Many New Zealanders have had chlamydia without realising it, Dunedin Study research has shown.
The findings from the Dunedin Multidisciplinary Health and Development Study show chlamydia, which can affect fertility in women, is more common in New Zealand than previously thought.
Based on the findings, the authors estimated one in three New Zealand women have had the sexually transmitted infection (STI) by the age of 38 as have one in five men.
Lead author Dr Antoinette Righarts, of the department of preventive and social medicine at the Dunedin School of Medicine, said the rate of infection was possibly even higher among people born more recently than those in 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," Dr Righarts said.
A unique aspect of the study was assessing past chlamydia infection, Dr Righarts said.
"Blood was tested for antibodies, which provides evidence of past infection, with an assay recently developed by Prof 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."
Fewer than half of those in the study had self-reported having chlamydia, which indicated many New Zealanders had the disease without ever realising.
It typically resolved itself within two years, but in that time people could spread it.
The results highlighted the importance of using condoms and testing for STIs.
Testing was particularly important for people entering into new relationships, even if they were over the age of 25.
Often information highlighting the importance of testing was aimed at younger people, which could cause older people entering new relationships to think they were not at risk, Dr Righarts said.
Because the testing was better at detecting past infection in women, it was possible the difference in infection rates between men and women might not be as large as they had found.
Co-author Dr Paddy Horner, from the University of Bristol, said high chlamydia rates were concerning given the impact on women’s reproductive health.
"Recent estimates in the United Kingdom indicate 17% of infections in women progress to pelvic inflammatory disease, with 0.5% of women becoming infertile and 0.2% having an ectopic pregnancy as a consequence of irreversible damage to the fallopian tubes," he said.
