ChatGPT Gets a B+ in an Essay on Germ Theory From an Epidemiology Professor

Not perfect, but perfectly scary.

René F. Najera, MPH, DrPH
4 min readDec 16, 2022


Screen capture of my request of ChatGPT to write a 500-word essay on germ theory.
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I teach epidemiology to graduate students at two universities, and I’ve decided to forgo the essay as a measure of their understanding of the material. It’s not that I don’t have time to read essay after essay on the same topic. The problem is ChatGPT, an artificial intelligence (AI) program that can write well.

I asked ChatGPT to write a 500-word essay on germ theory, and this is what it produced:

“Germ theory is a scientific concept that explains the cause of many infectious diseases. It proposes that microorganisms, such as bacteria and viruses, are responsible for these diseases and that they can be transmitted from one person to another or from animals to humans. Germ theory has revolutionized the way we understand and treat infectious diseases, and it has had a significant impact on public health.

The concept of germ theory has a long history. In the Middle Ages, people believed that diseases were caused by bad air or miasma. However, in the 19th century, scientists began to propose that microorganisms might be the cause of some diseases. In 1854, John Snow, a British physician, traced a cholera outbreak in London to a contaminated water supply, suggesting that the disease was transmitted through water. This was an early example of germ theory in action.

One of the main proponents of germ theory was a German physician named Robert Koch. Koch developed techniques for growing and studying bacteria in the laboratory and used these techniques to identify the causative agents of several infectious diseases. In 1876, he discovered the bacterium that causes tuberculosis, and in 1882, he identified the bacterium that causes cholera. Koch’s work helped to establish the link between microorganisms and disease and laid the foundation for modern bacteriology.

Germ theory has had a major impact on public health. Prior to the development of germ theory, people had very little understanding of how diseases were transmitted and how to prevent them. Germ theory provided a way to understand how diseases were spread and how to prevent their transmission. For example, the use of hand washing, sterilization, and vaccination have…



René F. Najera, MPH, DrPH

DrPH in Epidemiology. Associate/JHBSPH. Adjunct/GMU. Epidemiologist. Father. Husband. (He/Him/His/El)