TABLE 4.

Sensitivities of five PCR assays for detecting C. pneumoniae-infected U-937 mononuclear cells^a

No. of infected U-937 cells	PCR result for assayb:
	1	2	3	4	5
30	++	++	++	++	++
15	++	++	++	++	++
3	−−	−+	+−	−−	++
1.5	−−	−−	−−	−−	−−

^aA 25-cm² flask containing 7 × 10⁶ U-937 cells was inoculated with C. pneumoniae, and the infected cells were spiked into 8 ml of whole blood in a Vacutainer CPT tube. Mononuclear cells were collected, DNA was extracted by using a Qiagen DNA Mini-kit and eluted in 0.1 ml of elution buffer, and aliquots (2.5 μl) of DNA were tested in duplicate by five PCR assays. The number of infected cells was calculated from the total number of cells that stained by DFA with a fluorescein isothiocyanate-labeled anti-C. pneumoniae monoclonal antibody, assuming a CPT tube cell recovery rate of 71% as indicated by the manufacturer. 

^bPCR assays as described in Table 1.