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Clocktower.Tuesday 30 May 2017 10:46am

Chlamydia dunedin study image

One in three New Zealand women have had the sexually transmitted infection (STI) chlamydia by the age of 38 as have one in five men, based on estimates from a new study.

The latest findings from the Dunedin Multidisciplinary Health and Development Study, published in Sexually Transmitted Diseases, show chlamydia, which can affect fertility in women, is more common here than previously thought.

The “Dunedin Study”, as it is widely known, is a longitudinal study of about 1,000 individuals born in Dunedin between April 1972 and March 1973.

Lead author Dr Antoinette Righarts, of the Department of Preventive and Social Medicine at the Dunedin School of Medicine, says the rate of infection is possibly even higher in younger people, who were born more recently than the study group.

“This high cumulative exposure we found at age 38 was mainly due to infections occurring when this cohort were teenagers and young adults, which was before New Zealand - and other high-income countries - experienced a marked increase in chlamydia in the late 1990s.”

A unique aspect of the study was assessing past chlamydia infection, Dr Righarts says.

“Blood was tested for antibodies, which provides evidence of past infection, with an assay recently developed by Professor Myra McClure and colleagues at Imperial College, University of London. As chlamydial infection is frequently not recognised, relying solely on reports of diagnosed infection underestimates how common it is.

“The assay, however, is better at detecting past infection in women than men, which is one reason for finding more women than men had been infected. So the true gender difference might not be as marked as we found.”

Co-author Dr Paddy Horner, from the University of Bristol, says high chlamydia rates are concerning for the impact on women's reproductive health.

“Recent estimates in the United Kingdom indicate 17 per cent of infections in women progress to pelvic inflammatory disease, with 0.5 per cent of women becoming infertile and 0.2 per cent having an ectopic pregnancy as a consequence of irreversible damage to the fallopian tubes."

Otago University Honorary Research Associate Professor Nigel Dickson, also of the Department of Preventive and Social Medicine, says data collected on several occasions allowed an examination of the rates of infection at various ages.

“We showed that overall the chlamydia rates in the cohort were lower after age 26, but this decline was mainly because fewer individuals had multiple sexual partners as they got older.”

Hamilton-based sexual health specialist and study team member Dr Jane Morgan says for clinicians and policy makers the findings highlight that primary prevention with condoms and early detection through testing needs to be aimed at the wide age group of men and women whose behaviour puts them at increased risk, “not just 'young people'”.

The study of sexual and reproductive health was funded by the Health Research Council of New Zealand.

For more information, please contact:

Dr Antoinette Righarts
Department of Preventive and Social Medicine, Dunedin School of Medicine

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