I recently saw a patient who had the misfortune of being stuck by a needle used to anesthetize an HIV patient during a dental procedure. We got into a discussion regarding the risk of contracting AIDS from a single needle stick. It's really quite remarkable how low the risk is. Apparently, it's about 3 per 1000. Various factors can raise or lower your risk, including: Figure 1: 95% confidence interval of odds ratio of risk factors for seroconversion Please Register or Log in to view the hidden image! http://bja.oxfordjournals.org/cgi/reprint/84/6/767.pdf http://www.jr2.ox.ac.uk/bandolier/booth/needlestick/HIVsero.html The various factors that modify your risk of infection seem to suggest that, as one might expect, the greater the amount of viral particles you're exposed to; the greater the chance of infection. What happens to the virus in patients exposed to HIV who do not seroconvert? Is it engulfed by macrophages? Are they, perhaps, defective in some way? Or is it possible that there was no viable HIV in the small amount of blood transferred in the typical needle stick?
I would guess that the immune response to the prick would be pretty overwhelming for the small number of viral particles transfered by the needle. But this really isn't the forum to get a "I know hard science" answer. Maybe a "I hardly know science" answer.
This is off topic, but I'd still like to ask: How did the above happen? Was the same needle used on two people?
Factors: Often people who carry HIV have very low blood concentrations of virus at a given time - it booms and busts among the blood cells vulnerable, like the plague in a prairie dog population. And on similar considerations, some people are less vulnerable to infection - last I heard 1-4% of the northern European population was thought to be effectively immune. And the HIV virus mutates very rapidly, they say - which means that in some populations of the virus (such as the survivors of recent medical assault) most actual virus particles may be genetically defective, incapable of reproducing. On the down side, if only a very small number of active and competent HIV viruses did make it, and they were of some dormant or slow variety hiding from the treatment regime of the source patient, it could be a very long time before they take hold in enough numbers to show up in a diagnostic assay.
