key: cord-292236-eudcs9t2 authors: Wang, Yishan; Kang, Hanyujie; Liu, Xuefeng; Tong, Zhaohui title: Asymptomatic cases with SARS‐CoV‐2 infection date: 2020-05-22 journal: J Med Virol DOI: 10.1002/jmv.25990 sha: doc_id: 292236 cord_uid: eudcs9t2 On 31 March 2020, Chinese Health Authorization announced that numbers of asymptomatic cases with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection will be made to the public daily. This was a very important step since different counties have different capacities for the detection of SARS‐CoV‐2 infection and control strategy for the Coronavirus Disease 2019 outbreak. We summarized the characteristics of asymptomatic SARS‐CoV‐2 infections and the transmission potential of asymptomatic cases. Then we provided guidelines for the management of asymptomatic cases through quarantine and nucleic acid/serology tests. The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic. Till 31 March 2020, there were more than 82 600 confirmed cases in the mainland China and 855 000 cases worldwide, leading to over 42 000 cases of death, causing heavy economic loss and continually threatening life safety. The infection with SARS-CoV-2 seems to spread more easily than other diseases, including seasonal influenza. Calculations of R0 (the number of people on an average one infected person will pass on the virus) suggest a range of 2 to 2.5. 1 Recently, "asymptomatic infection," also known as "hidden coronavirus infections" (https://www.sciencemag.org/news/2020/02/labs-scramblespot-hidden-coronavirus-infections#) or "covert coronavirus infections" There are two classes of asymptomatic cases with SARS-CoV-2 infection: first, cases with little or mild symptoms within the incubation period but with symptoms onset in the coming 14-day quarantine period or typical changes on the chest-radiograph. The other refers to the patient with no symptoms all the time but tested positive for viral nucleic acid or antibodies. Asymptomatic cases are often screened for close contacts both in the clinic and in community, such as cohabiting family members of COVID-19 patients or suspected patients or individuals who have exposed to COVID-19 patients within a short distance and relatively long time. Other circumstances include screening for clustering occurrence or tracing the source of infection. Currently, asymptomatic cases are not included in the confirmed patients in everyday-report according to the "Novel Coronavirus Pneumonia Diagnosis and Treatment Protocol (7th edition, trial)." Once found, the patient will be put into medical isolation for up to 14-days, if the patient has symptoms onset within the isolation period, he/she will be reported as a confirmed case immediately. Evidence is accumulating on the existence of many asymptomatic or and cases who had not yet developed symptoms at the time of data collection but became symptomatic later. As predicted using a statistical model, the estimated total number of true asymptomatic cases was at 113.3 and the estimated asymptomatic proportion (among all infected cases) was 17.9%. Another study reported that the asymptomatic ratio was estimated at 30.8% among evacuees tested positive for SARS-CoV-2 using the information on Japanese nationals that were evacuated from Wuhan, China. 2 In this study, the length of observation was long enough to cover the COVID-19 incubation period. 3, 4 A recent study reported a familial cluster with three asymptomatic cases. Studies from single-center reported 4% to 6% cases with SARS-CoV-2 did not develop any symptom during the course of the disease. 5, 6 Thus, there is very little probability that the virus-positive asymptomatic individuals will develop symptoms later, the ratio is slightly smaller than that of influenza, which was estimated at 56% to 80%. Recently, a preprint published on medRxiv analyzed the evolving epidemiology before and after nonpharmaceutical interventions put into effect using an SEIR model. The study indicated at least 59% of infected cases were unascertained in Wuhan which in- With the existence of disagreement in the actual number of asymptomatic cases and their infectivity, larger observational studies including serological tests with a longer period are needed. 15 Currently, for asymptomatic patients to follow strict quarantine is of great importance in the control of the COVID-19 epidemic. If various feasible measures are taken to control the transmission, then the outbreak could be ended as soon as possible. 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