HIV Can Live in Syringes for More Than a Month When Kept Cold

The virus that causes AIDS can remain alive and well in syringes with infected blood for at least 42 days when kept in near-freezing temperatures, according to a new study by Yale researchers.

But when stored above room temperature, or hotter than about 80 degrees, there's a less than 1 percent chance that a syringe will still contain viable samples of the human immunodeficiency virus (HIV), the study found.

The study, published in the journal Substance Use and Misuse, was conducted to help assess the various risks that drug injectors might face when they share or reuse discarded needles.

"Behaviors of injectors vary tremendously, '' said Robert Heimer, an associate professor of epidemiology and public health at the Yale School of Medicine. "Some injectors rapidly discard syringes when they are done, mostly out of fear of being spotted by police. Improperly discarded syringes can be reused and can transmit the virus.

"But this research shows that depending on the temperature, you can decrease from weeks to just one day the period of time for which syringes can spread the virus.''

Heimer said the information is important not only to substance abusers but to police, fire and emergency medical personnel who regularly come in contact with used needles and are at risk for accidental needle sticks.

The study may also be useful to public health and medical workers in the developing world, where needle recycling is common.

Earlier research at Yale had found that HIV survival in syringes was strongly linked to the volume of blood left in a syringe and the duration of storage at room temperature.

"We were really surprised that no one had studied this issue before in the decades this virus has been a public health concern,'' Heimer said.

In the new study, researchers loaded syringes with HIV-infected blood, then fully depressed the plunger to remove almost all the blood, and then stored the syringes at various temperatures for periods of one day up to six weeks.

Then, the residual contents of the syringes were introduced into a tissue culture that allowed HIV to proliferate.

At 39 degrees Fahrenheit, 50 percent of all syringes contained viable HIV after 42 days of storage, the longest period tested.

At room temperature, or 68 degrees, the longest that syringes with infected blood tested positive was 21 days. HIV capable of replicating was found in 8 percent of those syringes.

And above 80 degrees, and at temperatures up to 98.6, less than 1 percent of syringes contained viable HIV after one week.

"The practical implications of these findings are that when people do not have access to clean syringes, storing used syringes in warmer temperatures decreases the likelihood of HIV transmission,'' Heimer said.

While warmer temperatures may knock back the HIV in used needles, that still doesn't make them safe. They're still even more likely to harbor liver-damaging hepatitis B and hepatitis C viruses in even larger quantities - 10 to 20 times more in the same volume of blood - than HIV and for an unknown period of time.

"No one knows how persistent (hepatitis C) is because, again, no one has studied it,'' Heimer said. "We'd like to, but so far we haven't been able to get anyone to support the lab work with a grant. Yet we know that (hepatitis C virus) is much more infectious among drug users than HIV."

Other studies have shown that 90 percent of IV drug users are infected with hepatitis C after six years of injecting, compared with 15 percent who are HIV-positive.

Heimer added that his findings highlight the benefit of needle-exchange programs, which allow drug users to turn in used needles in return for sterile syringes.