I'd like to know just how at-risk a person is from being stuck by an HIV-infected needle. When I was working at a hospital, we were informed that unless the bodily fluid was injected from the syringe, the possibility of being infected from a mere sticking was quite low, and that if one suspected HIV and started taking medication right away, there was a chance of holding back infection. If there is any truth to this, then what is the window period for successful treatment after infection?

A.

Becoming infected with HIV (human immunodeficiency virus, the cause of AIDS) is a legitimate concern of all health-care workers. At least, it should be. In some hospitals, more than 10 percent of patients are infected with HIV. Standard precautions for handling potentially infected body fluids presume that samples from ALL patients could be contaminated with HIV.

There have been many reported cases (though fewer than 100 have been proven) in which a health-care worker has contracted HIV from a patient. The most common means of transmission from a patient to a worker has been through a needle stick. Usually this involves a needle that had been used for blood, but a few cases of transmission with other body fluids have been documented. The overall risk of contracting HIV from a needle stick is about 1 in 300. That means that for approximately 300 typical needle-stick exposures when the patient is known to have HIV, one health-care worker will contract HIV.

Several risk factors for needle-stick transmission have been described. Higher-risk needle sticks occur with needles that had been in a patient's artery or vein, with needles that had visible blood on them, with hollow-bore rather than suture needles and with deep sticks. In addition, if the patient had late-stage AIDS rather than early HIV infection, the exposure is considered higher risk.

If a health-care worker is exposed to HIV, should he or she consider taking anti-retroviral drugs to prevent transmission entirely? As you might expect, this problem is difficult to study. Usually, to examine the effectiveness of a given treatment, we treat a group of patients with standard therapy or a placebo (dummy pill) and another group with the treatment to be studied. Then we decide how effective the new treatment was in comparison with the standard therapy or placebo. In the case of HIV exposure, there was no previous standard treatment, and it does not seem ethical to give a placebo in a situation in which a person could contract HIV. In addition, the number of people who would develop HIV in such a situation is rather low. This would require studying thousands of health-care workers who had an HIV exposure. It would take many years to find thousands of such exposures.

Only a single study has looked at this issue. In this study, health-care workers exposed to HIV were asked whether they took zidovudine (trade name AZT) to prevent HIV. The examiners planned to determine afterward whether or not those who had taken AZT were less likely to have become infected. That was rather difficult, because health-care workers who had higher-risk exposures were more likely to take AZT than those with low-risk exposures, since the first group was more worried about getting HIV. The examiners tried to adjust for this and other variables. They determined that AZT could prevent up to 80 percent of the transmissions to health-care workers.

Nowadays, we have drugs that are more effective than AZT in treating HIV. Therefore, it makes sense that these drugs would be more effective in preventing HIV transmission. While this is not necessarily true, experts now recommended that with exposure to HIV in the health-care setting, especially after high-risk exposure, workers receive two or three anti-HIV drugs for one month, in an effort to prevent transmission. One of these drugs should be AZT, because that was the drug studied in this situation and actually found to be effective.