The internet has helped love bloom for many couples, but it’s also played a role in a 45 percent jump in sexually transmitted diseases over five years in California, a surge not seen in nearly three decades, health officials said Monday.

More than 300,000 cases of chlamydia, gonorrhea, and early syphilis were reported in California in 2017, a 45 percent increase compared with five years ago, according to a report by the California Department of Public Health.

The increases in infection rates are the result of numerous factors, including a decrease in condom usage, lack of education and fewer STD clinics, but Dr. James Watt, chief of the division of communicable disease control for the Department of Health, said social media played a significant role by helping people find anonymous sex partners.

“It makes it easier for people to meet people they don’t already know to have sex,” Watt said. “The internet allows for a broadening of sexual networks, and the broader that gets the more opportunity you have for sexually transmitted diseases to spread.”

The jump is all the more alarming for health officials considering that sexually transmitted diseases have increased every year for six years.

“The levels we are seeing now are higher than they’ve been since 1990,” said Watt. “We’ve been seeing increases for all three diseases for the last five or six years. It’s concerning because that slope, that uptick, doesn’t seem to be coming down. In fact, it seems to be getting steeper.”

Infection rates went up dramatically between 2016 and 2017 for each the three most commonly reported sexual diseases, particularly among African Americans, who were five times more likely than whites to get chlamydia and gonorrhea and twice as likely to contract syphilis.

The report documented 218,710 cases of chlamydia last year, the highest number since 1990. Chlamydia rates, which increased 9 percent over 2016, were 60 percent higher among women than men, and 54 percent of the cases were in people under age 25, the report said.

Watt said the higher rates of chlamydia among women are likely the result of a national campaign to persuade more women to come in for screening.

There were 75,450 cases of gonorrhea in 2017, the highest number since 1988, the report said. The rate of gonorrhea infection, which is highest among people under age 30, increased 16 percent over 2016. Males were two times more likely to get the disease than females.

If left untreated, chlamydia and gonorrhea can cause pelvic inflammatory disease and lead to infertility, ectopic pregnancy and chronic pelvic pain.

The number of cases of syphilis reported in California, 13,605, was the highest since 1987 and amounted to a 20 percent increase in the rate of infection compared with 2016. Males are also more likely to be diagnosed with syphilis, but female cases have increased sevenfold since 2012, according to the report.

“That’s particularly concerning because syphilis can have long-term complications like blindness, hearing loss and other neurological problems,” Watt said.

The rates of gonorrhea and syphilis are higher among men because male-on-male sex carries with it a higher risk of transmission, he said.

Health department officials are particularly worried about the 30 stillbirths last year caused by congenital syphilis, a 30 percent increase in one year and the highest number since 1995. It marked the fifth consecutive year that the number of infants born with syphilis has increased.

The department of public health is working with local health departments, schools, community groups and youth organizations across the state to raise awareness about the problem.

“We want people to get tested, because even when people don’t have symptoms they are still infectious,” Watt said. “More people are getting tested, so we’re hoping that some of this will be an improvement that could lead to the lowering of infection rates.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite