What is the Most Common STD in Australia?

Sexually transmitted diseases are a serious public health problem. Worldwide, it is estimated that about 1 million of sexually transmitted infections are acquired every day (1). According to the WHO estimations for the year 2016, there were 376 million new infections with one of the following sexually transmitted diseases: trichomoniasis (156 million), chlamydia (127 million), gonorrhoea (87 million), and syphilis (6.3 million) (1). Scientific data about Australia show that almost 16% of Australians report having a sexually transmitted infection in their lifetime (2).

Available scientific data including countries like the United Kingdom, the United States, and Australia suggest that between 3 – 5% of people under the age of 30 years will have a Chlamydia infection at some point of their life. Chlamydia trachomatis is a Gram-negative, bacterial pathogen (3).

Chlamydia infections in Australia

According to Australian data, Chlamydia is the most frequent among sexually transmitted infections. In 2017, the total of chlamydia notifications in Australia was 100 775 (4).

On the other hand, the second most common sexually transmitted disease in Australia for the year 2017 was gonorrhoea with more than 28.000 notifications.

There is a significant increase in the chlamydia notification rates between 1999 and 2011—from 74 to 363 infections/100,000 people. Since 2011, the increase was slower until 2016 when it reached the peak of 385 infections per 100,000 people. In 2017 the rate was slightly lower and decreased to 379 infections per 100,000 people (5).

The annual rate of notification of chlamydia in the Aboriginal and Torres Strait Islander population including Western Australia, South Australia, Queensland and Northern Territory, was 2.8 times higher compared to the non‑Indigenous population in 2017 (1193.9 vs 427.0 per 100 000) (4).

Age -Sex differences

It is worth of noticing that almost ¾ of the 2017 chlamydia notifications were among people aged 15–29 years. The highest rates were noticed in the age groups 20–24 years (1975.4 per 100 000), while in the age group of 15–19 (1185.3 per 100000) and 25–29 (1180.9 per 100000). In 2017, almost half (52%) of chlamydia notifications were in females and (72%) were in people residing in major cities (4).

Ways of infection with Chlamydia

Chlamydia can be transmitted sexually with the vagina, penis, anus, or mouth of an infected partner.  An additional way of transmission is during the childbirth from an infected mother to the newborn and can result to conditions like conjunctivitis or pneumonia at the time of delivery (6).

Symptoms of Chlamydia

Symptoms of Chlamydia

In females, the urethra and cervix are infected first. The symptoms that you can notice are related to cervicitis or urethritis, meaning endocervical bleeding or increased urinary frequency, pyuria and difficulty to urinate. On the other hand, men infected by chlamydia experience urethritis- related symptoms like mucoid urethral discharge, burning sensation during urination (7). Additionally, some men might develop epididymitis and feel testicular pain.

Another category of symptoms that can be noticed in both genders are related to proctitis characterised by bleeding and rectal pain. Specifically, chlamydia can infect the rectum either by direct sexual contact (in both genders) or spread from the cervix and vagina in infected females (8).  

Untreated chlamydia infections are more dangerous for females. There is the danger of pelvic inflammatory disease which is found in more than 10% of untreated chlamydia infected females (9-10). In pregnant women, even without sexual contact, the untreated chlamydia can be dangerous because it can lead to preterm delivery or conjunctivitis and pneumonia in the newborn (11).

Testing for chlamydia

Testing for chlamydia

Any individual with any of the following risk factors should be tested routinely for Chlamydia: sexually active and under 30 years of age, mucopurulent cervicitis, women with over 1 sex partner during the last 3 months, or inconsistent use of barrier contraception while in a non-monogamous relationship. HIV-positive people and males who have sex with men are an identified group of people with increased risk of infection with chlamydia. Moreover, men who change regularly sexual partners are also advised to be tested. In Australia, Chlamydia screening is offered to all women at their first antenatal visit, and a re-screening is recommended at the 36 weeks of gestation for high the risk women (12).

According to the Australian Sexually Transmitted Diseases Management Guidelines the test should be either first pass urine testing or vaginal, endocervical, or anorectal swabs (if the woman has anal sex or anorectal symptoms) and advice consideration of self-collection of samples by pregnant women (13).

Treatment for Chlamydia

Treatment for Chlamydia

The standard treatment for chlamydia is antibiotics. In case of uncomplicated genital infections in non-pregnant adolescents and adults, Doxycycline is the recommended antibiotic for 7 days. Alternatively, Azithromycin is available in a single dose (13-14).

Take away message

Chlamydia is the most common sexually transmitted disease in Australia. Prevention is always better than treatment, so it’s important to be tested for chlamydia even without symptoms. People between the ages 15-29, especially when they change sexual partners in a short period of time should have always in mind to test for chlamydia. Antibiotics can fully treat the disease; therefore, it is a matter of finding out early about the infection to manage to avoid any possible complications of untreated chlamydia, reinfection or further transmission.


1) Who.int. 2019. Sexually Transmitted Infections (Stis). [online] Available at: <https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-(stis)> [Accessed 21 December 2020].

2) n.d. [online] Available at: <https://www.health.gov.au/health-topics/sexual-health> [Accessed 21 December 2020].

3) Menon S, Timms P, Allan JA, Alexander K, Rombauts L, Horner P, Keltz M, Hocking J, Huston WM. Human and Pathogen Factors Associated with Chlamydia trachomatis-Related Infertility in Women. Clin Microbiol Rev. 2015 Oct;28(4):969-85. doi: 10.1128/CMR.00035-15.

4) Kirby.unsw.edu.au. 2019. HIV, Viral Hepatitis And Sexually Transmissible Infections In Australia: Annual Surveillance Report 2018 | UNSW – The Kirby Institute For Infection And Immunity In Society. [online] Available at: <https://kirby.unsw.edu.au/report/hiv-viral-hepatitis-and-sexually-transmissible-infections-australia-annual-surveillance> [Accessed 20 December 2020].

5) Australian Institute of Health and Welfare. 2018. Australia’s Health 2018, Incidence Of Sexually Transmissible Infections And Blood-Borne Viruses – Australian Institute Of Health And Welfare. [online] Available at: <https://www.aihw.gov.au/reports/australias-health/australias-health-2018/contents/indicators-of-australias-health/sexually-transmissible-infections-bloodborne-virus> [Accessed 21 December 2020].

6) Schachter J, Grossman M, Sweet RL, Holt J, Jordan C, Bishop E. Prospective study of perinatal transmission of Chlamydia trachomatis. JAMA : the journal of the American Medical Association 1986;255:3374-7.

7) Torrone E, Papp J, Weinstock H. Prevalence of Chlamydia trachomatis Genital Infection Among Persons Aged 14–39 Years — United States, 2007–2012. MMWR 2014;63:834-8.

 8) Bradshaw, C., Tabrizi, S., Read, T., Garland, S., Hopkins, C., Moss, L. and Fairley, C., 2006. Etiologies of Nongonococcal Urethritis: Bacteria, Viruses, and the Association with Orogenital Exposure. The Journal of Infectious Diseases, 193(3), pp.336-345.

9) Oakeshott P , Kerry S , Aghaizu A , Atherton H , Hay S , Taylor-Robinson D , Simms I , Hay P. 2010. Randomised controlled trial of screening for Chlamydia trachomatis to prevent pelvic inflammatory disease: the POPI (prevention of pelvic infection) trial. BMJ 340:c1642. doi:10.1136/bmj.c1642

10)  Cates W, Jr., Wasserheit JN. Genital chlamydial infections: epidemiology and reproductive sequelae. American journal of obstetrics and gynecology 1991;164:1771-81.

11) Rours GI, Duijts L, Moll HA, et al. Chlamydia trachomatis infection during pregnancy associated with preterm delivery: a population-based prospective cohort study. European journal of epidemiology 2011;26:493-502.

12) Kemh.health.wa.gov.au. 2020. [online] Available at: <https://www.kemh.health.wa.gov.au/~/media/Files/Hospitals/WNHS/For%20health%20professionals/Clinical%20guidelines/OG/WNHS.OG.SexuallyTransmittedInfections-ChlamydiainPregnancy.pdf> [Accessed 20 December 2020].

13) User, S., 2020. Chlamydia – Australian STI Management Guidelines. [online] Sti.guidelines.org.au. Available at: <http://www.sti.guidelines.org.au/sexually-transmissible-infections/chlamydia> [Accessed 20 December 2020]. 14) O’Connell, C. and Ferone, M., 2016. Chlamydia trachomatis Genital Infections. Microbial Cell, 3(9), pp.390-403.