The symptoms for early Covid-19 infection may differ among age groups and between men and women, new research published in The Lancet Digital Health, suggests.These differences are most notable between younger age groups (16-59 years) compared to older age groups (60-80 years and over) and men have different symptoms compared to women in the early stages of Covid-19 infection.Men were more likely to report shortness of breath, fatigue, chills and shivers, whereas women were more likely to report loss of smell, chest pain and a persistent cough."It's important people know the earliest symptoms are wide-ranging and may look different for each member of a family or household," said lead author Claire Steves from King's College London.For the study, the team analysed data from a Covid symptom study app between April 20 to October 15. They modelled the early signs of Covid-19 infection and successfully detected 80 per cent of cases when using three days of self-reported symptoms.Then, they, compared the ability to predict early signs of Covid-19 infection using a type of machine learning (ML).This ML model was able to incorporate some characteristics about the person affected, such as age, sex, and health conditions, and showed that symptoms of early Covid-19 infection are different among various groups.In the study, 18 symptoms were examined, which had different relevance for early detection in different groups.The most important symptoms for the 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 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 over 80). Fever, while a known symptom of disease, was not an early feature of the disease in any age group.