12.3 Bloodborne Infectious Disease Screening: HIV & Hepatitis C

Universal HIV Screening: USPSTF Grade A Mandates

Human Immunodeficiency Virus (HIV) infection is a chronic bloodborne and sexually transmitted infection that causes progressive CD4+ T-lymphocyte depletion, cellular immune failure, and opportunistic illness. Early diagnosis and prompt initiation of Antiretroviral Therapy (ART) suppress viral replication, halt disease progression, restore normal life expectancy, and eliminate sexual transmission (Undetectable = Untransmittable [U=U]).

The USPSTF Recommendations

• Universal Screening (Ages 15 to 65 Years; Grade A): The USPSTF recommends that clinicians screen for HIV infection in all adolescents and adults aged 15 to 65 years, regardless of reported risk behaviors or clinical presentation. Routine opt-out screening normalizes testing, reduces social stigma, and identifies the estimated 13% of individuals living with HIV who are unaware of their infection.
• Universal Screening in Pregnancy (Grade A): Universal HIV screening is recommended for all pregnant persons during each pregnancy, ideally at the initial prenatal visit. For individuals at high risk of HIV acquisition (e.g., PWID, partners living with HIV, commercial sex work, new STI diagnosis during pregnancy, or residing in high-prevalence areas), screening must be repeated during the third trimester (prior to 36 weeks gestation). Immediate rapid testing during labor and delivery is mandated for individuals whose HIV status is undocumented.
• High-Risk Individuals Outside Ages 15 to 65 (Grade A): Screen persons younger than 15 or older than 65 who exhibit increased risk factors (new or multiple partners, injection drug use, MSM, transactional sex).
• Screening Frequency for High-Risk Populations: Individuals at ongoing high risk—such as sexually active MSM, transgender individuals having condomless sex, PWID sharing injection paraphernalia, and commercial sex workers—should undergo screening at least annually, and as often as every 3 to 6 months.
• Opt-Out Consent Paradigm: HIV testing should be conducted using an opt-out model: the patient is notified verbally or in writing that HIV testing will be performed as part of routine preventive labs unless the patient explicitly declines. Formal separate written consent is no longer recommended by the CDC, as it creates administrative barriers to universal testing.

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The CDC / CLSI 4th-Generation HIV Diagnostic Algorithm

Modern clinical practice utilizes the Centers for Disease Control and Prevention and Clinical and Laboratory Standards Institute (CDC/CLSI) standardized diagnostic cascade, which replaced older Western blot algorithms:

STEP 1: 4th-Generation HIV-1/2 Combination Immunoassay
(Detects HIV-1/2 Antibodies & HIV-1 p24 Antigen)
                  |
        +---------+---------+
        |                   |
   NON-REACTIVE          REACTIVE
        |                   |
   HIV Negative             v
(Unless acute window  STEP 2: HIV-1 / HIV-2 Antibody Differentiation Immunoassay
 suspected; check RNA)      |
        +-------------------+-------------------+
        |                   |                   |
   HIV-1 (+)           HIV-2 (+)         BOTH (-) OR INDETERMINATE
        |                   |                   |
   HIV-1 Infection     HIV-2 Infection          v
      Confirmed           Confirmed       STEP 3: Qualitative / Quantitative
                                                HIV-1 RNA NAAT
                                                |
                                      +---------+---------+
                                      |                   |
                                   DETECTABLE        UNDETECTABLE
                                      |                   |
                                  ACUTE HIV-1      FALSE-POSITIVE
                                   INFECTION        SCREENING TEST
                                  (p24(+) / Ab(-))  (HIV Negative)

Detailed Breakdown of Algorithm Steps

1. Step 1: 4th-Generation Combination Immunoassay:
   • Detects both HIV-1 and HIV-2 antibodies (IgM and IgG) AND the HIV-1 p24 capsid antigen.
   • The Diagnostic Advantage: Free viral p24 antigen appears in the bloodstream within 14 to 20 days post-infection, significantly earlier than host IgG antibodies (which develop at 30 to 45 days). This test narrows the diagnostic "window period" to approximately 2 to 3 weeks.
   • If non-reactive: The patient is considered HIV-negative. (Caveat: If the patient reports a high-risk exposure within the preceding 14 days, the test may be in the pre-p24 eclipse window; order an HIV-1 RNA NAAT immediately). If reactive, reflex directly to Step 2.
2. Step 2: HIV-1 / HIV-2 Antibody Differentiation Immunoassay:
   • Rapid, multi-spot instrument immunoassay that discriminates whether reactive antibodies are directed against HIV-1 or HIV-2.
   • Clinical Distinction: Identifying HIV-2 is clinically vital: HIV-2 is endemic to West Africa and is intrinsically resistant to Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) and has decreased susceptibility to certain protease inhibitors.
   • If reactive for HIV-1 or HIV-2 antibodies: Diagnosis is established.
   • If non-reactive or indeterminate for both antibodies: Proceed directly to Step 3.
3. Step 3: HIV-1 RNA Nucleic Acid Amplification Test (NAAT):
   • Detects viral RNA genetic material (qualitative or quantitative viral load).
   • Scenario A (HIV-1 RNA Detectable): Confirms Acute HIV-1 Infection (the p24 antigen was detected in Step 1, but host antibodies have not yet formed in Step 2).
   • Scenario B (HIV-1 RNA Undetectable): Confirms that the initial Step 1 immunoassay was a biological false positive. The patient is uninfected.

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Acute Retroviral Syndrome (Primary HIV Infection)

Acute Retroviral Syndrome (ARS) represents the initial symptomatic phase of HIV infection, occurring in 50% to 80% of individuals approximately 2 to 4 weeks after viral inoculation.

Clinical Presentation

ARS typically presents as a severe, prolonged mononucleosis-like illness characterized by:

• High spiking fevers (96%) and severe fatigue.
• Generalized, non-tender cervical, axillary, and occipital lymphadenopathy (74%).
• Pharyngitis (70%), frequently non-exudative.
• Maculopapular morbilliform rash (70%): An erythematous, non-pruritic maculopapular eruption prominently distributed across the face, neck, upper trunk, and occasionally the extremities, palms, and soles.
• Severe myalgias and arthralgias (54%).
• Painful mucocutaneous ulcerations (33%): Shallow, sharply demarcated aphthous-like ulcers on the oral mucosa, tongue, esophagus, or anogenital region.
• Gastrointestinal symptoms: Nausea, vomiting, profuse watery diarrhea, and rapid weight loss.
• Neurologic manifestations: Aseptic meningitis, facial palsy, or radiculopathy.

Diagnostic Biomarker Dynamics & Exam Pearls

• Viremia Level: During ARS, viral replication is unconstrained by host cellular immunity; plasma HIV-1 RNA levels are massively elevated—routinely exceeding 100,000 to millions of copies/mL.
• The Diagnostic Trap: A 3rd-generation antibody test will be completely non-reactive (negative) because host IgG seroconversion takes 3 to 6 weeks. A 4th-generation combination assay may be reactive due to p24 antigen, but the Step 2 differentiation assay will be negative. The single most sensitive and definitive diagnostic test for Acute Retroviral Syndrome is quantitative plasma HIV-1 RNA PCR (viral load).
• Board Exam Pearl: A young patient presents with high fever, sore throat, generalized lymphadenopathy, and a diffuse maculopapular rash. A heterophile antibody test (Monospot) is negative. The primary care physician must immediately ask about sexual and injection history and order an HIV-1 RNA NAAT to diagnose acute HIV, which is the most critical "Monospot-negative mono" lookalike!
• Urgent Clinical Action: Immediate initiation of Antiretroviral Therapy (ART)—same-day or rapid start—preserves the latent CD4 cell reservoir, limits chronic immune activation, prevents opportunistic sequelae, and abruptly halts forward viral transmission.

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Universal Hepatitis C Screening: USPSTF Grade A Mandates

Hepatitis C Virus (HCV) is a single-stranded RNA flavivirus transmitted predominantly through parenteral blood contact. Chronic infection develops in 75% to 85% of exposed individuals, leading to progressive hepatic fibrosis, cirrhosis, end-stage liver disease, and hepatocellular carcinoma (HCC).

The Screening Guidelines

• Universal Screening for Adults Aged 18 to 79 Years (USPSTF Grade A): The USPSTF recommends one-time universal screening for HCV infection in all adults aged 18 to 79 years, regardless of risk factors. This universal recommendation expanded upon the previous "baby boomer" birth cohort (1945–1965) strategy due to the dramatic surge in acute HCV infections among adolescents and young adults fueled by the opioid and injection drug epidemic.
• Universal Screening in Pregnancy (USPSTF Grade A): Screen all pregnant persons during each pregnancy, typically at the initial prenatal visit. Identifying maternal infection enables postpartum curative treatment and guides pediatric testing for infants at risk of vertical transmission.
• Periodic / Annual Screening for Ongoing Risk: Individuals with persistent risk behaviors—such as ongoing injection drug use, intranasal illicit substance use, maintenance hemodialysis, men with HIV who have sex with men, commercial sex workers, and individuals who received unregulated tattoos or body piercings—must receive annual or more frequent HCV screening.

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Hepatitis C Diagnostic Testing Cascade & Serologic Patterns

The diagnostic cascade for Hepatitis C requires an initial screening test followed by mandatory, automated molecular confirmation:

INITIAL SCREENING: Anti-HCV Antibody Immunoassay
                       |
             +---------+---------+
             |                   |
        NON-REACTIVE          REACTIVE
             |                   |
        No Infection             v
   (Unless acute window;   MANDATORY REFLEX: Quantitative HCV RNA PCR
    check RNA if suspected)      |
                       +---------+---------+
                       |                   |
                   DETECTABLE         UNDETECTABLE
                       |                   |
                 ACTIVE CHRONIC      RESOLVED PAST
                 HCV INFECTION         INFECTION
                (Evaluate for DAA)  (Or Treated HCV;
                                    Anti-HCV stays (+))

Automated Reflex HCV RNA Testing

Clinicians should always order "HCV Antibody with Reflex to Quantitative HCV RNA." When the anti-HCV antibody is reactive, the laboratory automatically tests the original primary blood sample for HCV RNA PCR. This eliminates the catastrophic loss to follow-up (previously >30% to 50%) that occurred when patients were required to return for a separate venipuncture.

Master Interpretation Matrix: Hepatitis C Serologic Profiles

The Clinical Problem of Suspected Reinfection

Because anti-HCV antibodies persist indefinitely, an anti-HCV antibody test is completely useless for diagnosing reinfection in a patient who has previously cleared or been cured of Hepatitis C. If a patient with prior cured HCV resumes injection drug use and presents with acute malaise or elevated transaminases, the clinician must bypass the antibody test and order quantitative HCV RNA PCR directly.

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Primary Care Management of Active Hepatitis C

Once active viremia is documented (anti-HCV reactive + HCV RNA detectable), primary care physicians can easily manage and cure the infection using simplified treatment algorithms:

1. Non-Invasive Hepatic Fibrosis Assessment

Before prescribing DAAs, clinicians must determine whether the patient has progressed to cirrhosis (METAVIR stage F4):

• FIB-4 Index: Validated mathematical calculator utilizing four simple parameters: $\text{FIB-4} = \frac{\text{Age (years)} \times \text{AST (U/L)}}{\text{Platelet Count } (10^9/\text{L}) \times \sqrt{\text{ALT (U/L)}}}$
  • A calculated FIB-4 < 1.45 has a >90% negative predictive value for advanced fibrosis (F0–F2; non-cirrhotic).
  • A calculated FIB-4 > 3.25 has a 97% specificity for advanced fibrosis/cirrhosis (F3–F4).
• Transient Elastography (FibroScan): Measures liver stiffness in kilopascals (kPa). Values >=12.5 kPa indicate cirrhosis.

2. Pangenotypic Direct-Acting Antiviral (DAA) Regimens

Modern DAAs target non-structural viral proteins (NS3/4A protease inhibitors, NS5A replication complex inhibitors, and NS5B RNA-dependent RNA polymerase inhibitors). In treatment-naive patients without cirrhosis, two first-line pangenotypic regimens yield cure rates exceeding 95% to 98%:

1. Glecaprevir / Pibrentasvir (Mavyret):
   • Dosing: 3 tablets taken orally once daily with food for exactly 8 weeks.
   • Composition: Glecaprevir (NS3/4A protease inhibitor, 100 mg per tablet) + Pibrentasvir (NS5A inhibitor, 40 mg per tablet).
2. Sofosbuvir / Velpatasvir (Epclusa):
   • Dosing: 1 tablet taken orally once daily for exactly 12 weeks.
   • Composition: Sofosbuvir (NS5B nucleotide polymerase inhibitor, 400 mg) + Velpatasvir (NS5A inhibitor, 100 mg).
   • Drug Interaction Warning: Velpatasvir requires gastric acidity for oral absorption. Proton Pump Inhibitors (PPIs) severely decrease velpatasvir absorption and can cause treatment failure; PPIs must be withheld or taken 4 hours after Epclusa with food.

3. Sustained Virologic Response (SVR12) = Virologic Cure

• The therapeutic goal of DAA therapy is Sustained Virologic Response at 12 weeks post-treatment (SVR12), defined as an undetectable plasma HCV RNA level 12 weeks after completing the full antiviral course. Achieving SVR12 signifies definitive virologic cure, decreases all-cause mortality, and reduces the risk of hepatic failure.

4. Post-Cure Surveillance in Cirrhotic Patients

• CRITICAL BOARD EXAM RULE: Cirrhosis Surveillance Continues for Life: If a patient had underlying cirrhosis (F4) prior to DAA treatment, achieving SVR12 virologic cure does NOT eliminate their risk of hepatocellular carcinoma (HCC). Although the relative risk of HCC declines, the absolute annual risk remains >1% to 1.5% per year. Therefore, all patients with pre-existing cirrhosis must continue lifetime surveillance for hepatocellular carcinoma with abdominal ultrasound (with or without serum alpha-fetoprotein [AFP]) every 6 months, alongside periodic screening for esophageal varices via upper endoscopy.