Just when you think you've heard it all.
Back in the days before AIDS became a manageable condition rather than a gruesome death sentence, nothing was more terrifying to medical professionals than a needlestick. And they happened all the time. The National Institute for Occupational Safety and Health (NIOSH) estimated that about 600,000 of these accidents occurred each year. (The CDC estimate is 385,000 per year.)
A similar, but far more controversial issue, needle exchange to prevent IV drug users from spreading the virus, began in Europe in the 1980s. In the US, this practice – a form of harm reduction – wasn't initiated until the late 1980s due to concern that it would encourage drug use. [1]
Although the volume of blood retained in a used syringe varied markedly depending on the syringe type, the range is roughly 1-100 microliters. Although dead-space volume [2] is a determinant of the degree of transmission, residual blood in even the best syringe is at least thousands of times greater than that of a needlestick.
What's going on now in parts of Asia, especially Fiji, and Africa dwarfs these numbers. Drug users are engaging in a practice called "bluetoothing" or "flashblooding," where one person injects a drug – usually methamphetamine – and then fills the syringe with drug-laced blood so that another user can get a "secondary high."
Infective and ineffective.
Although it's possible (more like a certainty) that a syringe of blood from an HIV+ person will infect anyone who injects it, this quantity will not produce a meaningful stimulant effect.
But, very small quantities—tens to hundreds of virions—can establish infection in animal models; the precise human minimum is uncertain. But once infection starts – after HIV infects a CD4+ T cell – the virus can produce millions of progeny viruses. The opposite is true when it comes to drugs. While viral levels rise, drug levels decrease.
The methamphetamine blood concentration in people who took the prescription drug is estimated to be .02-.05 mg/L. Using the lower concentration and an estimated 5 liters of blood per person, one can calculate the blood level if a syringe containing 10 mL of blood is shared with another person; it's a dilution of 500-fold, so the person receiving the injection will have a blood level of 0.00004 mg/L – roughly 500-1,000 times below the estimated therapeutic concentration. In other words, the "secondary high." Although the effect has been referred to as "weak," I would argue that it's more like a placebo, albeit one that comes at a very high price.
It’s the perfect way of spreading H.I.V.
Catherine Cook, executive director of Harm Reduction International, in a New York Times interview [3]
Ironically, this awful practice provides a perverted lesson in pharmacology: The risk is enormous, and the "benefit,' such as it is, is zero. [4]
[1] There is more to this story than I am writing about.
[2] Dead-space volume refers to the small amount of fluid that remains trapped inside the device after the plunger is fully depressed.
[3]Pranav Baskar, “‘Bluetoothing’: Blood-Sharing Drug Trend Fuels Alarming Global HIV Surge,” The New York Times, syndicated via Business Standard, October 9, 2025.
[4] HIV is hardly the only virus that can be transmitted through blood contact. Hepatitis B is even more infectious, while hepatitis C is a bit less so.
Josh Bloom
Director of Chemical and Pharmaceutical Science
Dr. Josh Bloom, the Director of Chemical and Pharmaceutical Science, comes from the world of drug discovery, where he did research for more than 20 years. He holds a Ph.D. in chemistry.
