HIV and opportunistic infections

After studying this note, you will be able to evaluate, stage, and manage patients presenting with HIV and opportunistic infections; always verify regimens and local protocols against current Kenya MoH guidelines and your institutional formulary.

Definition

Human Immunodeficiency Virus (HIV) infection is a chronic retroviral disease characterized by progressive depletion of CD4+ T-helper lymphocytes, culminating in profound cell-mediated immunodeficiency. Acquired Immunodeficiency Syndrome (AIDS) is the advanced clinical stage of this infection, defined by a CD4+ T-lymphocyte count falling below a critical threshold (typically fewer than 200 cells/µL) or the clinical emergence of designated AIDS-defining illnesses and severe opportunistic infections (OIs). Opportunistic infections are severe, often fatal infections caused by pathogens (fungal, viral, bacterial, protozoal) that rarely cause serious disease in an immunocompetent host, or represent aggressive reactivations of latent infections.

Anatomy and physiology you need

• The CD4+ T-lymphocyte: The central coordinator of adaptive cell-mediated immunity. It recognizes antigens presented on major histocompatibility complex (MHC) class II molecules and secretes cytokines (interferon-gamma, interleukin-2) to activate macrophages, cytotoxic CD8+ T-cells, and natural killer (NK) cells.
• Viral entry co-receptors: Viral surface envelope glycoprotein gp120 binds to the host CD4 receptor; a conformational change enables secondary binding to chemokine coreceptors (CCR5 on macrophages and memory T-cells; CXCR4 on naive T-cells). Transmembrane glycoprotein gp41 then mediates viral envelope fusion with the host cell membrane.
• Gut-Associated Lymphoid Tissue (GALT): The anatomical site harboring the vast majority of the body's total CD4+ memory T-cells (specifically Th17 cells). It is the earliest and most severely depleted anatomical compartment during primary infection, compromising the integrity of the mucosal epithelial barrier.
• Mucosal and Blood-Brain Barriers: Loss of CD4+ Th17 and Th1 surveillance disrupts mucosal integrity in the respiratory, gastrointestinal, and central nervous systems, permitting transepithelial invasion of microbial flora and dissemination of neurotropic pathogens (e.g., Cryptococcus neoformans, Toxoplasma gondii) across the blood-brain barrier.
• Monocyte-Macrophage System: Macrophages and dendritic cells serve as initial targets and long-term viral sanctuaries. Impaired macrophage activation directly undermines granuloma formation and intracellular pathogen killing.

Causes and risk factors

The causative agents are Human Immunodeficiency Viruses: HIV-1 (predominant globally and in East Africa, highly pathogenic) and HIV-2 (primarily West Africa, lower transmissibility and slower progression). Both are enveloped, single-stranded RNA retroviruses of the Lentivirus genus.

Transmission routes

• Sexual transmission: Heterosexual intercourse accounts for the highest transmission burden in the Kenyan setting; viral entry is facilitated by concurrent ulcerative sexually transmitted infections (e.g., herpes simplex virus-2, syphilis).
• Vertical transmission: Mother-to-child transmission (MTCT) occurring in utero, intrapartum during delivery, or postpartum via breast milk.
• Parenteral exposure: Contaminated needle sharing among people who inject drugs (PWID), occupational needlestick injuries, or transfusion of unscreened blood products.

Vulnerabilities and co-morbidities in the tropical/Kenyan context

• Tuberculosis (TB): Mycobacterium tuberculosis is the leading cause of death in HIV-infected individuals locally. Active TB drives systemic immune activation, which accelerates HIV replication, while HIV destroys the cellular architecture required to maintain latent TB in caseating granulomas.
• **Malaria (Plasmodium falciparum):** Co-infection leads to reciprocal worsening: HIV-induced immunosuppression impairs acquired anti-malarial humoral immunity (causing higher parasitemia, treatment failure, and severe malaria), while acute malarial paroxysms trigger surges in viral replication.
• Endemic fungal and parasitic exposures: High environmental exposure to agricultural soils (Cryptococcus neoformans), contaminated water or livestock (Cryptosporidium, Cystoisospora), and feline vectors (Toxoplasma gondii).
• Structural and hematological factors: Malnutrition, sickle cell disease, and chronic parasitic helminthiases exacerbate baseline cytopenias and compromise cell-mediated barrier defense.

Pathophysiology

Viral entry and latency

Inoculation at mucosa $\rightarrow$ gp120 binds CD4 and chemokine co-receptor (CCR5/CXCR4) $\rightarrow$ gp41 induces membrane fusion $\rightarrow$ internal viral core uncoats into host cytoplasm $\rightarrow$ viral reverse transcriptase converts single-stranded RNA into double-stranded complementary DNA $\rightarrow$ pre-integration complex translocates to nucleus $\rightarrow$ viral integrase permanently incorporates proviral DNA into host genome $\rightarrow$ establishment of a transcriptionally silent, persistent latent viral reservoir.

Progressive immune collapse

Proviral transcription driven by host nuclear factors (e.g., NF-$\kappa$B) $\rightarrow$ viral protein synthesis, assembly, and budding $\rightarrow$ extensive cytopathic lysis of infected CD4+ cells $\rightarrow$ sustained systemic immune activation leads to chronic activation-induced apoptosis of uninfected bystander T-cells $\rightarrow$ irreversible depletion of GALT mucosal Th17 cells $\rightarrow$ breakdown of gut mucosal barrier $\rightarrow$ translocation of bacterial lipopolysaccharides into systemic circulation $\rightarrow$ persistent, exhausting immune hyperactivation $\rightarrow$ progressive decline in peripheral absolute CD4+ count and disruption of normal lymphoid tissue architecture.

Development of opportunistic infections

Absolute loss of CD4+ helper signals $\rightarrow$ impaired interferon-gamma and cytokine release $\rightarrow$ failure of macrophage activation and loss of delayed-type hypersensitivity $\rightarrow$ breakdown of existing calcified granulomas containing dormant M. tuberculosis $\rightarrow$ active pulmonary and disseminated TB $\rightarrow$ further CD4 depletion below critical thresholds:

• $\text{CD4} < 200 \text{ cells/µL} \rightarrow$ failure of alveolar macrophage-mediated clearing of fungal spores $\rightarrow$ Pneumocystis jirovecii pneumonia.
• $\text{CD4} < 100 \text{ cells/µL} \rightarrow$ loss of containment of encysted parasites and fungal dissemination $\rightarrow$ Toxoplasma gondii cerebral abscesses and Cryptococcus neoformans basilar meningitis.
• $\text{CD4} < 50 \text{ cells/µL} \rightarrow$ unchecked viral and atypical mycobacterial dissemination $\rightarrow$ Cytomegalovirus (CMV) retinitis and Mycobacterium avium complex (MAC) bacteremia.

Clinical features

History questions that matter

• Weight trajectory and fever: Document unmeasured weight loss ("loosened clothing") and drenching night sweats; points directly to advanced HIV, disseminated tuberculosis (TB), or lymphoma.
• Cough characteristics: Enquire about duration, sputum production, and hemoptysis. A dry cough with progressive dyspnea suggests Pneumocystis jirovecii pneumonia (PCP), whereas a productive cough with constitutional symptoms suggests pulmonary TB.
• Neurological symptoms: Ask about persistent dull headaches, neck stiffness, confusion, visual disturbances, or new-onset seizures. These indicate central nervous system (CNS) infections like cryptococcal meningitis, cerebral toxoplasmosis, or tuberculoma.
• Gastrointestinal symptoms: Ask about painful swallowing (odynophagia indicates esophageal candidiasis or CMV) and chronic diarrhea lasting over two weeks (suggests Cryptosporidium, Microsporidia, or Isospora belli).
• Treatment and adherence history: Prior antiretroviral therapy (ART) exposure, cotrimoxazole preventive therapy (CPT), TB preventive therapy (TPT), treatment interruptions, and recent clinic defaults to assess drug resistance risk or immune failure.

Examination findings and why each occurs

• Wasting (cachexia): Loss of muscle and fat mass driven by chronic hypermetabolism and tumor necrosis factor-alpha (cachectin) release from uncontrolled viral replication and secondary opportunistic infections (OIs).
• Oral lesions:
  • Oral thrush (pseudomembranous candidiasis): Curdy white plaques scraping off to reveal erythematous mucosa; signals falling CD4 cell counts (typically below 200 cells/µL) as mucosal cell-mediated immunity fails.
  • Oral hairy leukoplakia: Corrugated, white, non-scrapable lateral tongue patches caused by uncontrolled Epstein-Barr virus (EBV) replication in epithelial cells.
• Generalized lymphadenopathy: Nontender, firm, symmetrical nodes involving extra-inguinal sites; reflects persistent follicular hyperplasia in early disease, or tuberculous adenitis/lymphoma in advanced disease.
• Dermatological signs:
  • Pruritic papular eruption (PPE): Symmetrical, intensely itchy papules on extremities caused by hypersensitivity to insect bites in immune-dysregulated hosts.
  • Herpes zoster scars: Multi-dermatomal scarring indicating prior severe varicella-zoster reactivation.
  • Kaposi sarcoma: Violaceous, non-blanching macules, plaques, or nodules on the skin, palate, or conjunctiva due to Human Herpesvirus 8 (HHV-8)-driven endothelial proliferation.
• Respiratory signs: Tachypnea, cyanosis, and minimal chest findings despite severe hypoxia (PCP, due to alveolar-capillary block) versus localized crackles, bronchial breathing, or dullness (TB consolidation or pleural effusion).
• Neurological signs: Meningism (often subtle in cryptococcal meningitis due to blunted inflammatory response), focal motor/sensory deficits (focal toxoplasma abscesses or tuberculoma), or cranial nerve palsies (basal tuberculous meningitis).

Differential diagnosis

Investigations

Diagnosis and severity

Diagnosis of HIV infection requires confirmation using the national validated testing algorithm: an initial screening rapid diagnostic test (RDT), followed by a second confirmatory RDT using a different antigen target if reactive. In infants under 18 months, diagnosis relies on HIV DNA/RNA polymerase chain reaction (PCR) because maternal transplacental IgG antibodies persist.

Severity is graded using both immunological criteria and the WHO Clinical Staging system:

• Immunological staging (CD4 count): Normal immune status (above 500 cells/µL), mild immunodeficiency (350–499 cells/µL), advanced immunodeficiency (200–349 cells/µL), and severe immunodeficiency (below 200 cells/µL or percentage below 15%).
• WHO clinical staging:
  • Stage 1: Asymptomatic or persistent generalized lymphadenopathy.
  • Stage 2: Mild symptoms; unexplained moderate weight loss, recurrent respiratory infections, herpes zoster, angular cheilitis, fungal nail infections.
  • Stage 3: Advanced symptoms; unexplained severe weight loss, chronic diarrhea over one month, persistent fever, oral candidiasis, pulmonary TB, severe bacterial infections.
  • Stage 4: Severe symptoms (defining illnesses); HIV wasting syndrome, PCP, extrapulmonary TB, cryptococcal meningitis, cerebral toxoplasmosis, Kaposi sarcoma, CMV retinitis, and chronic herpes simplex ulcerations.

Patients presenting with WHO Stage 3 or 4, or any patient with a CD4 count below 200 cells/µL, have Advanced HIV Disease (AHD), carrying the highest risk of immediate mortality and requiring accelerated diagnostic workup and targeted prophylaxis.

Management

Immediate Stabilisation

The immediate priority is to address any life-threatening complications of opportunistic infections (OIs). This includes:

• Airway, Breathing, Circulation (ABC): Ensure a patent airway, adequate oxygenation, and circulatory stability. For example, patients with Pneumocystis pneumonia (PCP) may require supplemental oxygen. Those with severe dehydration from diarrhoea may need intravenous fluids.
• Symptomatic Relief: Manage fever with antipyretics, pain with analgesics, and nausea/vomiting with antiemetics.
• Seizure Management: If seizures are present (e.g., due to cerebral toxoplasmosis or cryptococcal meningitis), administer anticonvulsants.
• Fluid and Electrolyte Balance: Correct any significant electrolyte derangements, especially in patients with diarrhoea or vomiting.

Definitive Treatment

Definitive management involves treating the underlying HIV infection and the specific opportunistic infection.

• Antiretroviral Therapy (ART): Initiation or optimisation of ART is crucial for restoring immune function. ART suppresses viral replication, allowing the CD4 count to rise and reducing the risk of further OIs. ART should be initiated as soon as possible, ideally within the first week of diagnosis, unless there are contraindications.
• OI-Specific Treatment:
  • Tuberculosis (TB): Standard anti-TB regimens are used. ART should be initiated cautiously after starting TB treatment, considering the risk of IRIS.
  • Pneumocystis Pneumonia (PCP): Trimethoprim-sulfamethoxazole is the first-line treatment. Alternatives are used for sulfa-allergic patients. Prophylaxis is also important.
  • Cryptococcal Meningitis: Amphotericin B (often with flucytosine) followed by fluconazole is the standard. Lumbar punctures may be needed for cerebrospinal fluid (CSF) pressure management.
  • Toxoplasmosis: Pyrimethamine and sulfadiazine are used, often with leucovorin.
  • Candidiasis (Oropharyngeal/Oesophageal): Topical or systemic azole antifungals are effective.
  • Bacterial Pneumonia: Appropriate antibiotics based on likely pathogens and local resistance patterns.
  • Malaria: Standard antimalarial treatment based on the species and severity.
  • Other Tropical Infections: Treatment tailored to the specific diagnosis.

Monitoring and Follow-up

• Clinical Response: Monitor for improvement in symptoms, resolution of OI signs, and general well-being.
• Laboratory Parameters:
  • CD4 Count: Track the rise in CD4 count, indicating immune reconstitution.
  • Viral Load: Monitor viral suppression on ART.
  • OI-Specific Markers: For example, CSF parameters in meningitis, sputum microscopy in TB.
• ART Adherence: Crucial for long-term success. Regular counselling and support are vital.
• OI Prophylaxis: Continue or initiate prophylaxis for OIs (e.g., PCP, toxoplasmosis) based on CD4 count thresholds, even after starting ART, until immune reconstitution is adequate.
• Drug Toxicity Monitoring: Monitor for side effects of ART and OI medications.

Contraindications and Safety

• Drug Interactions: Be aware of potential interactions between ART drugs, OI medications, and other drugs the patient may be taking.
• Allergies: Document and avoid known drug allergies.
• Renal and Hepatic Function: Adjust doses or choose alternative agents based on organ function.
• IRIS (Immune Reconstitution Inflammatory Syndrome): A paradoxical worsening of OI symptoms after starting ART due to an overactive immune response. Management may involve continuing ART and treating the inflammation, sometimes with corticosteroids.

Complications and Prognosis

Complications:

• IRIS: Can be severe and life-threatening.
• Drug Toxicity: Side effects from ART and OI medications.
• Treatment Failure: Due to poor adherence, drug resistance, or inadequate treatment.
• Chronic Organ Damage: From untreated or recurrent OIs (e.g., neurological deficits from CNS infections, pulmonary fibrosis from PCP).
• Malignancies: Increased risk of certain cancers (e.g., Kaposi's sarcoma, lymphoma) in advanced HIV.
• Non-AIDS Defining Illnesses: Cardiovascular disease, renal disease, and metabolic complications become more prominent as ART improves survival.

Prognosis:

With timely diagnosis, effective ART, and appropriate management of OIs, the prognosis for individuals with HIV has dramatically improved. Many can achieve near-normal life expectancy and good quality of life. However, prognosis is poorer in those who present with advanced immunosuppression, multiple OIs, or delayed treatment initiation.

High-Yield Exam Points

• Look-alike Conditions:
  • TB vs. PCP: Both present with cough, fever, and dyspnea. CXR findings can overlap. CD4 count is a key differentiator for risk.
  • Cryptococcal Meningitis vs. Bacterial Meningitis: Both cause headache, fever, and neck stiffness. CSF analysis is critical.
  • Malaria vs. other febrile illnesses: In endemic areas, malaria is a common cause of fever and must be ruled out.
• Commonest Wrong First Steps:
  • Starting empiric treatment for a common OI without adequate investigation.
  • Delaying ART initiation in a patient with an OI without a clear contraindication.
  • Not considering TB in a patient with a persistent cough and fever.
• Examiner Questions at Bedside:
  • "What are the immediate priorities for this patient?" (ABC, symptomatic relief)
  • "What investigations would you order to confirm your suspected OI?"
  • "How would you manage the HIV infection in this patient?" (ART initiation/optimization)
  • "What are the potential complications of treating this OI and HIV?" (IRIS, drug toxicity)
  • "What is the role of prophylaxis in this patient?"

Clinical Case

A 35-year-old man presents with a two-week history of progressive shortness of breath, dry cough, and fever. He has lost weight and feels generally unwell. On examination, he is tachypneic, with bilateral crackles on auscultation. His oxygen saturation is 88% on room air. He has generalised lymphadenopathy.

Questions:

1. What is the most likely opportunistic infection given his presentation and the Kenyan setting?
2. What immediate management steps would you take?
3. What key investigations would you perform to confirm the diagnosis and assess his HIV status?

Model Answers:

1. Pneumocystis pneumonia (PCP) is the most likely opportunistic infection, given the subacute onset of dyspnea, dry cough, fever, and hypoxemia in an immunocompromised individual. Tuberculosis is also a strong consideration in this setting.
2. Immediate management includes supplemental oxygen to maintain saturation, symptomatic treatment for fever, and ensuring adequate hydration. Prompt initiation of empirical treatment for the suspected OI is crucial.
3. Key investigations would include a chest X-ray, sputum microscopy for AFB (to rule out TB), and HIV serology. Arterial blood gas analysis would assess the severity of hypoxemia. Induced sputum or bronchoalveolar lavage may be needed for PCP diagnosis if initial investigations are inconclusive.

Practice Questions

Question 1

A 40-year-old woman with known HIV presents with a two-week history of worsening headache, photophobia, and neck stiffness. Her CD4 count is 50 cells/µL. She has a low-grade fever.

What is the most appropriate next step in management?

A. Start empiric treatment for bacterial meningitis. B. Perform a lumbar puncture for cerebrospinal fluid analysis. C. Initiate antiretroviral therapy immediately. D. Order a CT scan of the brain.

Answer: B. Perform a lumbar puncture for cerebrospinal fluid analysis Explanation: Given her low CD4 count and symptoms suggestive of meningitis, a lumbar puncture is essential to identify the causative organism, especially considering the high prevalence of cryptococcal meningitis in this setting.

Question 2

A 28-year-old man presents with a two-week history of progressive dyspnea, dry cough, and fever. His oxygen saturation is 85% on room air. He is HIV-positive with a CD4 count of 75 cells/µL.

Which of the following is the most likely opportunistic infection?

A. Pulmonary tuberculosis B. Cryptococcal meningitis C. Pneumocystis pneumonia D. Oral candidiasis

Answer: C. Pneumocystis pneumonia Explanation: The constellation of subacute dyspnea, dry cough, fever, and hypoxemia in an HIV-positive individual with a CD4 count below 200 cells/µL is highly suggestive of Pneumocystis pneumonia.

Question 3

A 50-year-old man with HIV (CD4 count 150 cells/µL) presents with a persistent, non-productive cough, fever, and shortness of breath for three weeks. Chest X-ray shows bilateral interstitial infiltrates. He is started on trimethoprim-sulfamethoxazole. Two days later, his symptoms worsen, and he develops a rash.

What is the most likely explanation for his worsening symptoms and rash?

A. Drug resistance to trimethoprim-sulfamethoxazole. B. Development of Pneumocystis pneumonia. C. Immune Reconstitution Inflammatory Syndrome (IRIS). D. A new, unrelated infection.

Answer: C. Immune Reconstitution Inflammatory Syndrome (IRIS). Explanation: Worsening of OI symptoms and new symptoms (like rash) after starting ART or treatment for an OI, especially in the context of immune reconstitution, is characteristic of IRIS.

Question 4

Which of the following opportunistic infections is primarily associated with a CD4 count below 100 cells/µL?

A. Oropharyngeal candidiasis B. Pulmonary tuberculosis C. Cryptosporidiosis D. Cytomegalovirus retinitis

Answer: D. Cytomegalovirus retinitis Explanation: While other infections can occur at higher CD4 counts, CMV retinitis typically presents when the CD4 count drops significantly below 100 cells/µL.

Question 5

A 30-year-old HIV-positive patient with a CD4 count of 30 cells/µL presents with fever, headache, and confusion. Lumbar puncture reveals India ink positive cryptococci. He is started on amphotericin B.

What is the most crucial component of his long-term management?

A. High-dose antiretroviral therapy immediately. B. Prophylaxis for Pneumocystis pneumonia. C. Long-term suppressive therapy with fluconazole. D. Regular monitoring of liver function tests.

Answer: C. Long-term suppressive therapy with fluconazole. Explanation: After initial treatment for cryptococcal meningitis, long-term fluconazole is essential for secondary prophylaxis to prevent relapse, especially in patients with very low CD4 counts. ART should be initiated cautiously after initial OI treatment.

Drafted with AI assistance from standard references and reviewed for structure. Check details against your lecture notes and the Kenya MoH guideline.