The Influence of Social Network Graph Structure on Disease Dynamics in a Simulated Environment Page: 16
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(a commercial database) for business, the National Household Transportation Survey for schedul-
ing individuals, and the Digest of Education Statistics for school locations and enrollment. The
algorithm used to simulate an outbreak is a simple discrete event simulation, which implies that
the system only changes state when an event occurs. The system is composed of both people and
locations. An example of an event is a particular person leaving a specific location at a given time.
If an infectious person and a susceptible person are at the same location at the same time, there
is a possibility for transfer of the disease. The model includes realistic states in addition to the
fundamental SEIR, such as vaccinated and asymptomatic. EpiSimdemics has been used for real
studies by the Department of Homeland Security, the Department of Defense, and the Department
of Health and Human Services.
Closely related to EpiSims and EpiSimdemics, researchers at Virgina Tech have more recently
developed EpiFast, a parallel agent-based SEIR model . EpiFast has many of the same features
as EpiSimdemics, but it executes much faster as the model is significantly less complex. Unlike
EpiSimdemics, in which state changes can occur every hour, EpiFast measures discrete time steps
by the day. EpiFast also increases speed by using a pre-constructed people-people contact network,
i.e. social network. Intervention strategies include vaccination, individual behavioral changes,
and facility closures. On similar networks, EpiFast was shown to execute ten times faster than
2.3. The Basic Reproduction Number
Individuals who become infected at the onset of an outbreak play a key role in the progression
of a disease. For an epidemic or pandemic to occur, the rate of increase in the number of newly
infected individuals at the beginning of the outbreak must exceed an epidemic threshold referred
to as the basic reproduction number, Ro0. The value of Ro0 provides an indication of the transfer of
specific disease pathogens as well as the conduciveness of environmental conditions.
DEFINITION 2.1. The basic reproduction number, R0, is defined as the average number of ex-
pected secondary cases produced from a single primary infectious case in a completely susceptible
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Johnson, Tina V. The Influence of Social Network Graph Structure on Disease Dynamics in a Simulated Environment, dissertation, December 2010; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc33173/m1/26/: accessed May 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; .