Table 2.
Theoretical and actual number of tests performed, the proportion of tests that could be read and interpreted after 4, 6 and 8 h and the categorical errors with RAST at each reading time for the seven species (E. coli, K. pneumoniae, P. aeruginosa, S. aureus, E. faecalis, E. faecium and S. pneumoniae)
| E. coli (n = 60 isolates) | ||||
| Incubation time (h) | 4 | 6 | 8 | |
| Number of tests (n) | ||||
| Theoretical number of testsa | 960 | 960 | 960 | |
| Completed testsb | 958 | 958 | 958 | |
| Readable zones (% of completed tests)c | 886 (92) | 958 (100) | 958 (100) | |
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 19 | 20 | 20 | |
| Interpreted as S | 57 | 58 | 58 | |
| Interpreted as R | 24 | 22 | 22 | |
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 1.0 | 1.4 | 1.6 |
| ME | 2.2 | 0.0 | 0.0 | |
| VME | 0.1 | 0.0 | 0.0 | |
| Total errors | 3.3 | 1.4 | 1.6 | |
| K. pneumoniae (n = 52 isolates) | ||||
| Incubation time (h) | 4 | 6 | 8 | |
| Number of tests (n) | ||||
| Theoretical number of testsa | 832 | 832 | 832 | |
| Completed testsb | 831 | 831 | 831 | |
| Readable zones (% of completed tests)c | 820 (99) | 831 (100) | 831 (100) | |
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 28 | 23 | 19 | |
| Interpreted as S | 45 | 52 | 55 | |
| Interpreted as R | 27 | 25 | 25 | |
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 1.7 | 0.8 | 0.6 |
| ME | 0.7 | 0.0 | 0.0 | |
| VME | 0.0 | 0.0 | 0.1 | |
| Total errors | 2.4 | 0.8 | 0.6 | |
| P. aeruginosa (n = 53 isolates) | ||||
| Incubation time (h) | 6 | 8 | ||
| Number of tests (n) | ||||
| Theoretical number of testsa | 742 | 742 | ||
| Completed testsb | 741 | 741 | ||
| Readable zones (% of completed tests)c | 676 (91) | 727 (98) | ||
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 18 | 17 | ||
| Interpreted as S | 57 | 58 | ||
| Interpreted as R | 24 | 22 | ||
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 2.2 | 1.7 | |
| ME | 0.4 | 0.0 | ||
| VME | 0.2 | 0.0 | ||
| Total errors | 2.7 | 1.7 | ||
| S. aureus (n = 54 isolates) | ||||
| Incubation time (h) | 4 | 6 | 8 | |
| Number of tests (n) | ||||
| Theoretical number of testsa | 324 | 432 | 432 | |
| Completed testsb | 324 | 432 | 432 | |
| Readable zones (% of completed tests)c | 188 (58) | 385 (89) | 392 (91) | |
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 11 | 8 | 6 | |
| Interpreted as S | 73 | 66 | 67 | |
| Interpreted as R | 16 | 26 | 27 | |
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 0.0 | 0.0 | 0.5 |
| ME | 0.0 | 0.3 | 0.0 | |
| VME | 0.0 | 0.3 | 0.0 | |
| Total errors | 0.0 | 0.6 | 0.5 | |
| E. faecalis (n = 23 isolates)d | ||||
| Incubation time (h) | 4 | 6 | 8 | |
| Number of tests (n) | ||||
| Theoretical number of testsa | 260 | 260 | 260 | |
| Completed testsb | 260 | 260 | 260 | |
| Readable zones (% of completed tests)c | 242 (93) | 259 (100) | 260 (100) | |
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 31 | 30 | 25 | |
| Interpreted as S | 54 | 56 | 58 | |
| Interpreted as R | 15 | 14 | 17 | |
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 0.0 | 0.0 | 0.0 |
| ME | 0.0 | 0.0 | 0.0 | |
| VME | 0.0 | 0.0 | 0.0 | |
| Total errors | 0.0 | 0.0 | 0.0 | |
| E. faecium (n = 34 isolates)e | ||||
| Incubation time (h) | 6 | 8 | ||
| Number of tests (n) | ||||
| Theoretical number of testsa | 380 | 380 | ||
| Completed testsb | 380 | 380 | ||
| Readable zones (% of completed tests)c | 352 (93) | 375 (99) | ||
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 19 | 14 | ||
| Interpreted as S | 17 | 23 | ||
| Interpreted as R | 64 | 63 | ||
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 0.7 | 0.6 | |
| ME | 0.7 | 0.3 | ||
| VME | 0.0 | 0.0 | ||
| Total errors | 1.4 | 0.9 | ||
| S. pneumoniae (n = 66 isolates) | ||||
| Incubation time (h) | 4 | 6 | 8 | |
| Number of tests (n) | ||||
| Theoretical number of testsa | 560 | 560 | 560 | |
| Completed testsb | 560 | 560 | 560 | |
| Readable zones (% of completed tests)c | 461 (82) | 550 (98) | 558 (100) | |
| Results calculated on readable zones (%) | ||||
| Not interpreted as S or R (ATU) | 26 | 22 | 8 | |
| Interpreted as S | 48 | 52 | 66 | |
| Interpreted as R | 26 | 26 | 27 | |
| Errors calculated on the total number of zones interpreted as S or R (%) | ||||
| Errors | mE | 1.2 | 0.9 | 0.8 |
| ME | 1.2 | 0.5 | 0.4 | |
| VME | 0.6 | 0.9 | 1.2 | |
| Total errors | 2.9 | 2.3 | 2.3 | |
a
Theoretical number of tests = total number of possible isolate/agent combinations in duplicate (due to testing on media from two manufacturers).
b
Number of completed tests = number of completed tests after excluding missing data (e.g. disc dropped).
c
Readable zones = number of tests with readable inhibition zones.
d
For E. faecalis some isolates have been tested several times resulting in a total of 52 readings.
e
For E. faecium some isolates have been tested several times resulting in a total of 76 readings.