HONOLULU (AP) — Federal researchers say a cluster of gonorrhea cases in Hawaii are the first in the nation to show resistance to the strongest antibiotics available to combat the sexually transmitted disease.

The U.S. Centers for Disease Control and Prevention announced Wednesday that the seven Hawaii cases could mean treatment for gonorrhea is becoming less effective, Hawaii News Now reported (http://bit.ly/2d61AA4).

The cases, identified in Honolulu in April and May, showed resistance to azithromycin at much higher levels than other cases throughout the U.S. Test results also revealed that five individuals showed increased resistance to ceftriaxone, which is recommended in combination with azithromycin as a treatment by the CDC.

"Our last line of defense against gonorrhea is weakening," said Dr. Jonathan Mermin, director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention, in a news release. "If resistance continues to increase and spread, current treatment will ultimately fail and 800,000 Americans a year will be at risk for untreatable gonorrhea."

While CDC officials found the results concerning, they say an experimental oral antibiotic being tested in a clinical study could provide some new options for gonorrhea treatment.

Dr. Alan Katz, a professor of public health at the University of Hawaii, said Hawaii has become "extremely vigilant" in response to seeing declining effectiveness of the antibiotics over the years. The state was able to identify the cases early and successfully treat those linked to the cluster, he said.

"Hawaii is on the front line for antibiotic-resistant gonorrhea," said Katz, who is also a medical consultant at Hawaii's Diamond Head STD clinic. "But the future risk of gonorrhea becoming resistant to both of the recommended therapy medications in the United States is troubling."