The specific set of symptoms COVID-19 patients experience at the onset of the disease may predict how severe their case will become, according to a study by researchers at King's College London that analyzed self-reported symptoms.
The study identifies six "symptom clusters," or subtypes, of COVID-19:
Subtype 1, "flu-like with no fever": headache, loss of smell, muscle pain, cough, sore throat and chest pain.
Subtype 2, "flu-like with fever": fever and loss of appetite in addition to headache, loss of smell, cough, sore throat and hoarseness.
Subtype 3, "gastrointestinal": diarrhea and loss of appetite, no cough, headache, loss of smell, sore throat and chest pain.
Subtype 4, "severe level one, fatigue": fatigue in addition to headache, loss of smell, cough, fever, hoarseness and chest pain.
Subtype 5, "severe level two, confusion": confusion in addition to headache, loss of smell, loss of appetite, cough, fever, hoarseness, sore throat, chest pain, fatigue and muscle pain.
Subtype 6, "severe level three, abdominal and respiratory": shortness of breath, diarrhea and abdominal pain in addition to headache, loss of smell, loss of appetite, cough, fever, hoarseness, sore throat, chest pain, fatigue, confusion and muscle pain.
"We were able to work out these six subtypes ... that make a bit more sense of this strange disease," said Tim Spector, professor of genetic epidemiology at King's College London. "At the moment, we're treating it like it's all the same flu, but clearly everyone reacts very differently -- because they are different people or something about the virus is different."
Spector is also a co-founder of the ZOE COVID Symptom Study app, which collected the self-reported data for this study. The app asks users to log health information and potential COVID-19 symptoms daily. The study analyzed data from 1,600 app users in the U.S. and U.K. with confirmed COVID-19 cases and who logged their symptoms during March and April.