Cases of sexually transmitted diseases in the United States have reached new highs, including an increase in syphilis not seen since the mid-1990s, federal health officials said in a report this week.

There were 1.5 million chlamydia cases in 2015 — the last year that numbers were available — a 6 percent increase from the year before, and about 400,000 infections of gonorrhea, or a 13 percent rise, according to a report by the federal Centers for Disease Control and Prevention.

But syphilis cases increased to levels unseen since the mid-1990s. There were nearly 24,000 cases of primary and secondary syphilis cases last year, a 19 percent hike compared with 2014.

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Health officials attributed the rise to cuts in funding for prevention, and a decrease in the number of people going to clinics to be tested.

“We have reached a decisive moment for the nation,” said Dr. Jonathan Mermin, director of CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, 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.”

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California topped the list in number of cases, although the rate of infection for some sexually transmitted diseases, such as chlamydia, was highest in Alaska where there is a smaller population. But the Golden State saw rises in all three diseases. Gonorrhea cases nearly doubled in five years, from 27,500 infections in 2011, to 54,000 in 2015.

At the same time, funding for STD prevention stagnated in the state. In 2011, the state budget called for $4.5 million in spending funds for STD prevention when the population was at 37.7 million people. In 2015, Gov. Jerry Brown signed off on $5.1 million for STD prevention programs, when the population rose to 38.8 million people, according to a Daily News analysis. The latest budget allocates about the same amount.

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Officials with the state’s Department of Public Health attributed the rise to several factors, including changes in sexual behavior, increased awareness of the symptoms, better access to care and testing services, and improved public health reporting.

State officials also said while condoms may be widely accessible, many young people still face barriers to getting and using condoms. They also said evidence shows condoms aren’t being used correctly.

They point to data from a survey published this year that found of the California high school students who are sexually active, 43 percent reported that they did not use a condom the last time they had sex.

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The rise in STDs trickled down to the Los Angeles-Long Beach-Anaheim areas, according to the CDC.

Prevention funding is part of the reason why STD’s are rising but not the only cause, said Dr. Richard Seidman, chief medical officer for Northeast Valley Health Corp..

“If STDs are going up, it means people aren’t practicing safe sex,” Seidman said.

He said STDs are more common in young adults from 15 to 24 because they are otherwise healthy and are not coming in to doctors’ offices to be screened.

“They’re busy living their lives and not thinking about their risks,” Seidman said.

Northeast Valley, one of the nation’s largest health corporations of its kind, operates a teen health center on the San Fernando High School campus. All teens who come in get tested for sexually transmitted diseases, said Ellen Monaco, family nurse practitioner at the clinic. She said she talks to all students about STDs, even if they just come in with a headache. There have been no cases of syphilis, HIV or gonorrhea, but some positives for chlamydia so far this school year, she said.

“Because we have that trust with them, we have very low census of STDs here,” said Monaco, who estimates that the clinic sees 1 STD out of 100 tests. She said the clinic remains important to the community, which serves mostly Latinos, who are from low-income families, who may not have access to other health centers.

“Every high school should have a confidentiality program so they can feel safe,” Monaco said. “We do really well, because we’re trying to capture as many students as we can, and they talk to their friends.”

Most sexually transmitted diseases have no symptoms and are treatable with antibiotics. Going untreated means risks such as miscarriage, stillbirth, blindness or stroke, health experts said. The CDC estimates STD cases cost the U.S. health care system about $16 billion each year.

The CDC report also found:

• Those 15- to 24-years-old accounted for nearly more than 60 percent of chlamydia diagnoses and half of gonorrhea diagnoses.

• Men who have sex with men accounted for the majority of new gonorrhea and primary and secondary syphilis cases.

• Women’s rate of syphilis diagnosis rose by more than 27 percent from 2014 to 2015. The number of pregnant women who transmitted syphilis to their babies also increased by 6 percent.