It's often, but not always, the chicken

A few days before the media swung into full-time live coverage of the US elections, international headlines were made by the unpleasant symptoms experienced by more than 100 University of Canterbury students, suffering the unpleasant and unbecoming symptoms of a foodborne illness presumed to have been caused by a contaminated chicken dish.

“It’s always the chicken,” exclaimed RNZ’s Lisa Owen on Checkpoint that evening. It is quite often, but not always.

It wasn’t a happy story , but it makes for a good excuse to take the opportunity to explain to readers how one food-borne illness may differ from another, and what makes them different.

People who become unwell with vomiting and diarrhoea as the result of consuming contaminated food or drink can generally be classified as suffering from one of two relatively common disease processes.

People who become unwell within hours of swallowing the contaminated food or drink usually are suffering the effects of swallowing toxins that have been released into the food by a bacterium that had multiplied in the food between the time the food was prepared and the time that it was eaten.

People who become unwell a few days after swallowing the contaminated food or drink usually are suffering the effects of toxins that have been released into the intestines by a bacterium that had been present in the food, and then had multiplied and released toxins within the intestines of the affected person.

The first disease process is often termed “food poisoning”. In this disease the organism responsible for the illness has multiplied in the food before it was eaten and it is the presence of the toxin released by the organism into the food that is responsible for the rapid onset of vomiting and diarrhoea, often with abdominal cramping pain, and a relatively quick recovery over a few hours.

Fever is relatively uncommon in this illness. The diarrhoea and vomit from these people isn’t stuff you’d want to be around, but it usually does not pose a significant risk of transmission of illness to others.

The second disease process is often termed “gastroenteritis”. In this disease the organism responsible for the illness has been present in the food before it was eaten but the organism must multiply in the intestines over a few days, before it can release the toxins that will commonly cause a gradual onset of vomiting and/or diarrhoea, followed a gradual recovery over several days.

Fever is relatively common in this illness. The diarrhoea and vomit from these people does pose a potential risk of transmission of illness to others. Transmission can generally be avoided by careful hand hygiene after each bowel motion.

Many people will be familiar with the risk of gastroenteritis caused by intestinal infection with the pathogenic bacterium Campylobacter jejuni, that commonly contaminates chicken meat, and which may survive inadequate cooking.

The bacterium contaminating the uncooked chicken can transmitted to other foods such as salads, via contamination of hands, or bench or chopping surfaces, in the kitchen. This bacterium usually causes the onset of illness a couple of days after ingestion of the contaminated food (yes, potentially salads handled by unwashed hands can be dangerous) and illness commonly persists for several days.

Chicken meat also can be contaminated with various Salmonella species. These bacteria are a slightly less common cause of gastroenteritis, that is often indistinguishable from the gastroenteritis caused by Campylobacter jejuni.

Another common cause of illness caused by eating contaminated chicken is food poisoning due to toxins produced by Clostridium perfringens, a bacterium closely related to the bacterium that causes tetanus (Clostridium tetani).

Clostridium perfringens, like Campylobacter jejuni and various Salmonella species, commonly multiply in the intestines of chicken, and contaminate chicken meat during the processing that follows the chickens’ slaughter.

The rapid onset of illness after consumption of the suspect meal, and the relatively rapid recovery, in the students in Christchurch, suggests that Clostridium perfringens may be the cause of this outbreak. Results from tests performed on any remnants of the various foods eaten by the students, and on samples of vomit or diarrhoea, provided by affected students are likely to provide a definitive answer.

No treatment other than fluid replacement is necessary. Antibiotic treatment is not helpful. Full recovery without any significant consequences is the usual outcome.

And none of us should need to be reminded: cook chicken until none of the flesh is pink, and if you’ve handled raw chicken, don’t touch anything or anyone else until you have carefully washed your hands.