COVID-19: Transmission Dynamics in Taiwan

COVID-19: Transmission Dynamics in Taiwan. Spencer EA, Jefferson T, Heneghan C.

Published on June 22, 2020

Reference Cheng H, Jian S, Liu D, et al Contact Tracing Assessment of COVID-19 Transmission Dynamics in Taiwan and Risk at Different Exposure Periods Before and After Symptom Onset. JAMA Intern Med. Published online May 01, 2020. 2020
Study type
Country Taiwan
Setting Household, family and healthcare settings
Funding Details Taiwan Ministry of Science and Technology
Transmission mode Person to person
Exposures Close contacts, household contacts

Bottom Line

Most transmission of COVID-19 occurred at the early stage or even before symptom onset, as symptoms developed and progressed the secondary attack rate decreased

Evidence Summary

One hundred 100 confirmed patients enrolled, and 2,761 close contacts identified, and 22 paired index-secondary cases. The overall secondary clinical attack rate was 0.7 per cent.

All the secondary cases identified occurred when exposure to index cases started within 5 days of symptom onset, with no secondary cases later than 5 days after symptom onset.

  • The 299 contacts with only presymptomatic exposures experienced an attack rate of 0.7 per cent. 
  • The attack rate was higher among household (4.6%, 95%CI 2.3% to 9.3%) and non-household (5.3%, 95%CI 2.1% to 12.8%) family contacts than in healthcare or other settings. 
  • The attack rates were higher among those aged 40 to 59 years and those aged 60 years and older 

What did they do?

The study investigated the transmissibility of coronavirus disease 2019 (COVID-19) to close contacts? The authors recruited the first 100 cases diagnosed in Taiwan into a prospective study, identified their contacts and calculated what percentage developed COVID-19. 

The study period was from the 15th of January to the 18th of March 2020. All close contacts were quarantined at home for 14 days after their last exposure to the index case. During the quarantine period, any relevant symptoms (fever, cough, or other respiratory symptoms) of contacts triggered a COVID-19 test. The final follow-up date was 2nd of April 2020.

Contact tracing was implemented by the outbreak investigation team of the Taiwan CDC and local health authorities.

Study reliability

It is unclear if the case ascertainment was comprehensive. contacts were not completely examined prior to symptom onset of the index cases, which may underestimate early transmission. Increased transmissibility of COVID-19 in household and nonhousehold family contacts may be due to the closeness of contacts rather than early increased infectiousness.

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

What else should I consider?

This study indicated a relatively short infectious period and suggested high transmissibility of the disease near or prior to the day of symptom onset. The findings are in line with the recommendation from the WHO to use four days before symptom onset as the starting date for contact tracing.

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.

Tom Jefferson

Tom Jefferson, epidemiologist.