Although COVID-19 has become a pandemic for two months, widespread population testing is still not available in most countries, including the UK and the US. While most infected individuals tend to present flu-like symptoms, some mainstream media and case studies also reported SARS-CoV-2, the causative agent of COVID-19 might develop anosmia or the loss of smell in certain patients.

Symptoms indicating the presence of COVID-19

Researchers at King’s College London, Massachusetts General Hospital and nutritional science company Zoe Global had investigated whether the loss of smell and taste could be indicators to screen for mild COVID-19 cases and recommend potential carriers to self-isolate. They targeted their study at the UK and US populations and used data obtained from a free mobile application – COVID Symptom Study, that was launched in these two countries late in March.

The app tracks the pandemic progression in real-time by collecting self-reported health information such as symptoms, demographics, hospitalization, diagnostic test outcomes and pre-existing medical conditions, from asymptomatic and symptomatic users on a daily basis. Just under 2.5 million people’s data were analyzed and 32.2% of them said they have one or more potential COVID-19 symptoms but only 15,638 from the UK and 2763 from the US had undergone the RT-PCR SARs-CoV-2 test.

Close to two-thirds of the UK and US participants who came back with positive results indicated a loss of smell and taste. On the other hand, near 23% of the UK and 17% of the US participants with negative results also gave the same indications. The analysis found ten other symptoms including fever, shortness of breath, to persist cough, diarrhea and chest pain to be related to a positive diagnostic test result in the UK cohort. In the US cohort, only fatigue and skipped meals were related.

A new predictive model with nearly 80% accuracy

A new, predictive model was built using the data and analyses. They then applied it to more than 800,000 app users who are experiencing symptoms but have yet to be tested, to estimate the percentage who will eventually receive a positive diagnosis. According to the model, about 17.42% are most probably at risk of being infected. In addition, loss of smell and taste is a potential predictor of COVID-19 as compared to other more established symptoms such as high temperature.

Researchers noted despite the outcomes, it remains unclear whether anosmia was developed before or after other symptoms and during or after the illness. Besides, self-reported nature of the study cannot replace results gathered from systematic assessments. Last but not least, one cannot deny the presence of false positives and false negatives. Nevertheless, researchers are confident that combining the power of artificial intelligence (AI) driven predictions and a mobile app that is widely adopted, they can quickly identify those who are likely to be infectious once the earliest symptoms begin to emerge. This will subsequently reinforce contact tracing, testing and quarantine.

As Professor Tim Spector, Head of Department, Department of Twin Research & Genetic Epidemiology at King’s College London and one of the study’s leading researchers said, “Our results suggest that loss of taste or smell is a key early warning sign of COVID-19 infection and should be included in routine screening for the disease. We strongly urge governments and health authorities everywhere to make this information more widely known, and advise anyone experiencing sudden loss of smell or taste to assume that they are infected and follow local self-isolation guidelines.”

The study was published in Nature Medicine yesterday (12 May).

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Author Bio

Hazel Tang A science writer with data background and an interest in the current affair, culture, and arts; a no-med from an (almost) all-med family. Follow on Twitter.