into sub-locations. Workplaces have smaller work groups, schools are divided into classes, and malls are made up of several shops. At any point in time, each individual in the city will be in any one of the locations or sub-locations. Note that we classified hospital as a separate location entity, as it will be the main facility where diagnosis and treatment can be issued. The number of people in each location was obtained by fitting the model against demographic data for Singapore (Statistics Singapore 2009).