Question:medium
Known case of HIV with cough of sputum production & fever with examination finding of consolidation in right infrascapular area with x-ray showing right lower consolidation with CD4 of 55. What is the most common cause of this in these?
Known case of HIV with cough of sputum production & fever with examination finding of consolidation in right infrascapular area with x-ray showing right lower consolidation with CD4 of 55. What is the most common cause of this in these?
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Consider which encapsulated bacterium most commonly causes pneumonia across all CD4 count ranges in HIV patients.
Updated On: Jun 23, 2026
- Staph aureus
- Strep pneumonia
- Mycoplasma
- P. jiroveci
Show Solution
The Correct Option is B
Solution and Explanation
Approach via CD4 count and pathogen prevalence:
The patient has HIV with CD4 = 55 cells/mm³ and presents with productive cough, fever, and lobar consolidation - a classic bacterial pneumonia picture.
Key principle: In HIV-infected patients, $\textit{Streptococcus pneumoniae}$ is the single most common cause of bacterial pneumonia at any CD4 count. As CD4 count falls, the incidence of bacterial pneumonia including accompanying bacteremia and septicemia increases.
Why not the other options?
\[\boxed{\text{Strep pneumonia (Option B)}}\]
The patient has HIV with CD4 = 55 cells/mm³ and presents with productive cough, fever, and lobar consolidation - a classic bacterial pneumonia picture.
Key principle: In HIV-infected patients, $\textit{Streptococcus pneumoniae}$ is the single most common cause of bacterial pneumonia at any CD4 count. As CD4 count falls, the incidence of bacterial pneumonia including accompanying bacteremia and septicemia increases.
Why not the other options?
- $\textit{Staph aureus}$: Not the most common overall cause in HIV; more likely in IV drug users or post-influenza.
- $\textit{Mycoplasma}$: Atypical pathogen; causes interstitial pattern, not lobar consolidation typically.
- $\textit{P. jiroveci}$ (PCP): Classic CD4 < 200 opportunist, but causes bilateral ground-glass opacities, not unilateral lobar consolidation; also presents with dry cough, not productive sputum.
\[\boxed{\text{Strep pneumonia (Option B)}}\]
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