Prevalence of Listeria monocytogenes in mozzarella cheese: A systematic review and meta-analysis

Listeria monocytogenes is a human pathogen responsible for listeriosis, a sporadic but serious disease that poses significant health risks, particularly to vulnerable populations such as pregnant women, the elderly, and immunocompromised individuals. Mozzarella cheese, a widely consumed fresh dairy product, may represent as a potential vehicle for this pathogen, primarily due to the risk of post-processing contamination. This study presents a systematic review and meta-analysis aimed at estimating the prevalence of L. monocytogenes in mozzarella cheese at the end of the manufacturing process. The literature search identified 13 studies that met the predefined inclusion criteria from international citation databases. Additionally, 10 years of data were retrieved from an Italian laboratory database, covering mozzarella samples tested in Italy and 2 studies from gray literature. In total, 16 studies were analyzed using random-effects meta-analysis, and the pooled prevalence of L. monocytogenes in mozzarella was estimated at 1.2% (95% CI: 0.0-4.2) although a high heterogeneity among studies was observed (I² = 78%). Despite the detection of the pathogen in some studies, the concentration levels were below the limit of quantification, implying low levels of contamination. The results confirm that L. monocytogenes can occur in mozzarella, typically due to post-stretching cross-contamination. The findings underline the importance of implementing effective hygiene practices and highlight the need for further predictive microbiology models tailored to mozzarella's unique properties to better assess the consumer exposure.