What are the timelines and window periods for testing different Sexually Transmitted Infections (STIs)?

STI Testing Timelines and Window Periods After Sexual Exposure

Immediate Testing (Within 72 Hours)

Test immediately for bacterial STIs using nucleic acid amplification tests (NAATs), as these can detect chlamydia and gonorrhea even within 72 hours of exposure. 1

• Chlamydia and Gonorrhea: Collect specimens based on exposure sites—urine or genital swabs for urethral/vaginal exposure, rectal swabs for receptive anal sex, and pharyngeal swabs for gonorrhea only (pharyngeal chlamydia testing not recommended) 1, 2
• Syphilis: Perform baseline serologic testing (RPR/VDRL plus treponemal test) 1, 2
• HIV: Conduct baseline laboratory-based Ag/Ab test, though early infection may be missed 1, 2
• Hepatitis B: Baseline serology if not vaccinated 1, 2
• Trichomonas (women): Vaginal NAAT is preferred 1, 2

Critical caveat: Post-exposure prophylaxis with doxycycline 200 mg must be initiated within this 72-hour window for bacterial STI prevention in men who have sex with men. 1

2-Week Follow-Up Testing

Repeat testing at 1-2 weeks 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, 4

• Chlamydia and Gonorrhea: Repeat NAATs from all exposure sites 3, 2, 4
• This timing allows bacterial infections to reach detectable levels 2, 4

6-Week Testing (HIV Window Period)

HIV testing at 4-6 weeks post-exposure is critical, as the window period for laboratory-based Ag/Ab tests means early infection may be missed on initial testing. 1

3-Month (12-Week) Definitive Testing

A second screening at 3 months is mandatory for HIV and syphilis, as the initial test may not detect infection due to the window period. 1, 2, 4

• HIV: Definitive testing including both laboratory-based Ag/Ab test and diagnostic nucleic acid test (NAT) at 12 weeks after exposure (or 8 weeks after completing post-exposure prophylaxis if given) 1
• Syphilis: Repeat serologic testing at 6-12 weeks if initial test was negative 3, 1, 4
• Reinfection screening: If initial chlamydia or gonorrhea tests were positive and treated, retesting at 3 months is mandatory due to high reinfection rates—reinfection occurs within 3.6 months for chlamydia, 6 months for gonorrhea, and 4.8 months for trichomonas in 25% of previously infected individuals 3, 1, 2
• HSV-2: Serologic testing should not be repeated until 12 weeks after exposure to determine if HSV-2 was acquired 4

Summary of Window Periods by Infection

• Chlamydia/Gonorrhea: 1-2 weeks for adequate organism concentration, though detectable within 72 hours 1, 2
• Syphilis: 1-3 months for antibody development 2
• HIV: 4-12 weeks for antibody development 1, 2
• Hepatitis B: Baseline testing sufficient if vaccinated 1

High-Risk Populations Requiring More Frequent Screening

Individuals with multiple or anonymous partners, substance use during sex, previous STI history, or men who have sex with men should undergo screening every 3-6 months regardless of recent exposures. 3, 1, 4

• High STI positivity rates of 20% for chlamydia and 17% for gonorrhea are found with 2-3 monthly screening in high-risk populations 1
• Annual screening is recommended for all sexually active adolescents and young adults ≤25 years 3

Critical Pitfalls to Avoid

• Testing too early leads to false-negative results: Infections require time to develop detectable levels 2, 4
• Incomplete anatomical site testing misses infections: Failing to test at exposure-specific sites (pharynx, rectum) misses a substantial proportion of infections, particularly in men who have sex with men 1
• Relying on single negative test shortly after exposure does not rule out infection: Follow-up testing is essential 2, 4
• Assuming condom use eliminates all risk: Some STIs can be transmitted through skin-to-skin contact in areas not covered by condoms 4