Diagnoses of sexually transmitted diseases including HIV and syphilis are on the rise in the United States among certain groups, with experts attributing the uptick to growing complacency about sexually risky behavior.

Public health officials in Rhode Island said this week that an increase in STDs in the state from 2013 to 2014 — including a 79 percent rise in syphilis cases — was attributable at least in part to the use of social media and dating apps to arrange casual or anonymous hookups. People having sex without a condom, having multiple sex partners, and having sex while under the influence of drugs or alcohol were also to blame. The spike in diagnoses affected African Americans, Hispanics, and young adults more than other populations, they said.

The news out of Rhode Island has been echoed elsewhere in the US, from New York to Utah to Texas, where officials have warned of increased transmission of STDs including syphilis. New HIV diagnoses among gay and bisexual men between the ages of 13 and 24 increased by 132.5 percent between 2001 and 2011, according to data from the CDC published in the Journal of the American Medical Association, though rates of HIV infection dropped for the overall population by 30 percent during the same decade.

The New York City health department announced in March that men in the city's Chelsea neighborhood had the highest infection rate of syphilis in the country.

The CDC, which declined to comment on the causes of the increase, noted that chlamydia and gonorrhea diagnoses have been stable or down in recent years among the highest-risk population, ages 15 through 24, but syphilis diagnoses rose 10 percent. It also pointed out that men who have sex with men (MSM) are at increased rate for all of the above-mentioned STDs.

Earlier this year, two researchers from New York University released a study tracking the increase in HIV diagnoses dating from when the website Craiglist was created and became a place for individuals to set up casual sexual encounters with others interested in the same thing. They found that from 1999 to 2008, the arrival of Craiglist correlated with an increase in the number of HIV infections.

Anindya Ghose, co-author of that study, believes that online dating apps have had a similar effect. "Basically what the internet does is makes it a lot easier to find a casual partner," he told VICE News. "Without the internet you'd have to put effort into casual relationships, chatting with someone at the bar or hanging out in places, but these platforms make it a lot more convenient and easy. That's essentially what the primary driver is."

Ghose's co-author Jason Chan agrees. He told VICE News: "This technology coming into play aggregates the demand and supply of willing participants, so the spread will be more prevalent.

"Now we have apps on our mobile phones instead of a website so the access becomes that much easier. My suspicion, without empirical testing, is that it makes it even more widespread than with Craigslist, because now people are traveling with phones and can find someone to hook up with tonight, where they are," Chan said.

Anthony Hayes, a spokesman for the Gay Men's Health Crisis in New York, said the increase in STDs was not being driven by the internet but by a lack of education and investment into prevention.

"I'll say this, don't blame social media," he told VICE News. "We need to do a better job at educating young people on healthy sexual practices. This is about a failure of providing young people with competent sex education, giving them access to condoms and affordable healthcare. Until we make critical investments, these numbers are likely to go up, but it's not through the fault of social media."

Other health researchers cited another new development having what they believed was a significant impact on the HIV rate in recent years — PrEP, or Pre-Exposure Prophylaxis, a daily medication that can reduce rates of infection for individuals exposed to HIV. The approval of the drug — known commercially as Truvada — by the FDA in 2012 was hailed as a breakthrough moment in HIV prevention. New York Governor Andrew Cuomo said he hoped to end AIDS in New York by 2020 in part by widely implementing the new drug.

But uptake has been slow among HIV-negative individuals, according to researchers, which some say is down to doctors being reluctant to prescribe it as well as a stigma that its use fuels promiscuous behavior. Some argue the HIV prevention message has changed from simply telling people to practice safe sex to trying to get them to use PrEP — which only effectively prevents HIV if taken regularly and does not prevent other STDs — and this can fuel reckless sexual behaviour.

"In the last five years there's been a major change in the US in the way we approach trying to prevent HIV, in particular, PrEP, which is really good but it's led to people question whether they still need to use condoms, and it's decreased the stress on the need to have safe sex," said Simon Rosser, a professor of epidemiology and community health at the University of Minnesota.

"The community is very much in flux about that at the moment and any time you get multiple people in flux you run the risk of increasing diagnosis," Rosser told VICE News.

Rosser said that a decade ago, the messaging from the public health community was consistent and simple: wear condoms and practice safe sex.

"It was a behavioral approach, and those approaches are certainly not present to the same extent now, partly because now men can take a pill everyday," he said.

Others argue that blaming PrEP for an increase in risky sexual practices is thinly-veiled gay sex shaming. "This moralizing only serves to undermine our efforts to promote the health and well-being of gay and bisexual men," said gay activist Alex Garner. "'Promiscuity' is an arbitrary construct whose only purpose is to shame people for their sexual behavior. There is no evidence to suggest that PrEP will increase risky behavior or lead to sexual anarchy. We've heard this all before. Condoms do not promote promiscuity, watching Glee doesn't turn kids gay, and listening to rap music doesn't make you a thug."

A major 2013 study found there was no increase in risky sexual behavior in gay men who took PrEP.

Lois Takahashi, a professor of urban planning at UCLA who studies systemic and structural issues around HIV, said higher diagnoses rates may be attributable to better testing.

"Does Grindr cause transmission? We're not sure. We posit, we guess, you have more access to more people quickly, there are geospatial possibilities to find people and hook up, so it might be contributing but also might not be," she said.

Takahashi and Rosser said that syphilis was often seen rising together with HIV rates. Rosser called it a "canary in the coal mine" for HIV, in that when it starts increasing, health officials can expect HIV to start rising about a year later.

"If we see syphilis cases rising, if we don't already see HIV cases rising then we will. They kind of go in tandem. What does that tell us about behavior out there? What are the reasons for this? I think there are multiple alternative explanations depending on where you look. Rhode Island and New York are different from the Midwest and California, and there may be different explanations even among MSM of color," Takahashi said.

"It's entirely consistent with the breakdown and erosion of a single message about HIV prevention in the US," Rosser said.

Rosser said that another spur for the increase was the reduction in funding for research at the National Institutes for Health over the last decade, and a shift in priorities at the CDC to focus on biomedical prevention and cures for HIV rather than behavioral ones. Until a new, comprehensive strategy was agreed upon by researchers and community members, infection rates would likely continue to go up, he said.

"Unfortunately research is divided about what to do, and the community is tired of hearing about what to do about HIV. As HIV has become more manageable, it's become less frightening, so people are less scared of getting it," Rosser said.