COVID-19: Early Symptoms of Infection Vary

With COVID-19, early symptoms of infection vary among age groups and between men and women. That’s the conclusion of a paper that appeared recently in The Lancet Digital Health. The biggest differences occur between older adults (60 and over) and younger people (16–59 ). However, the first signs of illness also vary between women and men.

Researchers from King’s College London wanted to learn how to predict COVID-19 cases from the earliest symptoms of infection. To do this, they used diagnostic criteria and algorithms from the U.K.’s National Health Service and a “hierarchical Gaussian process model,” a type of machine learning.

The team initially gathered data from the ZOE COVID Symptom Study app between late April and mid-October 2020. They invited app contributors to get a COVID-19 test as soon as they reported signs of illness. The researchers used this data to “train” the Gaussian process model to detect COVID-19. Then, for about 6 weeks, they “tested” the model on users of the app—and successfully detected 80% of cases from 3 days of self-reported data. Approximately 183,000 people provided data in the “training” phase, and just over 15,000 reported symptoms in the “testing” phase.

Go here to read the full study.

Differences in Early Symptoms of Infection

The machine learning model incorporated some personal characteristics, like age and sex. This allowed the researchers to see that early symptoms of infection varied quite a bit by these criteria.

The scientists examined 18 symptoms. As summarized in a ScienceDaily press release, “The most important symptoms for earliest detection of COVID-19 overall included loss of smell, chest pain, persistent cough, abdominal pain, blisters on the feet, eye soreness and unusual muscle pain. However, loss of smell lost significance in people over 60 years of age and was not relevant for subjects over 80. Other early symptoms such as diarrhoea were key in older age groups (60–79 and >80). Fever, while a known symptom of disease, was not an early feature of the disease in any age group.”

For women, common early symptoms of infection were chest pain, loss of smell and a persistent cough. For men, they were shortness of breath, fatigue, chills and shivers.

Why Symptom Variations Matter

The data used in the study came from the first COVID-19 strain and Alpha variants, but the findings suggest that symptoms will also differ for the Delta variant and subsequent ones, according to the Science Daily press release.

Lead study author, Claire Steves, PhD, told ScienceDaily: “It’s important people know the earliest symptoms are wide-ranging and may look different for each member of a family or household.”

Marc Modat, PhD, senior lecturer at King’s College London, echoed that statement: “As part of our study, we have been able to identify that the profile of symptoms due to COVID-19 differs from one group to another. This suggests that the criteria to encourage people to get tested should be personalized using individuals’ information such as age.”

Modat added, “Alternatively, a larger set of symptoms could be considered, so the different manifestations of the disease across different groups are taken into account.” This may be less relevant in the United States than in the U.K. In Britain, “only a few symptoms are used to recommend self-isolation and further testing,” according to Liane dos Santos Canas, PhD, first author from King’s College London.

Note: U.S. readers who are experiencing possible symptoms of COVID-19 should follow CDC and state/local guidelines for self-isolation and testing.

Kate Watson is the executive managing editor of IDEA Publications.