Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
A sexually transmitted infection (STI) is a disease that spreads mainly through sexual contact. STIs are more common in teens and young adults than in older people. Bacterial STIs include chlamydia, gonorrhea, and syphilis. Viral STIs include genital warts, genital herpes, and AIDS.


Question: What are chlamydia, gonorrhea, and syphilis an example of?
bacterial stis
Bacterial STIs.