**1. Introduction**

*Chlamydia* spp. (order *Chlamydiales*; family *Chlamydiaceae*; genus *Chlamydia*) are obligatory intracellular gram-negative bacteria that cause acute and chronic infections in humans and animals. Genus *Chlamydia* is the sole member of the family *Chlamydiaceae* and includes nine different species. Among them, *C. trachomatis* and *C. pneumoniae* are primarily human pathogens, whereas *C. psitacii*, *Chlamydia abortus,* and *Chlamydia felis* mainly infect animals but occasionally cause zoonotic diseases [1, 2].

Sexually transmitted infections (STIs) are a major health problem with an estimated burden of disease transmission as high as one million new cases per day globally. *C. trachomatis* is one of the most common curable causative agents of STIs and usually affects sexually active young adults and adolescents. The pathogen is the causative agent of a disease called chlamydia, which constitutes a broad spectrum of illnesses varying from asymptomatic infection to severe genital infection leading

to infertility, especially in women. Apart from the spread by sexual activity, direct personal contact with shared contaminated items may also cause a chronic ocular infection called trachoma and result in blindness if left untreated. Finally, perinatal transmission of the agent is another undesired entity with adverse clinical outcomes. *C. pneumoniae* and *C. psittaci* are two other pathogens in the genus *Chlamydia* and are responsible for acute respiratory tract infections and febrile illness in humans. However, *C. trachomatis* draws much attention as chlamydial infections account for significant morbidity worldwide. The global control of chlamydia faces some difficulties such as diagnostic challenges, social stigma, and the necessity of routine screening programs due to the asymptomatic course of the disease also concerns about treatment adherence and antibiotic efficacy in extra-genital involvements. The incidence, pathophysiology, and diagnostic methods of chlamydial infections are discussed in detail in the previous chapters. The purpose of this chapter is to elucidate the management of human chlamydial infections in every aspect including antibiotic susceptibility and resistance mechanisms, treatment recommendations for ocular infections, genito-urinary and respiratory tract infections, and also the management of sex partners, pregnant women, neonates, and children according to the latest data.
