An evaluation of four methods for the detection of Pneumocystis carinii in clinical specimens
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S M Tiley1, D J Marriott, J L Harkness
1Department of Microbiology, St Vincent's Hospital, Darlinghurst, New South Wales.
Abstract:
We undertook a prospective evaluation of 4 methods for the detection of Pneumocystis carinii in clinical specimens and compared an indirect immunofluorescence assay (IFA) (Diagnostics Pasteur), and a fluorescent whitening agent (FWA) (Blankophor BA 267%, Bayer, Australia) with our standard methenamine silver (MeAg) and toluidine blue O (TB) stains. Two hundred and two specimens were received from 162 patients (133 HIV infected, 19 heart or heart-lung transplant recipients, and 10 "miscellaneous"). The specimens consisted of 132 induced sputa, 56 bronchoalveolar lavage specimens, 10 fine needle aspiration lung biopsies, and 4 pleural fluid specimens. P. carinii was detected in 44 (22%) of the specimens. The sensitivities for the detection of P. carinii pneumonia were IFA: 92% (95% CI, 83-100%), FWA: 57% (95% CI, 41-73%), MeAg: 54% (95% CI, 38-70%), and TB: 49% (95% CI, 33-65%). Discordant results were greatest in specimens from patients who were receiving specific anti-P. carinii prophylaxis, or who had received treatment for several days prior to sampling. IFA was the most sensitive test and relatively easy to perform. IFA was also the most expensive test. We found the FWA method a useful screening test as it is cheap and quick to perform. However, it is less sensitive than IFA, which should be performed on the negative specimens. With the increasing use of specific anti-P. carinii prophylaxis in HIV-infected patients, methods more specific and sensitive than MeAg and TB stains are required. We have found IFA to improve significantly the rate of detection of P. carinii in this patient group.
Insights
The indirect immunofluorescence assay (IFA) is the most sensitive method for detecting Pneumocystis pneumonia, outperforming fluorescent whitening agent (FWA), methenamine silver (MeAg), and toluidine blue O (TB) stains.
Area of Science:
- Medical Microbiology
- Diagnostic Pathology
- Infectious Diseases
Background:
- Pneumocystis pneumonia (PCP) is a significant opportunistic infection, particularly in immunocompromised individuals.
- Accurate and sensitive detection of Pneumocystis carinii is crucial for timely diagnosis and treatment.
- Traditional staining methods like methenamine silver (MeAg) and toluidine blue O (TB) have limitations in sensitivity.
Purpose of the Study:
- To prospectively evaluate and compare the diagnostic performance of four methods for detecting Pneumocystis carinii in clinical specimens.
- To assess the utility of indirect immunofluorescence assay (IFA) and fluorescent whitening agent (FWA) against standard MeAg and TB stains.
Main Methods:
- Prospective evaluation of 202 clinical specimens from 162 patients, including HIV-infected individuals and transplant recipients.
- Specimens analyzed included induced sputum, bronchoalveolar lavage, fine needle aspiration biopsies, and pleural fluid.
- Comparison of indirect immunofluorescence assay (IFA), fluorescent whitening agent (FWA), methenamine silver (MeAg), and toluidine blue O (TB) staining.
Main Results:
- Pneumocystis carinii was detected in 22% of specimens.
- Sensitivities for Pneumocystis pneumonia detection were: IFA (92%), FWA (57%), MeAg (54%), and TB (49%).
- IFA demonstrated the highest sensitivity, while FWA served as a useful, rapid screening test.
Conclusions:
- Indirect immunofluorescence assay (IFA) is the most sensitive method for detecting Pneumocystis carinii, significantly improving detection rates, especially in patients receiving prophylaxis.
- Fluorescent whitening agent (FWA) offers a quick and inexpensive screening option, but negative results should be confirmed with IFA.
- Given the increasing use of anti-Pneumocystis prophylaxis, more sensitive methods like IFA are essential for accurate diagnosis in at-risk populations.