Figure S1 Parameters optimization. a Green points represent the values of the score function F plotted versus the number of notified cases as predicted by the model (with B~200 ha {1 ) before intervention for Q different values of the model parameters as obtained by the LHS procedure. Red point represents the minimum of F . Black points represent the values of the score function F plotted versus the number of notified cases as predicted by the model before intervention as obtained by repeating 100 times the optimization procedure. The inset shows the minimum of F for the 100 replicates (red points). The blue vertical line represent the number of notified cases reported to the surveillance system before intervention, namely 132. b As a but for B~50 ha {1 . (TIF) Figure S2 Results for increasing number of simulations. a Mean (red points), median (blue points) and 95% CI (shaded grey area) of R 0 for increasing number of simulations with B~200 ha {1 in the absence of interventions (baseline scenario). b As a but for probability of observing a major outbreak. c As a but for the cumulative number of symptomatic cases. d As a but for the biting rate. (TIF) Figure S3 Temporal dynamics of the mosquito. a Average density (number per ha) of adult female mosquitoes over time as predicted by the model by assuming B~200 ha {1 (green line) and 95% CI (grey area). b As a but for B~150 ha {1 . c As a but for B~100 ha {1 . d As a but for B~50 ha {1 . (TIF) Probability of origin and destination (and rank over all possible origins/ destinations) of individuals commuting daily for work or school from/to other municipalities were local clusters of transmission were observed. The two most affected villages are located in the municipalities of Cervia and Ravenna. doi:10.1371/journal.pone.0018860.t004 Figure S4 Range of the optimal parameters values. Distribution of the model parameters (2.5%, 25%, 50%, 75% and 97.5% percentiles) after LHS optimization. Numbers below and over the boxplot represent the explored range of values. (TIF) Figure S5 Epidemic threshold and probability of major outbreak. a Epidemic threshold R 0 in relation to biting rate k and ratio of mosquitoes to humans N v =N h . The black line represents the average threshold condition and the shaded blue area represents 95% CI, as resulting from uncertainty of model parameters. The red rectangle identifies the likely range of the two parameters in the two Italian villages affected by CHIKV. b Probability of observing a major outbreak as a function of the ratio of mosquitoes to humans N v =N h for two extreme values of the biting rate k, namely k~0:1 days {1 in red (solid line black represents the average probability and the shaded area represents 95% CI) and k~0:2 days {1 in blue.