Sexually transmitted diseases (STDs) have been present among mankind for centuries. In most parts of the world, prevalence is still high despite advances in diagnosing and treating the infections.

Some of the challenges in curbing STDs include:

• The advent of sexual freedom, changing sexual attitudes and the use of oral contraceptives.
• Contraction of the infection while travelling to other countries. Historically, one of the main ways STDs were spread was through sexual contact with sailors who had picked up the infections during their voyages overseas.
• Microbial resistance to what were once effective treatments. For example, many of the bacteria that cause STDs are now resistant to the antibiotic penicillin, which was previously widely used with high success rates.

Epidemiology

Some STDs have a greater worldwide presence than others. Nearly two thirds of all STDs worldwide affect people under the age of 25 years. Of these, another third is less than 20 years of age. The rates are higher among teenage girls than in boys, with girls twice as likely to be infected. Examples of some of the statistics for STDs in the USA in 2011 include:

Chlamydia

The incident rate of Chlamydia infection per 100,000 individuals, was 457.6, an increase of 8% on the 2010 statistic. Individuals with Chlamydia may or may not have symptoms.

Gonorrhea

For gonorrhea the rate per 100,000 individuals was 104.2, an increase of 4% on 2010. Infected people may or may not have symptoms.

Syphilis

For syphilis, the numbers in 2011 remained unchanged from 2010 with an incidence rate per 100,000 individuals of 4.5.

Congenital Syphilis

The incidence rate of congenital syphilis, was 8.5 per 100,000 live births, a decrease of 7% on the 2010 rate.

According to estimates from the Centres for Disease Control and Prevention, 110 million people in the USA were infected with STDs in 2008. Nearly 22.1 million of those with an STD were aged between 15 and 24 years and nearly one quarter of all teenagers are affected with and STD every year.

In the UK, there were nearly 500,000 new cases of STDs diagnosed in 2009. Also in the UK, the vast majority of individuals infected are aged between15 and 24 years. In 2009, around two thirds of new infections diagnosed in women were in those aged under 25 and around half of the infections were in men aged under 25.