Canadian Journal of Fisheries and Aquatic Sciences, Ahead of Print.
Proper sample size must be considered when designing infectious-agent prevalence studies for mixed-stock fisheries, because bias and uncertainty complicate interpretation of apparent (test)-prevalence estimates. Sample size varies between stocks and are often smaller than expected during wild-salmonid surveys. Our case example of 2010–2016 survey of sockeye salmon (Oncorhynchus nerka) from different stocks of origin in British Columbia, Canada, illustrated the effect of sample size on apparent-prevalence interpretation. Molecular testing (viral RNA RT-qPCR) for infectious hematopoietic necrosis virus (IHNv) revealed large differences in apparent prevalence across wild salmon stocks (much higher from Chilko Lake) and sampling location (fresh water or marine), indicating differences in both stock and host life-stage effects. Ten of the 13 marine non-Chilko stock–years with IHNv-positive results had small sample sizes (<30 samples per stock–year), which, with imperfect diagnostic tests (particularly lower diagnostic sensitivity), could lead to inaccurate apparent-prevalence estimation. When calculating sample size for expected apparent prevalence using different approaches, smaller sample sizes often led to decreased confidence in apparent-prevalence results and decreased power to detect a true difference from a reference value.

中文翻译：

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样本量对估计患病率的重要性：加拿大不列颠哥伦比亚省弗雷泽河红鲑鱼（Oncorhynchus nerka）混合种群中传染性造血坏死病毒RNA检测的案例

《加拿大渔业和水生科学杂志》，印刷前。
在设计混合种群渔业的传染病流行率研究时，必须考虑适当的样本量，因为偏见和不确定性使表观（试验）流行率估计的解释变得复杂。样本量因种群而异，通常小于野生鲑鱼调查期间的预期。我们以2010-2016年加拿大不列颠哥伦比亚省不同来源的红鲑鱼（Oncorhynchus nerka）调查为例，说明了样本量对表观患病率解释的影响。对传染性造血坏死病毒（IHNv）进行的分子检测（病毒RNA RT-qPCR）显示，野生鲑鱼种群（奇尔科湖的水域较高）和采样地点（淡水或海水）的表观流行率存在很大差异，表明种群和承载生命阶段的影响。在IHNv阳性结果的13个非契尔科海洋非疫区年中，有10个样本量较小（每个畜库年小于30个样本），如果诊断测试不完善（特别是较低的诊断敏感性），可能导致表观患病率不准确估计。当使用不同的方法为预期的表观患病率计算样本量时，较小的样本量通常会导致对表观患病率结果的置信度降低，并且检测与参考值的真实差异的能力也会降低。