A 32-year-old woman comes to the emergency department due to 7 days of fever and dry cough. She has also had progressive shortness of breath with minimal walking and climbing stairs. The patient was diagnosed with HIV infection a year ago and is not currently on antiretroviral treatment. She does not use tobacco, alcohol, or illicit drugs. Temperature is 38.4 C (101.1 F) , blood pressure is 110/64 mm Hg, pulse is 106/min, and respiratory rate is 26/min. Pulse oxymetry is 87% on room air and decreases to 82% with minimal walking. Oropharyngeal thrush is present. Lung auscultation reveals scattered bilateral crackles and rhonchi. The abdomen is soft and nontender without organomegaly. No cyanosis, clubbing, or edema is present. Chest x-ray reveals diffuse interstitial opacities bilaterally. CD4 count is 85/mm³. The patient is admitted and started on empiric therapy. Twenty-four hours after admission, the induced sputum analysis is negative for Pneumocystis.
Which of the following is the likely cause of this patient's pneumonia?

Question

Quizplus · Accepted Answer

Explanation: This patient with advanced HIV has indolent pulmonary symptoms, significant hypoxia, and chest x-ray evidence of interstitial infiltrates, raising strong suspicion for Pneumocystis jirovecii pneumonia (PCP). P jirovecii is an atypical fungus that causes opportunistic pulmonary infections in those with significant immunocompromise. Patients with HIV who have CD4 counts <200/mm³ are at greatest risk and usually present with indolent fever, nonproductive cough, dyspnea, and weight loss. Profound hypoxia and tachypnea are common, and chest x-ray usually reveals bilateral interstitial or alveolar infiltrates. Patients with high pretest probability for PCP often receive empiric treatment, but definitive diagnosis requires the isolation of organisms in respiratory secretions. Induced sputum is the least invasive way to obtain respiratory samples; however, diagnostic sensitivity is 50%-90%. As such, negative results necessitate further testing if PCP is suspected. organisms (Choice A) Candida typically causes mucocutaneous infections (eg, oral thrush) in those with HIV; invasive infections are more common in patients with central venous catheter, significant neutropenia, or hospitalization in the intensive care unit. Pulmonary Candida infections usually cause airspace consolidation or cavitary lesions (not interstitial infiltrates). (Choice B) Pulmonary tuberculosis reactivation is common in those with advanced HIV and may manifest with fever, weight loss, malaise, shortness of breath, and cough. However, chest x-ray typically reveals cavitary infiltrates in the upper lobes and/or mediastinal lymphadenopathy, pleural effusion, and miliary/lobar opacities. pleural effusion (Choice D) Staphylococcus aureus pneumonia typically causes severe, rapidly progressive, necrotizing pneumonia with high fever, septic shock, and multilobar cavitary infiltrates. This patient with indolent symptoms and interstitial infiltrate is unlikely to have S aureus pneumonia. (Choice E) Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and typically manifests acutely (not indolently) with fever, chills, productive cough, dyspnea, and lobar (not interstitial) infiltrate. Educational objective: Patients with HIV with CD4 counts <200/mm³ are at high risk for Pneumocystis jirovecii pneumonia (PCP). Manifestations are typically indolent with fever, dry cough, dyspnea, weight loss, hypoxia, and interstitial infiltrate on chest x-ray. Organisms can be identified on induced sputum samples in 50%-90% of cases; negative results necessitate further testing if PCP is suspected. References: Suspected Pneumocystis carinii pneumonia with a negative induced sputum examination. Is early bronchoscopy useful? (http://www.ncbi.nlm.nih.gov/pubmed/7767533)

A 32-Year-Old Woman Comes to the Emergency Department Due to 7