A polymerase chain reaction assay was optimized to detect P. carinii cysts in composite dust samples. The optimal assay was capable of detecting as few as 10 3 P. carinii cysts in 50 mg of dust. Two dust collection devices were evaluated for efficiency and precision of collection of bulk dust and compatibility with the optimized PCR protocol for P.carinii DNA detection. A handheld vacuum cleaner equipped with a high-retention bag was found to be superior to a 37-mm filter cassette attached to an electrically powered vacuum pump in terms of dust collection efficiency (87% [n = 37] versus 81%[n = 35]), although the precision of the two devices as assessed by the standard deviation was similar (6.2% versus 6.3%). However, the vacuum cleaner method was not as compatible with the PCR-based detection assay as the filter cassette method. The filter cassette appears to be a better device for use in conjunction with PCR-based detection of P. carinii DNA in bulk dust samples from both smooth and carpeted surfaces.
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