Table 5. Four-way decomposition mediation analysis of the association between intervention and the number of secondary cases.

	ERR*	95% CI
Total effect	–0.1	–0.35–0.15
Controlled direct effect
Known contact (M=1)	–0.29	–0.61–0.03
Unknown contact (M=0)	0.31	–0.49 to –0.02
Pure indirect effect	–0.02	–0.10–0.07
Mediated interaction	–0.14	–0.28 to –0.01
Reference interaction
Known contact (M=1)	0.35	0.03–0.68
Unknown contact (M=0)	–0.25	–0.49 to –0.02

^*Adjusted for the type of school, type of index case, and class size.

ERR, excess relative risk; M, mediator (known source of infection of the index case).