His history was pertinent for mild asthma that did not require maintenance therapy and IV heroin use in his 20s, complicated by chronic hepatitis C that was successfully treated with interferon and ribavarin 5 years ago. He denied using alcohol or tobacco products, but did report regularly smoking marijuana. He denied any recent exotic travel or sick contacts and had no pets at home. He had diffuse wheezing on auscultation of his lungs and bilateral patchy opacities on his chest radiograph (Fig 1A). His laboratory work revealed an elevated WBC count of 18,900 mm3, with lymphocytosis but no neutrophilia, bandemia, or eosinophilia. His RBC count, platelet count, electrolytes, creatinine clearance, and transaminases were all within normal limits. He was admitted to the Medicine Service and treated for both community-acquired pneumonia (CAP) and an acute asthma exacerbation. He was placed on azithromycin and IV ceftriaxone for the presumed pneumonia along with prednisone and nebulized albuterol/ipratropium for his asthma. His expectorated sputum grew only normal respiratory flora, and both a rapid flu test and a comprehensive respiratory viral panel obtained by nasopharyngeal swab were negative. The appearance of the opacities in his initial chest radiograph (Fig 1A) coupled with his history of IV drug use raised the concern for an opportunistic infection in the setting of an immunocompromised host. He was, thus, tested for HIV, and both his serology and viral load by polymerase chain reaction (PCR) were negative. He transiently defervesced, and he was discharged home 2 days later on oral cefpodoxime, azithromycin, inhaled albuterol, and a short prednisone taper. Unfortunately, his improvement was quite transient, and he returned to the hospital with worsening dyspnea, fevers, and cough despite taking his discharge medications as prescribed.