EPIDEMIOLOGY OF CHLAMYDIA TRACHOMATIS INFECTION IN FINLAND DURING 1983–2009

Abstract

Chlamydia trachomatis epidemic continues at a slowly, albeit steadily increasing rate in the Western world despite health education, easy/user-friendly diagnostic measures, and effective treatment. In Finland, 8,031 and 13,227 C.trachomatis infections were reported in 1995 and 2012, respectively. Over half of the Chlamydia cases were diagnosed among young women, who suffer from the Chlamydia-related complications such as infertility many years after initial infection. The rates of all but first of the following major Chlamydia-related complications: cervical intraepithelial neoplasia, ectopic pregnancy, hospitalized pelvic inflammatory disease, tubal factor infertility have, however, decreased since the 1990s. The aim of this study was to clarify the discordance between the apparently increasing incidence of C. trachomatis and decreasing C.trachomatis IgG antibody rates (seroprevalence). The study material consisted of a random subsample of first trimester serum samples of 7,999 women from the population-based Finnish Maternity Cohort (FMC) registry from 1983 to 2005, and 147,148 women and men with a total of 177,138 C. trachomatis genital infections reported to the Finnish National Infectious Diseases Registry (NIDR) during 1995–2009. Both registries are maintained by the National Institute for Health and Welfare (THL). Serum IgG antibodies were measured by a C.trachomatis major outer membrane proteinspecific peptide enzyme immunoassay (EIA) and the standard micro-immunofluorescence (MIF) method. We found that while C. trachomatis seroprevalences decreased >50% among fertile-aged women the seroconversion rates (seroincidences) were comparable to the NIDR reported rates. The numbers of annual repeated C. trachomatis infection in the NIDR increased until 2009 by 49% in women and 39% in men. In 2009, about 25% of the females and 20% of the males had had an earlier C.trachomatis infection. During the whole follow-up time, 34% of all the repeat diagnoses occurred within 12 months. Most of the first infections were observed among females and males under 25 years of age, but the numbers of repeated chlamydial infections increased up to the age of 30 years. The C. trachomatis serotype distribution changed between the 1980s and 1990s, but the leading 1980 serotypes bounced back by 2005. The numbers of women with multiple serotype infections peaked in the 1990s, and serotypes G and J were temporarily replaced by serotypes E and D. In conclusion, the serological observations fit the polymerase chain reaction (PCR) -based data on C. trachomatis epidemiology. The observed increases in the repeated chlamydial infections among young women and men comply with increasing sexual risk-taking behaviour in Finland. Our observations help to understand the discrepancy between C. trachomatis occurrence and sequelae rates as the overall C. trachomatis infection burden in the population may be decreasing despite the increasing incidence trend.