What is a sexually transmitted infection (STI)?

A sexually transmitted infection (STI) is defined as an infection that is transmitted primarily through sexual contact. This encompasses a range of pathogens, including bacteria, viruses, and parasites, that can be spread through sexual activities such as vaginal intercourse, oral sex, and anal sex. The routes of transmission typically involve direct contact with an infected area or bodily fluids during sexual activity. This definition is crucial for understanding the nature of STIs and the importance of safe sexual practices to prevent their spread.

The other choices present different types of infections or factors contributing to health conditions that do not align with the definition of STIs. For instance, infections caused by environmental factors refer to pathogens that might be transmitted through the environment, such as waterborne diseases, while hormonal imbalances relate to internal physiological conditions rather than infectious agents. Finally, stating that an infection is only transmitted by blood is too restrictive, as many STIs can also be transmitted through sexual contact without necessarily involving blood.