Top questions man, I think theres a lot of overlap between the terms, so I wouldn't say specificity = efficacy as such. For a microbiology test to be 'safe' you'd want it to detect the pathogen in all instances (have high sensitivity) AND you would want it to correctly identify the pathogen (have high specificty)..same deal for 'efficacy'
From the APAS study posted above:
Segmentation of cases.
All 509 cases reported by the laboratory with significant growth were segmented as either positive or review by APAS and produced a segmentation sensitivity of 100%. A further 818 cases segmented as positive or review were reported by the laboratory as not having significant growth and contributed to the specificity of 66.9%.
So overall the APAS system has a low rate of false negatives but and a not so great rate of false positives. This means you can be confident in issuing a confirmed negative report but there will be a good number of plates that are actually 'no significant growth' but require review.
As for specificity of APAS in relation to organism identification:
TABLE 1
Colony identification performance by APAS compared with that of a reference panel
|
Colony morphologies on blood agar |
Examples of colony morphology |
Sensitivity (%) |
Specificity (%) |
| 1 |
Coliform-like colonies |
Escherichia coli |
98.9 |
83.9 |
| 2 |
Swarming colonies |
Proteus mirabilis |
97.2 |
99.9 |
| 3 |
Granular Gram-negative colonies |
Pseudomonas aeruginosa |
67.7 |
92.5 |
| 4 |
Staphylococcus-like colonies |
Staphylococcus spp. |
94 |
83.8 |
| 5 |
Small beta-hemolytic colonies |
Streptococcus agalactiae |
92.4 |
89.3 |
| 6 |
Small colonies |
Enterococci, lactobacilli, corynebacteria |
90 |
73.7 |
| 7 |
Colony morphologies on MacConkey agar |
|
|
|
| 8 |
Lactose fermenters |
Escherichia coli |
99.2 |
98.1 |
| 9 |
Non-lactose fermenters |
Proteus spp. |
92.6 |
95.9 |
The specificities weren't that great. To replace something like MALDI-TOF the specificities would need to approach 100%... Contrast this table with that for a MALDI-TOF analyser where specificity was 100% for all isolates.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016424
And that is why (for now anyway) I don't see these imaging technologies such as APAS being used to report
final, confirmed positive results in patients. Further layers of specificity (ie testing) will need to be incorporated. As the APAS marketing states they will be used for screening large numbers of plates.
But I never say never when it comes to science... The ELS technology I mentioned in above posts is exciting and may very likely form that added layer of specificity in a Clever Culture Systems set-up
Cheers
(20min delay)