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The Use of PCR on Oral Wash Specimens for the Non-Invasive Diagnosis of Pneumocystis carinii Pneumonia

The Use of PCR on Oral Wash Specimens for the Non-Invasive Diagnosis of Pneumocystis carinii Pneumonia

James Lewis, Jr., MD

March 14, 2002

P. carinii is an opportunistic respiratory pathogen associated with HIV/AIDS and less commonly with patients immunosuppressed from other causes. Because it cannot be cultured and exposure with serologic conversion is virtually universal, current diagnosis relies on high clinical suspicion and direct demonstration of organism on sputum, BAL, or tissue biopsy. Direct demonstration has a variable sensitivity but is reported to be >90% for BAL combined with DFA. However, direct demonstration of organism is considered essentially 100% specific for clinical disease. Numerous studies of PCR-based detection on respiratory specimens (BAL/sputum) have been published with sensitivities and specificities ranging from 95 to 100% and 50 to 98%, respectively, when compared with direct detection or a clinical picture consistent with PCP as the gold standard(s). More recent studies have focused on PCR of noninvasive oral wash specimens with sensitivities and specificities ranging from 77 to 100% and 94 to 100%, respectively. The major difference between current methods and PCR is that, unlike direct detection, positive PCR results are not 100% specific for clinical disease. As most patients positive by PCR and negative by direct detection are not shown to currently have PCP and do not go on to develop it, the higher specificity of oral wash PCR may make it the best specimen for molecular diagnosis. It is obviously the more easily obtained specimen as well. While the performance of PCR seems adequate for diagnostic use, how much it may add to current diagnostic testing or if it might replace current testing in the diagnostic algorithm isn’t entirely clear. Oral wash PCR would clearly be useful for patients where sputum induction and bronchoscopy are not possible (examples: coagulopathy, neonates). PCR on BAL when direct detection is negative and there is a high clinical suspicion for PCP would be another useful situation. Implementation for other scenarios will require careful use to assure proper interpretation, particularly for positive results.

References

General

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Direct Detection

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PCR on Respiratory Specimens

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PCR on Oral/Oropharyngeal Wash Specimens

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  5. Fischer S, et al. The use of oral washes to diagnose Pneumocystis carinii pneumonia: a blinded prospective study using a PCR-based detection system. The Journal of Infectious Diseases 2001; 184: 1485-1488.