Limits...
Of gastro and the gold standard: evaluation and policy implications of norovirus test performance for outbreak detection.

Fisman DN, Greer AL, Brouhanski G, Drews SJ - J Transl Med (2009)

Bottom Line: If all specimens contained norovirus, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested.Testing of more than 5 true negative specimens with RT2-PCR would be associated with a greater than 50% likelihood of a false positive test.Given risks of false positive test results, it is reasonable to limit the number of specimens tested when RT2-PCR or EIA are available.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Epidemiology and Surveillance, Ontario Agency for Health Protection and Promotion, Toronto, Canada. david.fisman@gmail.com

ABSTRACT

Background: The norovirus group (NVG) of caliciviruses are the etiological agents of most institutional outbreaks of gastroenteritis in North America and Europe. Identification of NVG is complicated by the non-culturable nature of this virus, and the absence of a diagnostic gold standard makes traditional evaluation of test characteristics problematic.

Methods: We evaluated 189 specimens derived from 440 acute gastroenteritis outbreaks investigated in Ontario in 2006-07. Parallel testing for NVG was performed with real-time reverse-transcriptase polymerase chain reaction (RT2-PCR), enzyme immunoassay (EIA) and electron microscopy (EM). Test characteristics (sensitivity and specificity) were estimated using latent class models and composite reference standard methods. The practical implications of test characteristics were evaluated using binomial probability models.

Results: Latent class modelling estimated sensitivities of RT2-PCR, EIA, and EM as 100%, 86%, and 17% respectively; specificities were 84%, 92%, and 100%; estimates obtained using a composite reference standard were similar. If all specimens contained norovirus, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested. Testing of more than 5 true negative specimens with RT2-PCR would be associated with a greater than 50% likelihood of a false positive test.

Conclusion: Our findings support the characterization of EM as lacking sensitivity for NVG outbreaks. The high sensitivity of RT2-PCR and EIA permit identification of NVG outbreaks with testing of limited numbers of clinical specimens. Given risks of false positive test results, it is reasonable to limit the number of specimens tested when RT2-PCR or EIA are available.

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Upper 95% Confidence Limit for Proportion of Specimens Containing Norovirus After Serial Negative Tests. Solid curve represents the upper 95% binomial confidence limit for test positivity (P(T+))using equation (1.0) in the text. Dashed lines represent upper 95% confidence limits for proportion of specimens truly positive for norovirus (P(NVG)). Solid horizontal line (at 55%) represents the approximate lower bound for proportion of positive specimens in documented outbreaks. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy; LCM, latent class model; CRS, composite reference standard.
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Figure 4: Upper 95% Confidence Limit for Proportion of Specimens Containing Norovirus After Serial Negative Tests. Solid curve represents the upper 95% binomial confidence limit for test positivity (P(T+))using equation (1.0) in the text. Dashed lines represent upper 95% confidence limits for proportion of specimens truly positive for norovirus (P(NVG)). Solid horizontal line (at 55%) represents the approximate lower bound for proportion of positive specimens in documented outbreaks. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy; LCM, latent class model; CRS, composite reference standard.

Mentions: In a situation where serial negative test results are obtained, it is possible to estimate the upper bound (95% confidence interval) probability that a given specimen contains NV material for a fixed test sensitivity and specificity (Figure 4). With five serial negative tests by either EIA or RT2-PCR, the upper confidence interval for the proportion of NVG-positive specimens falls below the lower bound confidence interval of empirically observed proportions of specimens containing NVG in outbreaks. By contrast, NVG cannot be ruled out by EM with 95% confidence until approximately 30 serial negative tests have been performed.


Of gastro and the gold standard: evaluation and policy implications of norovirus test performance for outbreak detection.

Fisman DN, Greer AL, Brouhanski G, Drews SJ - J Transl Med (2009)

Upper 95% Confidence Limit for Proportion of Specimens Containing Norovirus After Serial Negative Tests. Solid curve represents the upper 95% binomial confidence limit for test positivity (P(T+))using equation (1.0) in the text. Dashed lines represent upper 95% confidence limits for proportion of specimens truly positive for norovirus (P(NVG)). Solid horizontal line (at 55%) represents the approximate lower bound for proportion of positive specimens in documented outbreaks. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy; LCM, latent class model; CRS, composite reference standard.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667494&req=5

Figure 4: Upper 95% Confidence Limit for Proportion of Specimens Containing Norovirus After Serial Negative Tests. Solid curve represents the upper 95% binomial confidence limit for test positivity (P(T+))using equation (1.0) in the text. Dashed lines represent upper 95% confidence limits for proportion of specimens truly positive for norovirus (P(NVG)). Solid horizontal line (at 55%) represents the approximate lower bound for proportion of positive specimens in documented outbreaks. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy; LCM, latent class model; CRS, composite reference standard.
Mentions: In a situation where serial negative test results are obtained, it is possible to estimate the upper bound (95% confidence interval) probability that a given specimen contains NV material for a fixed test sensitivity and specificity (Figure 4). With five serial negative tests by either EIA or RT2-PCR, the upper confidence interval for the proportion of NVG-positive specimens falls below the lower bound confidence interval of empirically observed proportions of specimens containing NVG in outbreaks. By contrast, NVG cannot be ruled out by EM with 95% confidence until approximately 30 serial negative tests have been performed.

Bottom Line: If all specimens contained norovirus, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested.Testing of more than 5 true negative specimens with RT2-PCR would be associated with a greater than 50% likelihood of a false positive test.Given risks of false positive test results, it is reasonable to limit the number of specimens tested when RT2-PCR or EIA are available.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Epidemiology and Surveillance, Ontario Agency for Health Protection and Promotion, Toronto, Canada. david.fisman@gmail.com

ABSTRACT

Background: The norovirus group (NVG) of caliciviruses are the etiological agents of most institutional outbreaks of gastroenteritis in North America and Europe. Identification of NVG is complicated by the non-culturable nature of this virus, and the absence of a diagnostic gold standard makes traditional evaluation of test characteristics problematic.

Methods: We evaluated 189 specimens derived from 440 acute gastroenteritis outbreaks investigated in Ontario in 2006-07. Parallel testing for NVG was performed with real-time reverse-transcriptase polymerase chain reaction (RT2-PCR), enzyme immunoassay (EIA) and electron microscopy (EM). Test characteristics (sensitivity and specificity) were estimated using latent class models and composite reference standard methods. The practical implications of test characteristics were evaluated using binomial probability models.

Results: Latent class modelling estimated sensitivities of RT2-PCR, EIA, and EM as 100%, 86%, and 17% respectively; specificities were 84%, 92%, and 100%; estimates obtained using a composite reference standard were similar. If all specimens contained norovirus, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested. Testing of more than 5 true negative specimens with RT2-PCR would be associated with a greater than 50% likelihood of a false positive test.

Conclusion: Our findings support the characterization of EM as lacking sensitivity for NVG outbreaks. The high sensitivity of RT2-PCR and EIA permit identification of NVG outbreaks with testing of limited numbers of clinical specimens. Given risks of false positive test results, it is reasonable to limit the number of specimens tested when RT2-PCR or EIA are available.

Show MeSH
Related in: MedlinePlus