Effects of imperfect testing on presence‐absence sampling plans

Sampling inspection plans are used in the food industry to determine whether a batch of food is contaminated or not. Testing for pathogens is mandatory in several foodstuffs because some bacteria pose a significant risk to human health, even when these are consumed in minute quantity. Test performance measures such as sensitivity and specificity are generally ignored in microbiological risk assessment and food quality assurance. In this research, we examine the impact of imperfect analytical tests on sampling inspection plans for presence‐absence characteristics. We discuss several plausible scenarios and assess the risk for the consumers. The method is illustrated using data collected over 2 years for Cronobacter spp (formerly Enterobacter sakazakii) in skimmed milk powder. The probability of contamination and the test sensitivity and specificity are estimated using Bayesian methods. We examine the sampling plans proposed by the Codex Alimentarius and by the New Zealand's Ministry of Primary Industries for this pathogen. A cost analysis is performed to show the economic loss due to measurement errors. We describe the strengths and limitations of these plans under different conditions and propose a plan that could provide better protection to the consumers as well as to the producers.