Public health officials in South Dakota have confirmed 22 cases of Salmonella Newport that is similar to a strain of Salmonella Newport that has been identified as causing illness among residents of four other states. An outbreak investigation is under way to determine whether victims of the outbreak ate the same food, but so far investigators have not been able to pinpoint the source of the outbreak.
Genetic "fingerprinting" of the Salmonella strain isolated from victims’ stool has helped public health agencies in the five states and at the Centers for Disease Control and Prevention (CDC) in their investigation. 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.
The Rapid City Journal reported on the outbreak today:
So far, health officials have confirmed 22 cases of a specific strain of the bacterial-borne intestinal disorder in the four states. All of South Dakota’s 11 cases — nine adults and two children — were in the Black Hills area. Six of the 11 victims were hospitalized, five at Rapid City Regional Hospital.
"Everybody’s recovering," state epidemiologist Lon Kightlinger of the South Dakota Department of Health in Pierre said Monday. "But since we’ve had so many of these cases hospitalized, which is fairly unusual, it leads me to believe it is a fairly potent strain."