Table S1.

Parameter estimates when analysis uses the 681 cases detected by passive and active surveillance (baseline) and when it is restricted to the 495 cases detected by passive surveillance

Variable	Summary statistic	681 cases from passive-plus-active surveillance (baseline)	495 cases from passive surveillance
Serial interval	Mean	6.8 (6.0, 7.8)	7.6 (6.4, 9.0)
	SD	4.1 (3.4, 5.0)	4.8 (3.8, 6.1)
Reproduction numbers
Within cluster	Initial mean RC	0.45 (0.33, 0.58)	0.36 (0.24, 0.51)
	Initial SD σC	0.53 (0.35, 0.78)	0.55 (0.33, 0.90)
	Probability it starts >1	12% (6%, 18%)	10% (4%, 16%)
	Value after 10 cases (relative to starting value)	47% (34%, 63%)	46% (32%, 68%)
Within region	RR	0.24 (0.19, 0.29)	0.22 (0.17, 0.29)
Between region	RO	0.05 (0.02, 0.09)	0.04 (0.004, 0.09)
Risk of introduction from reservoir
	Nb at start of study period (weekly)	0.5 (0.2, 0.8)	0.4 (0.2, 0.7)
	Nb at end of study period (weekly)	2.1 (1.0, 3.6)	2.4 (1.2, 3.9)
	Exponential growth rate α (daily)	0.003 (0.001, 0.005)	0.003 (0.001, 0.005)
Source of infection, %
	Within cluster	60% (57%, 63%)	57% (54%, 60%)
	Within region	23% (20%, 27%)	22% (18%; 26%)
	Between region	5% (2%, 8%)	4% (0.4%, 8%)
	Reservoir	12% (9%, 15%)	17% (13%, 20%)