Understanding the burden of Chlamydia trachomatis in populations is based primarily on studies of prevalence of current infection, measured using sensitive and specific nucleic acid amplification tests on genital or urinary specimens. Such studies have produced widely varying results, but most have emphasised the high prevalence in young, sexually active women with many fewer studies in men. 1 Studies have frequently been based on clinic populations, which suffer from problems of selection bias (toward those at highest risk) and limited demographic and behavioural data. The few studies based on random and representative population samples have generally demonstrated lower prevalence and increased risk linked to increasing numbers of sexual partners. 2 Studies of Chlamydia incidence in population samples are few and far between. Data from national surveillance programmes consistently show rising rates of diagnosed infection in most developed countries over the last decade. But this cannot measure true incidence of infection because they are biased by the introduction and wider spread use of new sensitive tests leading to increased diagnosis of asymptomatic infection. All these studies measure current infection. They cannot account for past exposure or measure cumulative risk of infection over time, that screening programmes aim to minimise.
In this issue, Paavonen et al report on C. trachomatis antibody seroprevalence in a stratified probability sample of 8000 sera from a large Finnish population serum bank.2,3 Participants were women under 29, having at least two pregnancies. The paper illustrates an approach which could potentially be used more widely. The paper assesses prevalence of past exposure to genital C. trachomatis and explores changes over time by comparing age specific prevalence at different time points.
- Antibody tests