The US saw a record number of cases of chlamydia, gonorrhea, and syphilis last year, according to preliminary data released Tuesday by the Centers for Disease Control and Prevention.

From 2013 to 2017, the CDC said, the number of gonorrhea diagnoses increased by 67%, while those of syphilis increased by 76%. Chlamydia remained the most common condition reported to the CDC.

Sexually transmitted diseases do not always cause symptoms and can be spread by people who don't know they're infected.

Using condoms, being monogamous, reducing your number of sex partners, or abstaining from sex can reduce your risk of getting an STD.

Regular testing is important for catching infections.

There were 2.3 million cases of chlamydia, gonorrhea, and syphilis diagnosed in the US last year, according to preliminary data released by the Centers for Disease Control and Prevention. It marks a record high for the country and the fourth year in a row of "steep, sustained increases" in these three infections, according to a CDC press release.

The data was presented at the National STD Prevention Conference in Washington on Tuesday, CNN reported.

From 2013 to 2017, gonorrhea diagnoses increased by 67% and nearly doubled in men, syphilis diagnoses increased by 76%, and chlamydia remained the most common condition reported to the CDC.

This CDC graphic details rising STD diagnoses in the US. CDC

"We are sliding backward," Dr. Jonathan Mermin, the director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, said in the press release. "It is evident the systems that identify, treat, and ultimately prevent STDs are strained to near-breaking point."

Here's a closer look at the STDs in question — and how you can keep yourself safe.

Chlamydia, gonorrhea, and syphilis often go untreated

Chlamydia, gonorrhea, and syphilis can be treated with antibiotics. Getty Images/Joe Raedle

Chlamydia, gonorrhea, and syphilis are all caused by bacteria and treatable with antibiotics. When untreated, these infections can lead to more serious health problems, including infertility, ectopic pregnancy, and higher HIV risk.

One part of the problem is that people often do not know they're infected.

"It's important for the public to understand that most sexually transmitted infections are transmitted by people who do not know that they're infected," Dr. Edward Hook, the scientific committee chair of the National STD Prevention Conference, told CNN.

For example, chlamydia and gonorrhea infections cause no symptoms in some infected people, according to the CDC. HIV may not cause symptoms at first, either, and it's often transmitted by people who don't know they have it, according to the American Sexual Health Association.

Gonorrhea is getting harder to treat

Antibiotic-resistant gonorrhea is a major concern. James Archer/ CDC

The CDC's press release also notes the growing threat of antibiotic-resistant gonorrhea — sometimes called "super gonorrhea." Such gonorrhea has become resistant to "nearly every class of antibiotics" once used to treat it, the release said.

There have been no cases of untreatable gonorrhea in the US so far, but lab tests have shown "emerging resistance" to one of the antibiotics shown to be effective against the infection, the release added.

"We expect gonorrhea will eventually wear down our last highly effective antibiotic, and additional treatment options are urgently needed," Dr. Gail Bolan, the director of the CDC's Division of STD Prevention, said in the release. "We can't let our defenses down."

You can protect yourself

Condoms reduce the risk of STD transmission. Sergio Dionisio/Getty Images

The best way to deal with the threat of STDs is to prevent them in the first place.

There are a few ways to lower your risk of getting sexually transmitted diseases, including reducing your number of sexual partners, being monogamous, and abstaining from sex. There are vaccines for the sexually transmitted hepatitis B and HPV, though the HPV shot is recommended only for women up to age 26 and men up to age 21.

Finally, you can use condoms, which are "highly effective" for reducing the spread of STDs when used properly, according to the CDC. Just make sure the condoms you're using haven't hit their expiration date. Expired condoms are more likely to break. Don't try to recycle them, either; the CDC recently warned that reusing condoms rendered them ineffective.

Regular STD tests can catch infections

Regular STD testing is recommended in certain populations. Joe Raedle/Getty Images

If you're having sex, regular STD tests help protect your health. The CDC's website has a quiz to help you determine which STD tests you may need, but the basic recommendations are as follows:

Everyone ages 13 to 64 should be tested at least once for HIV. People who have unprotected sex or who share injection drug equipment should get tested at least once yearly.

Women younger than 25 (and older women with certain risk factors) should get tested for chlamydia and gonorrhea once a year.

All men who have sex with other men should get tested for syphilis, chlamydia, and gonorrhea at least once a year but more frequently if they have sex with multiple or anonymous partners.

All pregnant women should get tested for syphilis, HIV, and hepatitis B.

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