Reasons for the sharp increase of genital chlamydia infections reported in the first months of 2007 in Sweden

After a continuous increase in the reported chlamydia incidence over the past 10 years in Sweden, the incidence decreased by 2% in 2006. A new genetic variant of Chlamydia trachomatis (nvCT) was discovered in Sweden in October 2006 that could not be detected by some of the commonly used diagnostic tests, which led to underreporting of chlamydia cases. This variant has also been called 'swCT' by some authors. After the switch at the end of 2006 to other diagnostic tests that can detect nvCT, the reported incidence rose considerably (75 per 100,000 population) in the beginning of 2007. The objective of this study was to explore alternative explanations for this increase and to propose further action if needed.