Historical seroprevalence data for Anisakis in Spain vary greatly depending on the sampling region owing to different fish consumption habits. As a result of European Regulation (EC) No. 853/2004, the Royal Decree 1420/2006 on the prevention of parasitosis by Anisakis in fishery products supplied by establishments that serve food to final consumers or to communities came into force in Spain. In this study, a prevalence study of Anisakis in Madrid has been conducted to verify the prophylactic effects of the application of the law. Sera from 500 blood donors from the Fundación Jiménez Díaz University Hospital (Madrid/2021–2023) were collected, and the levels of anti-Anisakis IgG, IgA, and IgE were analyzed by ELISA, comparing them with those obtained with 110 donors from the Red Cross and the “Gómez Ulla” Central Defense Hospital (Madrid/2001–2002). The percentages of positivity in the 2021–2023 donor group were IgG (13.6%), IgA (13.6%), and IgE (2.2%), while in the 2001–2002 donors they were positive for IgG (15.45%), IgA (14.54%), and IgE (11.65%). A reduction of more than 80% was observed in the prevalence of anti-Anisakis IgE in the healthy population of Madrid, which confirmed the positive effect of RD1420/2006, which was later incorporated into RD1021/2022.
