High transmissibility of COVID-19 near symptom onset

  1. Hao-Yuan Cheng
  2. Shu-Wan Jian
  3. Ding-Ping Liu
  4. Ta-Chou Ng
  5. Wan-Ting Huang
  6. for Taiwan COVID-19 outbreak investigation team
  7. Hsien-Ho Lin

Reviewed by

Read the full article

Listed in

Log in to save this article

Abstract

Background

The dynamics of coronavirus disease 2019 (COVID-19) transmissibility after symptom onset remains unknown.

Methods

We conducted a prospective case-ascertained study on laboratory-confirmed COVID-19 cases and their contacts. Secondary clinical attack rate (considering symptomatic cases only) was analyzed for different exposure windows after symptom onset of index cases and for different exposure settings.

Results

Thirty-two confirmed patients were enrolled and 12 paired data (index-secondary cases) were identified among the 1,043 contacts. The secondary clinical attack rate was 0.9% (95% CI 0.5–1.7%). The attack rate was higher among those whose exposure to index cases started within five days of symptom onset (2.4%, 95% CI 1.1–4.5%) than those who were exposed later (zero case from 605 close contacts, 95% CI 0–0.61%). The attack rate was also higher among household contacts (13.6%, 95% CI 4.7–29.5%) and non- household family contacts (8.5%, 95% CI 2.4–20.3%) than that in healthcare or other settings. The higher secondary clinical attack rate for contacts near symptom onset remained when the analysis was restricted to household and family contacts. There was a trend of increasing attack rate with the age of contacts ( p for trend < 0.001).

Conclusions

High transmissibility of COVID-19 near symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic, and more generalized social distancing measures are required. Rapid reduction of transmissibility over time implies that prolonged hospitalization of mild cases might not be necessary in large epidemics.

Article activity feed

  1. ScreenIT

    SciScore for 10.1101/2020.03.18.20034561: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study has limitations. First, we did not completely examine contacts before the symptom onset of the index cases. Therefore, we might have underestimated the importance of early transmission. In other words, the actual importance of early transmission could be higher than our estimates. Our findings agree with the recommendation from WHO on using four days before symptom onset as the starting date for contact tracing.28 This modification might further reveal the pattern of early transmission in COVID-19. Second, we could not completely separate out the effect of close household contact and early contact given the strong correlation of the two. The increased transmissibility in the early stage of COVID-19 may be partially attributed to the effect of household and non-household family contacts rather than increased infectiousness at the early stage. But the pattern of early transmission remained when we stratified by type of exposure. In summary, our analysis suggested that the majority of transmission of COVID-19 occurred at the very early stage of the disease, and the secondary clinical attack rate among contacts decreased over the time line of symptom development. The pattern of high transmissibility near symptom onset and possible short infectious period may drastically change the thinking of control strategies for COVID-19. More studies are urged to elucidate the transmission dynamics of this novel disease clearly.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  2. Version published to 10.1101/2020.03.18.20034561v1 on medRxiv