The HIV virus remains alive in syringes containing infected blood for at least 42 days when stored in near-freezing temperatures, a study by Yale researchers shows.

Conversely, when stored above room temperature, the likelihood of encountering syringes with viable HIV-1 after one week decreases to less than 1%, the study reports.

"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," says Robert Heimer, associate professor of epidemiology and public health at the School of Medicine. "Depending on the temperature, you can decrease from weeks to just one day the period of time for which syringes can spread the virus."

The warmer conditions leading to HIV inactivation might include storage behind a radiator in winter or in the glove compartment of a car parked in the sun, says Heimer.

Published in the journal Substance Use and Misuse, the study built on earlier research at Yale showing that HIV-1 survival in syringes was strongly associated with the volume of blood remaining in the syringe and the duration of storage at room temperature.

The current study attempted to determine how storage temperature affected the survival of HIV-1 inside syringes, because drug injectors do not necessarily have access to climate controlled environments. The researchers loaded syringes with HIV -infected blood, fully depressed the plunger to remove almost all the blood, and then stored the syringes for periods of one day to six weeks. The residual contents of the syringes were then introduced into tissue culture that allowed viable HIV to proliferate.

At 4 degrees C (Celsius), 50% of all syringes contained viable HIV-1 at 42 days of storage, the longest storage duration tested.

At room temperature, or 20 degrees C, the last day that syringes with infected blood tested positive for HIV-1 was Day 21. Viable HIV-1 was recovered from 8% of these syringes.

Above room temperature, or 27, 32 and 37 degrees C, less than 1% of syringes contained viable HIV-1 after one week.

"The primary goal of our study is to understand ways to stop the spread of HIV through syringe borne transmission," Heimer explains. "Behaviors of injectors vary tremendously. Some injectors rapidly discard syringes when they are done, mostly out of fear of being spotted by police for having syringes. Improperly discarded syringes can be reused and, if contaminated with HIV, can transmit the virus."

The findings that syringes can remain potentially infectious for as long as six weeks highlight a benefit of syringe exchange programs, says Heimer. Because these programs allow drug injectors to exchange used syringes for new ones, they remove from circulation and possible reuse potentially infected syringes, he notes.

In addition, he points out, syringe exchange programs can help disseminate the information about the heat-related demise of viable HIV as part of outreach efforts seeking to reduce HIV transmission among injection drug users.

-- By Jacqueline Weaver

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