Information on the natural history of asymptomatic infection with the new coronavirus (COVID-19) remains scarce. We are just beginning to understand what happens with patients with severe disease.
The outbreak of COVID-19 on the cruise ship Diamond Princess provided a unique opportunity to study contacts and patients with asymptomatic infection within a closed population. This would have been impossible outside a cruise ship.
Among the 3711 on-board individuals (passengers and crew members included), approximately 712 had a positive COVID-19 test result, but more than half of them (58%) were asymptomatic. From this data, the natural history of asymptomatic patients could be described.
About 11 people who had a polymerase-chain-reaction (PCR) positive test result and were asymptomatic at the time the ship arrived developed symptoms a median of 4 days later, so they were actually presymptomatic. The risk of being presymptomatic increased with increasing age.
Eight cabinmates with a negative PCR test when the ship arrived had a positive PCR test within 72 hours. These people remained asymptomatic.
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Researchers were able to analyze the cohort of people who had a positive PCR test and remained asymptomatic throughout the infection (until they had a negative PCR testing result).
Almost a third of this cohort presented risk factors such as hypertension or diabetes.
The median number of days between the first positive PCR test (either on the ship or at the hospital) and the first of the two serial negative PCR tests was 9 days (range, 3 to 21 days).
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In almost half the population (48%) the infection was resolved after 8 days, and almost all patients (90%) were infection-free after 15 days.
The rate of delayed resolution of infection increased with increasing age. The older the patient, the greater the chances of developing symptoms and, if asymptomatic, greater the chances of a delayed resolution of infection.
Original Title: Natural History of Asymptomatic SARS-CoV-2 Infection.
Reference: N Engl J Med. 2020 Aug 27;383(9):885-886. doi: 10.1056/NEJMc2013020.
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