Can dengue fever or tetanus shot cause HIV false positive?

Question

Hello Dr. Frascino. About 1 month ago I returned from a trip to Nicaragua where I was stung in the foot by a stingray. As a result, I went to the hospital in Managua (the most reputable one according to my mother in-law) who lives there. The hospital seemed top notch, large building and very clean looking. Anyway, about 3 and a half days after getting the tetanus shot I came down with what I believe to be dengue fever especially because my brother in-law who lives there was diagnosed with it a few days earlier. I was bitten quite a few times by mosquitos while I was there and my symptoms seemed to match perfectly with dengue fever (fever for about 4 days, then a rash for another 4 days or so with needle-like pattern on my feet). Because I did not come down with the symptoms until my flight back to California, I wound up going to my primary physician to confirm my self diagnosis. Apparently, they tested me for HIV as well and the test came out positive. Keep in mind that I have been with the same woman (my wife) for the last ten years without any cheating what so ever (I'm very happily married). Moreover, she was a virgin when I married her and I know without question she has been faithful. In addition, I had gone through a 6 year dry spell of no sex before ever meeting my wife. So I have to say that I doubt I got HIV from sexual intercourse. I have also never done drugs with needles or anything of the like. So, just looking at this situation makes me believe it would have to be a false positive. My sister in-law also said she found an article stating that tetanus shots could cause false postives as well as dengue fever. My primary physician hadn't ever heard of dengue fever until a couple of months ago when studying for his boards so I almost feel like I know more than him. If my positive HIV test result really is legit (I'm currently waiting for a second test result), what are the chances that I got it from a dirty needle from the tetanus shot? Or what are the chances that the tetanus shot itself or the dengue caused the false positive? Given my ultra low-risk lifestyle, and the circumstances surrounding this positive HIV test result (bit by mosquitos, brother in-law just had dengue, tetanus shot just 3 days before symptoms appeared), could this be a false positive?

Answer

Hello,

Your chance of contracting HIV from a tetanus shot administered at the hospital in Managua is essentially nil. If you have had no HIV exposures, you cannot be HIV infected. I would agree your positive test is most likely a false positive. Immunizations, including tetanus, could case a false-positive HIV-antibody test. This can be easily determined by obtaining the appropriate follow-up studies.

Write back and I'll post your follow-up results for the benefit of our readers.

Good luck. Happy Holidays.

Dr. Bob