ETR has a great deal of expertise and a long history of providing materials around HIV prevention, and we believe the topic of HIV is important enough to merit its own lesson.
Although there are some STIs that can become life threatening if left untreated, HIV is unique in having been widely publicized and devastating in the earlier years of the epidemic. Even though that is changing, it is likely students may have heard of HIV apart from the context of other STIs, and have encountered myths or misinformation about its transmission or whom it affects. Having the separate lesson allows us to correct misconceptions and present important information that applies to HIV in particular, such as the newer treatment options that allow people living with HIV to stay healthy and greatly reduce their risk of transmitting it to others.
There is naturally some overlap across the two lessons—for example, in Lesson 7 of the Middle School HIV, STI & Pregnancy Prevention unit, the “handshake” activity could be used to model transmission of other types of STI as well. However, we believe there are enough unique things about HIV to justify a separate lesson that can also reinforce what students have learned about STIs in general in the previous lesson. Most of ETR's evidence-based prevention programs devote separate lessons to HIV and to other STIs.