Infectious Mononucleosis Presenting with Loss of Taste and S
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SARS-CoV-2 is not the only virus to cause loss of taste/smell and so other differential diagnoses should be considered. Loss of taste/smell is a subjective symptom, and therefore caution should be exercised in the context of an upper respiratory tract infection.

A 53-year-old woman presented with dyspnoea and fever. Her symptoms had originally started 18 days before her presentation, and were accompanied by fatigue, muscle aches and loss of taste and smell. She reported temperatures of up to 40° using a home thermometer. The symptoms had started a few days after she was in close contact with a friend who had subsequently tested positive for SARS-CoV-2.

Soon after her fevers began, she was tested for SARS-CoV-2 with a negative result. When her symptoms persisted for more than 7 days, she presented to the emergency department and was subsequently discharged after another SARS-CoV-2 swab was also negative. On admission, she was not in respiratory distress, and oxygen saturations and her respiratory rate were normal (SpO2 98% on air and 14 breaths per minute, respectively). She was tachycardic on admission with a heart rate of 103. Her blood pressure was in the normal range (128/72) and her temperature on admission was 37.2°C. Her chest was clear, with normal heart sounds, and there was no lymphadenopathy, no skin changes and no peripheral stigmata of endocarditis, and her abdomen was soft and non-tender.

Investigations showed a raised lymphocyte count of 5.7×109/l, mildly raised CRP (35 mg/l), raised ALT (149 U/l) and AST (137 U/l), and normal GGT and ALP. Ferritin was also raised at 1,168 µg/l. The chest x-ray was reported as clear. The SARS-CoV-2 swab on this admission was also negative, as were SARS-CoV-2 IgG antibodies. D-dimer was significantly raised at 3.1 µg/ml and a subsequent CT pulmonary angiogram did not reveal any pulmonary emboli, nor any changes in the lungs.

Further investigations during her admission showed a normal thyroid function and blood-borne virus screen. The blood film showed atypical lymphocytes and her Epstein–Barr virus serology was positive, confirming the diagnosis of infectious mononucleosis.

The symptoms of this patient were highly suggestive of SARS-CoV-2. Given that the sensitivity of SARS-CoV-2 PCR testing is approximately 70%, one negative swab result could be ignored if the pre-test probability is high. However with three negative swabs, the likelihood of the patient having SARS-CoV-2 is extremely small and therefore it is important to explore other differential diagnoses.