Many thousands of chlamydia cases undiagnosed

Revelations that thousands of New Zealanders are infected with chlamydia has prompted calls for screening guidelines and control measures for the sexually transmitted disease.

Research published today in the New Zealand Medical Journal showed that almost three per cent of female students aged 18 to 25 who attended a university student health service in 2003 were infected with the bacteria without knowing it.

The results suggested approximately 5400 undiagnosed infections among the 200,000 female New Zealanders aged 18 to 25 years -- although this was likely to be an underestimate, researchers said.

Chlamydia, which can lead to pelvic inflammatory disease, ectopic pregnancy and infertility in both men and women, usually has no symptoms.

While the infection persists for months, or even years, those infected will continue to pass it on to their partners.

Of the 715 students who took up the offer of chlamydia testing using a urine sample, 19 women -- or 2.7 per cent -- were found to have the infection.

The study also found that almost 10 per cent (9.3 per cent) of those surveyed never used a condom, 23.3 per cent only used one occasionally, and 43.3 per cent "sometimes" had protected sex.

Among those who reported having tested positive for a sexually transmitted disease previously, condom use was only 19.6 per cent.

Other studies suggest infection rates are even higher -- chlamydia prevalence was 12.2 per cent in pregnant women aged under 25 tested in the Wellington region from 1999 to 2005, and 2.3 per cent among sexually active Christchurch high school students screened in 2000.

Chlamydia infection was also diagnosed in 5.6 per cent of patients visits at New Zealand sexual health clinics in 2003, making it the most commonly reported sexually transmitted infection (STI).

In 2003, laboratory surveillance found an incidence of 613 per 100,000 in Auckland, 739 per 100,000 in the Waikato and Bay of Plenty regions.

The report writers said these rates were high by international standards -- being almost six times higher than those reported in Australia -- but the true prevalence was likely to be even higher.

Furthermore, there was strong evidence that the rate of infection was rising -- with a 65.5 per cent increase in cases presenting to sexual health clinics from 1999 to 2003, and a 25 per cent increase in laboratory diagnosed cases from 2001 to 2003.

Unlike many developed countries, including the United Kingdom, the United States and some European countries, New Zealand does not have screening guidelines for chlamydia.

Although national chlamydia screening had been widely advocated, the writers said more work was needed to prove this would be the most "cost-effective" way of preventing infection.

However, there was no doubt New Zealand needed "an adequately resourced and evidence-based chlamydia control strategy".

- NZPA