Typhoid fever is caused by bacteria in contaminated food or drink. In 1903, an outbreak of typhoid fever in Ithaca, New York, killed almost 80 people. In addition, more than 1,000 Ithaca residents became sick with the disease. The population shares the public water source. Which type of limiting factor was involved in the typhoid outbreak that occurred in Ithaca?

Typhoid spread through a shared water source, so residents’ risk depended on how many people were exposed and how readily the disease could spread among them. Disease is a density-dependent limiting factor because its effects generally increase when individuals live in close contact or in larger populations. Thus, the correct choice is density-dependent factor.

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