A 31-year-old woman comes to the emergency department due to 2 days of fever, chills, and cough productive of brown-tinged sputum. She has also had shortness of breath, and her chest hurts when she inhales deeply. She has not had any sick contacts. The patient has a history of HIV, hypertension, and generalized anxiety disorder. She is on antiretroviral therapy, and 2 months ago her CD4 cell count was 325 cells/mm³. The patient smokes a pack of cigarettes daily but does not drink alcohol or use illicit drugs. Temperature is 38.8 C (101.8 F), pulse is 90/min, blood pressure is 120/65 mm Hg, and respirations are 18/min. The patient is in no apparent distress. Mucous membranes are moist. Cardiopulmonary auscultation reveals decreased breath sounds over the right middle lung field and regular heart rate with no murmurs. The remainder of the examination is normal. Laboratory results are as follows: Chest x-ray is shown in the image. The most likely cause of the patient's symptoms is infection with which of the following?

Question

Quizplus · Accepted Answer

Explanation: This patient with HIV has acute fever, cough, and dyspnea with a right middle lobe infiltrate, suggesting community-acquired pneumonia (CAP). Patients with HIV are substantially more likely to develop bacterial pulmonary infections than the general population. The most common pathogen is Streptococcus pneumoniae, an encapsulated bacterium that is particularly invasive in patients with HIV due to deficits in opsonization, humoral immunity, and macrophage/neutrophil function. Manifestations of CAP are similar between HIV-infected and HIV-uninfected individuals; patients often have acute fever, chills, cough with sputum production, dyspnea, and pleuritic chest pain. Laboratory studies usually show a neutrophilic leukocytosis (except when CD4 count is very low), and chest imaging typically reveals a lobar pulmonary infiltrate. Blood cultures are often positive, particularly with pneumococcal pneumonia. Patients can usually receive outpatient treatment if a single lobe is involved and respiratory status is unaffected. (Choice A) Although risk for Legionella CAP is significantly higher in patients with HIV, this infection is much less common than pneumococcal pneumonia. Legionella usually causes high fever and prominent gastrointestinal symptoms prior to the development of pulmonary symptoms. (Choice B) Patients with HIV are at much greater risk of active Mycobacterium tuberculosis infection. Pulmonary tuberculosis usually manifests with subacute fever, cough, weight loss, and malaise. This patient with acute symptoms, a cough productive of brown sputum, and a lobar infiltrate is more likely to have S pneumoniae. (Choice C) Mycoplasma pneumoniae typically causes a subacute (not acute) illness with headache, fever, sore throat, cough, and dyspnea. Chest imaging typically reveals patchy interstitial infiltrates; a lobar infiltrate would be uncommon. (Choice D) Pneumocystis pneumonia usually causes pulmonary disease in patients with CD4 counts <200/mm³ and develops slowly over weeks (not days). Manifestations usually include fever, dyspnea, cough, and an interstitial (not lobar) pulmonary infiltrate. Educational objective: Patients with HIV are at greater risk for bacterial pulmonary infections than the general population. The leading cause is the encapsulated bacterium Streptococcus pneumoniae. In general, clinical manifestations of bacterial CAP are similar in HIV-infected and HIV-uninfected patients.

A 31-Year-Old Woman Comes to the Emergency Department Due to 2