September 14, 2009

expert reaction to E. coli outbreak

Experts offer their reactions to an outbreak of E coli on a farm in Surrey, which has led to the hospitalisation of several children.

Dr Anthony C. Hilton, Reader in Microbiology at Aston University, said:

“Given the multitude of routes of infection that E. coli O157 has available to pass from animals to humans, both directly and indirectly via the environment and other humans, it is likely not to be a straightforward task to piece together what went wrong in this case. It may even turn out to be multiple contamination events but we can only speculate until the epidemiological data becomes available, and this unfortunately takes time.”

Prof Norman Noah, Professor of Infectious Disease Epidemiology at the London School of Hygiene and Tropical Medicine, said:

“Escherichia coli [E. coli] is a bacterium commonly found in faeces of mammals and other warm-blooded creatures. Humans harbour many millions of these organisms in their gut, where they are generally symptomless and beneficial – making vitamins, and preventing overgrowth from harmful bacteria. Some of these ‘harmless’ E. coli can however can cause urinary tract infections, septicaemia [blood poisoning], meningitis in newborn babies and other infections.

“There are several different types that can also cause diarrhoea in humans; these types include enterotoxic [ETEC], enteroinvasive [EIEC] and enterohaemorrhagic [EHEC], among others. E. coli O157:H7 is one of the shiga-toxin group, named as such because it produces shiga- or vero- toxin, similar to shigella dysentery toxin [STEC].

“E. coli O157:H7 infection causes an acute gastroenteritis, with abdominal colic, watery diarrhoea sometimes leading to passing of blood. Usually that is all that happens, but in young children and older adults especially [about 8% of cases overall but anything from 0-15%] haemolytic–uraemic syndrome [HUS] may occur. This can lead to haemolysis [breakdown of red blood cells] and kidney failure [‘uraemia’]. Clues that a person is developing HUS include decreased frequency of urination, feeling very tired, and losing pink colour in cheeks and inside the lower eyelids [according to CDC Atlanta].

“E. coli O157:H7 usually infects ruminant animals, though they do not have symptoms. A very small dose of E. coli can cause infection – about 10 are said to be enough. If one considers that ruminants can excrete many millions of these organisms, the possibilities for infection are endless. This also means that the organism can be transferred from fingers to mouth, not just in food. Thus children and others who handle ruminant animals, particularly cows, but also goats and sheep amongst other animals, can pick up the organism. Outbreaks caused by children visiting farms and handling animals are well known, but fortunately not very common. It is quite possible that direct contact between animal and human is not always necessary, and that people can pick up the organism by touching various other objects in the farm.

“The farm implicated in the current outbreak had numerous signs warning children to wash their hands. Hand washing in children is notoriously perfunctory and needs to be supervised by responsible adults. Soap and water need to be provided, as well as disposable towels. Towels must never be shared. Other causes of infection may need to be investigated on this and any other farm of this type: these would include foods eaten at the farm, including food consumed in an on-farm café or picnic area; other sections of the farm environment, including toilets and play areas.

“Outside the farming environment, the food most commonly implicated is hamburger. E. coli comes from the cow’s intestine and will remain on the surface of raw meat until cooked. Steak can be lightly cooked as the process will destroy the bacteria on the surface of the meat. Mince your steak however and the organism will then be distributed into the inside of the burger, and will cause food poisoning if not cooked through.

“Almost any other food contaminated by animal faecal material or water containing faecal material can cause E. coli O157:H7 food poisoning. Such foods as raw milk, raw salads, fruit juices (including unpasteurised apple cider) and water have been implicated. The largest known reported outbreak occurred in Japan in 1996 which was caused by contaminated radish sprouts in school lunches – it caused 9,451 cases.

“Swallowing natural water (lakes, rivers) can also cause infection. Person-to-person spread may also occur.

“The incubation period for E. coli gastroenteritis is 16hrs to 10 days, but is usually 3-4 days.

“Suspected E. coli O157:H7 gastroenteritis must never be treated with antibiotics.”

Prof J Ralph Blanchfield MBE, consultant in food science, technology and law, said:

“The mere petting of animals whose hides are dirty is one way for the hand to pick up the bacterium. No matter what notices and hand washing facilities are provided, some children (and adults!) will neglect to use them, and some children will inevitably touch their mouths, suck their thumbs or bite their nails.

“In at least one major E. coli outbreak associated with petting animals in USA (Lorain, Ohio, County Fair between 20 and 26 Aug 2001) the absence of evidence implicating specific food or beverage sources and the recovery of E. coli O157 from the rafters of a barn suggest that airborne dispersion of bacteria contributed to the contamination. Because E. coli O157 can survive in the environment for more than 10 months, humans may be at risk of infection long after an environment is initially contaminated.”