The number of cases linked to an outbreak of E.coli O157 in Oregon, USA, has increased to at least 18. Four of them, including a 1-year-old, have been hospitalized with Haemolytic Uraemic Syndrome (HUS) and are suffering from acute kidney failure.

Officials have linked the outbreak to the consumption of raw (unpasteurised) milk from Foundation Farm. Lab testing found E.coli O157:H7 in manure samples from the farm. It also turned up in rectal swabs from two of four cows and most telling of all - it was found in the milk. To find it, epidemiologists have to test a contaminated sample and in this case, that means catching it in a few drops of milk. State epidemiologist, Dr. Katrina Hedberg said: "The fact that it was found in the milk itself shows that it was probably contaminated at a high level" .

This is Oregon's sixth raw milk outbreak since 1993 and comes on the heels of another E.coli outbreak in Missouri linked to unpasteurized milk.

Retail sales of raw cow's milk were banned by the Oregon Legislature in 1999 following four illness outbreaks between 1993 and 1997. But sales at small farms with no more than two lactating cows are allowed, provided they don't advertise.

Foundation Farm sold raw milk to 48 families through a program in which they bought shares in a herd. Herd-share programs in Oregon are not regulated and have sprung up in response to the state's ban on raw cow milk sales as a way to circumvent the law.

The cow's teats are cleaned before milking but there is always a risk of bacteria from the hair on the udders getting into the milking device when it's put in place. Then the milk has to be cooled down immediately to prevent any bacteria from multiplying. Many small farms can't afford expensive refrigeration equipment.