Define opportunistic infections in the context of HIV.

Opportunistic infections are specifically associated with individuals who have compromised immune systems, such as those living with HIV. The correct choice highlights that these are infections that are rare in healthy individuals because the immune system is functioning properly. In a healthy person, the body effectively combats pathogens and infections; however, in someone with a weakened immune response, such as in HIV/AIDS, common pathogens can take advantage of the body's inability to fight them off, leading to infections that would not typically cause illness.

Opportunistic infections are often caused by organisms that are normally not harmful to individuals with strong immunity. This can include certain bacteria, fungi, viruses, and parasites that would usually be kept in check by a healthy immune system. As a person living with HIV progresses through the stages of the disease and their CD4 T-cell count drops, their risk for these types of infections significantly increases.

In contrast, infections that occur due to regular exposure typically refer to common pathogens that can affect anyone regardless of immune status, chronic diseases often relate to ongoing health conditions not necessarily tied to infections, and genetic disorders are inherent conditions that do not relate to external pathogens. This context helps clearly differentiate opportunistic infections within the landscape of HIV and immune health.