Skip to main content

Table 2 Quantitative measures of the impact of quarantine on secondary cases in the community*.

From: Quantifying the impact of community quarantine on SARS transmission in Ontario: estimation of secondary case count difference and number needed to quarantine

Analysis approach Measure of association obtained from model Variance estimation method Estimated value of measure of association p-value 95% confidence interval
      Lower limit Upper limit
A) Generalized linear model with binomial error and identity link (additive logistic). Unit of analysis is community contacts, clustered within shared 204 index cases. (N = 8498). Naïve Secondary Attack Rate Difference (incorporates information only for 204 index cases with one or more community contact; see text) Asymptotic: Bootstrapped: 0.00105
0.00105†
0.786
0.881
-0.00665
-0.01269
0.00866
0.01479
B) Canonical Poisson and negative binomial regression with log link functions. Unit of analysis is all index cases. (N = 332). Beta coefficient Poisson, asymptotic:
Neg.Binomial asymptotic:
Poisson, bootstrapped:
-1.15209
-1.15209
-1.15209†
0.026
0.057
0.589
-2.16906
-2.33953
-5.32984
-0.13511
0.03535
3.02567
  Secondary Case Count Ratio (SCCR) (SCCR = exponentiated Beta for quarantine) Poisson, asymptotic:
Neg.Binomial asymptotic:
Poisson, bootstrapped:
0.31598
0.31598
0.31598†
0.026
0.057
0.573
0.11428
0.09637
0.00577
0.87362
1.03599
17.30158
C) Generalized linear model with Poisson error term and identity link function, yielding an additive effect measure. Secondary Case Count Difference (SCCD).(SCCD = Beta coefficient for quarantine) Poisson, asymptotic:
Neg.Binomial, asymptotic
Poisson, bootstrapped:
-0.13322
-0.13322
-0.13322†
0.001
0.002
1.000
-0.21346
-0.21812
-1.18 × 10 14
-0.05298
-0.04832
1.18 × 10 14
Unit of analysis is all index cases. (N = 332). Number needed to quarantine (NNQ). (NNQ = 1/|SCCD|, above) Poisson, asymptotic:
Neg.Binomial, asymptotic:
Poisson, bootstrapped:
7.50647
7.50648
7.50647†
0.001
0.002
1.000
4.68469
4.58462
-8.476 × 10 -15
18.87661
20.69733
8.476 × 10 -15
  1. * Data from 332 index community-living probable or suspect Severe Acute Respiratory Syndrome (SARS) cases and 8,498 associated community contacts. Ontario, Canada, SARS outbreak, 2003.
  2. † Bootstrapping used to obtain variance estimate; point estimate fixed from corresponding asymptotic model.