6.3 Common Foodborne Illnesses and Frequently Implicated Foods in Singapore

Figure 6.10: A Temporarily-Closed Dining Establishment Due to Salmonella

6.3.1 Salmonella

Figure 6.11: Bimodal Distribution in the Incidence of Salmonella Cases

Figure 6.11 displays a bimodal distribution between two extremes in age populations.

6.3.1.1 Research on Salmonella

HansenWester et al. notes that Salmonella bacteria are able to induce their own phagocytosis to gain access into host cells via Salmonella pathogenicity islands (i.e., SPIs): clusters of genes at the large chromosomal DNA region that encode for structures in the invasion process.

SPIs also have type III secretion systems: multi-channel proteins that allow Salmonella bacteria to injects effectors across intestinal epithelial cell membranes into their cytosol. The effectors then cause the cell’s actin cytoskeleton to extend outwards or ruffle to engulf the bacteria. Takaya et al. notes that this mechanism is similar to phagocytosis.

Furthermore, Salmonella bacteria are able to persist in host cells. This is because Salmonella’s type III secretion system remodels vacuoles via its effector proteins; this blocks the fusion of lysosomes, hence permitting intracellular survival and bacterial replication in cells.

6.3.1.2 Life cycle of Salmonella

Figure 6.12: CNA’s Interpretation of the Life Cycle of Salmonella

The above graphic taken from CNA sums up this topic nicely.

6.3.2 Listeria monocytogenes

Figure 6.13: Companies Recalling Frozen Products Because of L. monocytogenes

L. monocytogenes can live in many cold and salty environments (i.e., even in refrigerated environments, these pathogens still grow well). These pathogens are typically found in under-pasteurized milk and dairy products, smoked fish, deli meats, and raw vegetables, and can persist in food-processing plants.

The illness they cause can range from mild, flu-like symptoms to atypical blood-stream infections. However, severe infections typically have incubation periods between three days and three months.

The immunocompromised and the pregnant are more at risk for severe illness; pregnant women also risk having a miscarriage.

6.3.3 Bacillus cerus

Figure 6.14: Spore Formation in Bacterium

These bacterium live in the ground and can form spores that are difficult to eradicate. Illnesses caused by this bacterium are often associated with starchy foods.

These bacteria are also able to produce toxins that cause self-limiting food poisoning.

6.3.4 Staphlococcus aureus

S. aureus is part of the normal human skin flora (i.e., nose and fingers); foodborne illness caused by this bacterium is typically associated with unhygienically-prepared foods.

Like B. cereus, this bacterium is self-limiting and produce toxins.

6.3.5 Norovirus

Humans are the only known reservoirs of this disease. The norovirus easily spreads from human to human and has a low infectious dose.

Symptoms start in as little as 12 - 48 hours and include vomiting and diarrhea; foodborne illness caused by the norovirus are often associated with fruits, vegetables, meats, and salads that have been prepared by infected individuals.

Because of this, outbreaks of norovirus are associated with cruise ships, day-care centers, and enclosed environments.

Unfortunately, alcohol-based disinfectants do not work against the norovirus.

6.3.5.1 Mandarin Orchard, December 2018

Figure 6.15: Mandarin Orchard’s Grand Ballroom

In December of 2018, 315 cases of norovirus infections were reported after five events had been held in the grand ballroom.

Norovirus was detected in the stool samples from five attendees, three food handlers, and 28 service staff (including banquet waiters).

Norovirus was also found on environmental surfaces (e.g., carpets, tables, chairs, cutlery, drinking glasses, etc). B. cereus was also detected on the surface of utensils and door handles.

6.3.6 Managment of foodborne illness from the one health perspective

During 2006, a large, multistate outbreak of E. coli O157 happened in country A. The most common food implicated with the bacterium was beef hamburgers, yet the food source was bagged baby spinach.

The contaminated spinach was then traced to one processing plant and fields. The fecal material of pigs had likely contaminated the spinach.

The bacterium had been transported to swine from cattle in the same geographical region - surface water was determined to be a potential pathway for the transmission of E. coli.