handed to the patient to smell [28]. In the OSIT test, the researcher folds a piece of fragrant paraffin paper in half to crush the microcapsule and then offers it to the participant. The participant then opens and smells the paper [29]. For the Sniffin' Sticks and CCCRC tests, the odor threshold is considered along with the ability for odor discrimination, while discrimination alone is assessed in the UPSIT and OSIT.

As for the taste, since taste tests can be performed with disposable strips, they can be used safely in patients with taste disorders.

Many studies have been published on COVID-19 and odor disorders since the beginning of the pandemic, and because of the contamination risk, the vast majority were subjective reports based on questionnaires or self-reports [30–32]. However, in studies that will be done by performing objective odor tests on patients, reports about the importance of obtaining data started to increase; for example Leichen et al. examined 86 patients for anosmia and hyposmia rates by testing with Sniffin' Sticks test, which is a psychophysical odor test. A total of 33 (38%) patients who reported that they had a loss of smell were normosmic according to the Sniffin' Sticks test. In the anosmic group, 78.8% of the patients stated that they had a loss of smell [33]. We had managed to evaluate olfactory objectively, without any risk of contamination, by a method that we described at our study [34].

### **4. Clinical features**

The general feature of loss of smell in COVID-19 infection is sudden onset anosmia. Gane et al., stated in their case series, the isolated sudden onset anosmia syndrome (ISOA), could be the only finding of COVID-19 without any other symptoms [35]. Usually, olfactory disorder is not accompanied by nasal congestion or rhinorrhea.

Olfactory dysfunction due to COVID-19 infection seems to effect females and young individuals more commonly.

Is this odor dysfunction completely reversible, or how long should a patient wait for full recovery of olfactory function? There have been many studies on the alleviation of the loss of smell in COVID-19 [36–45].

Complete recovery of olfactory dysfunction varies between 11-49% and up to 25% of the patients seems to show no improvement at all.

#### **5. Treatment**

There is currently no specific treatment for COVID-19 related anosmia. Olfactory dysfunction can heal spontaneously. However, not a small number of patients may have permanent impairment. Efficacy of the treatments are unknown due to lack of data; treatments targeting post-infectious olfactory dysfunction could potentially be beneficial for COVID-19. While the use of systemic steroids is not recommended in patients with odor loss, the use of spray form and long applicators has been found appropriate for nasal steroids [46]. Fragrance therapy gives

successful results in postviral odor loss, especially when it is started early and used for at least three months. Therefore, in the loss of smell associated with COVID-19, fragrance therapy, including rose, lemon, clove and eucalyptus fragrances, each scent is sniffed for twenty seconds twice a day [47].
