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).