A 10 percent increase in sexually transmitted infections last year has Minnesota health leaders concerned that people are unaware of the risks and that doctors aren't pushing testing hard enough.

A record 18,724 chlamydia infections were reported last year, a 4 percent increase from 2012, the Minnesota Department of Health reported Wednesday. Infections involving gonorrhea and syphilis aren't as common, but the number of reported cases increased last year by 26 percent and 64 percent, respectively.

More than half of the chlamydia and gonorrhea infections involved teens and young adults ages 15 to 24, and health officials suspect there are many more whose infections are undiagnosed and are either unaware of the risks or afraid to get tested because it would mean disclosing they are sexually active to doctors and parents.

"They are basically silent carriers who can infect other people," said Dr. Andrew Zinkel, associate medical director for health plan quality at HealthPartners, a Bloomington-based medical provider. "That's why the rates are going up everywhere," including in urban, suburban and rural parts of the state.

While an increase in chlamydia cases could be due to more frequent testing, state clinic performance data suggest the opposite: that a lack of testing allows people to spread their infections to new sexual partners. Only 40 of the 138 clinic groups reporting to Minnesota Community Measurement test more than half of their young, sexually active females for chlamydia.

Major pediatric providers such as Southdale Pediatrics in Edina and Wayzata Children's Clinic tested no more than a quarter of recommended patients, while several rural clinics tested fewer than one in 10 sexually active women ages 16 to 24.

HealthPartners is planning a public awareness campaign this year to encourage more testing — particularly by clinics that serve minorities and low-income teens and young adults who are more likely to suffer infections — and to remove the stigma that discourages teens.

"They shouldn't let fear or fear of disapproval prevent that," said Zinkel, noting that the federal Affordable Care Act requires insurers to cover testing.

Chlamydia often causes no initial symptoms but can lead to infertility and complications for newborns of infected mothers. Gonorrhea infections can spread to organs and joints and cause life-threatening complications, and syphilis can lead to blindness, mental illness, dementia or death.

The state reported 3,872 gonorrhea infections last year and 193 cases of primary and secondary syphilis, with the latter largely among men in the Twin Cities who have sex with other men. However, the state noted an increase in early syphilis cases in women — 30 last year compared to 18 in 2012.

All three infections can be treated with antibiotics, and state "expedited partner therapy" rules allow doctors to write prescriptions not only for their patients, but also for their patients' sexual partners in an attempt to slow the spread.

A rise in sexually transmitted infections could be tied to an increase in dangerous behaviors that result in more unprotected sex, said Dr. Virginia Lupo, chairwoman of obstetrics and gynecology at Hennepin County Medical Center (HCMC) in Minneapolis. "Narcotic use is way up in this state, and exchanging sex for drugs is definitely done in this world. That could possibly be increasing some [STD] rates."

There were signs for optimism in the 2013 data. While STD rates remain higher in the 15-to-24 age group overall, the number of chlamydia infections declined from 2012 to 2013 when only looking at the 15-to-19 age group. Add in findings from the 2013 Minnesota Student Survey showing less sexual activity among ninth-graders compared to 2010, and they suggest an adolescent population that might be more concerned about the risks of unprotected sex and STDs, said Judith Kahn, executive director of Teenwise Minnesota, a nonprofit focused on adolescent sexual health.

"I'm moderately optimistic they will carry this through into their 20s," Kahn said, which would likely mean a decline in STDs in this population.

An emerging strategy at some clinics is to pursue universal testing of all young patients, and relieve them from the pressure of having to disclose their sexual activity levels. That type of approach allowed HCMC clinics to test 79 percent of its sexually active young females. (STDs can be detected through a swab during a vaginal exam for women or a urine sample for female or male patients.)

Universal screening catches teens who get out of testing by lying about their sex lives, Zinkel said. "You're not always going to get an honest answer from your patients."

The approach has downsides, including a small number of false positive tests that could be "pretty devastating" to teen patients who claim to be sexually inactive and to their parents, said Kelly Boie, a pediatric nurse practitioner at Wayzata Children's Clinic.

Her group tried universal screening as part of a study a few years ago and found it didn't identify many more cases. As for her group's current low rate of testing, Boie said that is because teens worry even during confidential clinic visits about being tested and then having that test show up on their parents' insurance statements.

"Then they're never going to come back and talk to you about anything that is important," she said. "Once you've blown it with a teenager, you've blown it."

While it doesn't show up in the data, the clinic has steered some sexually active women to a teen clinic where they receive testing for free.