A 17-year-old girl who was an overseas student studying in the United Kingdom returned to HKSAR on 20 March 2020.1–8 She subsequently underwent compulsory quarantine in a hotel in accordance with the “health quarantine arrangements on inbound travelers from overseas guidelines” from the Centre for Health Protection, HKSAR.9 She had no known contact with confirmed COVID-19 patients. On the day of arrival to HKSAR, there was sudden onset of complete loss of smell and taste sensation when she tried to eat spicy noodles. She had no fever, coryza, shortness of breath, or diarrhea. She was previously healthy without history of allergic rhinitis and was not taking any medications. She presented to the Accident and Emergency Department (AED) of a regional hospital on the 4th day after her symptom onset, where deep-throat saliva was saved for testing of COVID-19. SARS-CoV-2 was detected by reverse-transcription-polymerase chain reaction (RT-PCR) in her saliva sample. She was then admitted to our unit on the 8th day of her disease. She reported full spontaneous recovery of anosmia and ageusia since the previous day. She vomited once, and complained of mild chest discomfort and headache. She was afebrile with stable vital signs in room air. Examination of nostrils did not show congestion or obstruction by nasal turbinates, and systemic examination was normal. Chest radiograph was normal. She was managed conservatively with Paracetamol for pain relief. During the hospital stay, she remained stable with gradual resolution of chest discomfort and headache. At the time of writing, her pooled nasopharyngeal and throat swab for SARS-CoV-2 RT-PCR were still tested positive.
A 15-year-old girl who was an overseas student studying in the United Kingdom returned to HKSAR on 19 March 2020, after which she underwent compulsory quarantine at home. She was informed about a confirmed case of COVID-19 on the same inbound flight with her; deep-throat saliva was thus collected, and she was tested positive for SARS-CoV-2. She was called for admission to our unit for isolation and treatment a few days later. At the time when saliva was collected, she was asymptomatic, whereas 2 days later, she developed anosmia and ageusia associated with mild rhinorrhea. She could not smell nor taste any food, and only had sensation from the back of her throat. She had no fever, cough, shortness of breath, headache or vomiting. She enjoyed good past health without history of allergic rhinitis or use of long-term medications. She was afebrile with stable vital signs in room air. Systemic examination including ears, nose, throat and chest were all unremarkable. Chest radiograph was normal. She was managed conservatively. During her stay, her taste sensation started to return since the 8th day of illness, when she started to taste the sweetness of oatmeal and the saltiness of a seaweed snack. However, at the time of writing, her anosmia persisted, which is the 13th day since its onset, and her pooled nasopharyngeal and throat swab for SARS-CoV-2 RT-PCR was still tested positive.
A 14-year-old boy who was an overseas student studying in the United Kingdom returned to HKSAR on 28 March 2020. He had no known contact with confirmed COVID-19 patients. Following his return, deep-throat saliva was collected and he underwent compulsory quarantine at home. His saliva was tested positive for SARS-CoV-2 by RT-PCR, and he was called for admission to our unit for isolation and treatment. He reported no fever or respiratory symptoms upon admission, while further questioning revealed transient anosmia for 3 days associated with mild rhinorrhea prior to admission, but there was no ageusia. He attributed this to his history of allergic rhinitis, while he otherwise enjoyed good past health and was not taking any medications. He was afebrile with stable vital signs in room air. Systemic examination was unremarkable. Chest radiograph was normal. He was managed conservatively and remained stable without new complaints. At the time of writing, his pooled nasopharyngeal and throat swab for SARS-CoV-2 RT-PCR was equivocal.
Postviral anosmia and chronic rhinosinusitis are two common causes of anosmia, with their pathophysiology largely being conductive, sensorineural or mixed. Less common causes include nasal polyps, tumors, head trauma, chemotherapy or radiotherapy and drug-induced anosmia such as that due to tricyclic antidepressants or antipsychotics. Anosmia may recover after relief of nasal obstruction and inflammation, in addition to self-regeneration of olfactory neurons through stem cells in the olfactory neuroepithelium.10
Common viruses associated with postviral anosmia include human coronaviruses and rhinoviruses. Edema and congestion of the nasal mucosa in the olfactory cleft causes obstruction of airflow through the nose, resulting in conductive olfactory loss. Most cases of anosmia are temporary with spontaneous recovery. Chronic rhinosinusitis may produce more prolonged anosmia or hyposmia, with predominant sensorineural inflammation and death of olfactory neurons. However, in SARS-CoV-2 infection, rhinorrhea and nasal congestion were reported to be mild and often not the presenting symptoms. Thus, sensorineural inflammation of the olfactory neuroepithelium may play a more major role than conductive olfactory loss in causing anosmia. Is it possible that this virus preferentially targets olfactory neurons in the upper respiratory tract? It has to be answered by further molecular studies in this area. On the other hand, ageusia is less well understood. The sense of taste and identification of flavors are strongly related to the sense of smell; hence, inflammation of chemoreceptors can produce both anosmia and ageusia.
Anosmia was reported to be a rare occurrence in SARS infection.11 In a series reported by Mao et al analyzing the neurologic manifestation of 214 COVID-19 adult patients, hypogeusia occurred in 5.6% of patients, whereas 5.1% reported hyposmia.12 So far, we only have limited data on the significance of anosmia and ageusia in SARS-CoV-2 infection in children and adolescents. It may occur alone in an otherwise asymptomatic COVID-19 patient8 or in conjunction with other symptoms; it may precede fever or respiratory symptoms or present later in the disease course. The subjective nature of smell and taste sensation makes objective assessment difficult, especially in younger children. It may recover spontaneously within days or persist after resolution of other symptoms.
In our case series, children and adolescents with COVID-19 infection may present solely with anosmia in the absence of other respiratory symptoms, thus painting a new picture from its manifestations in adult patients. As it is not a commonly recognized symptom, there are likely more undiagnosed carriers in our community at risk of transmitting the virus. Therefore, in the present moment of the COVID-19 pandemic, we must be alert to any individual presenting with anosmia or ageusia. To reduce the potential of person-to-person transmission, the public should be advised, if they show symptoms of new-onset anosmia or ageusia, to self-isolate and seek help from healthcare professionals. Healthcare workers attending patients with such symptoms should implement strict infection control and isolation measures to protect against COVID-19 infection in healthcare settings. Testing for SARS-CoV-2 infection is recommended for these patients.
Lastly, anosmia or ageusia are not included in the current diagnostic or testing criteria for COVID-19 infection.13 In view of patients who may present solely with anosmia and/or ageusia as the predominant symptoms, we need to consider including them into the diagnostic and testing criteria for COVID-19 infection.
We thank the patients and their families for their contributions, and to all of the healthcare professionals dedicated to their care.
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13. Diagnosis and treatment Protocol of COVID-19
(Trial Version 7). Updated on March 29, 2020. Released by National Health Commission & State Administration of Traditional Chinese Medicine. National Health Commission of the People’s Republic of China. Available at https://www.chinadaily.com.cn/pdf/2020/1.Clinical.Protocols.for.the.Diagnosis.and.Treatment.of.COVID-19.V7.pdf