Quantitative PCR Outperforms Microscopy in Turkish Study of Pneumocystis Pneumonia

A prospective study at a Turkish tertiary care center has found that real-time quantitative PCR was the most sensitive method for detecting Pneumocystis jirovecii, the fungus responsible for a life-threatening pneumonia that disproportionately strikes non-HIV immunocompromised patients. The research, published in BMC Infectious Diseases, also documented a 30-day mortality rate of 47.6 percent among the patients studied and identified three laboratory markers that distinguished those who died from those who survived.

The team evaluated 102 specimens from 73 patients, enrolling 21 patients who tested positive by real-time quantitative PCR. To judge diagnostic performance, the researchers used a composite reference standard requiring at least two methods to be positive, and they measured agreement between methods using Cohen’s kappa. Against that standard, Giemsa staining detected 66.7 percent of cases while Calcofluor white staining detected only 40.0 percent. Notably, the quantitative PCR assay was positive in six patients who were composite-negative and had negative microscopy, underscoring how difficult it remains to separate active infection from mere colonization of the airways.

Agreement between the different diagnostic methods ranged from moderate to fair, with kappa values between 0.276 and 0.533. In an exploratory receiver operating characteristic analysis restricted to non-HIV patients, the investigators suggested a fungal load threshold of 41.6 copies per milliliter for predicting positivity by immunofluorescence microscopy, with an area under the curve of 0.750. The authors caution, however, that heterogeneity in specimen types and the inability of fungal load alone to distinguish infection from colonization mean this threshold requires further validation before it can guide practice.

Beyond diagnosis, the study mapped the molecular epidemiology of the fungus using multilocus sequence typing. The predominant genotypes were mitochondrial large subunit ribosomal RNA genotype 7, together with CYB1 and SOD1. Two patients carrying MLG X and two carrying MLG Y had overlapping hospital stays, raising the possibility of an epidemiological link between them, although the observational design cannot confirm transmission.

Drug resistance was also on the agenda. Mutations in the dihydropteroate synthase gene, which are associated with reduced susceptibility to trimethoprim-sulfamethoxazole, were screened using restriction fragment length polymorphism analysis. No such mutations were identified in any of the samples, a reassuring finding for a region where data on this pathogen have been scarce, particularly from the Eastern Mediterranean.

The clinical picture that emerged was sobering. Nearly half of the enrolled patients died within 30 days. Lactate dehydrogenase was significantly higher in non-survivors, while platelet count and albumin were significantly lower, each reaching a p value of 0.02. These markers, routinely measured in hospitalized patients, may help clinicians gauge prognosis in non-HIV patients with Pneumocystis pneumonia, a population for whom outcome data have long been limited.

The genotype distribution observed in the Turkish cohort appeared to differ from patterns reported in European studies, hinting at geographic variation in the circulating fungal populations. The authors emphasize that larger multicenter studies are needed to confirm both the genotyping and prognostic findings, since the single-center design and modest sample size constrain the conclusions.

The study’s central practical message concerns interpretation of quantitative PCR results. While the assay outperformed microscopy in sensitivity, the authors conclude that fungal load should not be used on its own to declare active infection, since colonized patients can also carry detectable organisms. Quantitative PCR results, they argue, should always be read together with clinical and radiological findings. For a pathogen that remains difficult to diagnose and carries a high mortality burden in vulnerable patients, the findings add much-needed regional evidence from the Eastern Mediterranean on how Pneumocystis pneumonia is detected and how it unfolds in immunocompromised hosts.

Subject of Research: Molecular epidemiology, genotype distribution and drug resistance of Pneumocystis jirovecii at a Turkish tertiary care center

Article Title: Molecular epidemiology, genotype distribution and drug resistance of Pneumocystis jirovecii in a Turkish tertiary care center

Article References: Unalan-Altintop, T., Toker-Onder, I., Bosnak, C., Metan, G., Prof, O. U., Prof, A. A., & Arikan-Akdagli, S. (2026). Molecular epidemiology, genotype distribution and drug resistance of Pneumocystis jirovecii in a Turkish tertiary care center. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14696-3

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14696-3

Keywords: Pneumocystis jirovecii, Pneumocystis pneumonia, quantitative PCR, diagnostic sensitivity, multilocus sequence typing, DHPS mutations, trimethoprim-sulfamethoxazole, mortality predictors, immunocompromised patients, Turkey, fungal epidemiology, BMC Infectious Diseases