Sexually transmitted diseases (STD) or sexually transmitted infections (STI) are quite widespread. Frequently, they present without any symptoms, and many people are not aware of being infected. While having doubts, concerns, and suspicion of infection after the latest sexual intercourse and seeking help on the internet, you may find out that various testing types exist. How soon after exposure can you get tested, and which test is definitive? Here is all you need to know about STD testing for different specific STIs.1
HIV testing
Which tests are used for early Human immunodeficiency virus (HIV) detection, and how accurate are they?
Neither of the existing HIV tests is informative directly after the exposure.
The period during which a person may have been infected with HIV, and the test will be able to detect the virus itself or its antigens and antibodies is called the Window period. Its duration varies from one individual to another and is different for each particular test.2
- HIV RNA detection tests are evaluating the viral load. During the early HIV phase, HIV ribonucleic acid (RNA) is detectable in the blood due to its high levels. The sensitive tests (at least 50 copies/ml) become positive after 10-15 days and ultrasensitive ones (at least 1-5 copies/ml) already after the 5th day of possible exposure. HIV RNA test has 90% accuracy if tested after 10-12 days. For more definitive results get tested after 42 days (99% accurate results). 3 4
- HIV p24 antigen detection test p24 is an HIV capsid protein that can be detected in the blood 5-7 days after HIV RNA strike (at least 30,000 to 50,000 copies/ml). Modern p24 assessment tests have higher accuracy (89%) in comparison with previous ones.3 After 42 days (6 weeks) this test will become for 99% definitive.4
- Fourth-generation combined antigen/antibody tests are capable of detecting both p24 antigen and antibodies against HIV-1 and HIV-2. The test is positive when either of them is detected, thus the window period for testing shortens to 15-20 days. They are less accurate when compared to HIV RNA testing , and accuracy constitutes only 80% for early detection.3 Samples are being collected either from the vein or with the help of a finger stick (rapid antigen/antibody test). Results from venous blood can be obtained within fewer days after exposure (window period is shorter) when compared to finger prick.2 Within 43-44 days this test will become for 99% definitive.5
- Rapid HIV tests provide results within 20 – 30 minutes. Mostly they are based on antibody detection (except rapid antigen/antibody tests). The window period is long and ranges from 23 to 90 days after exposure, because the production of antibodies, as part of the immune response against HIV, requires time. Blood (venous and from a finger) and saliva can be used.2 If tested after 42 days test will be accurate for 95%. These tests will become 99% definitive after 90 days from possible exposure.4
Table 1.
| HIV Test | Earliest time and accuracy for testing | Definitive time (99% accurate) |
|---|---|---|
| Ultrasensitive HIV RNA detection tests | after 5 days (90% accurate) | 42 days |
| Sensitive HIV RNA detection tests | after 10-15 days (90% accurate) | 42 days |
| HIV p24 antigen detection test | after 15-22 days (89% accurate) | 42 days |
| Fourth-generation combined antigen/antibody tests | after 15-20 days (80% accurate) | 43-44 days |
| Fourth-generation combined antigen/antibody tests | after 23 days (95% accurate after 6 weeks) | after 3 months |
Golden standard algorithm for early HIV testing
You should undergo Rapid HIV testing after unprotected sex and potential HIV exposure preferably with most accurate screening tests such as viral load assessment tests in combination with HIV antigen/antibody combined tests followed by HIV confirmatory differentiation tests (HIV-1 from HIV-2) if needed.3
- If HIV antigen/antibody combined tests and HIV viral load tests turned out to be negative there is no evidence of being infected with HIV . If the risk of HIV contamination is high, the primary negative immune assessment and the virologic test should be retaken 1-2 weeks after the initial testing for more conclusive results3
- HIV antigen/antibody combined test’s negative and HIV viral load test’s positive results are indicating early HIV infections
When is the test for HIV false-negative, and when is it definitive?
Likelihood of false-negative results is high if you took the test during the window period. To avoid false-negative results, you should repeat the test after the window period. If the initial testing was during the first 12 weeks after possible exposure, the test should be repeated after an extra 12 weeks for more reliable results.6
Chlamydia and Gonorrhea testing
The incubation period for Chlamydia
The incubation period for Chlamydia varies between 5 to 14 days, and common practice suggests getting tested 2 weeks after initial exposure.7
An earliest possible testing time for Gonorrhea
It is possible to get tested for Gonorrhea already as early as 2-3 days after exposure.8 Its incubation period varies from 2-7 days (sometimes till 14 days).9
Test of choice for Chlamydia and Gonorrhea. When to get tested?
Swabs from the vagina, which are more informative for women, and first-catch/first void urine, which is preferable for men, are used in the nucleic acid amplification tests (NAAT). These tests are the most reliable and preferred testing methods (also called as “gold standard”) for Chlamydia and Gonorrhea detection. Swabs from the rectum, oropharynx (for Gonorrhea), endocervix and the urethra may also be collected. Because of relatively high coinfection incidence, many physicians suggest getting tested for multiple infections simultaneously 2 weeks after possible exposure, considering financial and psychological aspects of intervention and several hospital visits issue.10
Trichomonas testing
The incubation period for Trichomonas constitutes 5-28 days. Tests using urine or swabs (NAAT) are very sensitive and specific also for Trichomonas detection, thus as mentioned above it is suggested to test for Trichomonas at the same time with Gonorrhea and Chlamydia (2 weeks after possible exposure). Microscopic tests are also widely applied, but they are less accurate.11
Mycoplasma and Ureaplasma testing
The incubation period for Mycoplasma Genitalium varies from 2 to 35 days.12 Incubation period for Ureaplasma constitutes 10-20 days.13 Common practice suggests testing for Mycoplasma and Ureaplasma only when the other pathogens causing the urethral infection are excluded. 14 Collection of swabs or urine (NAAT) is the best option if you want to get tested.15
Genital herpes testing
Genital herpes has a relatively short incubation period from 2-12 days, and symptoms usually develop within 3-6 days after exposure. In symptomatic patients, healthcare professionals suggest taking samples from blisters with the help of cotton buds (NAAT) 2 days after the blisters have developed. Herpes culture tests can also be performed, but they are shown to be less accurate. If the symptoms are absent, it is reasonable to take blood tests for IgG antibody detection. These antibodies are part of our immune defense against herpes virus, and for rather conclusive and definitive results it is suggested to wait for 12-16 weeks. IgM can be detected earlier, but it can provide misleading results, thus IgG detection is more accurate.16
Table 2.
| Disease | Incubation period | Earliest time for testing | Definitive time | Sample used |
|---|---|---|---|---|
| Chlamydia | 5-14 days (sometimes till 21 days) | 5 days (accuracy is unknown) | after 2-3 weeks (preferable time) | Swabs/urine |
| Gonorrhea | 2-7 days (sometimes till 14 days) | 2-3 days (accuracy is unknown) | after 2 weeks (preferable time) | Swabs/urine |
| Trichomonas | 5-28 days | 5-7 days (accuracy is unknown) | after 2-4 weeks (highly accurate after 4 weeks) | Swabs/urine |
| Mycoplasma | 2-35 | Get tested when the other infections causing urethritis are ruled out | after 35 days | Swabs/urine |
| Ureaplasma | 10-20 | Get tested when the other infections causing urethritis are ruled out | after 20 days | Swabs/urine |
| Genital Herpes | 2-12 | Within 48 hours after blister development (highly accurate) | 12-16 weeks later for IgG detection in blood (highly accurate) | Swab from blisters/blood |
References:
1. Mayo clinic. STD testing.
2. Testing | HIV Basics | HIV/AIDS | CDC.
3. Acute and early HIV infection: Clinical manifestations and diagnosis - UpToDate.
4. HIV window periods | SmartSexResource.
5. Hurt CB, Nelson JAE, Hightow-Weidman LB, Miller WC. Selecting an HIV Test. Sex Transm Dis.
6. Understanding HIV Test Results | HIV.gov.
7. Clinical manifestations and diagnosis of Chlamydia trachomatis infections - UpToDate.
8. STDs and HIV Testing: Frequently Asked Questions. Health Central.
9. Factsheet about gonorrhoea.ECDC Europa.
10. Clinical manifestations and diagnosis of Neisseria gonorrhoeae infection in adults and adolescents - UpToDate.
11. Trichomoniasis - 2015 STD Treatment Guidelines. CDC
12. Mycoplasma genitalium infection - including symptoms, treatment and prevention :: SA Health.
13. Pathogen Safety Data Sheets: Infectious Substances – Ureaplasma urealyticum - Canada.ca.
14. Horner P, Donders G, Cusini M, Gomberg M, Jensen JS, Unemo M. Should we be testing for urogenital Mycoplasma hominis, Ureaplasma parvum and Ureaplasma urealyticum in men and women? – a position statement from the European STI Guidelines Editorial Board. J Eur Acad Dermatology Venereol.
15. Mycoplasma genitalium - Q & A - 2015 STD Treatment Guidelines. https://www.cdc.gov/std/tg2015/qa/mycoplasma-genitaliumqa.htm. Accessed February 28, 2020.
16. Herpes testing |. http://www.ashasexualhealth.org/stdsstis/herpes/herpes-testing/. Accessed February 29, 2020.
