OPHEPR; Escherichia coli O157:H7 - Profile for Healthcare Workers

Causative Agent: Escherichia coli serotype O157:H7 is a gram-negative, rod-shaped bacterium that produces Shiga toxin(s). This rare variety of E.coli produces large quantities of potent toxins that cause severe damage to the lining of the intestines, leading to hemorrhagic colitis.

Routes of Exposure: Ingestion of contaminated food or water is the main route of exposure, but direct person-to-person contact can also spread infection.

Infective Dose & Infectivity: May be as few as 10 organisms. All people are believed to be susceptible to hemorrhagic colitis, but young children and the elderly appear to progress to more serious symptoms more frequently.

Incubation Period: The incubation can be from 2 to 8 days, but it usually ranges from 3 to 4 days.

Clinical Effects: The illness is characterized by severe cramping (abdominal pain) and diarrhea which is initially watery, but becomes grossly bloody. Occasionally vomiting occurs. Fever is either low-grade or absent. The illness is usually self-limited and lasts for an average of 8 days. Some individuals exhibit watery diarrhea only.

A severe clinical manifestation of E. coli O157:H7 infection is hemolytic uremic syndrome (HUS). Up to 15% of those with bloody diarrhea from E. coli 0157:H7 can develop HUS, which can lead to permanent kidney failure.

Lethality: The overall mortality rate for E. coli O157:H7 is <1%. For those who develop HUS, the death rate is between 3-5%.

Transmissibility: The major source of transmission is the consumption of raw or undercooked ground beef. Other sources of transmission include unpasteurized milk and juice, alfalfa sprouts, lettuce, dry-cured salami, and contact with infected animals. Waterborne transmission can occur by swimming in or drinking inadequately chlorinated water such as that found in contaminated lakes and swimming pools. The organism is easily transmitted from person-to-person when proper hand washing techniques are not used.

Primary Contamination & Methods of Dissemination: In a terrorist attack, E. coli would most likely occur due to intentional contamination of food or water supplies. In addition aerosolization could be a possibility.

Secondary Contamination & Persistence of organism: Secondary transmission can result from exposure to the stool of patients with overt disease. Diarrheal fluids are highly infectious. The period of infectivity of stool is typically a week or less in adults but 3 weeks in one-third of children. Prolonged carriage of E. coli O157:H7 in the stool is uncommon.

Decontamination & Isolation:

Patients – No decontamination necessary. Patients can be treated with standard precautions, with contact precautions for diapered or incontinent patients. Hand washing is of particular importance.
Equipment & other objects – 0.5% hypochlorite solution (one part household bleach and nine parts water), EPA approved disinfectants, and/or soap and water can be used for environmental decontamination.

Laboratory Testing: Clinical laboratories can screen for E. coli O157:H7 in stool samples by using sorbitol-MacConkey agar.

Therapeutic Treatment: Most people recover without specific treatment in five to ten days. For uncomplicated cases, rehydration may be all that is required. Fluid and electrolyte replacement is important when diarrhea is watery or there are signs of dehydration. Antibiotics are often avoided in E. coli O157:H7 infections, since some evidence suggests that antibiotic treatment may precipitate complications such as HUS.

Prophylactic Treatment: No vaccine is available to prevent E. coli O157:H7 infections.

Differential Diagnosis: Salmonella, Shigella, Campylobacter, Yersinia enterocolitis, and bacterial food poisoning may show similar signs and symptoms.

References:

Chin J. Control of Communicable Diseases Manual, Seventeenth Edition, American Public Health Association; 2000.
Foodborne Pathogenic Microorganisms and Natural Toxins Handbook, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration

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