Sexually transmitted infections: symptoms, transmission, prevention
STIs are increasing worldwide and many infections can occur without symptoms
According to the Centers for Disease Control and Prevention, the number of sexually transmitted infections (STIs) has been increasing, with no sign of slowing down. In 2022 alone, 2.5 million cases of chlamydia, gonorrhoea and syphilis were reported.¹
According to the World Health Organization (WHO), around 1 million sexually transmitted infections are acquired every day, most of which are asymptomatic.²
What are sexually transmitted infections?
STIs can be caused by viruses, bacteria and other microorganisms
The term STI refers to sexually transmitted infections caused by viruses, bacteria or other microorganisms.
The term STI is now generally preferred to STD, or sexually transmitted disease, because the word “disease” implies the presence of symptoms or observable signs.
As many STIs can remain asymptomatic both initially and during the development and transmission of the infection, the scientific community increasingly uses the term sexually transmitted infection.⁵
What is the difference between an STI and an STD?
An infection can be present and transmitted even when there are no symptoms
The terms STI and STD describe a range of conditions that can be transmitted through:
Unprotected vaginal, oral or anal sex
Blood contact
Skin-to-skin contact or contact with lesions, as may occur with human papillomavirus (HPV), herpes or mpox
Vertical transmission from mother to child, as may occur with HIV, syphilis or viral hepatitis
The term STD is less broad because it assumes that the infected person has developed signs or symptoms of disease.
An STI may be present without causing disease or symptoms. A person can therefore carry and transmit an infection without knowing it.⁵
For this reason, the term STI is now generally preferred.
How are sexually transmitted infections transmitted?
More than 30 different microorganisms can be transmitted through sexual contact
Oral, vaginal or anal sexual contact can transmit more than 30 different bacteria, viruses and parasites.
Some can also be transmitted during pregnancy, childbirth or breastfeeding.²
Eight pathogens are commonly associated with sexually transmitted infections. Four of these are currently curable:
Syphilis
Gonorrhoea
Chlamydia
Trichomoniasis
Other infections do not currently have a curative treatment, including HIV.²
What causes sexually transmitted infections?
Transmission commonly occurs through sexual contact and infected bodily fluids
STIs have different causes, most commonly the transmission of pathogenic microorganisms — viruses, bacteria or parasites — from one person to another during sexual contact.
Direct contact with infected bodily fluids such as blood, breast milk, semen, vaginal fluid and urethral discharge is one of the principal routes of transmission.³ ⁵
A sexually transmitted infection may progress to symptomatic disease if the infection damages cells and disrupts normal bodily functions.³
What are the most common symptoms of STIs?
Many infections cause no symptoms, while others can produce a wide range of signs
When symptoms occur, sexually transmitted infections may cause:³
Pain or discomfort during sexual activity or frequent urination
Sores, swelling or skin rashes around the vagina, penis, testicles, anus, buttocks, thighs or mouth
Unusual discharge or bleeding from the penis or vagina
Painful or swollen testicles
Itching in the genital area
Fever
Fatigue
Nausea
Weight loss
Swollen lymph nodes or lumps in the body
What complications can STIs cause?
Early identification and treatment can help prevent serious long-term consequences
STIs can be transmitted even when there are no obvious symptoms.
Identifying and treating infections early is therefore important to reduce the risk of future health problems, some of which may be irreversible.
Possible complications include:⁶
Pregnancy-related complications
Eye inflammation
Arthritis
Pelvic inflammatory disease
Infertility
Heart disease
Certain cancers, including cervical and rectal cancers associated with HPV
How are sexually transmitted infections treated?
Treatment depends on the microorganism causing the infection
Not all sexually transmitted infections can be cured, and it may not always be possible to reverse damage that has already occurred.
Depending on the infection, treatment may include:
Antibiotics
Other oral or topical medicines
Surgical procedures
Laser procedures
Behavioural measures, such as avoiding sexual contact until treatment has been completed
Common bacterial infections such as chlamydia, gonorrhoea and syphilis, as well as parasitic infections such as trichomoniasis, can be treated with appropriate antimicrobial therapy.² ³
For infections such as herpes simplex, hepatitis B and HIV, treatment may include antiviral medicines for herpes and hepatitis B or antiretroviral therapy for HIV.² ³
Can sexually transmitted infections be prevented?
Several measures can significantly reduce the risk of transmission
The only way to eliminate the risk of acquiring an STI through sexual activity completely is sexual abstinence.
However, several measures can substantially reduce the risk of infection:³ ⁷
Talk openly with sexual partners about testing and protection
Have regular medical examinations and appropriate STI testing when indicated
Use condoms during vaginal, anal and oral sex
Receive recommended vaccinations against infections such as HPV and hepatitis B
In situations involving potential HIV exposure, discuss pre-exposure prophylaxis (PrEP) with a healthcare professional
After a potential HIV exposure, seek medical care promptly to assess whether post-exposure prophylaxis (PEP) is appropriate
Sexually transmitted infections can cause serious health problems, and some cannot be cured. Awareness, prevention and appropriate medical follow-up therefore remain essential.
Sources
Scientific and medical references
Centers for Disease Control and Prevention. (2022). Preliminary data show 2.5 million reported cases of chlamydia, gonorrhea, and syphilis in 2021.
https://www.cdc.gov/std/statistics/2022/default.htmWorld Health Organization. (2022). Sexually transmitted infections (STIs).
https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-(stis)Healthline. (2022). Everything You Need to Know About Sexually Transmitted Diseases.
https://www.healthline.com/health/sexually-transmitted-diseasesServiço Nacional de Saúde. (2020). Testes rápidos de rastreio de infeções por VIH, VHB e VHC.
https://www.sns24.gov.pt/guia/testes-de-rastreio-de-infecoes/testes-rapidos-de-rastreio-de-infecoes-por-vih-vhb-e-vhc/#o-que-sao-testes-rapidosCleveland Clinic. (2022). Are STIs and STDs the Same Thing?
https://health.clevelandclinic.org/sti-vs-stdMayo Clinic. (2023). Sexually transmitted diseases (STDs).
https://www.mayoclinic.org/diseases-conditions/sexually-transmitted-diseases-stds/symptoms-causes/syc-20351240Associação Portuguesa para Prevenção e Desafio à Sida. Prevenção: tratamento antirretrovírico.
http://www.sermais.pt/content/default.asp?idcat=profilaxiaPosExposicao&idCatM=prevencao&idContent=83000B64-B94F-4D62-A7E5-217C8730492C