Discussion
Respiratory viral infections can put patients in the risk of secondary infections, especially by bacterial and fungal organisms (7). In a previous study, about 30% of SARS-CoV-2 infected cases were at the risk of developing secondary pneumonia without a known reason (8). In fact, SARS-CoV-2 infection can interfere with the immune system and its balance; therefore, it may result in an increased risk of fungal infections such as invasive candidiasis, pulmonary aspergillosis, and Pneumocystis jirovecii (9). Given the fact that Pneumocystis pneumonia (PCP) and COVID-19 may have similar and common clinical features such as profound hypoxemia and bilateral multifocal infiltrates, coinfection with PJP could be missed, especially in those with life-threatening forms of COVID-19 infection. Hence, it seems wise to apply additional diagnostic workup for PJP in severe COVID-19 patients, especially in the presence of clinical features that support coinfection, like cystic formations on chest CT scan and an increased level of lactate dehydrogenase, even if there were no risk factors for PJP (10).
It seems that immunosuppression plays an important role in the association of COVID-19 and PCP. Although impaired immune balance may be useful in the context of COVID-19 severity, due to the reduced immune respond and inflammation, which are related to the severity of manifestations, it is also a chief risk factor for the occurrence of PCP (11). In that case, preexisting immunodeficiency (e.g. HIV- or drug-induced) could increase the risk of COVID-19 and PJP coinfection. Importantly, it might be observed in those who are not included in the known risk groups, which could be a result of severe COVID-19-induced lymphopenia or immunosuppressive therapy (12).
PJP has two morphological forms in its life cycle, including cystic and trophic forms. It is an infection usually identified in patient with impaired T cell immunity, particularly CD4+lymphopenia. Unfortunately, severe COVID-19 infection is associated with severely diminished levels of CD4+ cells (9), which makes these patients highly susceptible to PJP. Moreover, COVID-19 infection could result in conditions like acute respiratory distress syndrome, which requires immunosuppressive therapies (e.g. corticosteroids), a familiar risk factor for developing PCP (9).