State health officials conducted a months-long investigation to find the cause of an E. coli bacterial infection that hospitalized four tourists and sickened four others on Kaua'i in March.

Their conclusion: All eight people were most likely infected by eating contaminated lettuce from a Kaua'i farm, where heavy rains and flooding had carried E. coli bacteria from a cattle pasture onto the lettuce patch.

Officials declined to name the farm they suspect was the source of the lettuce.

The state Department of Health said that the eight victims, including the four who required hospital care, have recovered without complications from the outbreak of a strain of E. coli O157, whose symptoms include abdominal cramps and bloody diarrhea and which in severe cases can cause kidney failure.

In a nationwide E. coli O157 outbreak last year involving California bagged spinach, nearly 200 people were affected and one died. In another outbreak of E. coli O157 in November and December, several dozen in five states became ill from infections associated with a fast-food restaurant chain.

When the cluster of bacterial infections appeared on Kaua'i, the source of the illness was not clear. The victims included seven tourists from five states, and one Kaua'i resident.

NATIONWIDE ALERT

The Department of Health was alerted of the initial cases April 2, and immediately sent out a statewide and a nationwide alert to physicians, since such cases can sometimes be widespread if the source is a product that is shipped across island or state lines — as happened in both of last year's Mainland outbreaks.

Eight victims were identified, all of whom were on Kaua'i or had returned to the Mainland but had been on Kaua'i in March.

"There probably were more cases than those diagnosed, because some people may not have sought medical care, and some doctors may not have taken stool samples" that positively identifed the illness, said Dr. Paul Effler, state epidemiologist.

The Health Department conducted extensive interviews with each of the known victims. The eight had not stayed in the same place on Kaua'i, had not swum in the same place or been in contact with the same animals. Between them, they had eaten in 37 different establishments.

Health investigators took DNA from the disease organisms in patients, and were able to determine that the strain of E. coli O157 bacteria in all the victims had the same DNA "fingerprint." That suggested there was a common source for the infections.

Escherichia coli is a common bacterium — one present in everyone's gut. But most strains are benign. Some, including E. coli O157, are not.

COMMON FACTOR FOUND

Investigators focused on food, and studied the menus at each of the 37 Kaua'i restaurants. Because no victims appeared to have contracted the disease outside Kaua'i, it was assumed it must come from some local source.

"It was determined that one item, locally produced lettuce, was common to at least one restaurant eaten at by each case during their probable exposure," said Janice Okubo, public information officer for the state Department of Health.

Investigators then headed out to local lettuce farms, and located one farm — which has not been named — that was situated near a cattle farm. There was evidence of local flooding in the area in late February and early March, which could have carried bacteria from cattle manure from the pasture to the crop. Effler said it is likely that the farm was the source of the contaminated lettuce, but not certain.

Cattle are a natural reservoir for E. coli O157, and when samples were taken from cattle in the region where the farm was located, they were found to have the same subtype of E. coli O157 that infected the eight people in Kaua'i in March.

"Fortunately, this cluster of cases was limited to eight individuals and we were able to track down the probable cause," Effler said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.