The number of cases of gonorrhoea has been rising since 1994, but this is the largest rise that has been seen in a single year since that time.

Gonorrhoea cases among men (1998 to 1999)

Northern and Yorkshire - up 22% Trent - up 16% Eastern - up 25% London - up 21% South East - up 9% South West - up 42% West Midlands - up 44% North West - up 35%

The PHLS warns that further analysis of the data is necessary before detailed conclusions can be drawn.

But it says the initial figures suggest that there have been substantial increases in all age groups and virtually all regions of England.

As in previous years, however, there have been particularly large increases amongst 16 to 19-year-olds.

Between 1998 and 1999, diagnoses in this age group rose by 52% in males and 39% in females.

'Very worrying' figures

Dr Mike , head of the sexually transmitted infection section at the PHLS Communicable Disease Surveillance Centre, said: "These figures are very worrying.

"Clearly, a lot of people, and especially young people, are putting themselves and their partners at risk through unsafe sex."

Dr Catchpole said that during the late 1980s more people paid heed to safe sex messages, and consequently there was a decline in STD infections.

Gonorrhoea cases among women (1998 to 1999)

Northern and Yorkshire - up 69% Trent - up 6% Eastern - up 48% London - up 27% South East - down 8% South West - up 19% West Midlands - up 27% North West - up 46%

However, he said that during the late 1990s increases in high-risk sexual behaviour were reported, initially amongst gay and bisexual men.

Dr Catchpole said new data suggest that levels of unsafe sex may also be increasing among heterosexuals.

"This is particularly concerning, as it clearly has implications for the transmission of other STDs, and of course HIV," he said.

Dr Catchpole said the data emphasised the need for effective promotion of good sexual health.

"Sexually transmitted infections need to be brought under control, by prevention and early testing and treatment," he said.

Gonorrhoea is one of a number of STD infections caused by bacteria.

It has important health consequences for women in particular because if left untreated it can lead to pelvic inflammatory disease which in turn often results in chronic ill-health, infertility or pregnancies taking place outside the womb which can be life-threatening.