A patient with HIV whose CD4+ count drops below 200 cells/mm³ doesn't die from HIV itself — they die from infections a healthy immune system would easily handle. Knowing which infections strike at which thresholds changes everything.
Opportunistic infections (OIs) are the primary cause of morbidity and mortality in HIV/AIDS. They emerge predictably based on CD4+ count thresholds. At CD4+ < 200 cells/mm³, Pneumocystis jirovecii pneumonia (PJP) becomes the most common and most tested OI — presenting with dry nonproductive cough, progressive dyspnea, and fever. Prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) begins when CD4+ falls below 200. At CD4+ < 100, Toxoplasma gondii encephalitis and Cryptosporidium emerge. At CD4+ < 50, Mycobacterium avium complex (MAC) and cytomegalovirus (CMV) retinitis become threats — MAC prophylaxis with azithromycin starts at this threshold. Oral candidiasis (thrush) and esophageal candidiasis can appear at higher CD4+ counts and often signal disease progression. Kaposi sarcoma — purple-red vascular skin lesions — is an AIDS-defining malignancy. Nursing priorities include strict infection precautions, respiratory isolation for active TB coinfection, meticulous oral and skin assessment, calorie-dense nutrition support, and monitoring for medication interactions between OI prophylaxis and antiretroviral therapy.
Key Distinctions
Don't confuse PJP (dry cough, dyspnea, no sputum) with bacterial pneumonia (productive cough, purulent sputum, high fever) — PJP is insidious and progressive. Students mix up prophylaxis thresholds: PJP prophylaxis starts at CD4+ < 200, MAC prophylaxis at CD4+ < 50. Oral thrush is not the same as esophageal candidiasis — thrush is visible white patches you can scrape; esophageal candidiasis causes painful swallowing and requires systemic antifungal treatment.
Clinical Pearl
Think "200-100-50": PJP at 200, Toxo at 100, MAC and CMV at 50. The lower the count, the more dangerous and disseminated the infection.
HIV Stages & Lab Monitoring
HIV staging drives every treatment decision and prophylaxis trigger. Stage 1 (CD4 ≥ 500 cells/mm³). Stage 2 (chronic/clinical latency): CD4 200–499 cells/mm³. Stage 3 (AIDS): CD4 < 200 cells/mm³ OR presence of an AIDS-defining condition, regardless of CD4 count. A patient can be asymptomatic at any stage — staging is lab-based, not symptom-based. Two labs anchor monitoring: the CD4 count reflects immune function and guides prophylaxis decisions, while the viral load (HIV RNA) measures treatment effectiveness. A rising viral load signals nonadherence or drug resistance. The goal of antiretroviral therapy is an undetectable viral load (< 20–50 copies/mL depending on assay), which means the virus cannot be sexually transmitted (U=U: Undetectable = Untransmittable). CD4 counts are monitored every 3–6 months; more frequently at diagnosis or with regimen changes. Prophylaxis thresholds are testable: start PCP prophylaxis (trimethoprim-sulfamethoxazole) when CD4 < 200; start MAC prophylaxis when CD4 < 50.
Key Distinctions
Don't confuse CD4 count (immune status, guides prophylaxis) with viral load (disease activity, guides treatment effectiveness) — they answer different clinical questions. Students assume AIDS requires symptoms, but a CD4 < 200 alone qualifies as Stage 3 even in an asymptomatic patient. A low viral load doesn't mean the immune system has recovered — CD4 may still be dangerously low.
Clinical Pearl
CD4 tells you WHERE you are (staging and prophylaxis). Viral load tells you WHERE you're headed (treatment working or failing). Track both, confuse neither.