On a recent afternoon, Hansel Tookes stood on a sidewalk in downtown Miami, peering into a thicket of scraggly weeds. “I found a bunch over here,” he said, edging toward an overpass. A small orange plastic cap came into sight, and next to it two slender insulin syringes, with the needles exposed. Scattered about were tiny plastic zipper bags — evidence that the needles had been used to inject heroin or cocaine.

Tookes, age 30, is an expert at identifying the detritus of injection drug use. As a public health student on hiatus from medical school, he led a group of researchers who walked the streets of Miami for four months, methodically counting discarded syringes in neighborhoods with high rates of drug arrests. As they crisscrossed more than 800 city blocks, the team spotted 328 used syringes, in parks, lots and along sidewalks.

“We found syringes every day we went out, in every neighborhood we went to,” he said. “We’re all at risk from accidental needle sticks.”

Miami is home to an estimated 10,500 people who inject illegal drugs, approximately one in five of whom is infected with HIV. Tookes and other public health researchers believe the high number of syringes on the city’s streets is largely due to Florida’s drug paraphernalia laws. For many years, these laws have made it illegal to give a syringe to anyone who is likely to use it to inject illegal drugs, thus preventing the establishment of large-scale programs to provide drug users with clean needles. Florida law bans carrying syringes for the purpose of illegal drug use, and police regularly arrest users for carrying syringes. Some users say this rule makes them more likely to throw away their paraphernalia anywhere that’s convenient. “The nervous types are going to throw it wherever they can without regard for who might come across it,” said Andrea E. Labbee, 52, an injection drug user who lives in South Florida. “They’re more worried about getting it out of their possession than they are about the consequences of where it ends up.”

Elsewhere, needle exchange programs have been embraced by public health officials as a means of reducing the spread of HIV and Hepatitis B and C. According to Evan Anderson, a senior legal fellow at the Robert Wood Johnson Foundation Center for Public Health Law Research at Temple University, 14 states have enacted laws explicitly allowing the existence of syringe exchange programs, and five states lack laws restricting the free distribution of syringes, thus allowing syringe exchange. In three other states, local governments have allowed syringe exchange programs to operate based on their interpretation of state law. The U.S. Department of Health and Human Services lifted rules preventing the use of federal funds for needle exchange programs in 2009, but, under political pressure, reinstated the ban in December of last year.

Most large-scale needle exchange programs do more than simply give out syringes. They usually hand out “sharps” containers for needle disposal, require that users return used needles in order to receive new ones, and offer condoms and information about drug treatment programs and local health clinics. “We don’t get too much controversy anymore,” said Katie Bouche, the manager of syringe access programs for the San Francisco AIDS Foundation, which runs the city’s largest needle-exchange program. “We’re really lucky here in that the Department of Public Health backs us.”

To study the effect of needle exchange programs on the number of unsafely discarded syringes, Tookes and his colleagues collaborated with researchers in San Francisco, where large-scale programs have operated openly for two decades, and where pharmacies are allowed to sell clean needles and syringes without a prescription. The San Francisco researchers walked along 1000 randomly selected blocks in neighborhoods with the city’s highest rates of drug arrests and hospital admissions for drug treatment. They counted only 11 syringes – a number Tookes’ team multiplied by 4, to account for their having stayed on one side of each block in San Francisco, as opposed to walking along each side of every block in Miami. In all, the researchers estimated that on average there were 44 syringes in every 1000 blocks in San Francisco, versus 371 syringes in every 1000 blocks in Miami.

The study, which was published late last year in the journal Drug and Alcohol Dependence, is the first to compare the number of publicly discarded needles in a city with needle exchange programs and a city without such programs. The authors admit that other factors might influence the number of syringes they found. But even though San Francisco and Miami differ significantly in geography, ethnic makeup, and politics, neither has an organized syringe clean-up plan, and their litter removal and street cleaning policies are similar. San Francisco also has more than twice as many injection drug users than Miami.

Tookes’ team supplemented their findings with a survey of more than 1000 active injection drug users in both cities. Of the 448 people interviewed in Miami, more than 2 out of 3 – 69 percent — said they had gotten rid of their used needles in public places, such as parks, alleyways, or bushes, over the preceding month. Of the 602 people interviewed in San Francisco, only 11 percent said they had discarded their needles in such a way. After adjusting for homelessness, sex, HIV status, and age, the researchers calculated that users in Miami were 34 times more likely to dispose of their syringes in a public place than were those in San Francisco.

Still, needle exchange opponents contend that the programs condone drug use and may lead to more drug activity and discarded needles in surrounding neighborhoods. “We’ve seen a lot of hope, but not a lot of results,” said W. Shepherd Smith, a former board member of the Children’s AIDS Fund, a non-profit HIV support and advocacy group. Smith acknowledged that South Florida has a needle disposal problem, but said the study’s results may have been affected by a culture of needle sharing that is more common on the East Coast of the U.S. “It would have been more helpful to compare two East Coast cities,” he said.

According to the U.S. Centers for Disease Control, there are no documented cases of anyone contracting HIV from an accidental needle stick outside of a health care setting. But the viruses that cause hepatitis B and C, which can cause liver cirrhosis and cancer, are far more infectious.

“Having a lot of used needles is really a hazard,” said Natalie Cramer, Director of Prevention for the National Alliance of State and Territorial AIDS Directors, a nonprofit scientific, policy and advocacy group. “Exchange programs have been a real help in preventing accidental needle sticks.”

There are no reliable estimates on how many children or passersby are inadvertently stuck by discarded syringes each year. For garbage collectors, street cleaners and recycling plant workers, however, needle sticks are a serious risk, according to Jenny Schumann of the Coalition for Safe Community Needle Disposal in Houston. The coalition estimates that 7.8 billion needles are discarded each year in household waste in the United States. Of these, an estimated 1.2 to 1.5 million were used to inject illegal drugs and the remainder for medications such as insulin. Even though some health departments (including Miami’s) accept used biomedical “sharps,” including needles, in secure containers for disposal, this program is aimed at people with chronic medical conditions and is virtually never used by the city’s illicit drug users, Tookes said.

But given the state’s current political climate, it’s unlikely Florida will change its drug paraphernalia laws any time soon — meaning the residents of inner city Miami will need to continue to watch their step. “They clog the court system up with things like a little petty syringe,” said Eugene Anthony Jones, 61, a native Miamian and longtime injection drug user. “There probably would be less of them thrown on the ground if it was legal. But this is the Deep South.”

Erin Marcus is an internal medicine physician and writes at New America Media.  This article originally appeared in The Huffington Post and New America Media.