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TABLE 4

Impact of Distancing on Secondary SARS-CoV-2 Transmission

DistrictsaStudentsStudent Primary InfectionsStudent Secondary InfectionsSecondary/Primary Infection RatiobRelative Rate of Secondary Transmissionc95% CIsd
Bus practice (children per seat)        
 1 13 36 975 190 12 0.06 — — 
 2 17 656 444 4388 210 0.05 0.76 0.19–2.96 
 3 17 205 996 1758 83 0.04 0.75 0.18–3.19 
 Othere 43 519 353 25 0.07 1.12 0.27–4.71 
Distancing, ft        
 6 10 (9%) 54 557 276 12 0.04 — — 
 3 76 (67%) 610 236 4140 207 0.05 1.15 0.31–4.24 
 <3 27 (24%) 278 141 2273 111 0.05 1.12 0.28–4.45 
DistrictsaStudentsStudent Primary InfectionsStudent Secondary InfectionsSecondary/Primary Infection RatiobRelative Rate of Secondary Transmissionc95% CIsd
Bus practice (children per seat)        
 1 13 36 975 190 12 0.06 — — 
 2 17 656 444 4388 210 0.05 0.76 0.19–2.96 
 3 17 205 996 1758 83 0.04 0.75 0.18–3.19 
 Othere 43 519 353 25 0.07 1.12 0.27–4.71 
Distancing, ft        
 6 10 (9%) 54 557 276 12 0.04 — — 
 3 76 (67%) 610 236 4140 207 0.05 1.15 0.31–4.24 
 <3 27 (24%) 278 141 2273 111 0.05 1.12 0.28–4.45 

CI, confidence interval; —, reference group for Poisson regression.

a

This analysis excludes the composite North Carolina charter schools district because of varying practices among schools.

b

Calculated by the composite number of student within-school–acquired infections (secondary infections) divided by the number of student community-acquired infections (secondary infections) for districts in each category of bus practices or distancing.

c

Relative rate of secondary transmission for each primary infection, compared with the reference range (for bus analysis: 1 child per seat; for distancing analysis: 6 ft of distancing). Relative rates were calculated by quasi Poisson regression, with the number of primary student cases as the denominator.

d

Robust CIs were calculated to account for overdispersion.

e

“Other” category was assigned when districts could not give a policy practice for children per bus seat because of widely varying practices.

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