Explaining how E. coli reached spinach fields not an easy task

It appears that California State health officials are at a loss to explain the source of a nationwide outbreak of E. coli food poisoning.

Despite the fact that manure from cattle living close to the spinach farm in California's Salinas Valley is the suspected source of the outbreak, it seems that the manure cannot be definitively proven to be the original site of the toxic E. coli bacteria.

The E. coli bacteria strain found in the spinach apparently matches the bacteria strain which has killed three Americans and sickened 200 others but the evidence is not conclusive according to Kevin Reilly, deputy director of the California Department of Health Services.

Reilly says they have failed to explain how the bacteria found it's way to the spinach field from a nearby cattle grazing pasture.

The suspect ranch is thought to cover several thousand acres around a spinach field separated from cattle by a paved road and fences and the manure samples were found a half-mile to a mile from the field leased by the rancher to a spinach grower.

Dean Cliver, a microbiologist and professor of food safety at the University of California, says the cow manure is an important clue, but they must now look at how agricultural practices have allowed the E. coli to travel a half-mile to a mile from pasture to spinach field.

Cliver says the same E. coli strain in the cow dung and in the spinach may be the result of some form of contamination which is much further away in other cattle pastures.

Cliver suggests that as cattle have been found close to a field in as many as nine outbreaks, loose soils higher up where cattle are defecating may be washed down in the soil by irrigation systems.

Investigators are looking into flooding, irrigation water, wild and domesticated animals and farm workers as possible links between the cattle manure and spinach.

The suggestion that the bacteria may have traveled from cattle to vegetables has prompted concerns that new limits on growers, such as buffer zones, will be imposed.

The Salinas Valley-area is known as the "salad bowl of the world" and farmers are now worried that state and federal regulators could insist on new rules restricting where they can grow produce.

This they say would jeopardise the century old history of the two leading agricultural industries of farming and ranching in the region and a buffer zone could place wide ares of valuable land out of bounds for growing.

Farmers who grow three-quarters of the nation's spinach say it is not possible to grow the vegetable outdoors and guarantee a 100% clean and safe product, but the alternatives would mean turning the Salinas Valley into a virtual greenhouse and would make the produce much more expensive.

Health officials argue that the Salinas Valley area has seen nine outbreaks of the virulent E. coli in the last decade which is an indication that agricultural practices need improvement and the Food and Drug Administration in the U.S. also says the issue of the proximity of cattle to farm fields has always been a concern.

This latest outbreak is the first time that investigators have matched the bacterium from an outbreak to an E. coli sample in the environment close to where the contaminated spinach or lettuce was grown.

Escherichia coli is as a rule a relatively harmless bacteria found in the guts of animals.

The E. coli O157:H7 strain was identified in 1982 and causes an estimated 73,000 cases of infection and 60 deaths in the United States each year.