STI Testing Timeline After Sexual Intercourse
Most bacterial STIs (chlamydia, gonorrhea) can be detected within 1-2 weeks using nucleic acid amplification tests, but definitive testing for HIV and syphilis requires waiting 12 weeks after exposure to rule out infection. 1
Immediate Testing (Within 72 Hours to 2 Weeks)
Bacterial STIs can be tested immediately using nucleic acid amplification tests (NAATs), which can detect chlamydia and gonorrhea even within 72 hours of exposure. 1, 2 However, this immediate testing serves primarily as baseline screening, as infectious agents may not have produced sufficient concentrations of organisms to result in positive tests at the initial examination. 3
Initial Baseline Testing Should Include:
- Chlamydia and gonorrhea via NAAT on urine or site-specific specimens (genital, rectal, pharyngeal based on exposure) 1, 2
- Syphilis serologic testing (RPR/VDRL and treponemal tests) 2
- HIV baseline testing (though follow-up required) 1, 2
- Hepatitis B serologic testing if unvaccinated 1, 2
- Trichomonas vaginal NAAT for women 2
Critical timing consideration: If post-exposure prophylaxis is being considered (doxycycline 200 mg for bacterial STIs in men who have sex with men), it must be initiated within 72 hours of exposure. 1, 2
Repeat Testing at 2 Weeks
Repeat testing at 1-2 weeks after exposure is essential for bacterial STIs if initial tests were negative and no presumptive treatment was given, as infectious agents may not have produced sufficient concentrations to be detected initially. 3, 1, 2 This window period of 1-2 weeks is particularly important for chlamydia and gonorrhea. 1
Definitive Testing at 12 Weeks (3 Months)
The 12-week mark is critical for ruling out HIV and syphilis definitively. 1, 2
Required Testing at 12 Weeks:
- HIV testing using both laboratory-based Ag/Ab test and diagnostic nucleic acid test (NAT) to definitively rule out infection 1, 2
- Syphilis repeat serologic testing (window period of 1-3 months) 1, 2
- Reinfection screening for chlamydia or gonorrhea if initial tests were positive and treated, due to high reinfection rates (25% reinfected within 3.6 months for chlamydia, 6 months for gonorrhea) 2, 4
Understanding Window Periods
The window period represents the time between infection and when tests can reliably detect that infection:
The one-month period is sufficient to detect most bacterial STIs but insufficient to rule out HIV and syphilis, hence the critical need for follow-up screening at 3 months. 2
Site-Specific Testing Considerations
Failing to test at exposure-specific sites (pharynx, rectum) misses a substantial proportion of infections, particularly in men who have sex with men. 2 Collection sites should be adapted according to exposure type:
- Vaginal/urethral penetration: Urine or genital specimens for chlamydia and gonorrhea 2
- Receptive anal penetration: Rectal specimens for chlamydia and gonorrhea 2
- Receptive oral sex: Pharyngeal specimens for gonorrhea (pharyngeal chlamydia testing not generally recommended) 2
High-Risk Populations Requiring More Frequent Screening
Individuals with ongoing risk factors need screening every 3-6 months regardless of recent exposures, including those with: 1, 2
- Multiple or anonymous partners
- Substance use during sex
- Previous STI history
- Men who have sex with men
High-risk populations show STI positivity rates of 20% for chlamydia and 17% for gonorrhea with frequent screening. 2
Common Pitfalls to Avoid
Testing too early and stopping there is the most critical error. A negative test at 1 week does not rule out infection—bacterial STIs need repeat testing at 2 weeks if initially negative, and HIV/syphilis require the full 12-week window. 3, 1, 2
Missing the 72-hour window for post-exposure prophylaxis eliminates this prevention option, though screening remains crucial to identify any acquired infection. 2