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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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Related in: MedlinePlus

Probability of True or False Positive Results with Serial Testing of True Positive or True Negative Specimens. (A) The probability of one or more tests positive for norovirus as a function of number of truly positive specimens tested, based on estimated test sensitivity by latent class modeling (LCM) or composite reference standard (CRS) methods. (B) The probability of a false positive test for norovirus as a function of number of truly negative specimens tested. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy.
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Figure 1: Probability of True or False Positive Results with Serial Testing of True Positive or True Negative Specimens. (A) The probability of one or more tests positive for norovirus as a function of number of truly positive specimens tested, based on estimated test sensitivity by latent class modeling (LCM) or composite reference standard (CRS) methods. (B) The probability of a false positive test for norovirus as a function of number of truly negative specimens tested. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy.

Mentions: Based on the test characteristics presented in Table 2, it is possible to estimate the mean number of tests required, in the presence of positive specimens, to have at least one true positive result, and the mean number of tests performed on negative specimens in order to have at least one false positive result. These calculations are presented in Figures 1A and 1B. If all submitted specimens contained NVG, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested. By contrast, even if all specimens actually contained norovirus, EM would require seven specimen submissions for the likelihood of identification to exceed 80%, and 12 specimens for the likelihood of identification to exceed 90%.


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)

Probability of True or False Positive Results with Serial Testing of True Positive or True Negative Specimens. (A) The probability of one or more tests positive for norovirus as a function of number of truly positive specimens tested, based on estimated test sensitivity by latent class modeling (LCM) or composite reference standard (CRS) methods. (B) The probability of a false positive test for norovirus as a function of number of truly negative specimens tested. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Probability of True or False Positive Results with Serial Testing of True Positive or True Negative Specimens. (A) The probability of one or more tests positive for norovirus as a function of number of truly positive specimens tested, based on estimated test sensitivity by latent class modeling (LCM) or composite reference standard (CRS) methods. (B) The probability of a false positive test for norovirus as a function of number of truly negative specimens tested. PCR, real-time reverse-transcriptase polymerase-chain reaction; EIA, enzyme immunoassay; EM, electron microscopy.
Mentions: Based on the test characteristics presented in Table 2, it is possible to estimate the mean number of tests required, in the presence of positive specimens, to have at least one true positive result, and the mean number of tests performed on negative specimens in order to have at least one false positive result. These calculations are presented in Figures 1A and 1B. If all submitted specimens contained NVG, RT2-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested. By contrast, even if all specimens actually contained norovirus, EM would require seven specimen submissions for the likelihood of identification to exceed 80%, and 12 specimens for the likelihood of identification to exceed 90%.

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