"Heterodox" Wolfgang, I fail to understand how their sexual preference matters! (Sorry.) I had to look that one up Heterodox: departing from or opposed to the usual beliefs or established doctrines, etc. In any case, Wolfgang, you're German. You're not supposed to know words like that. NOBODY should be expected to know words like that.)

Mark explained the negative results. If tests can be false-positive, they also can be false-negative. You have a disease which supresses the immune system and antibody response. If the test is for an antibody, and a person's ability to make antibody's is compromised, they can easily have a negative test result. Look at tuberculosis, which is on the list of opportunistic infections that AIDS patients may have. The TB mycobacterium may be isolated from sputum samples, but the individual can have repeat negative reactions to skin tests. They're still infected with TB.

Now, here's the CDC guidelines on Prevention and Treatment of TB in people infected with HIV. <--IF YOU CLICK, IT WILL START TO DOWNLOAD. One thing they DO say (page 15, 2nd para.) is that "these data suggest that pulmonary tuberculosis might act as a potent stimulus for the cellular-level replication of HIV."