• About Us
    • Contact Us
    • Login
    • ObGFirst
  • Alerts
  • OB
  • 2T US Atlas
  • The Genome
  • GYN
    • GYN
    • Sexual Health
  • Primary Care
  • Your Practice
  • GrandRounds
  • My Bookshelf
  • COVID-19
About Us Contact Us Login ObGFirst
  • Alerts
  • OB
  • 2T US Atlas
  • The Genome
  • GYN
    • GYN
    • Sexual Health
  • Primary Care
  • Your Practice
  • GrandRounds
  • My Bookshelf
  • COVID-19
Grand Rounds

What is the Risk of SARS-CoV-2 Transmission Among Close Contacts?

image_pdfFavoriteLoadingFavorite

BACKGROUND AND PURPOSE:

  • Ng et al. (The Lancet Infectious Diseases, 2020) determined asymptomatic attack rates and SARS-CoV-2 transmission risk factors among community close contacts of patients with COVID-19

METHODS:

  • Retrospective cohort study conducted in Singapore (January 23 and April 3, 2020)
    • Singapore’s COVID-19 contact tracing program identified close contacts of COVID-19 cases
    • These close contacts were then monitored during a 14-day quarantine at home
    • Contacts who reported symptoms were admitted to the hospital for testing
  • Participants
    • All close contacts of confirmed COVID-19 cases

Study Design

  • Definitions
    • Household contacts: Individuals who shared a residence with the index COVID-19 case
    • Non-household contacts: People who had contact for at least 30 min within 2 m of the index case
  • Contact tracing, quarantine and testing system
    •  All patients with COVID-19 in Singapore received inpatient treatment
    • All close contacts were quarantined for 14 days with 3 times per day symptom monitoring via telephone
    • Symptomatic contacts underwent PCR testing
  • Data analysis
    • Secondary clinical attack rates were derived from the prevalence of PCR-confirmed SARS-CoV-2 among close contacts
    • Consenting contacts underwent serology testing and detailed exposure risk assessment
    • Bayesian modelling was used to estimate the prevalence of missed diagnoses and asymptomatic positive cases
    • Univariable and multivariable logistic regression models were used to determine transmission risk factors

RESULTS:

  • 7,770 close contacts (linked to 1,114 confirmed cases) | 7,518 with complete data
    • Household contacts: 1,863 individuals
    • Work contacts: 2,319 individuals
    • Social contacts: 3,588 individuals
  • Symptom-based PCR testing among close contacts identified 188 COVID-19 cases
  • Secondary clinical attack rate
    • Household contacts: 5.9% (95% CI, 4.9 to 7.1)
    • Work contacts: 1.3% (95% CI, 0.9 to 1.9)
    • Social contacts: 1.3% (95% CI, 1.0 to 1.7)
  • Bayesian analysis of serology and symptom data performed on a subset of patients was used to estimate missed diagnoses by using symptom-based testing vs universal testing
    • Estimated missed diagnoses: 62%
    • Estimated asymptomatic cases: 36%

Factors associated with transmission

  • Household contacts
    • Sharing a bedroom: multivariable odds ratio (OR) 5.38 (95% CI, 1.82 to 15.84; p=0.0023)
    • Being spoken to for ≥30 min: OR 7.86 (95% CI, 3.86 to 16.02; p<0.0001)
  • Non-household contacts
    • Exposure to >1 case: OR 3.92 (95% CI, 2.07 to 7.40; p<0.0001)
    • Being spoken to for ≥30 min: OR 2.67 (95% CI, 1.21 to 5.88; p=0.015)
    • Sharing a vehicle: OR 3.07 (95% CI, 1.55 to 6.08; p=0.0013)
  • The following was not independently associated with increased transmission risk
    • Indirect contact | Meal sharing | Lavatory co-usage

CONCLUSION:

  • Among household contacts, sharing a bedroom was associated with >5x increased risk and speaking with the primary case for at least 30 minutes was associated with almost 8x increased risk
  • Among non-household contacts, exposure to more than 1 primary case was associated with almost 4x risk and speaking with the primary case for at least 30 minutes was associated with 2.7x increased risk | Sharing a vehicle was associated with 3x increased risk
  • The authors suggest that based on the above data

…physical distancing and minimising direct verbal interactions would help reduce community transmission

Learn More – Primary Sources:

SARS-CoV-2 seroprevalence and transmission risk factors among high-risk close contacts: a retrospective cohort study

Get COVID-19 Research Summaries Direct to Your Phone, with ObGFirst

ObGFirst® – Try It Free! »

image_pdfFavoriteLoadingFavorite
< Previous
All Grand Rounds Posts
Next >

Related ObG Topics:

What is the Probability of a False Negative When Taking a SARS-CoV-2 Test?
SARS-CoV-2 Antibody Testing Among NYC Healthcare Personnel: How Many are Seropositive?
How Long Does It Take for COVID-19 Patients to Develop Antibodies?

Sections

  • Alerts
  • OB
  • GYN
    • GYN
    • Sexual Health
  • 2T US Atlas
  • The Genome
  • Primary Care
  • Your Practice
  • Grand Rounds
  • My Bookshelf
  • COVID-19

Are you an
ObG Insider?

Get specially curated clinical summaries delivered to your inbox every week for free

  • Site Map/
  • © ObG Project/
  • Terms and Conditions/
  • Privacy/
  • Contact Us/
© ObG Project
SSL Certificate


  • Already an ObGFirst Member?
    Welcome back

    Log In

    Want to sign up?
    Get guideline notifications
    CME Included

    Sign Up

Sign In

Lost your password?

Sign Up for ObGFirst and Stay Ahead

  • - Professional guideline notifications
  • - Daily summary of a clinically relevant
    research paper
  • - Includes 1 hour of CME every month

ObGFirst Free Trial

Already a Member of ObGFirst®?

Please log in to ObGFirst to access the 2T US Atlas

Password Trouble?

Not an ObGFirst® Member Yet?

  • - Access 2T US Atlas
  • - Guideline notifications
  • - Daily research paper summaries
  • - And lots more!
ObGFirst Free Trial

Media - Internet

Computer System Requirements

OBG Project CME requires a modern web browser (Internet Explorer 10+, Mozilla Firefox, Apple Safari, Google Chrome, Microsoft Edge). Certain educational activities may require additional software to view multimedia, presentation, or printable versions of their content. These activities will be marked as such and will provide links to the required software. That software may be: Adobe Flash, Apple QuickTime, Adobe Acrobat, Microsoft PowerPoint, Windows Media Player, or Real Networks Real One Player.

Disclosure of Unlabeled Use

This educational activity may contain discussion of published and/or investigational uses of agents that are not indicated by the FDA. The planners of this activity do not recommend the use of any agent outside of the labeled indications.

The opinions expressed in the educational activity are those of the faculty and do not necessarily represent the views of the planners. Please refer to the official prescribing information for each product for discussion of approved indications, contraindications, and warnings.

Disclaimer

Participants have an implied responsibility to use the newly acquired information to enhance patient outcomes and their own professional development. The information
presented in this activity is not meant to serve as a guideline for patient management. Any procedures, medications, or other courses of diagnosis or treatment discussed or suggested in this activity should not be used by clinicians without evaluation of their patient’s conditions and possible contraindications and/or dangers in use, review of any applicable manufacturer’s product information, and comparison with recommendations of other authorities.

Jointly provided by

NOT ENOUGH CME HOURS

It appears you don't have enough CME Hours to take this Post-Test. Feel free to buy additional CME hours or upgrade your current CME subscription plan

Subscribe

JOIN OBGFIRST AND GET CME/CE CREDITS

One of the benefits of an ObGFirst subscription is the ability to earn CME/CE credits from the ObG entries you read. Tap the button to learn more about ObGFirst

Learn More
Leaving ObG Website

You are now leaving the ObG website and on your way to PRIORITY at UCSF, an independent website. Therefore, we are not responsible for the content or availability of this site