Through sexual contact

Transmission of some STIs e.g. non gonococcal urethritis (NGU), HIV, Hepatitis B and gonorrhoea occurs when there is transfer of body fluids (e.g. semen from the male genital tract or vaginal secretions from the female genital tract) from an infected person to the sex partner. Transmission of some STIs e.g. gonorrhoea and chlamydia may also occur with transfer of oral saliva or fluids from a person’s infected mouth to the sex partner.

Through skin to skin contact

Transmission of other STIs, e.g. scabies, pubic lice, syphilis, herpes and warts occurs when there is close skin-to-skin contact.

Through blood contact

Some STIs e.g. syphilis, hepatitis B and HIV may be transmitted through direct contact with contaminated blood, for example through sharing of injection needles or through contaminated blood transfusions.

The incubation period is the period of time from infection to the appearance of signs and symptoms; it can vary among the different types of STIs.

Some infections such as gonorrhoea, non-gonococcal urethritis (NGU) and genital herpes have short incubation periods, ranging from 2 days to 3 weeks. The incubation period of other STIs such as syphilis may range from 2 weeks to many months, and that for HIV infections may be several years. You should see a doctor as soon as you notice any of the signs and symptoms of an STI.

Not all infections will present with signs or symptoms. Some patients may be asymptomatic carriers of the infection but will have the risk of transmitting to other partners unknowingly. More than 10% of males, and more than half of females with gonorrhoea and chlamydia infection do not show any sign or symptom.

If none of the signs or symptoms occurs, blood tests for syphilis and HIV should be carried out after 4 weeks. Conclusive results can usually be obtained after 12 weeks. Swab or urine tests for infections like gonorrhea and chlamydia may be carried out after 2 weeks.