Gonorrhoea may become "untreatable" as drug-resistant strains are spreading across Europe, health officials said.

Strains of the sexually transmitted infection (STI) have become more resistant to common treatments and are showing reduced susceptibility to newer antibiotics, the European Centre for Disease Prevention and Control (ECDC) said.

Gonorrhoea, the second most common STI in Europe in 2010, is usually treated with the drug cefixime but an increasing number of patients have shown resistance to the antibiotic.

The proportion of cases with resistance rose from 4% in 2009 to 9% in 2010.

The drug-resistant strains are spreading fast around Europe. They were found in 17 European countries, seven more than the previous year.

In 2010, more than 32,000 cases were recorded across Europe, data from the Stokholm-based ECDC found.

Even though chlamydia was the most frequently reported STI, with almost 350,000 cases in the same period, the ECDC director singled out the gonorrhoea threat as a "critical situation".

Marc Sprenger said: "This indicates the risk that gonorrhoea may become an untreatable disease in the near future.

"Public health experts and clinicians need to be aware of the current critical situation and should be vigilant for treatment failures.

"The findings of the ECDC reports also imply that the European gonorrhoea treatment guidelines need to be reviewed."

He added: "Decreasing susceptibility to recommended antimicrobials and increasing numbers of treatment failures across Europe ask for careful monitoring of the European gonococcal population as the loss of the current recommended treatments could result in untreatable gonorrhoea.

"Only continued surveillance of antimicrobial resistance in gonococci will inform existing and future treatment guidelines adequately in order to ensure that patients are treated with effective drugs and morbidity is reduced in infected patients."

Gonorrhoea can infect areas of the reproductive tract, including the cervix, uterus and egg canals in women as well as the urine canal in women and men. The bacterium can also grow in the mouth, throat, eyes and anus.

It is spread through vaginal, oral or anal sex.

If untreated, it can lead to severe secondary diseases, abortions and infertility. It also plays a role in facilitating HIV transmission.