**2. Epidemiology**

In 2016, the World Health Organization (WHO) estimated the global prevalence and incidence of bacterial sexually transmitted diseases in population from 15 to 49 years of age; for this estimation, almost 130 studies were reviewed. The estimated prevalence for Chlamydia, Trichomonas, Syphilis, and Gonorrhea taking into account the prevalence data from 2009 to 2016 and per gender is presented in **Table 1**. The prevalence of these diseases is inversely proportional to the income in the countries and regions; with higher incomes, the prevalence goes lower. Incidence of these pathogens per gender is presented in **Table 2** [1].

In the 2020 National Surveillance of STDs in the United States, a total of 1,579,885 cases of Chlamydia trachomatis infection were reported to the CDC, making it the most common notifiable sexually transmitted infection in the United States for that year. This case count corresponds to a rate of 481.3 per 100,000 population; for syphilis, 133,945 cases were reported including 41,655 cases of primary and secondary syphilis, the most infectious stages of the disease. Since 2000, rates of primary and secondary syphilis have increased among men, likely attributable to increases in cases among men having sex with men (MSM). For Gonorrhea, a total of 677,769 cases were reported do the CDC, making it the second most common notifiable sexually transmitted infection in the United States for that year. In the case of Trichomoniasis, in 2018, 2.6 million infections were reported; this pathogen can increase the risk of HIV and preterm deliveries with low birth weight. The prevalence of Trichomonas vaginalis in the United States is 2.1% among women aged 14–59 and 0.5% among men (representative sample from 2013 to2016). If we compare 2016 report with the 2020 report, it seems that there was a decrease in the number of cases; but this is indeed an artifact due to COVID-19 pandemic. Even in the face of COVID-19, an important number of STDs were reported; [2, 3] number of cases by selected groups of age and from this survey (Trichomoniasis was not included) are presented in **Table 3**.

From **Table 3**, Chlamydia, Gonorrhea, and Syphilis cases start rising at 15 years of age; with the highest peak from 20 to 24 years of age; 25–29 years, it is still higher, and the cases start to decline at 30 years of age and keep decreasing. This epidemiological


**Table 1.**

*2016 WHO prevalence estimates of chlamydia, gonorrhea, Trichomoniasis, and syphilis, global by gender.*


**Table 2.**

*2016 WHO incidence estimates of chlamydia, gonorrhea, Trichomoniasis, and syphilis, global by gender.*
