The State Hygienic Laboratory continues to work with the Iowa Department of Public Health and Linn County Public Health to determine the source of a large Shigellosis cluster in Linn County that began in May. As of July 24, the Hygienic Laboratory confirmed a total of 173 cases.

Shigellosis is a gastrointestinal disease that is caused by Shigella bacteria and can be spread either person to person or by food. The role of the laboratory is to perform identification, analysis and surveillance of the cases in Iowa.

Drug-resistant Shigella (Image courtesy of CDC)

One of the most important roles of the laboratory is to assist epidemiologists in tracking the source of the outbreak by determining the molecular fingerprint of the bacterial strains. By looking at exposures, this fingerprint can distinguish cases that are part of the cluster. For example, the exposures may be traced to a similar food product consumed by people suspected of having Shigellosis.

Molecular subtyping identifies clusters using pulsed-field gel electrophoresis (PFGE). The subtyping information is uploaded to the national molecular subtyping network known as PulseNet. The Hygienic Laboratory is the designated PulseNet laboratory for the state of Iowa. The Linn County outbreak is made up of two unique PFGE clusters grouped into the larger national outbreak code.

Another critical role of the Hygienic Lab is culturing the stools of patients after symptoms have resolved to ensure they no longer carry the bacteria that causes the disease and that they are no longer a risk for spreading the illness. Washing hands is the best way to prevent passing on bacterial infections such as Shigellosis.

According to the CDC, Shigella symptoms typically start one to two days after exposure, and include diarrhea (sometimes bloody), fever, abdominal pain, and tenesmus (a painful sensation when trying to pass stools, which may occur even when bowels are empty). Shigellosis can be serious for the very young and the elderly, and also for those who are immune-compromised. Shigellosis is self-limiting, which means it typically resolves itself without direct treatment. In rare cases, complications can occur.

Patients suspected of having Shigellosis should contact their health care provider for more information.