STI Testing: How Long After Exposure Each Test Becomes Reliable

A negative STI test taken soon after a risk contact does not mean you are not infected. Every test has a window period, the interval between infection and the point at which that particular test can detect it, and the interval belongs to the test rather than to the infection. NACO's National Guidelines for HIV Testing (July 2015) put the HIV antibody window at, on average, three weeks to three months; the US CDC gives 10 to 33 days for a nucleic acid test, 18 to 45 days for a laboratory antigen/antibody test on venous blood, 18 to 90 days for a rapid antigen/antibody test on a finger-stick sample, and 23 to 90 days for antibody tests. Which test you had matters more than how many weeks have passed, so take the report itself to the consultation.

Written by Dr. A. Ameer Jahan, Senior Consultant · Reproductive Medicine, Male Infertility & STD, Chairman, AJSMC, Egmore, Chennai (TNMC 28017). This page is about how long after a possible exposure each test becomes reliable, and what a negative result does and does not rule out at each interval. It follows the National Technical Guidelines on Sexually Transmitted Infections and Reproductive Tract Infections (2024), issued by the National AIDS and STD Control Programme, Ministry of Health and Family Welfare, Government of India, which supersede the 2014 national RTI and STI guidelines. Where CDC, WHO, European or UK guidance gives a different figure, both figures are named, with the reason they differ.

Some of what brings a person to a page like this is not a booking at all. Sudden pain and swelling in one testicle is a surgical emergency until proved otherwise; NACO's own flowchart for painful scrotal swelling routes suspected testicular torsion straight to an emergency department, ahead of any STI treatment, and the testicle is lost by waiting. Lower abdominal pain in a woman with a missed or overdue period, a recent delivery, abortion or miscarriage, abdominal guarding, bleeding heavier than spotting, or an abdominal mass needs immediate surgical or gynaecological assessment; ectopic pregnancy and a twisted ovarian cyst are on NACO's own list of differentials. Pelvic pain not improving 72 hours into treatment, suspected pelvic inflammatory disease in pregnancy, and sexual assault at any interval all need a hospital that can admit. So does a possible HIV exposure within the last 72 hours, because NACO's guidance makes what an emergency facility can start afterwards a decision measured in hours rather than days, and that assessment cannot wait for an outpatient slot. In any of these, call 108 or go to the nearest hospital with a 24-hour emergency department. AJSMC is a multi-speciality centre on Police Commissioner Office Road, Egmore, Chennai 600008, with no casualty unit, no 24-hour emergency department and no critical care: its ten beds take planned, stable admissions, with a nurse on site overnight and no doctor on the premises. Consultations run Monday to Saturday, 10am to 9pm, and there is no clinic outside those hours or on a Sunday.

Why can a test taken three days after a risk contact be negative and still be wrong?

Because most of these tests do not look for the organism. They look for the body's antibody response to it, and that response takes weeks to build. A few look for the organism's genetic material or one of its proteins, and those turn positive earlier, though not immediately. Until whatever the test is looking for has appeared in the sample, the test reads negative in an infected person exactly as it reads negative in an uninfected one. The two reports are identical. Nothing on the printed line records which assay was run, or how many days had passed since the exposure, and those are the two facts that decide whether the negative means anything at all.

How long after exposure does each test become reliable?

The intervals below are not interchangeable. Two rows for the same infection can differ by two months, and the difference is the assay, not the infection.

The last row is the honest one. The figure repeated across most websites for chlamydia and gonorrhoea, that a NAAT is reliable two weeks after exposure, could not be traced to any named guideline in preparing this page, and neither could the incubation periods usually quoted for those two infections. What the guidelines do fix is the other end, after treatment. The pre-test interval for these two should come from the doctor seeing you, not from a table on any website, including this one.

Hepatitis B and trichomoniasis have been kept out of that table deliberately. No test window period for either is stated in the sources consulted. What those sources give instead is incubation to symptoms, which is a different quantity and must not be read as a detection interval: CDC's hepatitis B clinical overview puts incubation to symptoms at an average of 90 days, range 60 to 150, and to abnormal liver enzymes at 60 days, range 40 to 90, while CDC's trichomoniasis page says symptoms appear in some people 5 to 28 days after infection and in others much later or never, with about 70% having none at all, and that the infection cannot be diagnosed on symptoms alone. Neither figure says when a test would turn positive.

Why do India's and America's HIV window figures differ?

Because they describe different assays, and India's public-sector algorithm is antibody-based. NACO's 2015 guidelines require that the three tests establishing a reactive result at an Integrated Counselling and Testing Centre, A1, A2 and A3, be based on different serological principles or use different HIV antigens, with sensitivity of at least 99.5% and specificity of at least 98%. Those are antibody-detecting assays. Someone tested at an ICTC is generally not having a fourth-generation antigen/antibody test, so CDC's 18 to 45 day figure, which belongs to a laboratory antigen/antibody test on blood drawn from a vein, does not describe their result.

The reverse mistake is as common. CDC's rapid antigen/antibody test on a finger-stick sample runs to 90 days, not 45, and most rapid tests and self-tests are antibody tests with the same 90-day outer limit. Quoting the shorter figure for a rapid kit is the error that falsely reassures someone who tested at four weeks. BHIVA, BASHH and BIA make it a Grade 1A recommendation that window periods of 45, 60 and 90 days apply to fourth-generation laboratory tests, third-generation laboratory tests and all point-of-care tests, on the reasoning that clinic policy should rest on 99th-percentile estimates rather than medians.

Self-testing is not offered under India's national programme; kits are sold, and NACO's position is that a self-test is a screening test only, not a confirmatory test of status. Retesting policy is not settled between bodies either: WHO's Consolidated guidelines on HIV testing services (2019) calls routine three-monthly retesting of everyone who tests negative an inefficient use of resources, reserving it for people reporting recent or ongoing risk. And an indeterminate result is not a negative one. It carries its own repeat schedule, beginning two weeks after the first sample under NACO's National Guidelines for HIV Testing (2015), with a wider 14 to 28 days used elsewhere in NACO's counselling guidance.

Why do syphilis tests give two different waiting times?

Because the Indian guidelines count from two different events in different chapters, and you know only one of them. NACO 2024 puts the start of the primary stage at about 21 days after infection, range 10 to 90 days (Chapter 4, section 2.1). Its serology chapter says non-treponemal tests may read negative for up to four weeks after the sore appears, that a repeat after 2 to 4 weeks may be needed where primary syphilis is suspected, and that a negative non-treponemal test three months after the onset of the primary chancre excludes the diagnosis (section 5.3.1). Those are anchored to the sore. NACO's clinic algorithm (Figures 4.1 and 4.2) is anchored to the exposure instead: a history of high-risk contact within the past four weeks with a non-reactive test prompts a repeat four weeks later.

Chain the lesion-anchored figures together and the arithmetic goes wrong for anyone working from an exposure date, because the sore can appear as late as 90 days after infection, so "three months after the chancre" can fall around six months after the contact. Do not attempt that calculation yourself. BASHH's 2024 UK guideline states the exposure-anchored version directly: a negative result within three months of infection cannot exclude early syphilis, and contacts should be re-screened 12 weeks after their last exposure.

Two conditions from the same NACO page belong with that exclusion sentence. A non-treponemal test can also be negative in late latent syphilis, and it can be falsely negative in primary and secondary syphilis through the prozone phenomenon. So a negative VDRL or RPR rules out early syphilis as the cause of the sore being investigated; it does not rule out syphilis at every stage. Treponemal tests may turn positive earlier and then stay positive for life in about 85% of people whether or not they were treated, so a positive treponemal test cannot on its own separate active infection from an old, treated one.

Other authorities do not use NACO's exclusion rule at all. The 2020 European (IUSTI) guideline instead advises repeat serology at 1, 2 and 6 weeks to exclude the diagnosis, and reports that non-treponemal tests usually turn positive about 10 to 15 days after the chancre appears, around six weeks after infection, which is markedly earlier than NACO's four weeks. Where they differ, this page follows NACO as the Indian national standard.

Why test when you feel completely well?

Because for several of these infections, feeling well is the usual presentation. NACO's own figures: chlamydial urogenital infection is asymptomatic in up to 50% of men and up to 90% of women; gonorrhoea is asymptomatic in a minority of men and around 50% of women, with pharyngeal and rectal infections commonly asymptomatic and approximately 85% of gonococcal infection in adolescent girls asymptomatic; trichomoniasis may be asymptomatic in at least 50% of women and 70 to 80% of men. WHO's position is that more than a million curable STIs are acquired every day among people aged 15 to 49, the majority without symptoms.

NACO states the consequence plainly: absence of signs or symptoms does not rule out an STI, and an asymptomatic person can still pass the infection to a partner or, in pregnancy, to the baby, while it ascends the reproductive tract. This is the acknowledged limit of India's syndromic system, which NACO lists in its own words as "not useful in asymptomatic patients". Most asymptomatic cases are found through partner notification or incidental screening. For scale, in NFHS-5 (2019–21), 5% of women and 2.1% of men aged 15 to 49 who had ever had intercourse self-reported an STI in the previous 12 months, rising to 12.3% and 9.3% when genital discharge, sore or ulcer were included.

How does India actually run STI testing and treatment?

Through syndromic case management, which treats the pattern of symptoms on the day of the visit rather than waiting for a laboratory result. NACO's 2024 guidelines recognise six syndromes, with inguinal bubo handled as a sub-section under genital ulcer disease.

Source: NACO 2024, Table 3.2 and sections 3.2.1 to 3.2.6. The programme dispenses treatment through colour-coded kits matched to those syndromes, so that someone attending a government clinic is treated on the day rather than sent away to wait. One detail is worth correcting, because the older scheme is still widely reproduced: the 2024 edition runs eight colour-coded kits numbered 1 to 8, not seven, the additional one being for anorectal discharge syndrome. Which kit applies, and what is in it, is decided by the treating clinician and is not reproduced here. NACO names the trade-offs of the approach in its own words: it is not useful in asymptomatic patients, it over-treats someone who has only one of the infections causing a syndrome, and it may be associated with decreased antibiotic susceptibility. The programme therefore now uses enhanced syndromic case management, adding whatever on-site diagnostics are available without delaying treatment.

Services run through Designated STI/RTI Clinics branded as Suraksha Clinics, at district hospitals and medical colleges. NACO's Sankalak report (Sixth Edition, 2024) counts 1,127 nationally, of which Tamil Nadu has 106, second only to Uttar Pradesh. HIV testing runs through a separate network of more than 4,400 Integrated Counselling and Testing Centres (NACO, National HIV Counselling and Testing Guidelines, 2024), with a national AIDS helpline on 1097. NACO describes HIV prevention and care services as available free of cost at government facilities under the national programme. For STI and RTI services the guidelines go no further than saying that the colour-coded kits are supplied under the national programme to designated government facilities, so ask the particular facility what applies there.

One figure from those clinics needs reading carefully. Syphilis screening positivity among people attending Designated STI/RTI Clinics is reported at 0.60% in 2021–22, 0.70% in 2022–23, 0.9% in 2023–24 and 0.94% in 2024–25, with 4,615,548 clients screened in 2024–25 and 43,482 reactive, being 1.54% of men, 0.48% of women and 4.12% of hijra and transgender clients (NACO, Sankalak, Seventh Edition, 2025, Table 7.2; earlier years from the Sixth Edition, 2024, Table 6.1). Read that series carefully rather than as a rising line. The Sixth Edition counted RPR tests; the Seventh counts syphilis screening of any approved type, and only 4.61 million of the 7.19 million clients who attended in 2024–25 were screened at all. Whether the four years rest on the same test mix is not stated in either report, so this is not a clean trend. These are also test-positivity figures among people who came to an STI clinic and were screened, and they exclude pregnant women, screened separately in antenatal care. On that wider denominator NACO reports national positivity among pregnant women of 0.05% in 2024–25, and WHO records India's reported antenatal figure at 0.04% for 2024. They measure different groups, which is why the clinic figure must never be quoted as a national rate.

Do I have to tell my partner?

NACO's 2024 guidelines set out four approaches, in Table 7.1. Patient referral means telling your own partners yourself; enhanced patient referral adds written and digital information for the partner to take away. Provider referral is a health professional notifying the partner of potential exposure without disclosing your identity, used most often for casual or former partners. Contract or conditional referral is an agreement that you will inform your partners within a set time, failing which the provider proceeds. The look-back interval is 60 days for three syndromes: partners whose last contact was within 60 days before the onset of symptoms or the diagnosis should be evaluated and treated, for urethral discharge, for painful scrotal swelling, and for lower abdominal pain or pelvic inflammatory disease in women. CDC uses the same 60-day look-back for chlamydia and gonorrhoea. NACO advises abstinence until treatment is complete and symptoms have resolved, and for genital ulcer disease until treatment is completed or the lesions have healed, whichever is later.

NACO asks that the potential consequences of disclosure be weighed first: stigma, discrimination, abuse or violence. The balance, it says, tilts towards your own needs, so that nobody is dissuaded from seeking sexual health care in future by an overly aggressive approach to notification. If you are afraid of what disclosure will cause at home, say so in the consultation. It changes which of the four approaches is used.

Can the clinic tell your family, your employer or your partner?

For HIV this is governed by statute, and the statute is precise. Under section 5 of the Human Immunodeficiency Virus and Acquired Immune Deficiency Syndrome (Prevention and Control) Act, 2017 (Act 16 of 2017), no HIV test may be performed on any person except with informed consent, and that consent must include pre-test and post-test counselling. Section 6 sets out the only four situations where consent is not required: a court order that the test is necessary to determine an issue before it; procuring, processing, distribution or use of a human body or any part of it, including tissues, blood, semen or other body fluids, for medical research or therapy; anonymous epidemiological or surveillance testing not aimed at determining any individual's status; and screening in a licensed blood bank. Section 3 prohibits discrimination against a protected person and lists, at clause (l), HIV testing as a pre-requisite for obtaining employment, or for accessing healthcare services, education or any other service or facility, or for the continuation of the same. Section 8 provides that nobody shall be compelled to disclose their HIV status except by order of a court in the interest of justice.

Partner disclosure, at section 9, is the provision most often misdescribed in both directions. It is neither a duty to tell nor a blanket bar on telling.

Source: Act 16 of 2017, sections 2(h), 2(p), 3, 5, 6, 8 and 9. Beyond the statute, NACO applies the WHO five Cs to all HIV testing: consent, confidentiality, counselling, correct results, and connection to prevention, treatment and care. The 2024 STI guidelines go into the room itself, asking for audio-visual privacy during history-taking and examination, a separate space not marked with an STI nameplate, and, where a couple attends together, each person interviewed and examined separately. Where sexual violence is involved, NACO's position is that police intimation and an FIR should follow only when the survivor wants it and gives informed consent. Child sexual abuse is the exception, and reporting there is mandatory: under the Protection of Children from Sexual Offences Act, 2012, a person under 18 cannot consent, sexual acts with a child are offences under that Act whatever the circumstances, and the Act makes reporting mandatory for anyone who knows of such an offence. If that is the situation, a general outpatient clinic is not the right place; a facility equipped for medico-legal care is.

Is gonorrhoea becoming untreatable in India?

Nobody in India has the data to say, and two Delhi centres of national standing, publishing months apart in 2025, reach opposite conclusions. There is no large, recent, geographically representative Indian survey. The most recent multicentre study tested 124 isolates collected between September 2013 and August 2016, of which 82 came from New Delhi alone, three each from Pune and Mumbai, 20 from Secunderabad and 16 from Hyderabad, and none from Tamil Nadu. It found near-total resistance to the older agents tested, 98% (CI 96.2 to 100) for one of them, with all isolates susceptible to the agents relied on for current first-line treatment apart from two showing decreased susceptibility.

Single-centre series published since do not agree with each other. India's national STI reference centre in Delhi, reporting 231 isolates over five years, described a surge in multidrug-resistant and extensively drug-resistant gonococci: 16 multidrug-resistant isolates, one extensively drug-resistant isolate, decreased susceptibility to the agents underpinning first-line treatment in 6.06%, and resistance to the second agent used alongside them in 13.4%, of which 22.5% was high-level. A Chandigarh centre found that same resistance in 5 of 50 isolates across 2016 to 2024. AIIMS New Delhi, reviewing 183 isolates over about fifteen years to June 2023, found it below 5%, decreased susceptibility below 10%, no outright resistance to the first-line agent at any point, and concluded there appears to be no immediate threat to the therapies in current use.

A denominator of 50 across nine years, or of 124 collected a decade ago, is not a population rate. The studies used different susceptibility-testing methods, so the percentages should not be lined up as a trend. And every series is drawn overwhelmingly or entirely from men with urethral discharge, so none describes resistance in women. India does report to WHO's Gonococcal Antimicrobial Surveillance Programme and joined the enhanced programme in 2024, but the volumes are small, roughly 29 isolates for 2021 and about 49 for 2022, and WHO describes surveillance across its South-East Asia Region as inadequate. None of this is a reason for alarm. NACO's own response is procedural: culture with antimicrobial susceptibility testing is required in every case of treatment failure, and failure is suspected when symptoms do not settle within 3 to 5 days. Self-medicating an STI is one of the mechanisms by which the problem is made worse.

Do I need an HPV test, and does my partner?

Most HPV infections clear by themselves and are never noticed, and NACO records the majority as self-limiting and asymptomatic or unrecognised. Types 16 and 18 cause most HPV-related cancers of the cervix and elsewhere, and they are two of a larger group of high-risk types; types 6 and 11 cause most anogenital warts (NACO 2024, section 4, Group 3). On the partner question the same guidelines are direct: HPV testing of sex partners is not recommended, and partners should be physically examined instead. NACO also states that vaccination prevents infection and does not treat an existing one, which is why it is advised ideally before sexual debut. What India's campaign currently delivers, at what age and with which vaccine, is set out with its source on the AJSMC page about the Pap smear, which also covers cervical screening in full; neither is repeated here.

When should you see a doctor?

Outpatient consultations at AJSMC, Police Commissioner Office Road, Egmore, Chennai 600008, run Monday to Saturday, 10am to 9pm, on 044 2532 2021. Say when booking that it is a sexual health consultation. Take the date of the exposure, written down. It is the single most useful thing you can bring, because it decides which test can be interpreted on the day you come. Take any previous test report as well, and this matters more than it sounds: the report needs to show which assay was run and on what kind of sample, since a rapid finger-stick result and a laboratory result carry window periods six weeks apart. The consultation is the same whether or not anything has appeared, which is what the asymptomatic figures above are for. Ask to be seen sooner, and say so on the phone, if there is a genital sore, if there is discharge with fever, if a partner has been diagnosed, or if an earlier test was taken very soon after the exposure and has not been repeated. Say so too if you are pregnant, if you are afraid of what a diagnosis will mean at home, or if you are under 18, because each of those changes what happens next.

Do not come here, and do not wait for opening hours, for sudden pain and swelling in one testicle, for lower abdominal pain in a woman with a missed period or with guarding or heavy bleeding, for fever with severe pelvic pain, for pelvic pain not improving 72 hours into treatment, after a sexual assault, or within 72 hours of a possible HIV exposure, where what can be offered afterwards is decided in hours rather than days. Call 108, or go to the nearest hospital with a 24-hour emergency department. HIV testing and counselling is available at government Integrated Counselling and Testing Centres and STI care at Designated STI/RTI Clinics, and the national AIDS helpline is 1097. AJSMC is on Police Commissioner Office Road, Egmore, Chennai 600008, with consultations Monday to Saturday, 10am to 9pm and no clinic on a Sunday. It has no emergency department and no critical care, and its ten beds take planned, stable admissions only. The outpatient number is 044 2532 2021.