Quantitative model predicts implementing school cafeteria share tables will not compromise milk safety

Share table model framework, where the cafeteria system consists of (1) the service, (2) the break (or breaks), and (3) overnight refrigeration. A typical day of school cafeteria meal services has n number of services, with n − 1 breaks. All milk cartons served during service or services on a given day are assumed to be in the defined storage condition for the entire day (i.e., throughout services and breaks) until a milk carton is consumed or the day is over and the milk cartons are moved to overnight refrigeration. At the end of each day, leftover milk cartons on the service line or share table can be reserviced on the following day. Each day was simulated 5 times to represent a school week. At the end of the school week, all leftover milk cartons are discarded. Each week is simulated 37 times (a typical school year). This process is repeated 50 times to simulate 50 school years of meal services in cafeterias with share tables.

Abstract

School cafeteria share tables can address food waste and improve food security by allowing students to share unopened items, such as milk. However, unresolved safety concerns present a barrier to recovering milk cartons on share tables. We adapted our previous share table model to study Listeria monocytogenes in pasteurized milk, assuming a concentration distribution that reflects the realistically low prevalence of the pathogen. Student sharing behavior was simulated for 50 yr of school weeks (5 d/wk over 37 wk/yr). Milk safety is assessed by quantifying (1) time to L. monocytogenes growth of 1 log₁₀, (2) L. monocytogenes concentration at consumption, and (3) listeriosis risk. We compare these measures across 23 what-if scenarios to identify potential risk factors and mitigation strategies. Under the baseline scenario (with no share table temperature management), L. monocytogenes increases by 1 log₁₀ after 1 reservice (after service 2). With share table temperature management, improved overnight refrigeration, or shorter services, L. monocytogenes did not increase by 1 log₁₀ until after 2 d of reservice (after service 3). Under excessive time-temperature abuse (inadequate overnight refrigeration or long services), L. monocytogenes increases by 1 log₁₀ before the first day of reservice (before service 2). Comparing the baseline scenarios of share table and no share table, L. monocytogenes concentration at consumption did not substantially differ. Importantly, L. monocytogenes concentration at consumption never exceeded 100 cfu/mL, except under the longest (266 min) service scenario, for only 0.0006% of milk cartons (11/1,794,887). The mean probability of illness per serving (P_Illness) was low across all scenarios. Comparing the baseline share table and no share table scenarios, P_Illness was 3.32 × 10⁻¹³ and 2.72 × 10⁻¹³, respectively, translating to 1 listeriosis illness in every 2,100 (2,000–2,400) and 3,000 (2,700–3,400) yr across all public schools in the United States. These results demonstrate the extremely small predicted risk of listeriosis from consuming milk cartons in cafeterias with share tables, providing an evidence base to support school nutrition staff in conversations with health departments during the approval of share table management practices.

DOI

https://doi.org/10.3168/jds.2025-27069