key: cord-311479-8pjoz64q
authors: He, Daihai; Zhao, Shi; Lin, Qianying; Zhuang, Zian; Cao, Peihua; Wang, Maggie H; Yang, Lin
title: The relative transmissibility of asymptomatic cases among close contacts
date: 2020-04-18
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.04.034
sha: 
doc_id: 311479
cord_uid: 8pjoz64q

Abstract Asymptomatic transmission of the coronavirus disease 2019 is an important topic. A recent study in China showed that transmissibility of the asymptomatic cases is comparable to that of symptomatic cases. Here we showed that the conclusion may depend on how we interpret the data. To the best of our knowledge, this is the first time the relative transmissibility of asymptomatic COVID-19 cases is quantified.

Asymptomatic transmission of the coronavirus disease 2019 is an important topic. A recent 24 study in China showed that transmissibility of the asymptomatic cases is comparable to that 25 of symptomatic cases. Here we showed that the conclusion may depend on how we interpret 26 the data. To the best of our knowledge, this is the first time the relative transmissibility of 27 asymptomatic COVID-19 cases is quantified. 28 29 Keywords: COVID-19; asymptomatic cases; relative transmissibility 30 31 32 33 Main text 35 Nishiura et al (Nishiura et al, 2020 ) estimated the asymptomatic ratio of COVID-19 was 41.6% 36 (5 out of 12 confirmed cases) among 565 Japanese individuals evacuated from Wuhan, China. 37

Mao et al (Mao et al, 2020) reported that 2 out of 78 confirmed cases are asymptomatic. One 38 of the two cases showed RT-PCT positivity 15 th days after first diagnosis. Mizumoto et al 39 estimated that the 17.9% of cases on the Diamond Princess Cruise Ship were asymptomatic 40 case during the outbreak in February 2020 (Mizumoto et al, 2020) . However, the 41 transmissibility of asymptomatic case is unclear, and the positive RT-PCT results only imply 42 the potential infectivity. It is important to study the pattern of viral shedding and live virus 43 isolation. Wölfel et al studied 9 hospitalized cases and found that live virus was isolated from 44 throat and lung-derived samples between 3 and 8 days after symptom onset (Wölfel et al, 45 2020) . When the RNA concentration is above 10 6 copies per ml (or equivalent Ct-value lower 46 than 24), but not from stool samples, despite of high virus RNA concentration. Above the 47 threshold, high RNA concentration yields high probability of live virus isolation. This 'dose-48 response' association highlights a patient's RT-PCR level should be higher than a threshold 49 to be effectively infectious. However, the mean infectious period (γ −1 ) of a symptomatic case may be longer than that of 102 an asymptomatic case hypothetically. Therefore, the combined effects of ρ and γ −1 probably 103 lead to a higher reproduction number in the symptomatic group. 104 105 Additionally, Chen et al (Chen et al, 2020) showed that asymptomatic cases are more likely 106 to produce asymptomatic cases relatively speaking, since the 6 secondary cases from 107 asymptomatic primary cases consist 3 asymptomatic cases (50%). Whereas, 19 out of 126 108 (15%) are asymptomatic from symptomatic primary cases. The odds ratio (OR) is estimated 109 In summary, we conclude that the relatively transmissibility of asymptomatic case could be 127 significantly smaller than that of the symptomatic cases. The main contribution of (Chen et al, 128 2020) is that they raise the alarm of the existence of the transmissibility of the asymptomatic 129 cases. We remark that how efficient of the transmissibility of asymptomatic cases comparing 130 to symptomatic cases warrants more study. 131 132 133 Here we showed that the conclusion may depend on how we interpret the data. 287 288 We also reported the asymptomatic case ratio in Hong Kong over time due to a large number 289 of young imported case. 290 291

To the best of our knowledge, this is the first time the relative transmissibility of 292 asymptomatic COVID-19 cases is quantified. 293 294 295

Estimation of the asymptomatic ratio of novel coronavirus infections (COVID-158 19)

Estimating the asymptomatic 161 proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess 162 cruise ship

The enlightenment from two 165 cases of asymptomatic infection with SARS-CoV-2: is it safe after 14 days of 166 isolation?

SARS-CoV-2 169 viral load in upper respiratory specimens of infected patients

Virological assessment of hospitalized patients 174 with COVID-2019

Coronavirus Disease 2019 in China. The New England Journal of Medicine

Serial Interval of COVID-19 180 among Publicly Reported Confirmed Cases. Emerging Infectious Diseases

Covert coronavirus infections could be seeding new outbreaks

The 185 epidemiological characteristics of infection in close contacts of COVID-19 in Ningbo city

Modelling the coronavirus disease (COVID-19) outbreak on 190 the Diamond Princess ship using the public surveillance data from

DH was supported by an Alibaba (China)-Hong Kong Polytechnic University Collaborative 237 Research project. Other authors declared no competing interests