The Centers for Disease Control and Prevention updated its reporting on the E. coli outbreak linked to Topps Meats yesterday. 28 cases of E. coli have been identified as part of the outbreak. According to CDC:

Health officials in several states who were investigating reports of E. coli O157 illnesses found that many ill persons had consumed the same brand of frozen ground beef patties. Ground beef patties recovered from patients’ home were tested by state public health department and federal laboratories. Tests conducted by the New York State Wadsworth Center Laboratory and by a USDA-FSIS laboratory on opened and unopened packages of Topp’s brand frozen ground beef patties yielded E. coli O157 isolates with several different “DNA fingerprint” patterns.

E. coli outbreakInvestigators compared the “DNA fingerprints” patterns of E. coli O157 strains found in ground beef with “DNA fingerprints” patterns of E. coli O157 strains isolated from ill persons. As of 12 PM (ET) October 2, 2007, 28 cases of E. coli O157:H7 infection have been identified with PFGE patterns that match at least one of the patterns of E. coli strains found in Topp’s brand frozen ground beef patties. Ill persons reside in 8 states [Connecticut (2), Florida (1), Indiana (1), Maine (1), New Jersey (6), New York (8), Ohio (1), and Pennsylvania (8)]. Seventeen (94%) of 18 patients with a detailed food history consumed ground beef. Three illnesses have confirmed associations with recalled products because the strain isolated from the person was also isolated from the meat in their home. The first reported illness began on July 5, 2007, and the last began on September11, 2007. Among fifteen ill persons for whom hospitalization status is known, ten (67%) patients were hospitalized. One patient developed a type of kidney failure called hemolytic-uremic syndrome (HUS). No deaths have been reported. Twelve (43%) patients are female. The ages of patients range from 3 to 77 years; 33% are between 15 and 24 years old (only 14% of the US population is in this age group).

DNA "fingerprints" or Pulsed Field Gel Electrophoresis patterns, are explained as follows:

When a sample is taken from either a piece of meat or poultry that is contaminated with a dangerous form of bacteria, such as E. coli O157:H7, listeria, or campylobacter, it can be cultured to obtain and identify the bacterial isolate. If a person consumes some of the contaminated meat or poultry, and becomes infected as a result, a stool sample can then be cultured to obtain and identify the bacterial isolate. These bacterial isolates are then broken down into their various component parts creating a DNA "fingerprint".

The process of obtaining the DNA fingerprint is called Pulse Field Gel Electrophoresis, or PFGE. This technique is used to separate the DNA of the bacterial isolate into its component parts. It operates by causing alternating electric fields to run the DNA through a flat gel matrix of agarose, a polysaccharide obtained from agar. The pattern of bands of the DNA fragments — or “fingerprints” — in the gel after exposure to the electrical current is unique for each strain and sub-type of bacteria. By performing this procedure, scientists can identify hundreds of strains of E. coli O157:H7 as well as strains of listeria and campylobacter, and other pathogenic bacteria.

The PFGE pattern of the bacteria can then be compared and matched up to the PFGE pattern of the strain of infected persons who consumed the contaminated product. When PFGE patterns match, they, along with solid epidemiological work, are proof that the contaminated product was the source of a person’s illness.