Background Chlamydia trachomatis is the most commonly reported STI in Europe. We present the epidemiology of C trachomatis in Norway from 1988 to 2009.
Methods Until 2004 the Norwegian Surveillance system of infectious diseases (MSIS) captured the total number of diagnosed cases and tests performed from all diagnosing laboratories. From 2005 date of diagnosis, birth year, sex and municipality of living has been included for each diagnosed case. We calculated testing rates, incidence rates (IR) and incidence rate ratios (IRR) with 95% CIs.
Results The IR of diagnosed cases was at its lowest in 1995 (287/100 000) and increased yearly until 2008 (467/100 000). The testing rate reached a peak in 1991 (8000/100 000), decreased towards year 2000 (5300/100 000) and has been stable until 2009 (5500/100 000). The proportion positive tests has increased yearly from 4.1 % in 1993 to 8.6 % in 2009. The highest mean annual IR was found in the age group 20–24 years for both men (2983/100 000) and women (4818/100 000). Women were 1.6 times more likely (IRR of 1.6, 95% CI 1.6 to 1.62) to be diagnosed with C trachomatis compared to men, and inhabitants in the two most northern regions were more likely to be diagnosed than the rest of the country (IRR 1.6, 95% CI 1.5 to 1.7).
Conclusion The IR of C trachomatis in Norway is increasing while the testing rate is stable. More detailed data of the case mix among the tested subjects is needed to interpret the observed trends.
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