1. Exposure: An event when an individual is exposed to the SARS-CoV-2 virus while in close contact (< 6 feet for >15 minutes) with someone who has been infected with COVID-19.
2. Symptom Onset: The time when symptoms start. This is typically 2-14 days after exposure to the virus. Symptoms may include fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea or vomiting, or diarrhea (from CDC).
Pre-symptomatic (translation “before symptom onset”): a person who is infected and has not yet shown symptoms, but later does show symptoms and tests positive for the disease.
Symptomatic case: a person who is infected and has symptoms
Asymptomatic case: a person who is infected but does not have symptoms while infected
3. Disease Severity: Symptoms range in their severity. They may be mild and/or they may progress to requiring hospitalization and short-term care.
Hospitalized case: In the most severe presentation of cases, some infected individuals will need to be hospitalized. However, this does not happen to everyone who becomes infected.
4. Disease Outcome: The result of COVID-19 infection, which may be recovery, disability, or sometimes death
Recovered case: a COVID-19 infected individual who no longer shows signs or symptoms of infection. The definition of a recovered case varies widely in practice and is not consistently measured in COVID-19 infected individuals. Therefore, it is not a reliable measure for comparing populations across place and time.
Long-term effects: It is well documented that a proportion of COVID-19 cases experience long-term effects due to bodily damage caused by COVID-19 infection. Such long-term effects include shortness of breath, fatigue, cough, and other cardiovascular effects such as myocarditis or pericarditis.
Death: COVID-19 mortality refers to deaths where SARS-CoV-2 infection was a contributing cause.
For a general overview of a disease timeline, see this page from the CDC.