The California Department of Public Health has reported that the Golden State has seen a 40 percent increase in cases of sexually-transmitted diseases (STDs) since five years ago.

“Countries like Cuba and Thailand have eliminated mother-child transmission [of syphilis],” Dr. Jeffrey Klausner, a UCLA professor of medicine and public health, told Southern California Public Radio. “So to see an increase in the United States is frightening.”

Klausner noted the rise in rates of chlamydia, gonorrhea and syphilis for the third year in a row.

California also has the second-highest rates of congenital syphilis in the nation, with 41 cases per 100,000 live births. (Louisiana is first, with 74.4 per 100,000.)

These STDs could potentially be deadly if not treated properly.

The California Department of Public Health also noted that California reported 250,000 cases of STDs in 2016 alone, noting that young people, African-Americans and gay and bisexual men had the highest infection rates.

However, SCPR notes that “[c]hlamydia remains the most common reportable disease in California,” and the highest rates of this highly-transmissible disease are among young women.

A report released by the Centers for Disease Control and Prevention Tuesday noted that, “[i]n 2016, a total of 1,598,354 chlamydial infections were reported to CDC in 50 states and the District of Columbia.”

While there are a few theories as to what could be pushing this rise in STDs, Mario Perez, director of the department’s Division of HIV and STD Programs, told SCPR that he believes the decrease in condom use could be due to an increased use of birth control and long-acting contraceptives.

“They are protecting themselves against pregnancy, but not protecting themselves against STDs,” Perez told SPRC. “Condoms continue to play an important role in disease transmission.”

Also of concern is the fact that many of these STDs have become resistant to antibiotics. As the bacteria causing these diseases mutate, they become much harder to treat.

Adelle Nazarian is a politics and national security reporter for Breitbart News. Follow her on Facebook and Twitter.