A patient had renal transplant 2 months back and now presented with difficulty in breathing. X ray showed bilateral diffuse interstitial infiltrates, which are more in the perihilar region. The probable etiologic agent would be:

The appearance of a pulmonary infiltrate, with or without signs of infection (e.g., fever), is one of the most common and serious complications in patients whose immune defenses are suppressed by disease, immunosuppressive therapy for organ or hematopoietic stem cell transplants, chemotherapy for tumors, or irradiation. The ones that commonly involve the lung can be classified according to the etiologic agent: Bacteria Viruses fungi P. aeruginosa Mycobacterium species L. pneumophila Listeria monocytogenes Cytomegalovirus herpesvirus P. jiroveci Candida species Aspergillus species Phycomycetes Cryptococcus neoformans Causes of Pulmonary infiltrates in Immunocomprimised Hosts Diffuse Infiltrates Focal Infiltrates Common Cytomegalovirus (m/c in lung transplant) Pneumocystis jirovecii (m/c overall) Drug reaction Gram-negative bacterial infections Staphylococcus aureus Aspergillus Candida Malignancy Uncommon Bacterial pneumonia Aspergillus Cryptococcus Malignancy Cryptococcus Mucor Pneumocystis jiroveci Legionella pneumophila