Potential Bioterrorism Agent: Category B
Hospital: Report by IDSS, facsimile, mail or phone
Lab: Report by IDSS, facsimile, mail or phone
Physician: Report by facsimile, mail or phone
Local Public Health Agency (LPHA): Report by IDSS, facsimile, mail or phone. Follow-up required
Iowa Department of Public Health
Disease Reporting Hotline: (800) 362-2736
Secure Fax: (515) 281-5698
Shigellosis refers to disease caused by any bacteria in the genus Shigella. There are four Shigella species: S. dysenteriae (Group A), S. flexneri (Group B), S. boydii (Group C), and S. sonnei (Group D). Groups A, B, C, and D are further divided into 15, 8, and 19 serotypes, respectively, but S. sonnei consists of only one serotype. Some strains produce enterotoxin and Shiga toxin, which probably play a role in destructive ulcerations in the intestines once the organisms have invaded. This explains the watery and sometimes bloody diarrhea seen the first or second day of illness.
B. Clinical Description
Symptoms are characterized by diarrhea accompanied by fever, nausea and sometimes, vomiting, cramps and tenesmus (painful, especially ineffectual straining at stool or urination).
Onset typically includes blood and mucus in stools, resulting from mucosal ulcerations and minute abscesses caused by the invasive organisms. Milder cases may have a watery diarrhea. Illness is usually self-limited, lasting an average of 4 - 7 days
Complications: The most common complication is dehydration, but they may also include convulsions in young children. Other complications include intestinal perforation, hemolytic uremic syndrome and reactive postinfectious arthropathy. The severity of illness is a function of the host (age and preexisting nutritional state), the serotype, and bacteria’s ability to produce toxin. Death is uncommon in U.S., but common worldwide.
Common reservoirs: Humans are the only significant reservoir.
D. Modes of Transmission
Person-to-person: Transmitted via the fecal-oral route. People shedding bacteria may contaminate food by failing to properly wash their hands before food handling, potentially causing large numbers of people to become ill. A very small dose of Shigella is needed to cause illness (probably 10 – 100 organisms); thus, it can be easily spread. Person-to-person spread typically occurs among household contacts, pre-school children in child care, and the elderly and developmentally disabled living in residential facilities. Secondary attack rate in households can be as high as 40%. Transmission can also occur person-to-person through certain types of sexual contact (e.g., oral-anal contact).
Foodborne: Flies can potentially spread the bacteria by landing on contaminated feces and then on food. This is most common during international travel.
Waterborne: Fecal contaminated recreational water, such as fill and drain wading pools, can be a source for spread.
E. Incubation period
The incubation period can vary from 12 - 96 hours, but is usually about 24 - 72 hours. It can be up to a week for S. dysenteriae.
F. Period of Communicability or Infectious Period
The disease is communicable as long as infected people excrete Shigella in their stool. This usually lasts less than 4 weeks from onset of illness; however, people are most infectious while having diarrhea. Very rarely, the asymptomatic carrier state may persist for months or longer; appropriate antibiotic treatment usually reduces duration of carriage to a few days.
Shigellosis has a worldwide distribution, with approximately 125 million illnesses and 14,000 deaths reported annually throughout the world. Two-thirds of these cases and most of the deaths are in children under 10. Secondary attack rates can be as high as 40% in households. In the United States, there are an estimated 500,000 cases of shigellosis every year, making it the third most common bacterial enteric disease. Approximately 100 cases are reported in Iowa annually. Outbreaks most often occur in child care centers, among men who have sex with men, and in jails. Outbreaks have also been caused by contaminated imported food. S. sonnei is the most common Shigella species reported in Iowa. Diapered children playing in “kiddie” pools or other recreational water for young children filled with tap water without addition of chlorine or bleach can also easily spread Shigella.
H. Bioterrorism Potential
Category B Agent: Shigella has been identified as a potential category B bioterrorism agent as a food safety threat.
I. Additional Information
The Council of State and Territorial Epidemiologists (CSTE) surveillance case definitions for Shigellosis can be found at: http://wwwn.cdc.gov/nndss/case-definitions.html
CSTE case definitions should not affect the investigation or reporting of a case that fulfills the criteria in this chapter. (CSTE case definitions are used by the state health department and the CDC to maintain uniform standards for national reporting.)
American Academy of Pediatrics. Red Book: 2015 Report of the Committee on Infectious Diseases, 30th Edition. Illinois, American Academy of Pediatrics, 2015.
Centers for Disease Control. Shigella website: www.cdc.gov/shigella/index.html
Heymann, D.L., ed. Control of Communicable Diseases Manual, 20th Edition. Washington, DC, American Public Health Association, 2015.