  This letter investigates the multiple routes transmitted epidemic process on
multiplex networks. We propose detailed theoretical analysis that allows us to
accurately calculate the epidemic threshold and outbreak size. It is found that
the epidemic can spread across the multiplex network even if all the network
layers are well below their respective epidemic thresholds. Strong positive
degree-degree correlation of nodes in multiplex network could lead to a much
lower epidemic threshold and a relatively smaller outbreak size. However, the
average similarity of neighbors from different layers of nodes has no obvious
effect on the epidemic threshold and outbreak size.
