Let's say that someone uses a needle which has some old blood infected with HIV. In this case, is it possible for them to get infected with HIV?
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$\begingroup$ Doesn't the oxygen of air eliminate the virus? $\endgroup$ – Alex Jun 22 '14 at 18:54
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$\begingroup$ It's important to define how old is "old", here, I think. I rephrased the question a bit so that it focuses more on the science than an individual diagnosis. $\endgroup$ – jonsca Jun 22 '14 at 19:13
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$\begingroup$ Thanks. Let's not define old in order to have a complete answer. I suppose the answer is based on that. $\endgroup$ – Alex Jun 22 '14 at 19:17
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Yes, you can transmit HIV with infected needles/syringes. This is a quite common mechanism of transmission when drug addicts share and re-use needles and syringes and also in third world hospitals with poor hygiene standards.
A drop of blood is considered infectious at least until it has completely dried up (some research showed that it might be contagious for up to 5 days longer when the conditions are right, see reference 1 below). Mostly HIV is senstive against high temperatures (over 60°C), while it is stable at low temperatures. It is very sensitive against shifts in pH (below 7 or above 8) and also against desinfectants like bleach. Have a look at the references below, a lot of research has been done by Abdala et al. in this field. You can find his whole reference list here (it contains more articles in this field).
References:
