Recent outbreaks of enterohaemorrhagic Escherichia coli (e-coli) in Germany and reports about the emergence of “new superbug” Salmonella Kentucky have re-focused public attention on food-borne diseases.
Both pathogens aren’t really new and have been recognised as bio-threats for decades.
Salmonella, for instance, is a well-known bacterial cause of food-borne disease with a significant impact on the population and health-care systems.
Typhoid caused by Salmonella Typhi is its most severe and epidemic type.
But improvements in sanitation have drastically reduced the frequency of people in the developed world getting ill from bacteria. It has essentially been reduced to a condition travellers contract in countries where it occurs naturally.
In the last century, microbiologists have discovered hundreds of other types of Salmonella that can infect humans and some warm-blooded animals.
They are especially widespread in areas with sub-standard farming practices and supplies of drinking water.
These types of Salmonella have been responsible for acute gastroenteritis following the ingestion of contaminated water and undercooked meat or other animal products.
Illness caused by these bacteria ranges from mild abdominal discomfort to vomiting and dehydration and can be life-threatening for children and the elderly.
It’s a major international public health problem.
Salmonella enterica serotype Kentucky represents one of the non-typhoidal types of Salmonella that microbiologists and public health professionals encounter from time to time.
In Australia, more than 12,000 cases of Salmonella infection were reported in 2010 but only five of them were related to Salmonella Kentucky.
What makes Salmonella Kentucky stand out and explains its rather hyperbolic label of “new superbug” is that this pathogen has managed to develop resistance to some antibiotics. So it’s more difficult to treat.
Of particular concern is the fact that many strains of this serotype circulating in countries in the Middle East and Africa display high-level resistance to ciprofloxacin, which is one of drugs used for treatment of Salmonella disease.
The development and dissemination of its antimicrobial resistance is thought to be caused by the antibiotics used in animals farmed for food.
Multinational surveillance has noted a recent increase in the frequency of the detection of drug-resistant Salmonella enterica serotype Kentucky and its potential for global spread.
A recently published report suggested this drug-resistant type spread from Africa and the Middle East to Western Europe and Asia.
It’s very likely that this epidemic variety of Salmonella can occasionally arrive to Australia as one of the “unseen travellers” in the gut of an infected tourist.
Indeed, the New South Wales Enteric Reference Laboratory, based in Westmead Hospital, recently confirmed two cases of infection with ciprofloxacin-resistant Salmonella Kentucky in overseas travellers who picked up the pathogen in India and South-east Asia.
But there’s no evidence of local transmission of the pathogen in this country at this stage.
The importance of prevention
This observation reinforces the importance of prevention and control of food-borne Salmonella disease.
The global human health impact of non-typhoidal Salmonella infection could be as high as a 100,000,000 illnesses and 155,000 deaths each year.
Many cases of salmonellosis would be prevented if common outbreak sources could be rapidly identified to allow for earlier public health interventions.
But changes in food-borne disease epidemiology have complicated recognition and investigation of outbreaks. The most important contributors to the evolution of disease epidemiology are as follows.
Socioeconomic changes because of booming South-east Asian economies has affected food production, food supply and food consumption habits resulting in an increase in the number of food-borne diseases like Salmonella.
Increased mobility of people and complex food production, processing and distribution systems as well as the plethora of retail fast-food outlets means we need more efficient and effective ways to identify sources of food-borne outbreaks.
Salmonella-related outbreaks are increasingly linked to a diverse range of food sources, but the mechanisms of contamination often remain poorly understood.
True rates of infection are likely to be under-reported because of this.
Health, food and agriculture authorities need to coordinate their efforts to monitor and limit the spread of the drug-resistant strains like Salmonella Kentucky.
Increasing the timeliness of case follow up and linking laboratory results to public health actions is critical for reducing delays in the investigation of outbreaks.