HIV/AIDS & STIs

HIV/AIDS remains one of the most heavily tested Community Medicine topics, blending virology, epidemiology, national programme (NACP/NACO) structure, and clinical algorithms. This note integrates transmission, the serological window, diagnostic algorithms, WHO staging, ART thresholds, PMTCT, PEP timing, and STI syndromic management into one exam-ready resource.

Definitions & classification

HIV (Human Immunodeficiency Virus) is an enveloped, single-stranded RNA retrovirus of the Lentivirus genus, family Retroviridae. It carries reverse transcriptase, integrase, and protease enzymes. Two types exist:

• HIV-1 — worldwide, more virulent, faster progression, the cause of the global pandemic.
• HIV-2 — largely confined to West Africa, lower transmissibility, slower progression, and intrinsically resistant to NNRTIs (an important pharmacology fact).

The principal target is the CD4+ T helper lymphocyte; the virus enters via the CD4 receptor plus a co-receptor (CCR5 or CXCR4). The CCR5-delta32 homozygous mutation confers natural resistance to infection.

AIDS (Acquired Immunodeficiency Syndrome) is the advanced clinical stage, defined epidemiologically by a CD4 count < 200 cells/µL and/or the presence of an AIDS-defining illness (e.g., Pneumocystis jirovecii pneumonia, oesophageal candidiasis, CNS toxoplasmosis, Kaposi sarcoma, extrapulmonary TB, cryptococcal meningitis).

High-yield: A normal CD4 count is 500–1500 cells/µL. AIDS = CD4 < 200/µL OR an AIDS-defining illness, irrespective of count.

Transmission & natural history

Routes and efficiency

HIV is transmitted through blood, sexual contact, and vertical (mother-to-child) routes. It is NOT spread by casual contact, fomites, mosquitoes, or sharing food.

Route	Approximate transmission risk per exposure
Blood transfusion (infected unit)	>90% (highest)
Perinatal / vertical (no intervention)	15–45%
Needle-stick injury (percutaneous)	~0.3%
Mucous membrane splash	~0.09%
Receptive anal intercourse	~0.5–3%
Receptive vaginal intercourse	~0.1–0.2%
Sharing injection needles (IDU)	~0.6–0.8%

High-yield: Blood transfusion carries the highest per-exposure risk, but heterosexual transmission accounts for the majority of cases in India (the commonest route worldwide and in India).

Stages of infection

1. Acute retroviral / seroconversion illness (2–4 weeks): flu-like or mononucleosis-like syndrome, high viraemia, very infectious.
2. Clinical latency / asymptomatic stage: may last 8–10 years; persistent generalised lymphadenopathy possible.
3. Symptomatic HIV: weight loss, oral candidiasis, recurrent infections.
4. AIDS: opportunistic infections and malignancies.

Window period & serological dynamics

The window period is the interval between infection and detectability of the chosen marker. It is critical for both diagnosis and blood-bank safety.

Marker	Becomes detectable after infection
HIV RNA (NAT/viral load)	~10–12 days
p24 antigen	~2–3 weeks
4th-generation Ag/Ab combo ELISA	~2–3 weeks
HIV antibody (3rd-generation ELISA)	~3–12 weeks (classically "up to 3 months")

High-yield: The classic antibody window period quoted in exams is 3 weeks to 3 months (up to 6 months in rare cases). Fourth-generation assays detecting p24 antigen shorten this to ~2–3 weeks.

Diagnostic algorithm

The diagnostic strategy depends on purpose. WHO/NACO define three testing strategies:

• Strategy I (one test) — blood/organ donor screening and surveillance. Maximises sensitivity; a single reactive ELISA is sufficient to discard a unit.
• Strategy II (two tests) — surveillance and high-prevalence symptomatic diagnosis.
• Strategy III (three tests) — diagnosis in asymptomatic individuals / low-prevalence settings, requiring three different antigen-system reactive tests.

Classic confirmatory flow

Screening ELISA (sensitive) → repeat reactive ELISA → confirmatory Western blot (specific)

• ELISA is the screening test of choice — highest sensitivity, fewest false negatives.
• Western blot is the traditional confirmatory test — highest specificity. Positivity requires bands against ≥2 of p24, gp41, gp120/160.
• In neonates born to HIV-positive mothers, maternal antibody crosses the placenta, so antibody tests are unreliable until ~18 months. HIV DNA PCR (or RNA NAT) is the test of choice for infant diagnosis (done at 6 weeks, often termed Early Infant Diagnosis, EID).

High-yield: ELISA = best screening test (sensitive). Western blot / NAT = confirmatory (specific). For an infant < 18 months, use HIV DNA PCR, not antibody testing.

Best single test for monitoring response to ART = plasma viral load (HIV RNA). Best test for staging immunosuppression / opportunistic-infection risk = CD4 count.

WHO clinical staging

WHO defines four clinical stages used where CD4 testing is unavailable:

Stage	Representative features
Stage 1	Asymptomatic; persistent generalised lymphadenopathy
Stage 2	Minor weight loss (<10%), recurrent respiratory infections, herpes zoster, angular cheilitis, seborrhoeic dermatitis
Stage 3	Weight loss >10%, chronic diarrhoea >1 month, oral candidiasis/hairy leukoplakia, pulmonary TB, severe bacterial infections
Stage 4 (AIDS)	HIV wasting, PCP, oesophageal candidiasis, extrapulmonary TB, Kaposi sarcoma, CNS toxoplasmosis, cryptococcal meningitis

Management & ART thresholds

The single biggest shift in recent years is the "Treat All" / Universal Test and Treat policy.

High-yield: Since 2017, NACO follows "Test and Treat" — ART is started in ALL HIV-positive persons regardless of CD4 count or WHO stage, as early as possible. The old CD4 thresholds (≤350, then ≤500) are historical.

Evolution of CD4 thresholds (commonly tested)

Era / guideline	ART initiation threshold
Earlier WHO/NACO	CD4 ≤ 200/µL
Revised	CD4 ≤ 350/µL
2013 WHO	CD4 ≤ 500/µL
2015 WHO / 2017 NACO onward	All, regardless of CD4 ("Treat All")

First-line regimen

NACO first-line ART for adults is a single fixed-dose combination: Tenofovir (TDF) + Lamivudine (3TC) + Dolutegravir (DTG) — the TLD regimen, now preferred for its high potency, low pill burden, and high genetic barrier to resistance. (Efavirenz, EFV, was the older third drug.)

• Co-trimoxazole prophylaxis is given to prevent PCP and toxoplasmosis when CD4 < 200/µL.
• Isoniazid preventive therapy (IPT) is offered after ruling out active TB.

High-yield: A regimen always combines drugs from ≥2 classes (HAART). Monotherapy is never used because of rapid resistance.

PMTCT / PPTCT (Prevention of Parent-to-Child Transmission)

Without intervention, vertical transmission is 15–45%; with full PMTCT it falls to <2–5%. Transmission can occur antenatally (transplacental), intrapartum (the major contributor), and postnatally (breastfeeding).

PPTCT stepwise approach:

1. Universal antenatal HIV testing (opt-out) at the first ANC visit via ICTC.
2. Lifelong ART for the mother regardless of CD4 (Option B+).
3. Safe delivery practices; avoid invasive procedures, prefer institutional delivery.
4. Infant ARV prophylaxis (e.g., nevirapine syrup) for 6 weeks.
5. Infant feeding counselling — exclusive breastfeeding is recommended in the Indian context (mother on ART), as mixed feeding carries the highest transmission risk.
6. Co-trimoxazole prophylaxis + EID (HIV DNA PCR at 6 weeks) for the infant.

High-yield: Option B+ = lifelong ART for every HIV-positive pregnant woman regardless of CD4. Mixed feeding has a higher transmission risk than exclusive breastfeeding.

Post-Exposure Prophylaxis (PEP)

PEP applies to occupational (needle-stick) and non-occupational (sexual assault, accidental) exposures.

PEP flow: Wash the site (no squeezing/no antiseptic scrubbing) → assess exposure & source status → start ARVs ASAP, ideally within 2 hours → continue 28 days → baseline & follow-up HIV testing.

• Start within 72 hours (maximum window); efficacy is greatest the earlier it begins — ideally within 1–2 hours.
• Duration = 28 days of a 3-drug regimen (e.g., TDF + 3TC + DTG).
• Do not wash needle-stick wounds with bleach; do not squeeze to "bleed out" the site.
• Follow-up HIV testing at baseline, 6 weeks, 3 months (and 6 months in some protocols).

High-yield: PEP must begin within 72 hours, best within 1–2 hours, and continue for 28 days. Beyond 72 hours, prophylaxis is not effective.

PrEP (Pre-Exposure Prophylaxis): TDF/FTC for high-risk HIV-negative individuals — taken before exposure, distinct from PEP.

National AIDS Control Programme (NACP) & NACO

NACO (National AIDS Control Organisation), under the Ministry of Health & Family Welfare, runs the National AIDS Control Programme, launched in 1992.

Phase	Period	Key thrust
NACP-I	1992–1999	Awareness, blood safety, surveillance set-up
NACP-II	1999–2007	Targeted interventions for high-risk groups; decentralisation to State AIDS Control Societies (SACS)
NACP-III	2007–2012	Goal: halt and reverse the epidemic; scale-up of ICTC, ART centres
NACP-IV	2012–2017	Accelerate reversal & integrate response; expand PPTCT, link ART
NACP-V	2021–2026	Move toward ending AIDS as a public health threat by 2030 (SDG/95-95-95)

High-yield: 95-95-95 targets (by 2025/2030): 95% of people with HIV know their status → 95% of those diagnosed are on ART → 95% of those on ART are virally suppressed. (Earlier 90-90-90 by 2020.)

Key service delivery points

• ICTC (Integrated Counselling and Testing Centre): entry point for testing with pre-test and post-test counselling; confidentiality is mandatory.
• ART centres: initiate and monitor antiretroviral therapy.
• PPTCT clinics: integrated into ANC.
• STI/RTI clinics (Suraksha clinics): syndromic management.
• Targeted Interventions (TIs): for high-risk groups — FSWs, MSM, IDUs, truckers, migrants.
• Blood safety programme and Red Ribbon Express (awareness train).

The HIV/AIDS (Prevention and Control) Act, 2017 prohibits discrimination, mandates informed consent and confidentiality, and recognises the right to treatment.

STIs & syndromic management

NACO promotes syndromic case management because lab confirmation is often unavailable at the periphery; patients are treated based on a recognisable group of symptoms/signs using colour-coded pre-packed kits.

Syndrome	Common organisms	NACO kit (colour)
Urethral discharge / cervicitis	N. gonorrhoeae, C. trachomatis	Kit 1 (Grey) — Azithromycin + Cefixime
Vaginal discharge	Trichomonas, BV, Candida	Kit 2 (Green)
Genital ulcer — non-herpetic	T. pallidum (syphilis), H. ducreyi (chancroid)	Kit 3 (White) — Benzathine penicillin + Azithromycin
Genital ulcer — herpetic	HSV	Kit 4 (Blue) — Aciclovir
Lower abdominal pain (PID)	Mixed	Kit 5 (Yellow)
Inguinal bubo (LGV/chancroid)	C. trachomatis L1–L3, H. ducreyi	Kit 6 (Pink)

High-yield: Syndromic management treats for all likely organisms of a syndrome in a single visit, ensures partner treatment, condom promotion, counselling, and HIV testing — the classic "4 Cs" → Counselling, Contact tracing, Condom promotion, Compliance.

Genital ulcer differentials (frequently tested)

Feature	Syphilis (chancre)	Chancroid	Herpes	LGV
Organism	T. pallidum	H. ducreyi	HSV-2	C. trachomatis L1–3
Number	Single	Multiple	Multiple vesicles	Transient
Pain	Painless	Painful	Painful	Painless ulcer
Base	Clean, indurated	Ragged, soft, undermined	Shallow	—
Lymph nodes	Non-tender, rubbery	Tender, suppurative (bubo)	Tender	Suppurative, "groove sign"

Syphilis diagnosis flow: Dark-ground microscopy (primary chancre) → non-treponemal screen (VDRL/RPR) → treponemal confirmation (TPHA/FTA-ABS). Drug of choice = benzathine penicillin G.

Complications

• Opportunistic infections: PCP, oesophageal/oral candidiasis, CNS toxoplasmosis, cryptococcal meningitis, CMV retinitis, MAC.
• TB — the commonest opportunistic infection and leading cause of death in HIV in India; HIV is the strongest risk factor for reactivation of latent TB.
• Malignancies: Kaposi sarcoma (HHV-8), non-Hodgkin lymphoma, cervical cancer (HPV).
• Neurological: HIV-associated dementia, peripheral neuropathy.
• IRIS (Immune Reconstitution Inflammatory Syndrome): paradoxical worsening after ART initiation as immunity recovers.
• STI synergy: ulcerative STIs increase HIV acquisition/transmission several-fold — a key public-health rationale for STI control.

Key differentials

• Acute seroconversion illness vs infectious mononucleosis (EBV), secondary syphilis, acute CMV.
• Generalised lymphadenopathy vs TB, lymphoma, sarcoidosis.
• HIV wasting vs TB, malignancy, malabsorption.
• Genital ulcers — distinguish syphilis/chancroid/herpes/LGV as tabulated above.

Recently asked / exam angle

• CD4 cut-offs: AIDS-defining count = <200/µL; PCP prophylaxis when <200; co-trimoxazole prophylaxis trigger.
• "Test and Treat" — ART for all regardless of CD4 (very frequently tested as a "what changed" question).
• First-line regimen = TLD (Tenofovir + Lamivudine + Dolutegravir).
• PEP timing — within 72 hours, 28-day course (a perennial favourite).
• Window period — up to 3 months for antibodies; NAT detects in ~10–12 days.
• ELISA = screening; Western blot = confirmatory; infant < 18 months = DNA PCR.
• NACP launch year 1992; NACP-V (2021–2026); 95-95-95 targets.
• PPTCT Option B+ = lifelong ART; exclusive breastfeeding preferred; mixed feeding worst.
• HIV-2 is resistant to NNRTIs.
• Syndromic management kits and genital ulcer differentials (painless = syphilis, painful = chancroid).
• ICTC = entry point with pre/post-test counselling; confidentiality protected by HIV Act 2017.
• Commonest mode of transmission in India = heterosexual; highest per-exposure risk = transfusion.

Rapid revision

1. HIV-1 = global, virulent; HIV-2 = West Africa, slow, NNRTI-resistant.
2. Normal CD4 = 500–1500; AIDS = CD4 <200 or AIDS-defining illness.
3. Highest per-exposure risk = blood transfusion (>90%); commonest route in India = heterosexual.
4. Antibody window = up to 3 months; NAT detectable ~10–12 days; p24 ~2–3 weeks.
5. ELISA screens (sensitive); Western blot confirms (specific); infant <18 months → HIV DNA PCR.
6. Test and Treat — ART for ALL regardless of CD4 since 2017 (NACO).
7. First-line = TLD (Tenofovir + Lamivudine + Dolutegravir).
8. PEP within 72 hours (best <1–2 h), for 28 days; never squeeze/wash with bleach.
9. PMTCT Option B+ = lifelong ART; PMTCT cuts vertical transmission from 15–45% to <5%; mixed feeding is worst.
10. NACP launched 1992; current NACP-V (2021–26); targets 95-95-95.
11. TB = commonest OI and leading cause of death in HIV in India; co-trimoxazole prophylaxis when CD4 <200.
12. Syndromic management uses colour-coded kits; painless ulcer = syphilis (DOC benzathine penicillin), painful = chancroid; remember the 4 Cs.