In the first module, you will learn about the organisms that can infect us and make us sick: pathogens. We will first take a look at the various types of pathogens that exist, and then learn about what it means to be infectious, and what it means to cause disease. After that, we will cover the various methods by which pathogens can transmit from one person to the next, thereby causing an epidemic. You will learn about the most important number in all of epidemiology, R0, and why this number is so important. Finally, we will learn that microorganisms are not always harmful, but can be beneficial to us as well.

The second module of the course covers host factors that determine the outcome of infection. We will first focus on host immunity and present both the general immune capabilities—the innate immune response—that are encoded in our genes and that provide the initial response to infection and the adaptive immune response, which arises from highly specialized cells that protect against a specific pathogen. You will then learn about the ways that pathogens circumvent these two types of immunity and consider other factors that can contribute to an individual becoming infected or diseased—including genetic factors, other microbes, and how social and emotional factors influence immunity. We will then consider how infection with a microorganism causes disease and how public health officials determine whether a disease outbreak is caused by an infectious organism.

The third module of the course covers ecological factors that influence the dynamic patterns of infectious disease. We will discuss the conditions under which a pathogen can drive its host to extinction. We will look at how the demography of the host may allow the pathogen to persist in some populations but not others. We will talk about how host and pathogen characteristics interact to shape different temporal patterns of disease incidence at the population level and discuss the ecological consequences of infecting more than one host species.

Where humans live and how they are connected to each other, have strong effects on how infectious diseases can spread. In this module, you will learn about some of the related key concepts of epidemiology. After looking at some fascinating history, we’ll learn about social networks as the ultimate “road map” on which diseases can travel and we’ll talk about how the structure of the network can influence disease dynamics. After that, we’ll cover three topics that all affect infectious disease epidemiology in dramatic ways: human transport systems, population density and so-called superspreaders - individuals who can spread a disease to dozens or even hundreds of other individuals. We’ll close by identifying what information is required for disease surveillance.