DURHAM - City officials sampled tap water in homes in the 2300 block of West Club Boulevard on Friday after a house there tested positive for contamination from coliform bacteria.

Additional tests should be completed today to determine what type of coliform was found. Among the possibilities is E. coli, bacteria present in human waste that can cause symptoms such as stomachache, fever, vomiting and diarrhea. A city inspection of the home did not find any sign of faulty plumbing that would have contributed to the contamination.

City officials stressed Friday that there is no evidence yet that any harmful bacteria is in the tap water or that the coliform has spread beyond the house where it was detected. Water in the home was sampled Wednesday after the owner requested that it be tested for lead contamination. But it takes 24 hours to conduct the test for the presence of coliform, and the results were not known until Thursday.

"It's an isolated incident in a single residence," said Ted Voorhees, the deputy city manager who supervises the city water department. "That does not indicate an E. coli problem."

The family that lives where the coliform was found has been told not to drink or cook with the tap water unless it is boiled, a precaution that kills the bacteria. The homeowner said his son was very ill last week with what was then assumed to be food poisoning. There is no evidence the illness was caused by the family's tap water, however.

Samples from neighboring homes were collected Friday, as well as from nearby fire hydrants. The samples were delivered to the city's laboratory for testing. Workers are also boosting the level of chlorine in the water supply in the hopes of killing any harmful bacteria.

The city made no public notice of the test result and disclosed it only when asked by The News & Observer.

State officials said Durham is proceeding properly, though the city missed a chance to know whether the coliform found in the original sample was E. coli. If the city had followed proper testing procedures with that sample, the results would have been known Friday, officials said.

"They should have continued the test on that sample, but they did not," said Bob Midgette, a regional supervisor at the public water supply section of the N.C. Department of Environment and Natural Resources. "All we have been able to get out of them is that there was a lab error."