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Opportunistic infections of aids community medicine

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Opportunistic Infections (OIs) in AIDS - Community Medicine

Definition and Background

AIDS (Acquired Immunodeficiency Syndrome) is caused by HIV-1 (or HIV-2), which depletes CD4+ T lymphocytes over 8-10 years. Without treatment, >90% of HIV-infected patients progress to AIDS. The CDC defines AIDS as:
  • CD4+ T cell count <200 cells/μL, OR
  • CD4+ percentage <14%, OR
  • Development of one of 25 AIDS-defining conditions
Opportunistic infections (OIs) arise because pathogens that a healthy immune system would normally suppress exploit the profound immunodeficiency of AIDS. The type of OI depends strongly on the CD4+ count.
  • Harrison's Principles of Internal Medicine, 22E

CD4 Count and OI Risk - The Threshold Principle

CD4+ CountInfections at Risk
Any levelTB, bacterial pneumonia (S. pneumoniae, H. influenzae), Herpes zoster
<500/μLOral candidiasis (thrush), hairy leukoplakia
<200/μLPneumocystis jirovecii pneumonia (PCP), Toxoplasma encephalitis, Cryptosporidiosis, Histoplasmosis, Coccidioidomycosis
<100/μLCryptococcal meningitis, CMV retinitis/colitis
<50/μLM. avium complex (MAC), CMV disease (severe), CNS lymphoma, Progressive multifocal leukoencephalopathy (PML)
  • Harrison's Principles of Internal Medicine, 22E, p. 1634

Major Opportunistic Infections - Organised by System

1. Pulmonary OIs

Pneumocystis jirovecii Pneumonia (PCP)
  • Most common cause of pneumonia in HIV patients in developed countries; 25% of all HIV-associated pneumonias
  • Incidence ~1 case/100 person-years; 95% have CD4 <200/μL
  • Clinical features: Fever, non-productive cough, retrosternal chest pain worse on inspiration; insidious onset over weeks
  • CXR: Normal early; bilateral interstitial infiltrate (perihilar); thin-section CT shows ground-glass opacity
  • Labs: Elevated LDH, hypoxemia, widened A-a gradient
  • Dx: Demonstration of organism in induced sputum, BAL, or transbronchial biopsy; PCR
  • Treatment: TMP-SMX (21 days); alternatives: dapsone/trimethoprim, clindamycin/primaquine, atovaquone; IV pentamidine for severe disease; add glucocorticoids if PaO2 <70 mmHg or A-a gradient >35 mmHg
  • Prophylaxis: TMP-SMX DS 1 tab daily when CD4 <200/μL
Tuberculosis (HIV-TB Co-infection) - Most important in India and developing countries
  • TB can occur at any CD4 count and is the #1 killer of PLHIV worldwide
  • Advanced HIV: atypical presentations - fewer cavities, more disseminated (lymphatic, miliary, extrapulmonary), more negative smears/TST
  • Treat with standard 4-drug regimen + ART; ART should be started within 2-8 weeks of TB treatment
  • Diagnosis in HIV: Four-symptom screen (cough, weight loss, fever, night sweats) preferred; CBNAAT/Xpert-MTB/RIF recommended
  • Park's Textbook of Preventive and Social Medicine
Bacterial Pneumonia
  • S. pneumoniae and H. influenzae most common; 6-fold increase in pneumococcal pneumonia; 100-fold increase in bacteremia
  • Baseline CD4 ~300/μL at first episode
  • Prevention: conjugated pneumococcal vaccine + 23-valent polysaccharide booster; smoking cessation halves risk

2. CNS OIs

Toxoplasma gondii Encephalitis
  • Most common cause of focal brain lesion in AIDS; CD4 <100/μL
  • Presents with focal neurological deficits, fever, headache
  • CT/MRI: Multiple ring-enhancing lesions (basal ganglia predominance)
  • Prophylaxis: TMP-SMX (same dose as PCP prophylaxis covers both)
  • Treatment: Pyrimethamine + sulfadiazine + leucovorin
Cryptococcal Meningitis
  • Caused by Cryptococcus neoformans; CD4 typically <100/μL
  • Presents with subacute meningitis: headache, fever, meningism
  • Dx: India ink stain, cryptococcal antigen (CSF/serum), CSF culture
  • Treatment: Amphotericin B + flucytosine (induction) → fluconazole (consolidation/maintenance)
  • Secondary prophylaxis: Fluconazole 200 mg/day PO until CD4 >100/μL for >3 months on ART
HIV Dementia / AIDS Dementia Complex
  • Subcortical dementia: cognitive slowing, memory loss, psychomotor retardation
  • Most common neurologic complication overall
Progressive Multifocal Leukoencephalopathy (PML)
  • JC virus reactivation; CD4 <50/μL
  • White matter demyelination; focal neurological deficits without fever
  • No specific treatment; effective ART is the main management

3. GI OIs

Oral Candidiasis (Thrush)
  • Most common early OI; indicator of progressive immunosuppression
  • White pseudomembraneous plaques on tongue/palate
  • Treatment: Fluconazole; secondary prophylaxis for frequent recurrences
Esophageal Candidiasis - AIDS-defining illness
  • Odynophagia + dysphagia
  • Endoscopy: white plaques extending to esophagus
Cryptosporidiosis
  • Cryptosporidium parvum; profuse watery diarrhea, malabsorption
  • CD4 <200/μL; AIDS-defining
  • No curative antiparasitic; nitazoxanide has limited efficacy; ART is key
CMV Colitis
  • Bloody diarrhea, abdominal pain, weight loss; CD4 <50/μL
  • Treatment: Ganciclovir or valganciclovir

4. Systemic/Disseminated OIs

Mycobacterium avium Complex (MAC)
  • CD4 <50/μL; disseminated disease
  • Fever, weight loss, drenching night sweats, hepatosplenomegaly, pancytopenia
  • Dx: Blood culture (lysis-centrifugation)
  • Primary prophylaxis: Azithromycin 1200 mg weekly (or clarithromycin 500 mg BID) when CD4 <50/μL
  • Treatment: Clarithromycin + ethambutol ± rifabutin
CMV Disease (Systemic)
  • Retinitis (most common): painless progressive visual loss, "pizza pie" appearance on fundoscopy
  • Also: colitis, esophagitis, encephalitis, pneumonitis
  • Secondary prophylaxis: Valganciclovir 900 mg once daily; may stop when CD4 >100/μL for 6 months
Disseminated Histoplasmosis
  • Endemic areas (SE USA, parts of Asia); CD4 <150/μL
  • Fever, weight loss, hepatosplenomegaly, mucosal ulcers
  • Prophylaxis in endemic areas: Itraconazole 200 mg BID

5. Malignancies (AIDS-defining)

Kaposi's Sarcoma (KS)
  • HHV-8 related; violaceous skin/mucosal lesions; can involve viscera
  • Most common AIDS-defining cancer; CD4 any level but worse at <200
Non-Hodgkin's Lymphoma
  • EBV-associated; usually aggressive B-cell lymphoma
  • CNS primary lymphoma at CD4 <50/μL
Invasive Cervical Carcinoma
  • HPV-driven; AIDS-defining in women

WHO/CDC Guidelines: Primary Prophylaxis of OIs

PathogenCD4 ThresholdFirst-Choice Prophylaxis
Pneumocystis jirovecii (PCP)CD4 <200/μL or <14%TMP-SMX DS 1 tab/day PO
Toxoplasma gondiiCD4 <100/μL + seropositiveTMP-SMX DS 1 tab/day (same as PCP)
M. avium complex (MAC)CD4 <50/μLAzithromycin 1200 mg/week OR Clarithromycin 500 mg BID
CryptococcusPrior disease only (secondary)Fluconazole 200 mg/day
Histoplasma capsulatumCD4 <150/μL (endemic area)Itraconazole 200 mg BID
CMVPrior end-organ disease (secondary)Valganciclovir 900 mg/day
Herpes simplexFrequent/severe recurrencesValacyclovir 500 mg BID or Acyclovir 400 mg BID
  • Harrison's Principles of Internal Medicine, 22E (2025), Table 208-14

Community Medicine Perspective

Epidemiology (2023 Data)

  • 39.9 million people living with HIV worldwide
  • 1.3 million new infections in 2023 (60% reduction from 1995 peak)
  • ~95% in low- and middle-income countries
  • WHO Eastern/Southern Africa most affected (>5.7% adult prevalence)
  • High-risk groups: MSM, sex workers, PWID, prisoners, transgender persons - account for 55% of new infections
  • In India: HIV-TB co-infection is the dominant OI burden

Prevention and Control

  1. ART for all - reduces transmission and OI risk dramatically; most OIs preventable with ART
  2. Chemoprophylaxis - per CD4-based thresholds above
  3. Immunization: Pneumococcal vaccine (when CD4 >200/μL preferred); Hepatitis B vaccine; Influenza annually; Avoid live vaccines when CD4 <200/μL
  4. COTRIMOXAZOLE PREVENTIVE THERAPY (CPT) - TMP-SMX 960 mg daily for all HIV-positive patients, particularly in low-resource settings per WHO - prevents PCP, toxoplasmosis, some bacterial infections, isosporiasis
  5. Integrated HIV-TB services - 4-symptom screen, CBNAAT for all presumptive TB in PLHIV
  6. Safe sex, harm reduction (NSPs for PWID), PMTCT programs

Impact of ART on OIs

Since the introduction of ART, incidence of PCP, CMV, and MAC have declined by >80%. In ART-treated patients with suppressed viral loads, stopping primary prophylaxis is safe once CD4 recovers above thresholds (e.g., >200/μL for PCP for 3+ months).

AIDS-Defining Illnesses (25 CDC Conditions) - Key List

  1. Candidiasis (esophageal, tracheal, bronchial, pulmonary)
  2. Cervical cancer (invasive)
  3. Coccidioidomycosis (disseminated/extrapulmonary)
  4. Cryptococcosis (extrapulmonary)
  5. Cryptosporidiosis (chronic intestinal, >1 month)
  6. CMV disease (other than liver, spleen, nodes)
  7. CMV retinitis with loss of vision
  8. Encephalopathy, HIV-related
  9. Herpes simplex: chronic ulcers (>1 month), bronchitis, pneumonitis, esophagitis
  10. Histoplasmosis (disseminated/extrapulmonary)
  11. Isosporiasis (chronic intestinal, >1 month)
  12. Kaposi's sarcoma
  13. Lymphoma (Burkitt's, immunoblastic, primary CNS)
  14. MAC (disseminated or extrapulmonary)
  15. M. tuberculosis (pulmonary or extrapulmonary)
  16. Other mycobacterial diseases (disseminated)
  17. Pneumocystis jirovecii pneumonia
  18. Pneumonia, recurrent bacterial (≥2 episodes/year)
  19. Progressive multifocal leukoencephalopathy (PML)
  20. Salmonella septicemia (recurrent)
  21. Toxoplasmosis of the brain
  22. Wasting syndrome due to HIV
Sources:
  • Harrison's Principles of Internal Medicine, 22E (2025, McGraw Hill) - Chapter 208
  • Park's Textbook of Preventive and Social Medicine - HIV/AIDS and TB-HIV section
  • Washington Manual of Medical Therapeutics - HIV Classification
  • CDC/WHO 2014 Guidelines for Prevention of Opportunistic Infections in Persons with HIV
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