Pneumocystis jirovecii Pneumonia:: Current Advances in Laboratory Diagnosis

Pneumocystis jirovecii pneumonia (PcP) remains a major cause of respiratory illness among immunocompromised patients. PcP is difficult to diagnose, in particular in non-HIV-infected patients due to the lack of specific clinical data associated. Since P. jirovecii could not be cultivated for many years, microscopic visualization of cystic or trophic forms in respiratory specimens based on cytochemical or immunofluorescence staining are the standard procedures to identify this fungus. Polymerase chain reaction (PCR)-based methodologies have been developed to overcome the low sensitivity of microscopy in respiratory specimens especially those with low fungal load, and in non-HIV-infected patients. Real-time quantitative PCR is the only format suitable for a quantitative diagnosis and these results have been used to differentiate PcP (high fungal load) from carriage/colonization (low fungal load), however, it is inconclusive with limited results in intermediate fungal loads. New strategies based on measurement of blood biomarkers could be a way to perform PcP diagnosis non-invasively. Several studies explored the usefulness of candidate serum biomarkers, such as (1-3)-β-D-Glucan, Krebs von den Lungen-6 antigen, lactate dehydrogenase or S-adenosylmethionine, with the former presenting the most promising results. More recently, approaches based on the detection of specific anti-P. jirovecii antibodies in patients’ sera are showing promising results that could enable a faster and inexpensive screening/diagnosis of this opportunistic infectious disease, helping better-tailored therapeutic interventions, the disease control and retrenchment to healthcare systems.