Which of these terms indicates the presence of harmful microorganisms in the body?

The term that indicates the presence of harmful microorganisms in the body is infection. This term specifically refers to the invasion and multiplication of pathogenic microorganisms, such as bacteria or viruses, within the body, which can lead to disease or illness. An infection typically results in an immune response and can manifest in various symptoms depending on the type of microorganisms involved and the body systems affected.

In contrast, contagion refers to the transmission of an infectious disease from one individual to another. Infestation signifies the presence of parasites within or on the body, rather than directly implying infection with microorganisms that cause illness. Pathogenicity describes the ability of a microorganism to cause disease, but it does not, by itself, imply that there are harmful microorganisms currently present in the body. Thus, infection is the most precise term for reflecting that harmful microorganisms have taken hold within the body.