Asymptomatic and paucisymptomatic SARS-CoV-2 infections

Asymptomatic and paucisymptomatic SARS-CoV-2 infections.. Spencer EA, Heneghan C.

Published on July 6, 2020

Reference Jiang XL, Zhang XL, Zhao XN, et al. Transmission potential of asymptomatic and paucisymptomatic SARS-CoV-2 infections: a three-family cluster study in China. J Infect Dis. 2020.  2020
Study type
Country China
Setting Households
Funding Details Special National Project on Investigation of Basic Resources of China; the National Major Project for Control and Prevention of Infectious Disease of China; the Key Research and Development Program of Shandong Province; and the National Natural Science Foundation of China.
Transmission mode Person to person, Close contact
Exposures Close family contact; asymptomatic case exposure

Bottom Line

This study of two cases and six subsequent infections amongst close family contacts suggests SARS-CoV-2 transmission through asymptomatic or paucisymptomatic infections is possible.

Evidence Summary

Two initial patients who were spouses had 15 close family member contacts, spanning three families. Six more cases of SARS-CoV-2 infection within the 15 family contacts were identified.

Among the total eight cases, three were asymptomatic and one was paucisymptomatic. 

It appeared that an asymptomatic mother transmitted the virus to her son, and a paucisymptomatic father transmitted the virus to his 3-month-old daughter. 

What did they do?

The study investigates a 3-family cluster of infections in which 8 of 15 members were confirmed with SARS-CoV-2 infection, involving asymptomatic and paucisymptomatic transmission. 

All close contacts of two initial 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 m without wearing proper personal protection. Close contacts were quarantined at home and monitored for fever (≥ 38°C) and symptoms. In addition, nasopharyngeal (NP) swabs of close contacts were collected every 24 hours from day 1 to day 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.

Exposure history before the onset of illness was recorded, such as travel history to Wuhan or Hubei provinces, 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.

All patients with positive rRT-PCR results in this study were confirmed by whole-genome sequencing, including those who were asymptomatic or paucisymptomatic

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 handle, light switch, rice cooker plug), and bathroom (door handle, handrail, surface of the toilet bowl, sink). One swab per site (room) with multiple surfaces was collected.

Eight of 15 (53%) 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 3-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.


Study reliability

This is a very small study and needs replicating with a larger sample size. 

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Yes Yes No

What else should I consider?

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.