Question:medium
A known case of AIDS with productive cough and fever was found to have consolidation in the right infrascapular area. X-Ray chest showed right lower lobe consolidation with CD4 count of 55 per microlitre. What is the most common cause of this?
A known case of AIDS with productive cough and fever was found to have consolidation in the right infrascapular area. X-Ray chest showed right lower lobe consolidation with CD4 count of 55 per microlitre. What is the most common cause of this?
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HIV patients are highly susceptible to encapsulated bacteria; think about which organism most commonly causes lobar pneumonia.
Updated On: Jun 23, 2026
- Staphylococcus aureus
- Streptococcus pneumoniae
- Mycoplasma
- Pneumocystis jirovecii
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The Correct Option is B
Solution and Explanation
Approach: CD4 count and infection correlation in HIV
HIV infection causes progressive depletion of CD4+ T lymphocytes, increasing susceptibility to specific pathogens:
$Streptococcus$ $pneumoniae$ remains the single most common bacterial pulmonary pathogen in HIV at any CD4 level. HIV-1 impairs opsonization and phagocytosis of encapsulated bacteria, making pneumococcus especially dangerous.
\[\boxed{\text{Streptococcus pneumoniae}}\]
HIV infection causes progressive depletion of CD4+ T lymphocytes, increasing susceptibility to specific pathogens:
- CD4 >500: Bacterial infections (e.g., $S.$ pneumoniae, TB)
- CD4 200-500: Candidiasis, herpes zoster
- CD4 <200: PCP, toxoplasmosis
- CD4 <100: Cryptococcus, MAC, CMV
$Streptococcus$ $pneumoniae$ remains the single most common bacterial pulmonary pathogen in HIV at any CD4 level. HIV-1 impairs opsonization and phagocytosis of encapsulated bacteria, making pneumococcus especially dangerous.
\[\boxed{\text{Streptococcus pneumoniae}}\]
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