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Cytomegalovirus
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Haemophilus influenzae
Mycoplasma pneumoniae
Pneumocystis jirovecii
Streptococcus pneumoniae
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This patient with fever, a productive cough, focal decreased breath sounds, and dyspnea with a lobar consolidation on chest radiograph likely has community-acquired pneumonia, which is most commonly caused by S. pneumoniae. Community-acquired pneumonia (CAP) is an infection of the lower respiratory tract that is acquired outside of the healthcare setting. Risk factors for CAP include a history of chronic lung disease, diabetes mellitus, smoking, and aspiration. Symptoms of CAP include fever, dyspnea, cough (which may be either productive or non-productive), fatigue, and increased work of breathing. Physical exam may reveal dullness to percussion over the affected lung or an increase in tactile fremitus. A finding of a lobar consolidation on chest radiograph in the context of these symptoms is diagnostic of CAP. The most common cause of CAP is S. pneumoniae, including in patients with HIV infection. Other causes of CAP include S. aureus, M. pneumoniae, H. influenzae, and Legionella pneumophila. Treatment of CAP consists of empiric antibiotics, usually with combination therapy consisting of a beta-lactam (e.g., ceftriaxone) plus a macrolide or doxycycline. Alternatively, monotherapy with a respiratory fluoroquinolone (e.g., levofloxacin) may be used. Cillóniz et al. reviewed the epidemiology of CAP in HIV patients. They found that these patients are at increased risk for bacterial pneumonia, though antiretroviral therapy does reduce that risk. The authors recommended that vaccination and smoking cessation be performed as vital strategies for preventing CAP in this population. Figure/Illustration A show a focal opacification in the right upper lobe (red circle) that is consistent with lobar pneumonia. Incorrect Answers: Answer 1: Cytomegalovirus (CMV) may cause pneumonia in patients with HIV. However, infection with CMV usually occurs in patients who are severely immunocompromised (CD4 cell count <50 cells/μL). Furthermore, diffuse interstitial infiltrates would be expected, similar to other viral pneumonias, as opposed to a lobar consolidation. Answer 2: H. influenzae is another common cause of CAP that would present with a productive cough and lobar consolidation. H. influenzae pneumonia usually occurs in patients with underlying chronic lung disease (e.g., emphysema, chronic bronchitis). Nevertheless, S. pneumoniae is a more common cause of CAP. Answer 3: M. pneumoniae is an atypical organism that is a common cause of CAP in young adults. It is a less common cause of CAP in older adults. Pneumonia caused by M. pneumoniae is usually described as a "walking" pneumonia as it does not cause severe symptoms. On imaging, Mycoplasma pneumonia exhibits a diffuse reticulonodular pattern, in contrast with the lobar consolidation seen in CAP due to S. pneumoniae. Answer 4: P. jirovecii is a fungal cause of pneumonia in patients with HIV. However, Pneumocystis pneumonia typically occurs in patients with CD4 cell count <200 cells/μL and would present with diffuse infiltrates on chest radiograph rather than lobar consolidation. Patients with HIV and a CD4 cell count <200 cells/μL should receive trimethoprim-sulfamethoxazole as prophylaxis, or dapsone if they have a sulfa allergy. Bullet Summary: The most common cause of lobar pneumonia in patients with HIV is Streptococcus pneumoniae.
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