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Table 3 Association between exposure attributes and a contact’s positive test result

From: SARS-CoV-2 viral load is associated with risk of transmission to household and community contacts

Characteristic

Unadjusted RR (95% CI)

p-value

Adjusted RR* (95% CI)

p-value

Index case viral load at time of test (log10 RNA copies per mL of saliva)

1.25 (1.06–1.46)

0.007

1.27 (1.22–1.32)

p < 0.001

Time between index case test and exposure (days)

1.12 (1.10–1.15)

p < 0.001

1.14 (1.11–1.17)

p < 0.001

Age of case (years)

0.99 (0.94–1.04)

0.7

–

–

Case comorbidities

0.89 (0.45–1.74)

0.7

–

–

Symptomatic status on day of exposure

 Asymptomatic

Reference

–

–

–

 Pre-symptomatic

2.23 (1.00–4.97)

0.05

–

–

 Symptomatic

2.05 (0.94–4.48)

0.07

–

–

 Case had cough on day of exposure

1.85 (1.15–2.99)

0.01

1.41 (1.04–1.92)

0.03

 Case congested or with runny nose on day of exposure

1.46 (0.94–2.29)

0.09

–

–

Mask use

 No masks used

Reference

–

–

–

 Case and/or contact wore a mask

1.02 (0.59–1.78)

0.9

–

–

Duration (min)

    

 < 30

Reference

–

–

–

 ≥ 30

1.61 (0.84–3.09)

0.1

–

–

Location

 

 Outdoor

Reference

–

–

–

 Indoor

2.39 (0.69–8.24)

0.2

–

–

Contact type

 Non-physical contact

Reference

–

–

–

 Physical contact

2.14 (1.34–3.44)

0.001

1.78 (1.26–2.53)

0.001

Contact relationship

 Household

Reference

–

–

–

 Non-household

1.19 (0.77–1.83)

0.4

–

–

  1. *Adjusted for viral load, time between index case test and exposure with contact, cough and contact type