A highly antibiotic-resistant variety of Neisseria gonorrhoeae, the germ behind gonorrhea, is quickly spreading and may soon become unbeatable, according to Sally Davies, chief medical officer of England, and Chief Pharmaceutical Officer Keith Ridge.

In a letter to the nation’s general practitioners and pharmacies, the pair urged doctors to use the strongest pharmaceutical weapons available to combat the health threat.

"Gonorrhoea has rapidly acquired resistance to new antibiotics, leaving few alternatives to the current recommendations,” the letter stated. "It is therefore extremely important that suboptimal treatment does not occur."

The letter follows news in September of an outbreak of 15 cases of “super-gonorrhea” in Northern England. The infections were resistant to azithromycin, a macrolide-class antibiotic used in combination with ceftriaxone, a cephalosporin, to treat gonorrhea.

The azithromycin-ceftriaxone combination therapy is only the latest strategy for defeating gonorrhea, which is spread through unprotected sexual contact. In the early 1990s, health experts recommended using ciprofloxacin, a fluoroquinolone-class antibiotic, or a cephalosporin, such as ceftriaxone or cefixime. However, starting in the late 1990s, doctors began seeing ciprofloxacin-resistant gonorrhea cases. By 2006, researchers found 14 percent of all infections were cipro-resistant, leaving experts to recommend only using the cephalosporin drugs (ceftriaxone or cefixime).

But by 2010, health experts noticed that those cephalosporin drugs were not working as well, particularly cefixime, and experts recommended boosting the doses. By 2012, the Centers for Disease Control and Prevention ditched cefixime and recommended a combination therapy of a ceftriaxone plus either azithromycin or doxycycline.

But, after the 15-case outbreak earlier this year, health experts were concerned that some patients may not be getting both drugs, but just the azithromycin. This would make it much more likely that N. gonorrhoeae will become resistant because, alone, either drug isn't as effective at killing the bacteria, Davies and Ridge warned.

Gonorrhea symptoms include yellow-to-green discharge from sexual organs and a burning sensation during urination. However, many people who are infected have no symptoms or have such mild symptoms that they go unnoticed. Untreated, the infection can lead to pelvic inflammatory disease and infertility.

In the US, gonorrhea is one of the most common sexually transmitted infections reported, causing an estimated 820,000 cases each year. In England, gonorrhea is the second most common sexually transmitted infection reported, causing around 35,000 cases each year.