  Improved mobility not only contributes to more intensive human activities but
also facilitates the spread of communicable disease, thus constituting a major
threat to billions of urban commuters. In this study, we present a multi-city
investigation of communicable diseases percolating among metro travelers. We
use smart card data from three megacities in China to construct
individual-level contact networks, based on which the spread of disease is
modeled and studied. We observe that, though differing in urban forms, network
layouts, and mobility patterns, the metro systems of the three cities share
similar contact network structures. This motivates us to develop a universal
generation model that captures the distributions of the number of contacts as
well as the contact duration among individual travelers. This model explains
how the structural properties of the metro contact network are associated with
the risk level of communicable diseases. Our results highlight the
vulnerability of urban mass transit systems during disease outbreaks and
suggest important planning and operation strategies for mitigating the risk of
communicable diseases.
