HIV: diagnosis, ART, and prevention

Screen with a 4th-generation antigen/antibody assay; HIV RNA if acute infection suspected. Start ART in everyone regardless of CD4 (START (2015)), ideally same day to within 7 days. First-line: bictegravir/TAF/FTC or dolutegravir + tenofovir/(FTC or 3TC). Suppressed viral load = no sexual transmission (U=U). PrEP: daily or on-demand TDF/FTC, or injectable cabotegravir/lenacapavir. PEP within 72 h × 28 days: dolutegravir + TDF/FTC or bictegravir/TAF/FTC.

diagnosis

screen: 4th-generation HIV-1/2 antigen/antibody assay → confirm with HIV-1/2 differentiation assay (per provincial lab algorithm)
acute HIV (2–4 weeks post-exposure): mononucleosis-like illness, rash, oral/genital ulcers, aseptic meningitis — antibody may be negative → send HIV RNA
reportable to public health; partner notification
test everyone with: TB, any STI, hepatitis B/C, zoster <50 years, unexplained lymphopaenia/thrombocytopaenia, oral thrush, any AIDS-defining illness

baseline workup

domain	tests
HIV	CD4 count, HIV RNA, genotype (RT/protease; integrase if prior cabotegravir PrEP)
drug safety	*HLA-B5701** (before abacavir), creatinine/eGFR, urinalysis, LFTs, G6PD (before dapsone, primaquine)
co-infection	HBsAg/anti-HBs/anti-HBc, HAV IgG, HCV Ab, syphilis, GC/CT NAAT from all exposed sites, IGRA or TST (≥5 mm positive), toxoplasma IgG; serum CrAg if CD4 <100
metabolic	lipids, HbA1c, pregnancy test
cancer	cervical screening; anal cancer screening in higher-risk groups
vaccines	HBV, HAV, pneumococcal, recombinant zoster, HPV, meningococcal, influenza, COVID

starting ART

all people with HIV, regardless of CD4 — START (2015): immediate ART reduced serious AIDS and non-AIDS events
rapid start (same day to ≤7 days) — do not wait for genotype or HLA-B*5701 if using a bictegravir- or dolutegravir-based 3-drug regimen
delay only for cryptococcal meningitis (4–6 weeks) and TB meningitis (~8 weeks) — see HIV opportunistic infections and tuberculosis

preferred initial regimens (IAS-USA 2024)

regimen	notes
bictegravir/TAF/FTC (Biktarvy)	single tablet; high barrier to resistance; suitable for rapid start; not with rifampin
dolutegravir + TAF or TDF + FTC or 3TC	high barrier; with rifampin → dolutegravir 50 mg BID
dolutegravir/3TC (2-drug)	only if HIV RNA <500,000, no HBV, genotype shows no RT resistance — not for rapid start

HBV coinfection → regimen must include tenofovir (TAF or TDF) + FTC/3TC; stopping it → HBV flare.

key drug issues

issue	detail
TDF vs TAF	TDF: more renal tubular and bone toxicity, better lipids, cheaper; TAF: more weight gain
abacavir	HLA-B*5701 → hypersensitivity (never rechallenge); possible increased MI risk
INSTI + polyvalent cations	Ca, Mg, Al, Fe chelate INSTIs → take INSTI 2 h before or 6 h after
rifampin	bictegravir contraindicated, TAF not recommended; dolutegravir 50 mg BID; rifabutin if boosted PI needed
boosters (ritonavir, cobicistat)	CYP3A4 inhibition → inhaled/intranasal fluticasone or injected triamcinolone → Cushing’s; simvastatin/lovastatin contraindicated; DOAC, amiodarone, sildenafil levels ↑
INSTI + TAF	weight gain

monitoring and failure

HIV RNA at 4–8 weeks, then q3–6 months; goal <50 copies/mL (usually by 24 weeks)
CD4 q3–6 months until >200 on suppressed ART; less often thereafter
virological failure: confirmed HIV RNA >200 copies/mL → adherence, interactions, absorption (cation chelation) → genotype while on the failing regimen
U=U: sustained HIV RNA <200 copies/mL → no sexual transmission (PARTNER2 (2019))

long-acting injectable ART

cabotegravir + rilpivirine IM q1–2 months — maintenance only: suppressed ≥3–6 months on oral ART, no resistance to either drug, no HBV (no HBV activity)
missed injections → INSTI resistance risk

cardiometabolic and cancer care

REPRIEVE (2023): pitavastatin 4 mg in people with HIV aged 40–75 at low–moderate 10-year risk → 35% fewer major cardiovascular events
→ statin for most people with HIV aged ≥40; choose one without booster interactions (pitavastatin, rosuvastatin, atorvastatin at lower dose with boosters)
screen for anal and cervical cancer; smoking cessation (dominant driver of cancer and CVD)

pregnancy

dolutegravir-based ART preferred (neural tube defect signal resolved); continue effective ART started before pregnancy
HIV RNA >1000 copies/mL near delivery → IV zidovudine intrapartum + caesarean at 38 weeks
suppressed → vaginal delivery; perinatal transmission <1%
infant post-exposure prophylaxis and feeding plan with the perinatal HIV team

pre-exposure prophylaxis (Canadian 2025 guideline)

Offer to: anyone who requests it; condomless sex outside a mutually monogamous relationship with an HIV-negative partner, bacterial STI in past year, multiple partners, sex with methamphetamine/nitrates, shared injection equipment, recurrent PEP use.

regimen	who
TDF/FTC daily	everyone (strong recommendation)
TDF/FTC on-demand (“2-1-1”: 2 tabs 2–24 h before sex, then 1 at 24 h and 48 h)	cisgender men and transgender women with sexual exposure to men — not cisgender women or PWID
TAF/FTC daily	alternative; limited data for receptive vaginal sex or PWID
cabotegravir 600 mg IM q2 months	MSM, transgender women, cisgender women
lenacapavir SC q6 months	Health Canada approved 2026 (after the guideline)

baseline: 4th-generation HIV test (exclude acute HIV), creatinine, HBV serology (vaccinate if non-immune), HCV, STI screen
follow-up: HIV test q3 months (every injection for cabotegravir), STIs q3–4 months from all exposed sites, creatinine q3–6 months
do not start TDF/FTC if eGFR <60 mL/min

post-exposure prophylaxis

start as soon as possible, ≤72 h after exposure; 28 days
indicated for a meaningful exposure (receptive/insertive anal or vaginal sex, shared needles, percutaneous occupational) to a source with possible transmissible HIV
not indicated if the source has a sustained undetectable viral load or is confirmed HIV-negative
regimen: dolutegravir 50 mg daily + TDF/FTC, or bictegravir/TAF/FTC
baseline HIV, HBV, HCV, syphilis/STI testing; HBV vaccine ± HBIG if non-immune and source HBsAg-positive
repeat HIV testing after completion; move directly to PrEP if ongoing risk
occupational percutaneous exposure to HIV-positive blood: transmission risk ~0.3%

traps

negative antibody test in a febrile patient with a recent exposure → acute HIV possible → HIV RNA
starting dolutegravir/3TC before HBV status and genotype are known
stopping TDF/TAF/FTC/3TC in HBV coinfection → hepatitis flare
rifampin with bictegravir — switch to dolutegravir BID
fluticasone inhaler in a patient on ritonavir/cobicistat → iatrogenic Cushing’s and adrenal suppression
long-acting cabotegravir/rilpivirine in HBV coinfection — no HBV cover