clinical presentation and natural history of COVID-19

he spectrum of illness associated with COVID-19 is wide, ranging from asymptomatic infection to life-threatening respiratory failure. When symptoms are present, they typically arise three to five days after exposure. Most symptomatic infections are mild. Nasal congestion, sneezing, sore throat, cough, myalgias, and headache are the most commonly reported symptoms. Other features, including diarrhea and smell or taste abnormalities, are also well described.

Pneumonia, with fever, cough, dyspnea, and infiltrates on chest imaging, is the most frequent serious manifestation of infection. Progression from dyspnea to acute respiratory distress syndrome (ARDS) can be rapid; thus, the onset of dyspnea is generally an indication for hospital evaluation and management.

ARDS can be associated with an exuberant inflammatory response, which is characterized by fever, progressive hypoxia and/or hypotension, and markedly elevated inflammatory markers. Other complications of severe illness include thromboembolic events, acute cardiac injury, kidney injury, and inflammatory complications.

The time to recovery is highly variable and depends on age and pre-existing comorbidities in addition to illness severity. Individuals with mild infection are expected to recover relatively quickly (eg, within two weeks), whereas many individuals with severe disease have a longer time to recovery (eg, two to three months). The most common persistent symptoms include fatigue, dyspnea, chest pain, cough, and cognitive deficits.

The overall case fatality rate in unvaccinated individuals is estimated to be between 0.15 and 1 percent, although it varies widely by age and other patient characteristics. While severe and fatal illness can occur in anyone, the risk rises with age and the presence of chronic illnesses, including cardiovascular disease, pulmonary disease, diabetes mellitus, kidney disease, and cancer