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Published on: February 4, 2012
Comparison of quantitative real-time PCR and direct immunofluorescence for the detection of Pneumocystis jirovecii
Bhavani Moodley1, Stefano Tempia2,3,4, John Andrew Frean1,5
1Centre for Emerging, Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
Background:
Pneumocystis pneumonia (PCP) is a serious risk for HIV-positive patients. Asymptomatic infection or colonisation with P. jirovecii has been shown to occur frequently. PCR assays frequently identify such cases, due to their high sensitivity. Quantitative real-time PCR (qPCR) gene copy number cut-off values have been suggested to differentiate colonisation and infection; these need to be standardised for routine use. We compared the results of qPCR with an immunofluorescence assay (IFA) to determine a specific cut-off value.
Methods:
From March 2005 through June 2009, induced sputum specimens were collected from adult patients who were clinically suspected of having PCP, at the Chris Hani Baragwanath Hospital in Gauteng, South Africa. Laboratory diagnosis of PCP was done by a conventional direct IFA and a qPCR assay. A receiver operating characteristic (ROC) analysis was performed to determine a suitable copy number cut-off value.
Results:
P. jirovecii was identified in 51% (156/305) and 67% (204/305) of specimens using IFA and qPCR, respectively. The cut-off value for the qPCR that best predicted the IFA results was 78 copies/5 μl (area under ROC curve 0.92). The sensitivity and specificity of qPCR using this cut-off was 94.6% and 89.1%, respectively, compared with the IFA.
Discussion:
The results of the ROC curve analysis indicate an excellent predictive value of the qPCR using the proposed cut-off. However, the IFA test is an imperfect gold standard and so this cut-off should not be used in isolation; clinical data should also contribute to the interpretation of the qPCR result.
Insights
Quantitative real-time PCR (qPCR) can differentiate Pneumocystis pneumonia (PCP) infection from colonization in HIV patients. A validated qPCR cut-off value improves diagnostic accuracy when used alongside clinical data.
Area of Science:
- Medical Diagnostics
- Infectious Diseases
- Molecular Biology
Background:
- Pneumocystis pneumonia (PCP) poses a significant risk to HIV-positive individuals.
- Distinguishing PCP infection from asymptomatic colonization is crucial for effective treatment.
- Quantitative real-time PCR (qPCR) offers high sensitivity but requires standardized cut-off values.
Purpose of the Study:
- To compare qPCR with immunofluorescence assay (IFA) for PCP diagnosis.
- To establish a reliable qPCR gene copy number cut-off value for differentiating infection from colonization.
- To assess the diagnostic performance of qPCR against IFA.
Main Methods:
- Induced sputum specimens were collected from patients suspected of PCP.
- Conventional direct immunofluorescence assay (IFA) and qPCR were used for laboratory diagnosis.
- Receiver operating characteristic (ROC) analysis was performed to determine the optimal qPCR cut-off value.
Main Results:
- P. jirovecii was detected in 67% of specimens by qPCR, versus 51% by IFA.
- An optimal qPCR cut-off of 78 copies/5 μl was identified, with an area under the ROC curve of 0.92.
- qPCR demonstrated 94.6% sensitivity and 89.1% specificity compared to IFA at this cut-off.
Conclusions:
- The proposed qPCR cut-off value shows excellent predictive value for PCP diagnosis.
- IFA serves as an imperfect gold standard, necessitating the integration of clinical data for qPCR interpretation.
- Standardized qPCR cut-offs are essential for routine clinical application in PCP diagnostics.
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