Government heath officials are warning that gonorrhea, one of the most common sexually transmitted diseases, and usually very treatable, is becoming increasingly resistant to the last type of antibiotics left to treat it.

Although no cases of resistant gonorrhea have been reported in the United States, the Centers for Disease Control and Prevention says its own laboratory studies are detecting growing signs of resistance to a class of antibiotic drugs called cephalosporins. In addition, resistant strains already have shown up in other countries, including Canada. 

 Recently, two cases in which gonorrhea treatment failed were reported in Norway among heterosexual men, and a new resistant strain of the bacteria was identified from a female sex worker in Japan, a finding reported this week at the International Society for Sexually Transmitted Disease Research conference in Quebec.

The new strain may be “a true superbug that initiates a future era of untreatable gonorrhea,’’ wrote the team of Japanese and Swedish scientists in a recent report about the new strain.