(CNN) Herpes infections are decreasing across nearly every demographic in the United States, according to a new report.

The report, published Wednesday by the National Center for Health Statistics , part of the US Centers for Disease Control and Prevention, looks at the prevalence of both types of herpes simplex viruses, HSV-1 and HSV-2, from 1999 to 2016.

It found that approximately 48% of all Americans were infected with HSV-1 and 12% with HSV-2 in 2015-16. This represents an 11.3 percentage point decrease in HSV-1 and a 5.9 percentage point decrease in HSV-2 since 1999.

"This is good news," said Geraldine McQuillan , an infectious disease epidemiologist at the CDC and a lead author of the report. "I think its take-home message is that two of our most prevalent viruses, HSV-1 and HSV-2, are steadily declining in the US population."

The report was based on a survey administered annually by the CDC that looks at a nationally representative sample of about 5,000 people.

Herpes infections were identified based on antibody testing among all participants ages 14 to 49.

HSV-1 and HSV-2 are transmitted through contact with an infected person's lesions or secretions. Symptoms include painful blisters and sores at the site of infection.

HSV-1 typically affects oral mucous membranes and is often contracted during childhood. HSV-2, on the other hand, typically affects the genitals and is usually contracted after a person becomes sexually active. But either type can occur on the genitals or elsewhere.

The viruses are not usually life-threatening but, once in the body, typically remain there for life, according to Dr. William Schaffner , a professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center, who was not involved in the study.

Reactivation of the viruses can occur at any time, but it often occurs during periods of stress, sunlight exposure or when the immune system is weakened, Schaffner said.

"You can have tingling sensations and be aware of very early-onset lesions," he said. "And if you treat it at that point, you can actually reduce the likelihood that you will get a full-blown infection."

Symptoms such as pain and fever can be treated with ibuprofen or Tylenol. Antiviral medications such as acyclovir can also decrease the severity and duration of symptoms, according to Schaffner.

"The more sexual partners you have, the more likely you are to encounter the virus," he added. "The more often you use condoms, the less likely you are to acquire the infection."

HSV-1 was most common in Mexican-Americans (71.7%), while HSV-2 was highest among African-Americans (34.6%). Both viruses were more common in women than men.

"Access to diagnosis and treatment may play a worthy role" in the disparity between racial and ethnic groups, Schaffer said. "This may be yet another reflection of differential access to medical care in the United States."

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The drop in herpes infections comes at a time when other sexually transmitted diseases are increasing nationwide . In 2016, more than 2 million cases of chlamydia, gonorrhea and syphilis were reported to the CDC -- the highest number ever recorded.

It is still unclear why herpes infections are dropping while other STDs are on the rise.

"I don't know for sure," Schaffner said. "My inclination would be that we have to look very carefully at subsets of population beyond age and race, which are the two major distinguishing features in this investigation.

"Treatment for gonorrhea has also become much more difficult because of progressive antibiotic resistance, so for that particular disease, that may be a contributing factor," he added.