Laboratory surveillance of urogenital Chlamydia trachomatis infections in Denmark 1988-2007.

In 1994 laboratory reporting of urogenital chlamydia was integrated in the countrywide notification system for infectious diseases. Previously (1988-1993), laboratory confirmed cases had been reported on a voluntary basis. The applied laboratory technologies changed significantly: in 1988, 48% of cases were diagnosed by culture; in 1994, 88% by enzyme immunoassays; and since 2004 more than 99% by nucleic acid amplification tests. The proportions of chlamydia-positive men diagnosed by testing urine were <1% in 1994, 10% in 2001 and 75% in 2007. From 1994 to 2002 the annual incidence rates of chlamydia per 100,000 population among women were around 350-400 and then increased to 586 in 2007. Among men the incidence rate rose from 125 in 1994 to 358 in 2007. In conclusion, the annual incidence rates of urogenital chlamydia remained high and possibly increasing during a 14-y period (1994-2007), with a high testing activity, improving technologies and countrywide information campaigns. The observed increase is likely to be associated with the introduction of more sensitive diagnostic methods and with increasing testing of men. A possible change in target groups from low- to high-prevalence could not be assessed due to lack of information about persons being tested.