2011 saw a couple of unusual outbreaks of food-borne disease, one from a previously unknown pathogen and the other from a well-known one in a food not usually associated with such outbreaks. The outbreaks highlighted the difficulties associated with identifying the source of food-borne disease outbreaks, and the importance of being alert.
Australia has a very good record in food safety management and large food-borne illness outbreaks are rare here but these major events highlight the how important it is to be prepared and avoid complacency.
E. coli in Germany
The first major outbreak was the result of a previously unknown hybrid bacterium, E. coli O104:H4, a cross between an Enterohaemorrhagic E. coli (EHEC) and a lesser known pathogenic group of the bacteria called Enteroaggregative E. coli (EAEC). This E. coli outbreak was the most severe ever caused by the bacteria due to the large number of people who suffered serious illness and death.
This particular strain of E. coli had rarely been found prior to the outbreak in Germany, but it ended up affecting 15 other countries as well. Out of the 4075 cases, 908 people suffered a severe form of illness called Haemolytic Uraemic Syndrome (HUS) and 50 died. HUS is a serious complication of EHEC infection brought about when the toxin produced by the bacterium attacks the kidneys, resulting in seizures, strokes and death in some patients. Most of the victims from this outbreak were healthy adults.
Initially, the cause was thought to be Spanish cucumbers, as E. coli had been found when testing them to determine the source of the outbreak. But the isolated strain was subsequently found not to be the one responsible. Efforts to prevent the outbreak spreading included urging consumers to avoid eating fresh produce, and this led to the collapse of the income of fresh produce farmers.
Further investigation and one particular French outbreak led to the source being identified as fenugreek seeds imported from Egypt, which were used to produce sprouts. Vegetable farmers who were originally impacted by the advice against eating cucumbers and other fresh produce have sought compensation. They have been offered €210 million by the European Commission.
This episode in Germany highlights the difficulty in identifying the source of food-borne outbreaks. Such difficulties include the time it takes for bacteria to cause an infection (often days after consumption), and the time it takes to determine that an outbreak is occurring, which means the food has often been consumed or thrown away before it can be tested for pathogens.
The hybrid nature of the E. coli O104:H4 strain became apparent through genome sequencing, which happened rapidly during the outbreak. The sequence information indicated that while the German E. coli O104:H4 produces classical Shiga toxin type 2, it otherwise resembles enteroaggerative E. coli (which don’t normally cause HUS). The reassortment of Shiga toxin type 2 into EAEC produced an alarmingly infectious bacterial pathogen, able to cause severe illness by virtue of the unique combination of its newly acquired Shiga toxin payload and normally present diarrhoea-causing capacity. The strain is resistant to many antibiotics used to treat patients with bacterial infections.
Listeria in the United States
The second outbreak occurred in the United States and was caused by Listeria monocytogenes infection resulting from the consumption of cantaloupe or rockmelon. This outbreak was the first where L. monocytogenes have been associated with rockmelon and the worst L. monocytogenes such event in the United States in over a decade.
Since the outbreak began in September of this year, 139 people have been infected and 29 have died. The majority of reported cases (with an age range of between 48 and 96 years) led to the hospitalisation (132 cases) of those affected, and a pregnant woman who contracted the disease had a miscarriage.
Listeria is an environmental organism and can grow (albeit slowly) at refrigeration temperatures making it difficult to control once it contaminates products that are stored chilled. The United States typically sees about 800 cases of L. monocytogenes and three to four outbreaks every year. Foods that are commonly associated with such outbreaks include processed meats (such as deli meats and hot dogs) and soft cheeses.
Produce is rarely a source of outbreaks and the melons associated with this outbreak were all from the same farm located in Colorado, although infections occurred across 28 states. Investigations into how the fruit became contaminated are continuing.
Could this happen in Australia?
Despite Australia’s good food safety record and infrequent large food-borne outbreaks, constant vigilance and avoiding complacency are vital if we are to avoid bouts of illness from food contamination.
One of the most significant food contamination outbreaks in Australia occurred back in 1995, the result of infection with E. coli O111, an EHEC. It was associated with the consumption of mettwurst from a manufacturer based in South Australia. There were over 100 cases, 23 children were hospitalised and one died from complications associated with HUS. The court case that followed has taken until November 2011 to finalise in one of the longest running legal cases in South Australia’s history.
The Australian food industry will continue to apply best practice to ensure the safety of food produced in this country. Maintaining expertise to deal with such unexpected events and understanding emerging food-borne pathogens is also paramount for ensuring the safety of our food supply.