key: cord-267458-uofy7jyx
authors: Jiang, Xiao-Lin; Zhang, Xiao-Li; Zhao, Xiang-Na; Li, Cun-Bao; Lei, Jie; Kou, Zeng-Qiang; Sun, Wen-Kui; Hang, Yang; Gao, Feng; Ji, Sheng-Xiang; Lin, Can-Fang; Pang, Bo; Yao, Ming-Xiao; Anderson, Benjamin D; Wang, Guo-Lin; Yao, Lin; Duan, Li-Jun; Kang, Dian-Ming; Ma, Mai-Juan
title: Transmission potential of asymptomatic and paucisymptomatic SARS-CoV-2 infections: a three-family cluster study in China
date: 2020-04-22
journal: J Infect Dis
DOI: 10.1093/infdis/jiaa206
sha: 
doc_id: 267458
cord_uid: uofy7jyx

Data concerning the transmission of SARS-CoV-2 in asymptomatic and paucisymptomatic patients are lacking. We report a three-family cluster of infections involving asymptomatic and paucisymptomatic transmission. Eight (53%) of 15 members from three families were confirmed with SARS-CoV-2 infection. Of eight patients, three were asymptomatic and one was paucisymptomatic. An asymptomatic mother transmitted the virus to her son, and a paucisymptomatic father transmitted the virus to his three-month-old daughter. SARS-CoV-2 was detected in the environment of one household. The complete genomes of SARS-CoV-2 from the patients were >99.9% identical and were clustered with other SARS-CoV-2 sequences reported from China and other countries.

M a n u s c r i p t

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), that causes coronavirus disease 2019 (COVID-19), emerged in December 2019 in Wuhan, China [1] . It has since been declared a global pandemic with over 1,000,000 cases reported as of April 3, 2020 [2] . Person-to-person transmission has been established [3] [4] [5] [6] [7] [8] , and asymptomatic transmission of SARS-CoV-2 has been reported [9] . However, studies on the potential transmission of SARS-CoV-2 by asymptomatic persons and those with mild illness have been limited [10] . Herein, we report a 3-family cluster study of eight patients associated with asymptomatic and pauciasymptomatic (one mild symptom only) SARS-CoV-2 transmission in Shandong Province, China.

The first positive SARS-CoV-2 patients in this cluster were identified on January 21, 2020 triggering an epidemiological investigation by the local center for disease control and prevention. To identify the possible infective source, the epidemiological investigation focused on exposure history before the onset of illness, such as travel history to Wuhan or Hubei Province, visiting live animal markets, and contact history with febrile persons. Medical records were also closely reviewed to verify the timelines of events and clarify clinical progressions.

To examine possible environmental contamination of SARS-CoV-2 in households, select surfaces that may be frequently touched by family members were sampled in the bedroom (door handle, bedside light switch, and sliding of wardrobe door), kitchen (door handle, faucet switch, light switch, rice cooker plug), and bathroom (door handle, handrail, the surface of the toilet bowl, sink).

One swab per site (room) with multiple surfaces was collected.

All close contacts of SARS-CoV-2 positive patients were traced, including family members who lived with the patients and individuals who had contact with the patients within 1 meter without wearing proper personal protection. Close contacts were quarantined at home and monitored for fever (≥38°C) and symptoms. In addition, nasopharyngeal swabs of close contacts were collected every 24 A c c e p t e d M a n u s c r i p t 5 hours from day 1 to 14 to detect SARS-CoV-2 by molecular assay. If any close contact had positive detection of SARS-CoV-2, they were sent to a hospital for isolation and treatment.

All collected environmental and patient samples were stored at −80°C before being transported using cold chain to a biosafety level 2 enhanced laboratory to perform molecular detection of SARS-CoV-2.

A real-time reverse transcriptase PCR (rRT-PCR) Test Kit (GZ-D2RM, Shanghai GeneoDx Biotech Co., Ltd) targeting the ORF1ab and N genes of SARS-CoV-2 was used. A cycle threshold (Ct) value less than 37 was interpreted as positive for SARS-CoV-2 RNA and a Ct value of 40 or more was defined as a negative test. A medium load (weakly positive), defined as a Ct value of 37 to less than 40, required confirmation by retesting. Positive samples were sequenced directly from the original specimens as previously described [11] . The maximum likelihood phylogenetic tree of the complete genomes was conducted by using RAxML software (version 8.2.9) [12] with 1000 bootstrap replicates, employing the general time-reversible nucleotide substitution model.

Patients 1 (62-year-old woman) and 2 (65-year-old man) were a couple who lived with their son (Patient 3), daughter-in-law (Patient 4), and two grandchildren. Patient 1 presented with cough, rhinorrhea, and sputum on January 12, 2020 ( Figure 1 ). On January 15, she visited a health clinic and was diagnosed with a common cold. She was prescribed intravenous infusions of ampicillin and sulbactam, ribavirin, and traditional medicine for five days. On January 16, she developed a fever (38°C). On January 17, Patient 2 reported symptoms of fever (37.8°C), cough, sputum, earache, and upset stomach. He was also diagnosed with a common cold at the health clinic and received the same prescription as Patient 1 for three days. However, their symptoms did not resolve at the conclusion of the treatment regimen leading both to seek care at a local hospital on January 21.

Nasopharyngeal swabs were collected from both patients at the hospital and confirmed positive for The infant had no clinical symptoms before, during, or after hospitalization.

The chest CT images on admission or hospitalization showed that Patients 1-6 had ground-glass opacities. However, no significant abnormalities were observed for Patients 7 and 8 (Supplemental A c c e p t e d M a n u s c r i p t 9

We report a unique three-family cluster of infection with SARS-CoV-2, in which eight of 15 members were confirmed with SARS-CoV-2 infection. Particularly interesting is that of 6 secondary patients, two were asymptomatic, one was paucisymptomatic, and three were symptomatic. Our findings show that the transmission of SARS-CoV-2 by individuals with asymptomatic or paucisymptomatic infections is possible. Patients 1 and 2 were likely first exposed to SARS-CoV-2 after visiting their hometown in Xiaogan Hubei Province, China. Their son (Patient 3) and daughter-in-law (Patient 4, asymptomatic), whom they live with, were later found to be infected with SARS-CoV-2. Patient 5 (asymptomatic) was identified to be infected with SARS-CoV-2 after frequent contact with Patients 3 and 4 during work and home visits. She transmitted the virus to her son (symptomatic) whom she lives with. Patient 7 (paucisymptomatic) was found to be infected with SARS-CoV-2 after frequent contact with Patient 3 during work. He likely transmitted the virus to his daughter (Patient 8, asymptomatic). In addition, consistent with previous studies [5] [6] [7] [8] , the transmission of SARS-CoV-2 during the incubation period of Patient 3 likely occurred. Patients 5 and 7 were infected after their exposures to a presymptomatic Patient 3 during working or home visits. These findings may help explain the rapid spread of SARS-CoV-2 between person-to-person.

The currently available evidence shows that SARS-CoV-2 is transmitted between people through droplets and close contact [13] . A recent study showed extensive environmental contamination by a SARS-CoV-2 patient [14] , suggesting the contaminated environment as a potential medium of transmission. In this study, we detected SARS-CoV-2 in two environmental swabs from the household of Patient 3. Such detection of SARS-CoV-2 in contaminated environments of the household may provide an additional contribution to virus transmission among family members as the virus can remain viable and infectious on the surface up to seven days [15] . However, the direct researchbased evidence describing exactly how SARS-CoV-2 is transmitted is limited, and further studies are required.

We cannot rule out the possibility of unknown COVID-19 patients (e.g., asymptomatic carriers) transmitting the virus. However, according to screening protocols implemented by the provincial, municipal, and county-level Center for Disease Control and Prevention, all close contacts were A c c e p t e d M a n u s c r i p t 10 traced, and all patients with positive rRT-PCR results in this study were confirmed by whole-genome sequencing, including those who were asymptomatic or pauciasymptomatic (Patients 4, 5, 7, and 8). M a n u s c r i p t 11

We thank all patients involved in the study. We also thank Dr. Hong-Guang Ren from Beijing Institute of Biotechnology for generating phylogenetic tree. 

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