Correspondence Address:
Dr. Anis Abobaker
Spire Fylde Coast Hospital, St Walburgas Road, Blackpool, FY3 8BP

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Dear Editor,

Patients with coronavirus disease 2019 (“COVID-19”) typically present with respiratory symptoms and febrile illness. However, many reports showed that a significant proportion of individuals who tested positive for COVID-19 were asymptomatic.[1],[2] It is argued that this percentage could be over-reported as patients who were classified as asymptomatic could have atypical symptoms which may not be recognized to be related to COVID-19. For instance, anosmia (loss of smell) has been recently reported as a possible clinical feature of COVID-19.[3],[4] Two-third of confirmed COVID-19 cases in Germany had anosmia, whereas one-third of patients with mild disease in South Korea had anosmia as the main presenting symptom.[4] Postviral anosmia represents 40% of all causes of anosmia.[4] Viruses causing common cold and upper respiratory tract infections, in addition to the previous generations of coronaviruses, are the common pathogenic cause of postviral anosmia.[4] That is why it is not unusual for the novel coronavirus (SARS-CoV-2) to cause anosmia. Although anosmia might occur in association with other classical features of COVID-19, at least one in six patients reported new onset anosmia in the absence of other symptoms.[3] Therefore, anosmia can be used as a clinical marker to detect asymptomatic patients with COVID-19.

Asymptomatic patients can be considered as a hidden source which facilitates the transmission of COVID-19 infection.[1],[4],[5] Therefore, early detection and self-isolation of asymptomatic patients might limit the spread of the infection.[1],[4],[5] Interestingly, the implementation of a large-scale strategy by testing the entire population of an isolated village in Italy (around 3000 people) identified large numbers of asymptomatic carriers of infection, which have been quarantined.[5] This approach reduced the incidence of infection in this village by 90% in just 10 days.[5] Applying similar strategy in cities with bigger population might not be feasible because of issues with test-kits availability. In addition, it can lead to wasting of the health-care system resources. Alternatively, anosmia can be used as a criterion to test as many people as possible to detect asymptomatic patients as 17% of them reported isolated anosmia.[3] This approach can be named as “targeted large-scale testing protocol,” which might be better than the random large-scale testing strategy in many aspects. First of all, the targeted approach has higher pretest probability, which means it helps to detect a higher percentage of asymptomatic patients. secondly, it is more practical approach to apply as it is more cost-effective compared with the random approach. The important question now is how to practically implement such a plan at a national level. This can be achieved by educating people to identify who noticed recent changes in their smell sensation, using online surveys, postletters, public posters, news and social media, and encouraging them to contact the local authorities to get tested.

In conclusion, the use of targeted large-scale testing strategy which is based on anosmia as a selection criterion can be applied at a national level to detect asymptomatic patients with COVID-19. Early isolation of asymptomatic patients could decrease both the spread and the severity of the epidemic.[5]

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Conflicts of interest

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