de Blas Ignacio, Muniesa Ana, Vallejo Adriana, Ruiz-Zarzuela Imanol
Laboratory of Fish Diseases, Department of Animal Pathology, Instituto Agroalimentario de Aragón IA2, Universidad de Zaragoza, Zaragoza, Spain.
Facultad de Medicina Veterinaria y Zootecnia, Universidad de Córdoba, Montería, Colombia.
Front Vet Sci. 2020 May 19;7:253. doi: 10.3389/fvets.2020.00253. eCollection 2020.
An adequate sampling methodology is the key to knowing the health status of aquatic populations. Usually, the aims of epidemiological surveys in aquaculture are to detect an infection and estimate the disease prevalence, and different formulas are used to calculate the sample size. The main objective of this study was to assess if the sample sizes calculated using classical epidemiological formulas are valid considering the sampling methodology, the population size, and the spatial distribution of diseased animals in the population (non-clustered or clustered). However, the use of sample sizes of 30, 60, and 150 fish is widely accepted in aquaculture, due to the requirements of the World Organization for Animal Health (OIE) for epidemiological surveillance. We have developed a specific software using ASP () language and MySQL database in order to generate aquatic populations from 100 to 10 000 brown trouts infected by with different levels of prevalence: 2, 5, 10, and 50%. Then we implemented several Monte Carlo simulations to estimate empirically the sample sizes corresponding to the different scenarios. Furthermore, we compared these results with the values calculated by classical formulas. We determined that simple random sampling was more accurate in detecting an infection, because it is independent of the distribution of infected animals in the population. However, if diseased animals are non-clustered it is more efficient to use systematic methods, even in the case of small populations. Finally, the formula to calculate sample size to estimate disease prevalence is not valid when the expected prevalence is far from 50%, and it is necessary to increase the sample size to reach the desired precision.
适当的抽样方法是了解水生生物种群健康状况的关键。通常，水产养殖流行病学调查的目的是检测感染情况并估计疾病流行率，会使用不同公式来计算样本量。本研究的主要目的是评估，考虑到抽样方法、种群规模以及患病动物在种群中的空间分布（非集群或集群分布），使用经典流行病学公式计算出的样本量是否有效。然而，由于世界动物卫生组织（OIE）对流行病学监测的要求，在水产养殖中使用30、60和150条鱼的样本量已被广泛接受。我们使用ASP（）语言和MySQL数据库开发了一个特定软件，以生成100至10000条感染不同流行率水平（2%、5%、10%和50%）的褐鳟水生种群。然后我们进行了多次蒙特卡洛模拟，以实证估计不同情况下对应的样本量。此外，我们将这些结果与经典公式计算的值进行了比较。我们确定简单随机抽样在检测感染方面更准确，因为它与种群中感染动物的分布无关。然而，如果患病动物是非集群分布的，即使在种群规模较小的情况下，使用系统抽样方法也更有效。最后，当预期流行率远非50%时，用于估计疾病流行率的样本量计算公式无效，有必要增加样本量以达到所需的精度。
