HIV is almost always fatal, but there are few cases where it doesn't reach the point where it's AIDS. Whether this is due to strong immune systems, strong will, or simply lack of the host living long enough to develop AIDS isn't always known, and quite honestly, irrelevant. HIV is in most cases fatal, yes, but not all.
Infections, on the other hand, are a broader term, and are not nearly as often fatal. There are many nonfatal infections, whether it's the characteristic of the infection to not be fatal, or whether it's taken care of in time.
In ending, these two tribes will not die. The strong will survive, and live to infect you all.