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Identifying people infected with 2019 novel coronavirus (2019-nCoV) in order to isolate them will be essential to halt virus spread. Can people transmit infection during asymptomatic or presymptomatic infection?
In a case reported from Germany, Rothe and colleagues describe a 33-year-old healthy businessman (patient 1) who attended meetings with a Chinese business partner who was well during the meetings but became ill on her flight back to China. She was positive for 2019-nCoV. A few days later, patient 1 developed fever and productive cough but improved and returned to work three days later. Although he was afebrile and feeling well, he was identified as a contact of the Chinese patient and tested positive for 2019-nCoV on quantitative reverse-transcriptase-polymerase-chain-reaction assay (qRT-PCR). Follow-up testing in the subsequent 2 days showed high viral load (108 copies/mL in sputum), while he remained asymptomatic. Three other employees who developed symptoms tested positive for 2019-nCoV. One had contact with the Chinese business partner; the other two had contact only with patient 1. All were admitted to an infectious disease unit in Munich for isolation and monitoring.
Holshue and colleagues describe the first 2019-nCoV case reported in the U.S. A 35-year-old man had visited Wuhan, China, but not the Huanan seafood market and reported no contact with ill persons. He was seen at a clinic in Snohomish County, Washington. Onset of pneumonia was delayed (day 9 of illness). Nasopharyngeal samples were persistently positive for 2019-nCoV by qRT-PCR through at least day 12, and stool sample, tested on day 7, was positive. He was treated with remdesivir (an antiviral drug not currently FDA approved) on a compassionate-use basis and was recovering.
Rothe C et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. N Engl J Med 2020 Jan 30; [e-pub]. (https://doi.org/10.1056/NEJMc2001468)
Holshue ML et al. First case of 2019 novel coronavirus in the United States. N Engl J Med 2020 Jan 31; [e-pub]. (https://doi.org/10.1056/NEJMoa2001191)
Comment
People who were infected with the related coronavirus, SARS CoV, generally developed fever before transmitting virus, so spread of SARS CoV could be stopped by screening for fever and isolating those potentially infected. These important new cases document that the 2019-nCoV can be transmitted in the absence of symptoms, which will make interruption of spread much more difficult. Still to be determined is how common asymptomatic transmission is.
The report by Rothe describes two generations of spread during infection that was presymptomatic or mild and self-limited. Whether the high-titer virus identified in sputum by qRT-PCR during convalescence was viable and transmissible remains unclear. The first case in the U.S. acquired infection from an unknown source in Wuhan and had persistent PCR positivity of respiratory samples.