Final answer:
Sexually transmitted infections (STIs) are caused by more than 30 pathogens that spread primarily through sexual contact, but can also be transmitted via body fluids in other ways. To be classified as an STI, the infection must mainly be spread through sexual means, separating them from other communicable diseases that have a higher chance of non-sexual transmission.
Step-by-step explanation:
Sexually transmitted infections (STIs) refers to more than 30 infectious organisms passed from person to person primarily through sexual contact. These infections are caused by pathogens, which can be viruses, bacteria, or other microorganisms, and they enter the body through the mucous membranes of the reproductive organs. Although STIs primarily spread through sexual activities including vaginal, and oral sex, they can also be transmitted via other exchanges of body fluids, such as sharing needles or from mother to child during childbirth and breastfeeding. It's important to note that to be considered an STI, an infection must have a relatively low chance of spreading by means other than sexual contact. While infections like the common cold can be transmitted through sexual activity, they are more commonly spread by other means and are not classified as STIs. Prevention of STIs includes abstinence, the use of prophylactics like condoms, and other safe-sex practices.