The number of cases of sexually transmitted infections (STI) reported in the US in 2015 is at an all-time high, according to the Centers for Disease Control and Prevention (CDC). That’s because budget cuts to state and local STI programs have left fewer people with access to testing and treatment, the agency says.

"We’re very concerned about these unprecedented high number of cases of STIs in the United States," Gail Bolan, the director of the CDC's Division of Sexually Transmitted Disease Prevention, tells The Verge. "These new number are making it really clear that many Americans are not getting the preventive services they need."

In 2015, there were more than 1.5 million reported cases of chlamydia (up nearly 6 percent since 2014), about 400,000 cases of gonorrhea (up nearly 13 percent), and about 24,000 cases of primary and secondary syphilis (up 19 percent), according to a report released today by the CDC. These three diseases are also the most commonly reported sexually transmitted infections (also known as sexually transmitted diseases, or STDs) in the US.

Fewer people have access to STI testing and treatment

Chlamydia is an infectious disease that affects both men and women, but is particularly dangerous for women. If left untreated, it can make it difficult or impossible for women to get pregnant later on. Gonorrhea can lead to lasting health problems like infertility, long-term abdominal pain in women, and even death if the infection spreads to a person’s blood or joints. And syphilis can create skin rashes and sores, and can damage the brain, nerves, and heart if left untreated. (Syphilis is divided into four stages: primary, secondary, latent, and late.)

All three STDs can be cured with antibiotics, but drug-resistant versions of the disease are much more dangerous and harder to treat. In July, the CDC announced that gonorrhea may soon become resistant to the only two antibiotics left to treat it. "We’re very concerned about the threat of untreatable gonorrhea," Bolan says. Chlamydia and syphilis are also increasingly becoming resistant to antibiotics, according to the World Health Organization.

The uptick in the number of cases is caused by reduced access to STD testing and treatment, the CDC says. More than half of state and local STD programs have experienced budget cuts, the agency says, and more than 20 health department STD clinics closed in one year alone. Sexually transmitted infections cost the US health care system nearly $16 billion each year, according to the CDC.

"We have reached a decisive moment for the nation."

"We have reached a decisive moment for the nation," Jonathan Mermin, director of CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, said in a statement. "STD rates are rising, and many of the country’s systems for preventing STDs have eroded. We must mobilize, rebuild and expand services — or the human and economic burden will continue to grow."

Young people, as well as gay and bisexual men, are most at risk of contracting an STD. In 2015, about two-thirds of chlamydia diagnoses and half of gonorrhea diagnoses were among Americans ages 15 to 24 years old. Men who have sex with men accounted for the majority of new gonorrhea and primary and secondary syphilis cases. But women’s rate of syphilis diagnosis also increased by more than 27 percent during that period. That’s concerning because pregnant women who have syphilis can pass the infection onto babies, causing the baby to be born dead or have developmental problems.

The only way to respond to the increasing number of STD cases is to expand access to screening and treatment, according to the CDC. "STD prevention resources across the nation are stretched thin, and we’re beginning to see people slip through the public health safety net," said Mermin. "Turning the STD epidemics around requires bolstering prevention efforts and addressing new challenges — but the payoff is substantial in terms of improving health, reducing disparities and saving billions of dollars."

Update October 19th 04:41PM ET: The story has been updated to include comments from Gail Bolan, the director of the CDC's Division of Sexually Transmitted Disease Prevention.