Table 2.

Relationship between the predicted number of PCR replicates needed to achieve various test sensitivities andC. pneumoniae concentrations

ProbitaC. pneumoniaeconcn (IFU/ml)bNo. of replicates needed to achieve sensitivity ofc:
50%80%90%95%
0.010.0169161230299
0.050.0314324559
0.100.057162229
0.200.09481114
0.300.152579
0.400.242456
0.500.351345
0.600.531234
0.700.811223
0.801.341122
0.902.701112
0.954.791111
0.9914.101111
• a Probit, predicted proportion of replicates positive from probit regression analysis (SPSS), based on 10 replicates of 16 dilutions of C. pneumoniae ATCC VR-1310 (see the text).

• b C. pneumoniae ATCC VR-1310 concentration as calculated from probit analysis.

• c Replicates calculated in Microsoft Excel spreadsheet from the following equation: probability (at least 1 positive in n replicates) = 1 − (1 − probit)n.