DES MOINES — Reported cases of gonorrhea in Iowa have more than doubled over four years, according to state public health department data.

There were 3,600 cases of the sexually transmitted disease in Iowa in 2017, according to the state’s preliminary data.

That would be a 145 percent increase since 2013, and a one-year increase of more than 38 percent.

“It doesn’t appear to be one issue only. It seems like there are a number of factors involved,” said George Walton, the state public health department’s STD program manager.

Walton said he thinks part of the overall increase is because gonorrhea is showing up in more segments of Iowa’s population.

Gonorrhea diagnoses are increasing among both men and women, but faster among men, according to the department, which said that likely indicates an increase among men who have sex with men.

The disease primarily impacts young Iowans: ages 15 to 34 account for 80 percent of diagnoses, according to the department.

It also disproportionately impacts Iowa’s black population, which accounts for nearly 30 percent of diagnoses even though it accounts for only 3.5 percent of the state’s population.

Walton said further analysis is needed to determine which factors impact the various populations that are disproportionately affected.

He said more robust testing also could be boosting diagnoses. He said the department is encouraging medical facilities to be more thorough in testing for gonorrhea.

“We’re starting to find more infections that in the past would have been missed,” Walton said. “That’s a part of it, certainly not all of it.”

Walton said the department cannot determine whether increased sexual activity or risky sexual behaviors — like failing to wear protection — are contributing to the increase in gonorrhea diagnoses. He said increases in diagnoses of other STDs like syphilis have been linked to increases in sexual activity as a result of more common use of dating sites, so it’s “conceivable” other STDs like gonorrhea are increasing for the same reason.

“That doesn’t mean that’s the case. I just means we don’t have that comprehensive information one way or the other,” Walton said.