Alice Cheong

It is noted that in the Prima Deli mass food poisoning episode with 153 reported cases of food poisoning, the tainted ingredients include hazelnut paste, chocolate cream and cake samples, while workers tested positive for salmonella enteritidis include six workers at the baking factory and two workers at franchise outlets.

Part A
Through the investigation has not reported the possible sources and means of transmission, several possible transmission paths are possible.

The simplistic reasoning will lead to the first transmission path. Since the workers are detected to be carrying the salmonella enteritidis, there must had been a hygiene lapse, causing the disease that is usually carried in the fecal to contaminate the ingredients.

In the first transmission path’s reasoning, we are assuming that the cause is human lapse, and the consequence is that the ingredients get infected. However, this reasoning suffers from the flaw that the 2 facts (that both human and ingredients are detected to borne the bacteria) taken together does not means that one has to be the cause of the other. The culprit could be the content within the ingredients such as eggs or dairy products, and that the infected workers are just another unlucky co-occurrence.

In this scenario, one possible content of the ingredients that has a high likelihood of contamination is eggs. The white of eggs are often used to make paste, cream and icing frost. Eggs are also used as base ingredients of cakes. However, as cakes are usually caked at high temperature, the likelihood that the germs can survive the heat is negligible. However, paste, cream and icing frost usually do not undergo high temperature heating process. This means that germs can survive the process, and are waiting for us to eat them.

Now, this leads us to reason that, “Oh well, now they are not cleaning up the egg shell. The egg shell must be infected with the germs. So, it is still a hygiene lapse!” However, according to the USA Centers for Disease Control and Prevention (CDC), the bacterium, Salmonella enteritidis, CAN be inside perfectly normal-appearing eggs, and unlike egg-shell borned salmonellosis of past decades, the Salmonella enteritidis silently infects the ovaries of healthy appearing hens and contaminates the eggs before the shells are formed, leading to intact and disinfected grade A eggs carrying Salmonella enteritidis. (“Disinfected grade A eggs carrying Salmonella enteritidis” sounds oxymoron, but yes, the egg-shell has been disinfected and are of grade A*, but they are also carrying Salmonella enteritidis within the egg white that is well-protected by the shell. So unless you break it to test, you will not find the bacterium. Thus, the egg is disinfected externally, but the bacterium is undetectable and is lurking within.)

Part B
So, the next question that comes to mind will be why does the food poisoning occurs now and not before?
In order for the food poisoning to occur, we need

(1) to have the bacterium,
(2) sufficient amount of the bacterium, and
(3) the processing procedure does not kill them.

These 3 issues must occur concurrently for the food poisoning to occur. So, lets tackle each of the issue one at the time.

So, pursuing this alternative reasoning instead of fingerpointing at possible human lapse, how did the bacterium enter the ingredients and why now. A possible reasoning is that the likelihood/probability is very small for an intact and disinfected eggs carrying Salmonella enteritidis to enter the ingredients. According to USA CDC, “in the USA Northeast, approximately one in 10,000 eggs may be internally contaminated. In other parts of the United States, contaminated eggs appear less common.” So, the probability finally hit jackpot.

Now that the bacterium has entered the chain of ingredients, it has to multiply to a sufficient amount in order to cause food sickness. So, how could sufficient amount of bacterium exist?
Actually, the bacterium Salmonella enteritidis multiplies at a very rapid rate in a suitable medium. It can divide itself into two every 20 minutes. Thus, the usual advise is that food should not be held in the temperature range of 40 to 140 for more than 2 hours, as this will allow sufficient amount of bacterium to have multiplied.

As for the final question, why doesn’t the processing procedure kill them?
This could occur as certain process such as creation of paste, cream and icing, depending on methods, some do not undergo high heat.

Part C 
So perhaps, the source of the bacterium might not be due to human hygiene-lapse. This will brings us to how can we avoid this incident from ever happening again.

(1) They can switch from the normal eggs with shell to those pasteurized packet egg whites and egg yolk. The responsibility of keeping the egg white and egg yolk free from bacterium will now be on the manufacturer of the pasteurized packet egg whites and egg yolk. As these manufacturers’ main business is to produce the pasteurized packet egg whites and egg yolk, they will have better facilities to ensure the quality of the eggs.

(2) The procedure of making of paste, creams and icing can be change to ensure that either all ingredients that enter the procedure had been pasteurized or the procedure involves a high temperature heating process that will kill all the germs.

Part D
However, if the mass food poisoning is due to human hygiene-lapse, Prima Deli will need to provide a really good explanation as we noted that they had taken great efforts in maintaining high standard of hygiene and sanitation. For the 14 years of operation, it has been getting an A rating by AVA for its high standard of hygiene, sanitation and processes. All its workers are immunised against the typhoid before they start work (mandatory in Singapore), and they wear protective sleeves, gloves, caps and face masks, and have to disinfect their shoes using foot baths before entering the bakery. So, why is the bacterium still found in the ingredients?

Thus, Prima Deli might now need to implement even stricter hygiene standards and possibly take additional steps to ensure that even non-hygiene related issues are taken care of, in order to convince all its customers from patronising their shops again.

*U.S. Grade A eggs have whites that are reasonably firm; yolks that are high, round, and practically free from defects; and clean, unbroken shells.

Disclaimer: The author is not related to Prima Deli in any manner.

This entry was posted on Sunday, December 9th, 2007 at 12:36 am and is filed under News & Views. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.