Microbial contamination in mass catering environments requires rapid assessment to implement effective countermeasures. In this study, nine rounds of swab testing (once before and eight times immediately after the practice sessions) were conducted at 22 locations in a mass catering training facility to investigate contaminated sites, the presence of persistent contamination, and their underlying factors. The median bacterial counts for flat surfaces and handles were 1.7 log cfu/100 cm² and 2.5 log cfu/100 cm², respectively. The counts were significantly higher for handles (p<0.05), indicating that they are critical control points. Identification of 96 strains isolated from the three representative handles revealed that Bacillus spp. were most prevalent (73%) on the blast chiller handle, whereas Staphylococcus spp. predominated on the refrigerator and tableware disinfection-storage cabinet handles (83% and 92%, respectively). These predominant genera were consistently detected on their respective handles throughout all eight practice sessions. The blast chiller handle was made of nylon, and microscopic observation revealed extensive surface damage; this was considered to contribute to the colonization of spore-forming bacteria, Bacillus spp. Furthermore, when a colony area threshold of 46 pixels on the sheet medium was used to identify spore-forming capability, the accuracy for the strains from culture collection (n=6) and environmental isolates (n=96) were 0.98 and 0.95, respectively. These findings highlight the potential of using colony area values on sheet media to rapidly assess the risk of contamination by spore-forming bacteria at the field level, thereby facilitating more effective hygiene management strategies.

We conducted an epidemiological analysis of 534,565 norovirus (NoV) stool tests commissioned by food business operators between September 2018 and August 2023. The aims were to clarify the implementation status of NoV testing, determine the prevalence of NoV carriers among food handlers, and evaluate the time required to achieve a negative test result. Approximately 83% of the tests were conducted during the testing period recommended by the Ministry of Health, Labour and Welfare (October to March), with the highest number performed in December. Although no significant differences in monthly testing volumes were observed among industry categories, substantial variation was found between individual businesses. The overall NoV positive rate was 0.90%; however, among businesses conducting testing throughout the year, the positive rate was lower at 0.33%. Monthly positive rates reflected both testing volume and seasonal trends in infectious gastroenteritis, with higher rates observed from April to June. By genotype, GII accounted for 82.8% of positive cases, GI for 16.4%, and mixed GI/GII infections for 0.7%. Detection of GII followed the seasonal pattern of infectious gastroenteritis, whereas GI was detected throughout the year. The positive rate declined during the COVID-19 pandemic. Among NoV-positive individuals, the mean duration of viral shedding was approximately 10 days, and the mean time to achieve a negative result was approximately 15 days; the longest observed duration of positivity was 60 days. Some individuals became positive again after initially testing negative, with re-positivity occurring more frequently within 10 days after a negative result. These findings provide scientific evidence to support the development of more effective and practical NoV control measures tailored to the operational realities of food business settings.