We know something about the "mature" symptoms based on the Chinese study noted before, but since some infection (perhaps a lot) is taking place because of people in the early stages of infection, what do those symptoms look like? This article offers some pointers, but I'd welcome other sources in the comments:
It is known that some people infected have no symptoms or ones so mild that they’re not noticed. Daniel Mueller, an infectious diseases doctor at Temple University Hospital, said infected people might feel “just slightly under the weather for a few days.… They might just feel a little tired or a little achy." It’s the sort of feeling you’d have if you thought you were coming down with something, but nothing very worrisome.
Then they might start having a dry cough. Later, in some people, shortness of breath comes on. “They don’t always happen together,” Mueller said....
Unlike the flu, which announces itself suddenly with fever and muscle aches, the early stages of COVID-19 can go on for a few days.
Reynold A. Panettieri Jr., vice chancellor for clinical and translational science at Rutgers University, said some mild cases last just three to four days. Others who are not sick enough for hospitalization still may have symptoms for two weeks. Presentation of the disease is, he said, “very individualistic and very heterogeneous." Some people are barely affected and some have “shaking chills” and muscle aches, he said....
[Dr.] Meyer [Penn Medicine] would add sore throat to the list of early symptoms. She said most patients will eventually have a fever, but it “may not be in the first five days.”
A report about the outbreak in China published in the New England Journal of Medicine said about 44% of COVID-19 patients had a fever when admitted to a hospital and 88% developed one during their stay. The researchers warned that cases could be missed if doctors considered fever part of the case definition....
A rarely mentioned early symptom is gastrointestinal distress. About 10% of cases can start with a couple of days of diarrhea, abdominal pain, nausea, or vomiting and then respiratory symptoms develop, said David A. Johnson, chief of gastroenterology at Eastern Virginia Medical School, who has reviewed studies on the new disease. He said this makes sense because the virus first targets a type of cell that lives both in the lungs and in parts of the digestive tract.
Obviously all these symptoms could be due to many other causes! But if you're in an area with a lot of COVID-19, or have recently travelled or been out-and-about, it would probably be wise to severely limit your social interactions for a few days in the presence of these symptoms to make sure more do not develop. (That's my intelligent layperson's advice, not medical advice, which I am incompetent to give.)
