Detection of Pneumocystis jirovecii and Toxoplasma gondii in patients with lung infections by a duplex qPCR assay

Pneumocystis pneumonia (PCP) and pulmonary toxoplasmosis (PT) are caused by Pneumocystis jirovecii and Toxoplasma gondii. The clinical symptoms and imaging of PCP and PT are indistinguishable. A duplex qPCR was developed to differentiate between these two pathogens. In testing 92 clinical samples to validate the performance of this method for P. jirovecii detection, it identified 31 positive samples for P. jirovecii infection, consistent with clinical diagnosis. Among the remainder of the 61 clinical samples with suspected PCP, yet showing as negative by the conventional PCR diagnosis approach, 6 of them proved positive using our new assay. Our new approach also produced similar results in identification of T. gondii infections, giving a result of 2 positive and 20 negative in clinical samples. An investigation was undertaken on the prevalence of P. jirovecii and T. gondii infections using 113 samples from lung infection patients. 9% (10/113) were shown to be positive with infections of P. jirovecii, 2% with T. gondii (2/113) and 5% (6/113) were co-infected with both pathogens. Although this duplex qPCR can detect individual P. jirovecii and T. gondii infection, and co-infection of both pathogens, further large-scale investigations are needed to validate its performance, especially in T. gondii detection. Our assay provides a rapid and accurate tool for PCP and PT diagnosis in immunocompromised population and clinical surveillance of these infections in patients with no immune defects. Author summaryPneumocystis jirovecii and Toxoplasma gondii are opportunistic pathogens that can cause pneumocystis pneumonia (PCP) and pulmonary toxoplasmosis (PT) in immunocompromised patients. Due to the non-specific clinical symptoms and similar imaging of lung pathology, these two deadly diseases are difficult to be clinically differential diagnosed. Early diagnosis of these infections would reduce medical costs, morbidity and mortality. A duplex qPCR method was developed for the detection of both P. jirovecii and T. gondii infection simultaneously. This new assay provides a potential application for diagnosis and surveillance of both PCP and PT. Further investigation for the prevalence of P. jirovecii and T. gondii infections indicated that P. jirovecii and T. gondii involvement in lung infection has been seriously underestimated.