Transmission of HIV through sharp instruments occurs when the virus is present on the instrument. So, in the case of a sewing needle, it will first have to have pricked a HIV positive person.
Secondly, an infective dose of the virus will have to be present on the needle. This may not happen if the person is on ART and has a low viral load. This may also not happen if the needle has been washed or it has dried out.
HIV does not survive for very long outside the body, especially on dry surfaces. Finally, the needle with HIV on it has to prick another person.
As you can see, a lot of things have to happen for HIV to be transmitted through needle pricks. However, you should not take a needle prick casually just because the chances are low. HIV is transmitted through needle pricks and sharing razors etc with HIV positive individuals.
The chances of HIV transmission are much higher when the needle is hollow, as in a injection needle or a blood collection needle. This occurs very commonly in intravenous drug abusers who share syringes and needles.
– Duta Doctor