Mao BMC Public Health 2011, 11:522 http://www.biomedcentral.com/1471-2458/11/522 Page 6 of 10 Figure 4 Continuous weekend-extension strategies (2). Spatial patterns of infections resulted from the three continuous weekend-extension strategies, given R0 = 1.4 and compliance level = 100%: (a) Mon, (b) Mon+Tue, and (c) Mon+Tue+Wed. Each 50 m × 50 m cell value indicates the total number of infections during the 200 days at the cell location (infections/per km2). All cell values are averages of 50 randomly seeded simulation runs. off work switched more frequently and posed more interruptions on flu transmission. The ANOVA indi- cated significant differences between the effectiveness of three strategies: F = 3.96 and p-value = 0.05, given R0 = 1.4; F = 5.62 and p-value = 0.02, given R0 = 2.0. The sensitivity analysis showed increased control effective- ness with a longer weekend period and a higher compli- ance level of businesses (Table 3). Only the three-day discontinuous extension (’Mon+Wed+Fri’) with a 90% compliance level can control the seasonal flu (attack rate <10%). If the compliance could be raised to 100%, the three-day extension would be adequate to prevent the seasonal flu epidemic (attack rate <5%). For the pan- demic flu, however, none of these three discontinuous strategies produced significant mitigation effects. Even the three-day extension strategy with a 100% compliance level failed to reduce the attack rate below 20%. From a spatial perspective, the ‘Wed’ strategy (Figure 6a) contributed little to containing the extensive spread of seasonal flu. A majority of the study area underwent Figure 5 Discontinuous weekend-extension strategies (1). Simulated epidemic curves from the three discontinuous weekend-extension strategies, in comparison with the baseline epidemic. Y axis indicates the number of newly influenza cases per day during the 200 day simulation. All curves are averages of 50 randomly seeded simulation runs.