Virtual Medical Centre

STI (Sexually Transmitted Infection) Protection

• What are sexually transmitted infections (STIs)?
• Who gets STIs?
• Predisposing factors of STIs

What are sexually transmitted infections (STIs)?

Sexually transmitted infections (STIs), as the name suggests, are a group of bacteria and viruses which can be, and most commonly are, transmitted through sexual contact, including vaginal, anal and oral sex. Many STIs also spread through other means (e.g. blood transmission). 

As a group of diseases, the infections are extremely varied. For example, some STIs result in symptoms such as genital discharges or abnormal growths in the genital area (e.g. herpes); some usually have no symptoms (e.g. chlamydia); and others have no apparent effect on the body but create a pathway for other deadly diseases to occur. Human immunodeficiency virus (HIV) is the causal agent of acquired immune deficiency syndrome (AIDS).

Some of the most commonly occurring STIs, and those which are a considerable health concern in Australia, include:

• Human immunodeficiency virus (HIV): HIV is a retrovirus transmitted through blood, breast milk and sexual fluids. It leads to AIDS, an immune deficiency syndrome for which there is no cure. HIV typically remains dormant for many years before AIDS develops (e.g. ten years). Individuals who become infected with HIV ultimately die of coexisting infections following the onset of immune deficiency.
• Human papilloma virus (HPV): HPV is an STI that causes warts on the genitals and other sites. It is often asymptomatic (but contagious) for considerable periods of time. Specific subtypes of the virus are the causal agents in cervical and anal cancer.
• Herpes simplex virus (HSV): There are two types of HSV: type 1 and type 2. They cause the condition commonly known as genital herpes, characterised by lesions on the genitals, and/or sores and blisters around the mouth. The symptoms of the disease are easily treatable, but once infected with herpes simplex, individuals will carry the virus throughout their lives and symptomatic outbreaks may occur periodically.
• Hepatitis B: Heptatis B virus affects liver function and typically leads to either acute or chronic inflammation of the liver. While the disease can be sexually transmitted, evidence suggests that in Australia it is most commonly acquired through intravenous drug use.
• Chlamydia: Chlamydia is the most commonly occurring STI in Australia, and the most commonly reported of all notifiable infections in Australia. It is caused by the bacteria Chlamydia trachomatis. Although it is often asymptomatic, it may also lead to genital infections (e.g. pelvic inflammatory disease), and discharges and blindness in neonates born to women with asymptomatic chlamydia. Infertility can result if chlamydia is left untreated in women.
• Gonorrhoea: Gonorrhoea is a bacterial infection of Neisseria gonorrhoea. It typically causes genital infections (e.g. pelvic inflammatory disease) and discharges. If left untreated, it can cause infertility in women and increases the risk of pregnancy complications (e.g. ectopic pregnancy).
• Syphilis: Syphilis is a bacterial infection caused by Treponema pallidum. It sometimes remains asymptomatic, but can also result in genital lesions, ulcers and discharges. The infection typically goes through infectious and non-infectious stages, in which symptoms resolve as the bacteria lie dormant. Syphilis is primarily transmitted sexually; it can also be transmitted from a pregnant woman to her foetus during pregnancy. Untreated syphilis can result in serious neurological and cardiovascular disorders, and can also have a severe impact on the developing foetus if transmitted during pregnancy.
• Trichomoniasis: Trichomoniasis is a bacterial infestation of Trichomonas vaginalis organisms that affects women. It typically results in a yellow/green frothy discharge, though it can also be asymptomatic.

Who gets STIs?

Globally, there are large differences in the incidence and prevalence of STIs. For example, in parts of southern Africa where STIs are very common, the prevalence of HIV is as high as 25% (amongst 16–59 years olds), and up to 19% of all pregnant women are carriers of other STIs (e.g. syphilis, chlamydia). Infection rates are much lower in Australia, but STIs remain a considerable public health burden, despite the availability of effective methods to prevent and treat many conditions. Evidence suggests that the incidence of a number of STIs has risen in recent years.

There is considerable variation in the incidence of particular STIs in Australia:

• HIV: 1,051 new cases of HIV were diagnosed in Australia in 2007. The annual incidence of HIV has increased by almost 50% since 1999, when 718 new cases were diagnosed. It is estimated that 85% of incident cases of HIV are diagnosed in homosexually active men. The estimated number of people currently living with HIV infection in Australia is 16,692.
• HPV: The most common sexually transmissible infection in developed countries. There is no data regarding the incidence of HPV in Australia, as it is not a notifiable infection.
• HSV: 2.1% of Australian men and 2.5% of women reported experiencing genital herpes at some point in their life to the Sex in Australia survey. The annual prevalence is estimated at 0.8% for men and 1.1% for women.
• Hepatitis B: 0.7% of Australian men and women reported infection with the hepatitis B virus at some point in their life. The annual incidence is less than 0.1%. Evidence suggests that, in Australia, this condition is most commonly transmitted through intravenous drug use and not sexual activity.
• Chlamydia: 51,867 new cases of chlamydia (or 245 cases per 100,000 people) were reported in 2007, making this the most commonly occurring notifiable infection in Australia. The incidence of chlamydia has increased steadily in Australia in the past decade; there was a 7% increase in cases of chlamydia from 2006 to 2007. The Sex in Australia survey reported that 1.7% of male and 3.1% of female respondents had ever experienced chlamydia, while 0.2% of men and women had experienced the disease in the year prior to being surveyed.
• Gonorrhoea: 36.1 cases per 100,000 people were diagnosed with gonorrhoea in 2007. In the Sex in Australia survey, 2.2% of men and 0.6% of women reported having ever had gonorrhoea.
• Syphilis: Around 2,500 cases of syphilis were reported in Australia in 2004 (3.1/100,000). The rate of incident cases more than doubled in 2006–07, when 6.6 cases per 100,000 people were reported. The increase was mainly due to increasing incidence amongst homosexually active men. The Sex in Australia survey reported that 0.6% of male and 0.1% of female respondents had ever experienced syphilis.
• Trichomoniasis: There are no accurate data available regarding the prevalence of trichomoniasis as the disease is not notifiable in Australia, though evidence suggests that the incidence has decreased markedly in recent years. The Sex in Australia survey reported a lifetime prevalence of 0.8% and an annual incidence of less than 0.1% for women.
• Genital warts: Genital warts are a symptom of a range of STIs, including HPV and HSV. 4.0% and 4.4% of Australian men and women respectively reported having genital warts at some time in their life, while 0.5% of men and 0.3% of women reported experiencing warts in the past year.

Predisposing factors of STIs

The prominence of sexually transmitted infections varies depending on the specific infections. However, as a group of infections, particular groups of people (characterised either by demographic or behavioural features) are more likely to experience STIs than others. In Australia, factors which are associated with an increased risk of STIs include:

• Indigenous Australian ethnicity: Rates of STIs reported for Indigenous Australians are significantly higher than for non-Indigenous Australians. In 2004, Indigenous Australians had an 8-fold higher risk of chlamydia, an 80-fold higher risk of gonorrhoea, and a 100-fold greater risk of syphilis.
• Gender: Men are more likely to have experienced STIs than women. The lifetime experience of any STI in men is 20.2%, and for women is 16.9%.
• Sexual orientation: Men who identify as homosexual are more than 6 times more likely to have experienced an STI in their lifetime than men who identify as heterosexual. Amongst women, those who identify as bisexual are more than 3 times more likely to have experienced STIs at some point in the past than their heterosexually identifying counterparts.
• Injecting drug use: Injecting drug use is a risk factor for lifetime and past year experience of STIs. Men and women are roughly three and five times more likely, respectively, to experience an STI if they use intravenous drugs.
• Speaking English at home: Individuals who speak a language other than English at home are half as likely to experience an STI in their lifetime, compared to those who speak English at home.
• Education: Women who attend post secondary education are 1.33 times more likely to experience an STI in their lifetime.
• Working as a sex worker: Both men and women who work in the sex industry have an increased risk of STI. Men are nearly four times more likely, and women nine times more likely, to have ever experienced an STI if they work in the sex industry.
• Paying for sex: Men who pay for sex are over three times more likely to have experienced an STI in their lifetime, and more than twice as likely to have experienced an STI in the past year, than men who have never paid for sex.
• Working in a managerial or professional occupation: Men and women with professional or managerial occupations are 1.25 times more likely to have experienced an STI in their lifetime than their counterparts working in white or blue collar occupations.
• Greater number of sexual partners: Respondents to the Sex in Australia survey who had ever experienced an STI, had, on average, a significantly greater number of sexual partners than respondents who had never experienced an STI (for men, 41.5 vs 12.2; for women, 16.2 vs 5.5). Men and women who have experienced an STI in the past year are three times more likely to have had more than one partner in the previous year.
• Non-use or inconsistent use of condoms: Not using condoms, or using them inconsistently, is an important risk factor for individuals who have sex with multiple partners, or with a single partner who has an STI.
• Age: Young people, particularly those aged 15–24, are more likely to contract STIs than their older counterparts. Of all cases of chlamydia newly diagnosed in Australian women in 2004, 70% were in women younger than 25.
• Imprisonment: Several studies have reported rates of STI in prisoner populations higher than those in the general population. One study reported that 2% of imprisoned men and 1% of women had syphilis. Another reported that some 58% of female inmates were positive for HSV2 antibodies.
• Intimate partner violence: Women who experience intimate partner violence are more likely to contract HIV or another STI. A study of teenage women in America found that those who experienced violence in their intimate relationships were 2.6 times more likely to have been diagnosed with an STI. An Australian survey found that women who experienced partner violence were more likely to have genital herpes than those who did not.

Related Diseases:

• Syphilis
• HIV AIDS (Human Immune Deficiency Virus & Acquired Immune Deficiency Syndrome)
• Hepatitis C virus (HCV)
• Psittacosis (Chlamydial pneumonia, Ornithosis, Chlamydia psittaci, Parrot fever)
• Chlamydia (trachomatis, pneumoniae, psittacci, pecorum)
• Gonorrhoea (GC)

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Article Dates:

Created: 27/4/2006

Modified: 23/7/2009