But 1st what is PrEP.
Extract from
https://www.cdc.gov/hiv/basics/prep.html
Pre-exposure prophylaxis (or PrEP) is when people at very high risk for HIV take HIV medicines daily to lower their chances of getting infected. PrEP can stop HIV from taking hold and spreading throughout your body. It is highly effective for preventing HIV if used as prescribed, but it is much less effective when not taken consistently.
Daily PrEP reduces the risk of getting HIV from sex by more than 90%. Among people who inject drugs, it reduces the risk by more than 70%. Your risk of getting HIV from sex can be even lower if you combine PrEP with condoms and other prevention methods
With at risk individuals using PrEP instead of protected sex, whilst they may be protected to some extent from HIV infection, they are of course at high risk from other infections such as Chlamydia, Gonorrhoea and Syphilis.
These common STIs are certainly prevalent in the sexually active population across all sexual orientations. If left untreated as well as direct complications they can stress and weaken the individuals immune system.
The takeaway here is that in fact whilst PrEP is saving lives it is not a safe replacement for protected sex or sex with a single partner of known status.
In order to determine the STI status of your sexual partner you must both abstain from any at risk behaviour for the period of time required for a safe post window period diagnosis. In the case of HIV for example this is deemed to be 3 months in most cases and Chlamydia is +- 1 week. At this time a negative result would be reliable. In Australia you can purchase test kits for HIV, Chlamydia Gonorrhoea, Hep B and Syphilis through www.buystdtestkits.com or you can visit an STI testing facility near you.