Clinical aspects of COVID-19

Virus shedding is highest early in the disease, and can start 24-48 hours before the onset of symptoms. Shedding then usually continues for one to two weeks in mild or moderate cases, or longer for more severe cases. Even after a patient has recovered, qPCR can still be positive.

COVID-19 is not a severe flu. It spreads more easily, and the mortality rate is significantly higher than seasonal flu. Data so far show that, overall, around 80% of cases are mild, 15% are severe, and 5% are critical. Recovery takes around two weeks for mild cases, and three to six weeks for more severe cases. In cases which lead to death, the progression from symptom onset to death is between two and eight weeks. Asymptomatic infections appear to be rare according to molecular testing; most “asymptomatic” cases will likely go on to develop symptoms.

The median age of hospital admissions in China was 47. Age was a major contributing factor in whether a patient would need to be admitted to Intensive Care; older patients were far more likely to become critical, whilst the disease tends to be more mild in younger adults and children. Children may also be less likely to become infected, although we will need seroprevalence studies to confirm this. Certain co-morbidities also increase the risk of a patient becoming severely unwell, particularly hypertension, diabetes, and existing respiratory problems.

Some laboratory markers, such as lymphocyte count, may be predictive of how the disease may progress in a patient. However, as we do not yet fully understand the relationship between these markers and the disease, they could confuse diagnosis.

Pregnancy does not yet appear to stand out as a significant risk factor for the development of severe disease, but this is still based on only a small number of cases. Intrauterine transmission has not been identified, but some cases of the disease in new-borns have been documented.

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