While symptoms of COVID-19 can be relatively non-specific and infected people may be asymptomatic, the two most common symptoms are fever (88%) and dry cough (68%). Less common symptoms include fatigue, respiratory sputum production (phlegm), loss of smell, shortness of breath, muscle and joint pain, sore throat, headache, or chills.
WHO states that approximately 1 person in 6 becomes seriously ill and has difficulty breathing. The U.S. Centers for Disease Control and Prevention (CDC) lists emergency symptoms as difficulty breathing, persistent chest pain or pressure, sudden confusion, difficulty waking, and bluish face or lips; immediate medical attention is advised if these symptoms are present.
Further development of the disease can lead to severe pneumonia, acute respiratory distress syndrome, sepsis, septic shock and death. Some of those infected may be asymptomatic, with no clinical symptoms but test results that confirm infection, so researchers have issued advice that those with close contact to confirmed infected people should be closely monitored and examined to rule out infection. Chinese estimates of the asymptomatic ratio range from few to 44%.
The usual incubation period (the time between infection and symptom onset) ranges from one to 14 days; it is most commonly five days. In one case, it may have had an incubation period of 27 days.
