You say candida balantis is not an opportunistic infection, yet oral thrush is?.. why the difference when they are (are they?) caused by the same thing?
Because candida balanitis or dermatitis (jock itch) is a common problem that happens all the time to people with perfectly normal immune systems. For an infection to be "opportunistic", it has to take advantage of a damaged immune system. Oral thrush is also not technically an "opportunistic" infection in the same way that candida esophagitis or PCP is, but it is relatively unusual in immunologically normal adults. In people with HIV, the development of oral thrush is an early event down the path of decreased immunity-- that is, it is a sign that eventually there is worse to come unless that person arrests the process of immune damage by taking medicines to control HIV.