Enterobacteriaceae Infections

Enterobacteriaceae - a group of mostly aerobic gram-negative bacilli -cause local and systemic infections, including an invasive diarrhea that resembles shigella and, more often, a noninvasive toxin-mediated diarrhea that resembles cholera.

Escherichia coli and other Enterobacteriaceae cause most nosocomial infections. Noninvasive, enterotoxinproducing E. coli infections may be a major cause of diarrheal illness in children in the United States.

The prognosis in mild to moderate infection is good. Severe infection requires immediate fluid and electrolyte replacement to avoid fatal dehydration, especially among children, in whom mortality may be quite high.

Causes

Although some strains of E. coli exist as part of the normal GI flora, infection usually results from certain non-indigenous strains. For example:

Noninvasive diarrhea results from two toxins produced by strains called enterotoxic or enteropathogenic E. coli. These toxins interact with intestinal juices and promote excessive loss of chloride and water.
In the invasive form, E. coli directly invades the intestinal mucosa without producing enterotoxins, thereby causing local irritation, inflammation, and diarrhea. Normal strains can cause infection in immunocompromised patients.

Transmission can occur directly from an infected person or indirectly by ingestion of contaminated food or water or contact with contaminated utensils. Incubation takes 12 to 72 hours.

Incidence

The incidence of E. coli infection is highest among travelers returning from other countries, particularly Mexico, Southeast Asia, and South America. E. coli infection also induces other diseases, especially in people whose resistance is low. Another strain, E. coli 0157:H7, has been reported. It's associated with undercooked hamburger.

Signs and symptoms

Effects of noninvasive diarrhea depend on the causative toxin but may include the abrupt onset of watery diarrhea with cramping abdominal pain and, in severe illness, acidosis. Invasive infection produces chills, abdominal cramps, and diarrheal stools that contain blood and pus.

Infantile diarrhea from an E. coli infection is usually noninvasive; it begins with loose, watery stools that change from yellow to green and contain little mucus or blood. Vomiting, listlessness, irritability, and anorexia often precede diarrhea. This condition can progress to fever, severe dehydration, acidosis, and shock. Bloody diarrhea may occur from an E. coli 0157:H7 infection.

Diagnosis

Because certain strains of E. coli normally reside in the GI tract, culturing is of little value; a working diagnosis depends on clinical observation alone.

A firm diagnosis requires sophisticated identification procedures such as bioassays that are expensive, time-consuming and, consequently, not widely available. The diagnosis must rule out salmonellosis and shigellosis, other common infections that produce similar signs and symptoms.

Treatment

Effective treatment consists of isolation, correction of fluid and electrolyte imbalance and, in an infant, I.V. antibiotics based on the organism's drug sensitivity. For cramping and diarrhea, bismuth subsalicylate may be given.

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