Lucan · Conditions

HIV diagnosis and management

Australian guidance: ASHM National HIV Testing Policy + Australian Commentary on US DHHS HIV Guidelines

1. Definition and epidemiology

Human immunodeficiency virus (HIV) is a retrovirus that progressively destroys CD4-positive T lymphocytes, leading to acquired immunodeficiency syndrome (AIDS) when the immune system can no longer mount effective responses against opportunistic pathogens. In Australia, overall HIV seroprevalence remains low at approximately 0.14% of the general population, with the highest prevalence among gay, bisexual, and other men who have sex with men (MSM) at 9.2%. The greatest proportion of people with undiagnosed HIV in Australia are those born in Southeast Asia and Latin America, and among people who inject drugs (PWID) the seroprevalence is approximately 1.5%.

2. Pathophysiology

HIV is a single-stranded RNA retrovirus belonging to the lentivirus family. After entry into the body via mucosal surfaces, blood, or vertical transmission, the viral envelope glycoprotein gp120 binds to CD4 receptors on T helper lymphocytes, macrophages, and dendritic cells, using CCR5 or CXCR4 as co-receptors. Fusion allows viral RNA and reverse transcriptase to enter the cytoplasm. Reverse transcriptase converts viral RNA into double-stranded DNA, which integrase then incorporates into the host genome as a provirus. The provirus drives ongoing viral replication, releasing new virions that bud from the cell surface. CD4 cell destruction occurs via direct cytopathic effect, apoptosis, and immune-mediated killing of infected cells. Progressive depletion of CD4 lymphocytes below 200 cells/microlitre defines AIDS and removes the cornerstone of cell-mediated immunity, permitting opportunistic infections and malignancies that would otherwise be contained (Robbins Ch 6). Viral load (VL) correlates with the rate of CD4 decline: when VL falls below 200 copies/mL on effective antiretroviral therapy (ART), sexual transmission is eliminated, a principle termed Undetectable equals Untransmissible (U=U).

3. Clinical presentation and diagnostic criteria

HIV infection passes through three recognisable phases. Acute seroconversion illness occurs two to four weeks after primary infection and resembles a glandular fever syndrome, with pharyngitis, fever, malaise, lymphadenopathy, headache, and a maculopapular rash. Many people have no symptoms during this phase. The clinical indicator conditions listed by ASHM provide a systematic trigger for testing: any AIDS-defining illness (oesophageal candidiasis, Pneumocystis jirovecii pneumonia, Kaposi sarcoma, cryptococcal meningitis, non-Hodgkin lymphoma, cytomegalovirus retinitis), unexplained constitutional symptoms (pyrexia of unknown origin, diarrhoea, unexplained weight loss), neurological presentations (primary cerebral lymphoma, toxoplasmosis, progressive multifocal leucoencephalopathy, peripheral neuropathy, dementia), haematological abnormalities (unexplained thrombocytopaenia, lymphopenia, or neutropenia persisting more than four weeks), and any concurrent sexually transmissible infection (STI), including syphilis and hepatitis B or C. High-risk groups warranting routine testing include MSM, trans and gender diverse people, PWID, Aboriginal and Torres Strait Islander people, people from high-prevalence countries, and those recently released from custodial settings.

4. Investigations and AU-specific cutoffs

The primary diagnostic test is fourth-generation HIV serology (antigen/antibody combination Ag/Ab test). The window period from infection to reliable detection is generally up to six weeks; if concern exists about an exposure within the preceding six weeks, a repeat test at six weeks is required. Initial positive Ag/Ab results are automatically sent to a reference laboratory for confirmation; the local sexual health specialist or an infectious diseases/microbiology specialist interprets indeterminate or positive results. Indeterminate results can occur during the window period or be associated with other medical conditions and require repeat testing four to six weeks later.

For individuals commencing post-exposure prophylaxis (PEP), the baseline investigations at week 0 are: HIV Ag/Ab serology, hepatitis B serology (HBsAg, Anti-HBs, Anti-HBc), hepatitis C serology, STI screen (from all relevant anatomical sites), syphilis serology, urea/electrolytes/creatinine (UEC; hold PEP or seek specialist input if estimated glomerular filtration rate (eGFR) falls below 60 mL/min given tenofovir nephrotoxicity), and a pregnancy test if clinically indicated. Follow-up HIV Ag/Ab testing occurs at week 6 (two weeks after completing PEP, or at week 4 if transitioning directly to PrEP) and week 12.

5. Management

Initial management of a potential HIV exposure requires immediate first-aid measures: wash wounds with soap and water, irrigate mucosal surfaces and eyes with water or saline, and do not inject antiseptics into wounds. For established HIV infection, linkage to a specialist HIV prescriber (s100 prescriber) or a sexual health clinic is required for initiation and ongoing management of ART.

Post-exposure prophylaxis should be commenced as soon as possible after a significant exposure and within 72 hours; initiation of PEP must not be delayed while awaiting source HIV status. Non-occupational PEP is routinely offered after anal or vaginal intercourse with a partner known to have HIV with an unknown or detectable viral load, receptive anal intercourse with a source of unknown HIV status from a high-prevalence population (MSM, trans and gender diverse, or high-prevalence country (HPC)), and sharing of needles or injecting equipment with a source known to have HIV. PEP is not routinely offered when the source is from a low-prevalence setting (general Australian-born heterosexual population), when the source has a confirmed undetectable viral load (below 200 copies/mL), or when the exposure itself poses negligible risk (community needlestick injury, oral sex). Pre-exposure prophylaxis (PrEP) can be prescribed by any general practitioner (GP) or nurse practitioner and is PBS-listed; the Australian PrEP guidelines are available at prepguidelines.com.au.

6. Pharmacology and AU PBS notes

Established HIV infection. First-line ART per the Australian Commentary on US DHHS Guidelines consists of an integrase strand transfer inhibitor (INSTI) backbone. Preferred regimens are bictegravir/tenofovir alafenamide/emtricitabine (Biktarvy, PBS streamlined authority) or dolutegravir plus tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC). Dolutegravir is available as Tivicay; the fixed-dose combination abacavir/dolutegravir/lamivudine is available as Triumeq. Long-acting injectable cabotegravir plus rilpivirine (Cabenuva) has TGA approval and is an option for patients with stable virological suppression. Efavirenz-based regimens (previously first-line) are now reserved for second-line or specific circumstances.

PEP. The recommended 2-drug PEP regimen is tenofovir disoproxil 300 mg/emtricitabine 200 mg (TD/FTC, e.g. Truvada or generic equivalent) once daily for 28 days. This is not PBS-listed for PEP; all GPs can prescribe it on a private prescription at a cost of approximately $40 to $50 for a 28-day course. The 3-drug PEP regimen adds dolutegravir 50 mg daily; generic dolutegravir is not yet widely available so prescribers should contact the local PEP phone support line. Unlike PrEP, PEP is not PBS-subsidised.

PrEP. TD/FTC (Truvada or generic) is PBS-listed for PrEP under a streamlined authority and can be prescribed by any GP or nurse practitioner. Daily oral PrEP and event-based dosing (2-1-1 regimen) are both supported by the Australian guidelines.

7. Complications and monitoring

AIDS-defining opportunistic infections arise when the CD4 count falls below 200 cells/microlitre and include Pneumocystis jirovecii pneumonia, cerebral toxoplasmosis, cryptococcal meningitis, cytomegalovirus (CMV) retinitis, oesophageal candidiasis, disseminated Mycobacterium avium complex, and progressive multifocal leucoencephalopathy. AIDS-defining malignancies include Kaposi sarcoma, non-Hodgkin lymphoma, primary cerebral lymphoma, and invasive cervical cancer.

Monitoring for people established on ART includes HIV viral load and CD4 count at baseline, then at four weeks after commencing or changing ART (to confirm virological response), and thereafter three to six-monthly until virologically suppressed, then six to twelve-monthly once stable. Renal function (UEC, eGFR) and phosphate are monitored at baseline and annually in people taking TDF. Liver function tests are checked at baseline and at routine follow-up. Fasting lipids are measured at baseline and one to two yearly given the metabolic effects of some regimens. Bone density (DEXA scan) is considered in those on TDF with risk factors. Annual cardiovascular risk assessment is recommended. People with HIV require regular STI and syphilis screening at intervals determined by sexual behaviour (three-monthly in sexually active MSM). The U=U principle means that people on effective ART with a sustained undetectable VL have no risk of sexual HIV transmission and have near-normal life expectancy.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.