Young women have the highest risk of contracting chlamydia

Fifteen to 19-year-olds are most likely to test positive for chlamydia, followed by 20 to 24-year-olds, with over 25s the least likely to be infected.

But two-thirds of samples sent for testing by GPs were from women aged over 25, Nottingham-based researchers have found.

Chlamydia is often symptomless, but it is the most common cause of infertility and ectopic pregnancy. It has also been linked to cervical cancer.

What we're trying to do is pick up people who aren't picked up elsewhere. Dr Philip Hay,

Recent estimates suggested one in 10 men had the condition without knowing it.

Health experts are looking at how best to screen for the disease to pick up the most cases.

In February, the government announced a second wave of centres around the country in a move towards a national screening programme for the condition.

Demand

The Nottingham researchers looked at 7,000 chlamydia samples sent during one year by 119 GP practices around Nottingham for testing at the district public health laboratory.

The researchers found that although 63% of tests were carried out on women over 25, the highest proportion of positive results was in 15 to 19-year-olds.

They also discovered female GPs were more likely to take samples from 20 to 24-year-olds.

How busy the practice is influenced how many tests doctors requested.

When there was a high ratio of doctors to female patients, tests were more likely to be requested, and the more positive tests were likely to be obtained.

The researchers suggest busier practices might not have the time to explain the implications of a test.

Cost-effective

A second study looked at whether opportunistic screening of people attending A&E department could pick up cases of chlamydia.

Patients and their companions aged 16 to 35 attending the casualty department at St George's Hospital London, were asked if they would undergo a chlamydia test.

Three-quarters of more than 700 people asked agreed to have a test.

Just over 4% tested positive for chlamydia.

Dr Philip Hay, who led the study, said this showed it might be feasible and cost effective to test for chlamydia in A&E departments.

Health economists estimate a detection rate of between 3 to 6% makes chlamydia screening cost effective.

Dr Hay told BBC News Online: "A&E is somewhere where young men, who don't necessarily go to other healthcare setting, do go.

"What we're trying to do is pick up people who aren't picked up elsewhere."

Awareness

Dr Kevin Fenton, head of the HIV and STI division at the Health Protection Agency, said community-wide chlamydia testing may be more effectively done elsewhere.

"We need to offer opportunistic screening where it is likely to be most effective."

He added: "Screening in family planning clinics, youth centres, general practice and genito-urinary medicine clinics, as shown in the chlamydia screening pilots in Portsmouth and the Wirral, is likely to pick up the majority of cases in the at-risk group.

"For enhanced strategies, moving to screen in A&Es or other settings could also be considered."

Dr Fenton added that GPs needed to be aware of the need to refer younger women for testing.

"Some GPs have reservations about asking for a urine sample or cervical swab for chlamydia opportunistically - which suggests a continuing need for awareness raising and training"