Isn’t it so natural that whenever there is a food borne illness incident the blame is laid squarely at the feet of the last food that was consumed before the symptoms of food poisoning began to emerge.
As a food safety practitioner I have heard again and again, when investigating food borne illness incidents, victims of food borne illness say “it was that mango that I ate in the morning, or it’s was the meal I had in the cafeteria during lunch time, or I shouldn’t have shared in the meat pie so and so was eating…etc etc”. However pointing an accusing finger at the last meal consumed could be misleading.
Firstly, the period between consumption of food and the first signs of illness is termed Onset Period in food safety parlance and it varies from as short as less than an hour to as long as 72 hours depending on a variety of factors.
So to simply assume that the last consumed meal is the culprit of a food borne illness is an oversimplification of how food borne illness plays out.
For instance chemical food borne illness (food borne illness caused by ingesting food contaminated by chemicals) can have a very short onset time (minutes instead of hours) between consumption and illness manifestation as the chemicals gets into the blood stream and circulates swiftly through the blood into the major organs of the body, triggering all forms of symptoms.
On the other hand the onset period of food borne illness caused by pathogenic bacteria could be influenced by amongst many other factors:
1. The time it takes the pathogen to multiply to dangerous levels in the body system.
2. The state of health of the person which has a bearing on the person’s resistance to infections. A sick or convalescing person may manifest symptoms of food borne illness faster than a healthy adult even if they both ate the same contaminated food. This refers to the resilience of ones natural body defenses, i.e. The time it takes for the antibodies to resist the germs before being overwhelmed and succumbing to the infection.
3. The dose (quantity) of the bacteria consumed, which is in turn dependent on the body mass weight of the person. For example children with lower body mass weight can get sickened quicker with a smaller amount of bacteria consumed in food than fully grown adults.
4. The classification of the bacteria i.e. Whether they are toxin forming bacteria (certain bacteria release poisons called toxins into the body system that act faster than a bacterium in causing illness).
From all these factors it can be seen that It is not an impossibility to begin to experience the symptoms of food borne illness several hours, or even days, after consuming contaminated food or drink even if one had eaten other food in the interval.
This has proved true in a number of food borne illness investigations. Typically when investigating incidents of food borne illness, investigators would want to know what and what the victim had eaten in the past 48 or 72 hours. This report will be needed among other reasons, to be compared with the results of causative agent determined from samples collected from the victim in an attempt to identify the culprit food or drink.
For example if the predominant bacteria isolated from feacal samples of a food borne illness victim is Vibrio parahaemolyticus, a food borne illness bacteria commonly associated with seafoods, and the victim had a meal of shellfishes like oysters and clams 3 days earlier and hadn’t eaten any such related foods thereafter, it’s is most likely that is the source of the food borne illness even if the victim had eaten other meals in the interval.
So…before passing a guilty verdict on the last meal that was eaten as being the cause of the food borne illness, further thought should be given to other meals that had been eaten down the line.