In addition, the Anatum, Newport and Heidelberg serotypes each produced two distinct PPGE patterns, meaning the outbreak involved at least nine different organisms.
And according to Dr. Dirk Haselow, Medical Director and Chief of the Arkansas Communicable Disease and Immunizations Unit, 4 of the PFGE patterns were previously unknown to the national tracking system known as PulseNet.
"Environmental health investigations have determined that there were multiple opportunities for contamination and cross-contamination during food preparation and that whole frozen chickens may not have been cooked sufficiently to kill all the salmonella present," said Dr. Haselow in his report to the International Society for Infectious Diseases.
"The peak of cases occurred 18 hours after consumption of a meal containing chicken salad," he said.
Located in Jefferson County about 25 miles northeast of Pine Bluff, the Tucker Unit holds 849 inmates. The outbreak began after the chicken salad was served on the weekend of Aug 4-5.
Haselow said investigators did collect few early reports of illnesses among food handlers at the prison. "However, among the 590 interviews conducted, 448 prisoners and staff ate the chicken salad," he reports. Of those, 354 became sick. Haselow called that "an attack rate" of 79 percent.
"At present, as multi-species contamination of raw chicken is common, our consensus opinion is that the dominant mode of transmission observed in this outbreak is related to undercooked chicken rather than person-to-person contamination or contamination by the food by a symptomatic food handler," said Haselow.
Laboratory analysis of both food samples and stool specimens, along with the epidemiological investigation, is continuing in Arkansas with assistance from the federal Centers for Disease Control and Prevention (CDC) in Atlanta.
The 4,000-acre Tucker Unit was formerly known as the Arkansas State Prison Farm. It continues to produce crops as part of it agricultural, trade and vocational programs.
The historic prison used the "Old Sparky" electric chair from 1926 to 1948 for executions and is also known for the electric shock device known as the "Tucker Telephone."
During the Salmonella outbreak, the prison had to cancel some visiting days and delay discharging some prisoners. A prison gymnasium was used as an infirmary until all the ill recovered.
