Table S3.

Parameter estimates for the baseline analysis where the daily number of introductions follows a Poisson distribution and for an alternative model where it follows a negative-binomial distribution with high overdispersion (k = 0.2)

VariableSummary statisticPoisson (baseline)Negative binomial
Serial intervalMean6.8 (6.0, 7.8)6.8 (6.0, 7.7)
SD4.1 (3.4, 5.0)4.1 (3.4, 5.0)
Reproduction numbers
 Within clusterInitial mean RC0.45 (0.33, 0.58)0.44 (0.32, 0.58)
Initial SD σC0.53 (0.35, 0.78)0.52 (0.35, 0.78)
Probability it starts >112% (6%, 18%)12% (6%, 19%)
Value after 10 cases (relative to starting value)47% (34%, 63%)46% (34%, 64%)
 Within regionRR0.24 (0.19, 0.29)0.24 (0.19, 0.30)
 Between regionRO0.05 (0.02, 0.09)0.06 (0.02, 0.10)
Risk of introduction from reservoir
Nb at start of study period (weekly)0.5 (0.2, 0.8)0.5 (0.2, 1.0)
Nb at end of study period (weekly)2.1 (1.0, 3.6)1.6 (0.7, 3.3)
Exponential growth rate α (daily)0.003 (0.001, 0.005)0.002 (0.000, 0.004)
Source of infection, %
Within cluster60% (57%, 63%)60% (57%, 63%)
Within region23% (20%, 27%)24% (20%, 28%)
Between region5% (2%, 8%)6% (3%, 9%)
Reservoir12% (9%, 15%)10% (7%, 13%)