Download Modeling 101. Modeling Infectious Diseases

Modeling 101.
Modeling Infectious Diseases
We use models to understand how infectious agents1 move through populations, and we use that
knowledge to devise and compare disease-control strategies.
Infectious Diseases
Are Big Problems
Infectious diseases are big problems in the United States and worldwide, for people of
all ages, as well as for livestock.
2005: More than 130,000 cases of cholera occur worldwide
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2006: More than 350,000 cases of gonorrhea are reported in the United States
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2007: 33.2 million people worldwide have HIV infections
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2007: More than 13 outbreaks of influenza occur in poultry flocks in the United
States since 1990
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Each year in the United States, 5% to 20% of the population gets the flu and
36,000 die
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In addition to frequently occurring disease epidemics, the threat of emergence or
re-emergence of new epidemics continues to be a concern for policy makers and the
public health services.
Policy Makers Have
Options, but the
Problems Are Complex
Public health officials and veterinarians have a number of options for combating diseases,
including vaccination, isolation, administration of medications, and social distancing.
However, many factors affect transmission of an infectious agent, and other factors affect
the susceptibility of an organism to infection. In addition, some causes of infection may
be hidden. For example, people2 can contract infections from insects, water, food, air (for
instance from droplets due to sneezes), sexual activity, and touching of surfaces. Each
of these means of transmission between infectious agents and people involves slightly
different factors. For instance, diseases transmitted through sneezing require that two
agents be physically close to one another. However, diseases transmitted through water
mean that one individual can infect another, even if they are not physically close to each
other, because they can be in contact with the same water. When diseases are transmitted
from insects to people, the contact between people is not the primary method of
dissemination. When many factors can affect the transmission of a disease to and between
people, the modeling of the transmission can be complex. Furthermore, there may be a
lack of data to completely understand what is happening when an infection occurs.
Models Can Help
A mathematical or computational model is a means of representing or manipulating
something that cannot be understood using research experimentation alone. In this
way, models are aids to thinking about and resolving a problem. As Box (1979) said,
“All models are wrong, but some are useful.”3 Models can
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help the user understand the spread of a disease and then specify the question that
needs to be answered;
identify important data needs, including regular surveillance and outbreak
investigations;
understand the relative importance of different factors on the spread of disease,
which can help health officials focus on critical factors;
indicate the relative effects of different policies on the spread of disease, which can
help with either responding to an outbreak or planning for future outbreaks; and
identify new research questions that are critical to a better understanding of the
infectious agent.
MIDAS. The Models of Infectious Disease Agent Study (MIDAS) is leading the research on using computational and
mathematical models to prepare the nation for responding to outbreaks of infectious diseases, whether these occur
deliberately or through natural means. Its work is funded by the National Institute of General Medical Sciences of the
National Institutes of Health.
MIDAS is a network of research groups who are developing models of the spread of infectious diseases. Each research
group consists of scientists from many disciplines, including computer scientists, epidemiologists, infectious disease
specialists, statisticians, computation biologists, informaticists, social scientists, veterinarians, and economists. All of
these researchers contribute to the building and testing of the models that involve the spread of disease in people and
in animals.
For more information about MIDAS
MIDAS Web site: http://www.midasmodels.org
National Institute of General Medical Sciences (NIGMS): http://www.nigms.nih.gov/Research/FeaturedPrograms/
MIDAS/
MIDAS Scientific Director at NIGMS: Irene Eckstrand, [email protected]
1 An infectious agent, more commonly referred to as a germ, is a biological agent (also called a pathogen) that causes disease
or illness in an organism.
2 Here we talk about “people,” but this discussion is equally relevant to animals and plants.
3 Box, G.E.P. (1979). Robustness in the strategy of scientific model building. In R.L. Launer and G.N. Wilkinson (Eds.),
Robustness in Statistics. New York: Academic Press.
About MIDAS
Funded by the National Institute of General Medical Sciences, NIH, MIDAS is a collaborative network
of research scientists who use computational, statistical and mathematical models to understand
infectious disease dynamics and thereby assist the nation to prepare for, detect and respond to
infectious disease threats.
http://www.midasmodels.org