A patient with CD4+ count below 200 presents with pneumonia. What fungal organism is most likely causing the infection?

In patients with a CD4+ T-cell count below 200 cells/mm³, the immune system is significantly compromised, making them highly susceptible to opportunistic infections. Pneumocystis jirovecii, a fungal organism, is a common cause of pneumonia in this population, particularly in individuals with advanced HIV/AIDS.

Pneumocystis jirovecii pneumonia (PCP) typically occurs when the CD4+ count drops below 200, as these patients lack the adequate immune response needed to combat this organism. PCP presents with symptoms such as dyspnea, cough, and fever, and can rapidly progress without treatment.

While other organisms like Candida, Cryptococcus, and Aspergillus also pose risks for immunocompromised individuals, they are not as directly associated with pneumonia in patients with such low CD4+ counts as Pneumocystis jirovecii. Candida typically causes oropharyngeal or esophageal infections rather than pneumonia, while Cryptococcus can cause meningitis and is commonly associated with pulmonary nodules or pneumonia in different patient contexts. Aspergillus might lead to invasive aspergillosis but usually occurs in patients with even more severe immunosuppression or those with neutropenia.

Thus