Decrease in number of genital chlamydia cases in Norrbotten, Sweden, October - November 2009: an indirect effect of pandemic influenza A(H1N1)?

A sudden reduction in the number of reported genital chlamydia cases was observed in Norrbotten County, Sweden, during October to November 2009. After exploring other possibilities, such as a reduction in the number of chlamydia tests analysed or a new Chlamydia trachomatis variant that had been undetected in standard laboratory tests, it was found likely that the decrease was an indirect effect of the 2009 influenza A(H1N1) pandemic due to reduced social interactions among young adults.