Having excluded drinking water as the likely source of an isolated outbreak of a bacterial infection in a Riverton neighborhood, health officials Friday began examining other possibilities.

The investigation began last week after several residents told the Salt Lake County Health Department and the news media that they had contracted giardia infections possibly from the city's culinary water supply.Kent Miner, director of the county's Bureau of Water Quality and Hazardous Wastes, said extensive testing of Riverton's culinary water supply revealed no problems.

"We've taken bacteriological samples and have found no positive indicators in the water. We have also reviewed all of the water samples taken during the past 12 weeks and have found nothing wrong," Miner said.

The implication, Miner said, is that the giardia infection came from another source. Giardia is endemic in Salt Lake County, commonly occurring in exposed waterways, he said.

Riverton Mayor James Warr noted that the city's water supply is derived entirely from deep wells.

"This water system and all others are controlled by the Federal Clean Water Act," Warr said, explaining that the law requires regular testing for coliform, organic compounds, herbicides, pesticides and radiation. "We test 12 random spots within Riverton every month."

The mayor also denied an assertion by one resident that the city has neglected to investigate the giardia outbreak.

"Each time a complaint is received regarding the quality of our water system, we immediately respond and submit lab tests for analysis, as we did in this particular situation," Warr said.

On Friday, a county epidemiologist began interviewing residents to determine where they might have contracted the infection. Miner said the procedure is routine.

"Once we have verified that there is no problem with the water, we then try to identify other possible sources," Miner said.

Those possible sources include pets and day care centers, he said. The infection can take from five days to three weeks to manifest itself, Miner added.

Symptoms include violent attacks of diarrhea, abdominal discomfort, cramps or swelling, loss of appetite and nausea. It usually clears up without medical intervention.

"We have had these outbreaks before in the county, and in 99 percent of the cases, the drinking water is not the problem. We feel confident that the water system is not the problem in Riverton."