Increased testing for sexually transmitted infections (STIs) may have caused the first decrease in new cases in a decade.
New cases of STIs were down 1% across in England in 2010, with 418,598 new diagnoses compared to 424,782 in the previous year.
The Health Protection Agency (HPA) said the decline in new cases was most apparent in young people.
The drop in new STI cases coincided with a 1% increase in STI testing, which amounted to 1.18 million tests in 2010.
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The HPA said new cases of chlamydia - common among people aged under 25 - remained stable at 189,625 cases in 2009 and 189,612 in 2010.
Figures reveal a 10% rise in the number of chlamydia tests in England last year. There were 2.2 million tests among 15 to 24-year-olds in 2010, an increase of more than 196,000.
Genital warts diagnoses also fell 3%, from 77,900 in 2009 to 75,615 in 2010.
Cases of syphilis fell 8%, from 2,846 in 2009 to 2,624 in 2010, and genital herpes dropped 8%, from 27,564 cases in 2009 to 29,703 in 2010.
Dr Gwenda Hughes, head of the HPA’s STI section, said: “For the first time ever we have seen chlamydia diagnoses stabilise when testing for that particular infection is at its highest ever, thanks to community based testing through the National Chlamydia Screening Programme.
“These are very early days but we hope that this is the beginning of a downward trend.”