A 34-year-old man with HIV comes to the emergency department due to fever, chills, productive cough, and left-sided chest pain that worsens with deep breathing. His symptoms began 3 days ago and have progressively worsened. The patient was diagnosed with HIV 4 years ago during routine screening, and he takes antiretroviral therapy. His CD4 count was 480 cells/mm3 a month ago. Temperature is 38.8 C (102 F), blood pressure is 110/66 mm Hg, pulse is 110/min, and respirations are 22/min. Physical examination shows dullness to percussion, bronchial breath sounds, and crackles over the left lower lung. The right lung and cardiac auscultation findings are normal. Laboratory testing reveals an elevated leukocyte count with left shift. Which of the following organisms is most likely responsible for this patient's current symptoms?
Although HIV is classically associated with impairment to the cell-mediated immune response, the virus also dramatically hampers the production of opsonizing antibodies and the recruitment of phagocytes to areas of infection. Therefore, patients with HIV are at much greater risk for invasive bacterial infections, particularly with encapsulated organisms such as Streptococcus pneumoniae.
S pneumoniae is the most common cause of community-acquired pneumonia in both HIV-infected and HIV-uninfected individuals, and usually presents with acute-onset fever, productive cough, leukocytosis, and signs of lobar consolidation (eg, dullness to percussion, crackles). S pneumoniae is also a frequent cause of sepsis and bacterial meningitis. To reduce the risk of invasive pneumococcal disease, all patients with HIV should be immunized with the pneumococcal vaccination, which provides immunity to the most common strains.
(Choice A) Although invasive Aspergillus is much more common in patients with HIV, it primarily affects those with extremely low CD4 counts (<50/mm3). Fever, cough, shortness of breath, and nodular or cavitary pulmonary infiltrate often occurs.
(Choice B) Influenza usually causes acute-onset fever, malaise, myalgias, and headache. Manifestations of lobar consolidation would be atypical and would likely indicate an influenza complication (eg, secondary pneumonia). Patients with HIV should receive yearly influenza vaccination.
(Choice C) Legionella is a common cause of atypical pneumonia and is far more common in patients with HIV than the general population. Although Legionella often causes lobar consolidation, most cases are marked by several days of gastrointestinal symptoms (eg, vomiting, diarrhea) prior to developing pulmonary symptoms.
(Choice D) Patients with HIV are at much greater risk of Mycobacterium tuberculosis infection, which usually presents over several weeks (not days) with cough, low-grade fever, weight loss, and fatigue. Active pulmonary tuberculosis is usually characterized by cavitary disease in the upper lobes of the lung; signs of lower lobe consolidation would be atypical.
(Choice E) Mycoplasma pneumoniae is a leading cause of "walking pneumonia," a form of atypical pneumonia. "Walking pneumonia" usually presents with several weeks (not days) of nonproductive cough and malaise. The infection usually affects multiple lobes of lung and causes a bilateral patchy infiltrate on chest x-ray.
(Choice F) Pneumocystis pneumonia (PCP) is common in patients with HIV, but occurs primarily in those with CD4 counts <200/mm3 (unlike this patient). It usually presents with several weeks (not days) of slowly worsening dyspnea and fever. In addition, PCP usually affects both lungs and appears as bilateral reticulonodular pulmonary infiltrates on chest x-ray.
Educational objective:
The most common cause of community-acquired pneumonia in both HIV-infected and HIV-uninfected individuals is Streptococcus pneumoniae. Risk of invasive pneumococcal disease is significantly increased in patients with HIV regardless of CD4 count.