Clusters of E. coli infection reported in Eastern Tennessee could be the “new normal” as non-O157 Shiga toxin-producing Escherichia coli (STEC) take their place beside O157, making outbreaks all that more difficult to sort out.

“It is very confusing,” said Tennessee’s State Epidemiologist, Dr. Tim F. Jones on Monday, as he explained that in addition to three O157:H7 cases, two cases of E. coli O103 and one of O169 have been confirmed in the eastern end of the state.

Tennessee is being assisted by the Centers for Disease Control and Prevention (CDC) in investigating a total of 11 cases of E. coli infection.

Dr. Jones said further complicating the investigation is the fact that in the DNA “fingerprinting” by pulsed-field gel electrophoresis, no two of the PFGE patterns are the same for any of the E. coli strains. PFGE patterns of bacteria isolated from the people who are ill are often used to link cases to a common source.

E. coli O103 is one of the “Big Six” among the non-O157 STEC.  (The others being 026, O111, O121, O45  and O145.)  E. coli O169 is rare, but was reported in 1999 as responsible for two outbreaks in Japan, one involving 132 cases and the second with 126 cases.

Jones said the lab-test results have left Tennessee health officials with a difficult investigation, trying to determine common foods and activities for victims. At this point, he said, sources of contamination could be anything from exposure to petting farm animals or swallowing water from the wrong swimming hole.

After health officials confirmed they were dealing with STEC bacteria, two western Virginia siblings turned up in Tennessee hospitals on June 5 with illnesses caused by E. coli O157:H7.  The two-year-old girl died, while her five-year-old brother recovered after being treated at the Vanderbilt Medical Center in Knoxville.

But Jones said there appears to be no connection between those two cases from western Virginia and the 11 eastern Tennessee cases, not even the O157 cases in Tennessee.

Eastern Tennessee annually sees 7 or 8 cases of E. coli illness, and the spike in infections has health officials troubled. The good news may be that three suspected cases came back negative for any STEC bacteria.

Only E. coli O157:H7 has been declared an “adulterant” in meat. That means it is an unacceptable, impure substance that regulators will not tolerate.

USDA’s Food Safety & Inspection Service (FSIS) currently is considering a petition filed in late 2009 by the Seattle food safety law firm of Marler Clark, sponsor of Food Safety News, to declare the “Big Six” as adulterants.

According to CDC figures, there are 31,229 illnesses from non-O157 Shiga toxin-producing E. coli annually in the U.S.

The current deadly outbreak in Germany is caused by a strain of non-O157 Shiga toxin-producing E. coli called O104:H4.  Except for a handful of returning tourists, cases involving that strain have not been seen in the U.S.

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Photo: Tennessee State Epidemiologist Dr. Tim F. Jones