© Springer Science+Business Media New York 2013. Chlamydia trachomatis infection (chlamydia) is the most common notifiable bacterial sexually transmitted infection (STI) worldwide. In the United States of America (USA) in 2009, 1,244,180 cases of chlamydia were reported to the Centers for Disease Control and Prevention (CDC), the largest number of cases ever reported to CDC for any notifiable disease . It has been estimated, from population prevalence surveys, that approximately 2 % of sexually active adults aged 18–44 years old in the UK  and 2.2 % (CI, 1.8–2.8 %) of the US population aged 14–39 years  are infected with chlamydia. This level of prevalence in the USA translates into an estimated 2,291,000 (95 % confidence interval, CI, 1,857,000–2,838,000) chlamydia infections each year . Globally, the World Health Organization (WHO) estimates that there are about 92 million new cases of chlamydia each year .