Enterobacterial infections

Definition

Enterobacterial infections are disorders of the digestive tract and other organ systems produced by a group of rod-shaped bacteria called Enterobacteriaceae.

Description

Enterobacterial infections can be produced by bacteria that normally live in the human digestive tract without causing serious disease or by bacteria that enter from the outside. The most troublesome organism in this group is Escherichia coli . Other examples of enterobacteria are species of Salmonella , Shigella , Klebsiella , Enterobacter , Serratia , Proteus , and Yersinia .

Transmission

Enterobacterial infections in the digestive tract typically start when the organisms invade the mucous tissues that line the digestive tract. They may be bacteria that are already present in the stomach and intestines, or they may be transmitted by contaminated food and water. It is also possible for enterobacterial infections to spread by person-to-person contact. In many cases these infections are nosocomial, which means that they can be acquired in the hospital. The usual incubation period is 12 to 72 hours.

Demographics

Diarrhea caused by enterobacteria is a common problem in the United States. It is estimated that each person has an average of 1.5 episodes of diarrhea each year, with higher rates in children, institutionalized people, and Native Americans. This type of enterobacterial infection can range from a minor nuisance to a life-threatening disorder, especially in infants; elderly persons; patients with immunodeficiency , including acquired immunodeficiency syndrome ( AIDS ); and malnourished people. Enterobacterial infections are one of the two leading killers of children in developing countries.

Causes and symptoms

E. coli infections cause most of the enterobacterial infections in the United States. The organisms are categorized according to whether they are invasive or noninvasive. Noninvasive types of E. coli include what are called enteropathogenic E. coli (EPEC), and enterotoxigenic E. coli (ETEC). EPEC and ETEC types produce a bacterial poison (toxin) in the stomach that interacts with the digestive juices and causes the patient to lose large amounts of water through the intestines.

The invasive types of E. coli are called enterohemorrhagic E. coli (EHEC), and enteroinvasive E. coli, (EIEC). These subtypes invade the stomach tissues directly, causing tissue destruction and bloody stools. EHEC can produce complications leading to hemolyticuremic syndrome (HUS), a potentially fatal disorder marked by the destruction of red blood cells and kidney failure. EHEC has become a growing problem in the United States because of outbreaks caused by contaminated food. A particular type of EHEC known as O157:H7 has been identified since 1982 in undercooked hamburgers and unpasteurized milk and apple juice. Between 2 and 7 percent of infections caused by O157:H7 develop into HUS.

Klebsiella and Proteus sometimes cause urinary tract infections; pneumonia occurs generally in immunocompromised hosts or alcoholics, and ear and sinus infections in immunocompromised hosts. Enterobacter and Serratia can cause bacterial infection of the blood (bacteremia), particularly in patients with weakened immune systems.

Symptoms

The symptoms of enterobacterial infections are sometimes classified according to the type of diarrhea they produce.

WATERY DIARRHEA Patients infected with ETEC and some types of EPEC develop watery diarrhea. Rarely Shigella and Salmonella cause watery diarrhea. These infections are located in the small intestine, result from bacterial toxins interacting with digestive juices, do not produce inflammation, and do not usually need treatment with antibiotics .

BLOODY DIARRHEA (DYSENTERY) Bloody diarrhea, sometimes called dysentery, is produced by EHEC, EIEC, some types of Salmonella , some types of Shigella , and Yersinia . In dysentery, the infection is located in the colon, cells and tissues are destroyed, inflammation is present, and antibiotic therapy is usually required.

NECROTIZING ENTEROCOLITIS (NEC) Necrotizing enterocolitis (NEC) is a disorder that begins in newborn infants shortly after birth. Although NEC was not as of 2004 fully understood, it is thought that it results from a bacterial or viral invasion of damaged intestinal tissues. The disease organisms then cause the death (necrosis) of bowel tissue or gangrene of the bowel. NEC is primarily a disease of prematurity ; 60–80 percent of cases occur in high-risk preterm infants. NEC is responsible for 2–5 percent of cases in newborn intensive care units (NICU). Enterobacteriaceae that have been identified in infants with NEC include Salmonella , E. coli , Klebsiella , and Enterobacter .

When to call the doctor

A healthcare professional should be called if an infected child exhibits any of the following symptoms:

• symptoms of dehydration such as decreased urination, dry mouth, irritability, and few or no tears when crying
• vomiting for more than three days
• fever greater than 102.2°F (39°C) in a toddler or older child, or any fever in an infant less than six months old
• fever that cannot be controlled with acetaminophen (Tylenol) or ibuprofen (Motrin), or that lasts more than three days
• presence of blood in diarrhea
• hard, swollen belly

Diagnosis

In order to confirm a diagnosis of enterobacterial infection, physicians usually rely on patient history, physical examination, and laboratory tests.

Patient history

The diagnosis of enterobacterial infections is complicated by the fact that viruses, protozoa, and other types of bacteria can also cause diarrhea. In most cases of mild diarrhea, it is not critical to identify the organism because the disorder is self-limiting. Some groups of patients, however, should have stool tests. They include:

• patients with bloody diarrhea
• patients with watery diarrhea who have become dehydrated
• patients with watery diarrhea that has lasted longer than three days without decreasing in amount
• patients with disorders of the immune system

The patient history is useful for public health reasons as well as a help to the doctor in determining what type of enterobacterium may be causing the infection. The doctor will ask about the frequency and appearance of the diarrhea as well as about other digestive symptoms. If the patient is nauseated and vomiting, the infection is more likely to be located in the small intestine. If the patient is running a fever, a diagnosis of dysentery is more likely. The doctor will also ask if anyone else in the patient's family or workplace is sick. Some types of enterobacteriaceae are more likely to cause group outbreaks than others. Other questions pertain to the patient's food intake over the previous few days and recent travels to countries with typhoid fever or cholera outbreaks.

Physical examination

The most important parts of the physical examination are checking for signs of severe fluid loss and examining the abdomen. The doctor will look at the inside of the patient's mouth and evaluate the skin for signs of dehydration. The presence of a skin rash and an enlarged spleen suggests typhoid fever rather than a bacterial infection. If the patient's abdomen hurts when the doctor examines it, a diagnosis of dysentery is more likely.

Laboratory tests

The stool test is most commonly used for identifying the cause of diarrhea. Examining a stool sample under a microscope can help to rule out parasitic and protozoal infections. Routine stool cultures, however, cannot be used to identify any of the four types of E. coli that cause intestinal infections. ETEC, EPEC, and EIEC are unusual in the United States and can usually be identified only by specialists in research laboratories. Because of concern about EHEC outbreaks, however, most laboratories in the United States as of 204 screen for O157:H7 with a test that identifies its characteristic toxin. All patients with bloody diarrhea should have a stool sample tested for E. coli O157:H7.

Treatment

The initial treatment of enterobacterial diarrhea is usually empiric. Empiric means that the doctor treats the patient on the basis of the visible symptoms and professional experience in treating infections, without waiting for laboratory test results. In uncomplicated cases, symptoms usually go away within five to ten days without treatment of antibiotics. In other cases, antibiotics may be necessary to overcome the infection. Newborn infants and patients with immune system disorders are given antibiotics once the organism has been identified. Gentamicin, tobramycin, and amikacin are in the early 2000s used more frequently to treat enterobacterial infections because many of the organisms are becoming resistant to ampicillin and cephalosporin antibiotics.

Alternative treatment

Alternative treatments for diarrhea are intended to relieve the discomfort of abdominal cramping. Most alternative practitioners advise consulting a medical doctor if the patient has sunken eyes, dry eyes or mouth, or other signs of dehydration.

HERBAL MEDICINE Herbalists may recommend cloves taken as an infusion or ginger given in drop doses to control intestinal cramps, eliminate gas, and prevent vomiting. Peppermint ( Mentha piperita ) or chamomile ( Matricaria recutita ) tea may also ease cramps and intestinal spasms.

HOMEOPATHY Homeopathic practitioners frequently recommend Arsenicum album for diarrhea caused by contaminated food and Belladonna for diarrhea that comes on suddenly with mucus in the stools. Veratrum album would be given for watery diarrhea, and Podophyllum for diarrhea with few other symptoms.

Nutritional concerns

Because of the extensive loss of water through diarrhea, it is important to prevent dehydration. The affected child should be encouraged to drink fluids such as water, breast milk or formula (if applicable), electrolyte replacement drinks, or clear broths. Diluted juice should be avoided because juice can worsen diarrhea. Drinks with caffeine should be avoided because of caffeine's diuretic effects (i.e., causes water to be lost through urine).

Prognosis

The prognosis for most enterobacterial infections is good; most patients recover in about a week or ten days without needing antibiotics. HUS, on the other hand, has a mortality rate of 35 percent even with intensive care. About one-third of the survivors have long-term problems with kidney function, and another 8 percent develop high blood pressure, seizure disorders, and blindness.

Prevention

The World Health Organization (WHO) offers the following suggestions for preventing enterobacterial infections, including E. coli O157:H7 dysentery:

• Cook ground beef or hamburgers until the meat is thoroughly done. Juices from the meat should be completely clear, not pink or red. All parts of the meat should reach a temperature of 158°F (70°C) or higher.
• Do not drink unpasteurized milk or fruit juices or use products made from raw milk.
• Wash hands thoroughly and frequently, especially after using the toilet.
• Wash fruits and vegetables carefully or peel them. Keep all kitchen surfaces and serving utensils clean.
• If drinking water is not known to be safe, boil it or drink bottled water.
• Keep cooked foods separate from raw foods and avoid touching cooked foods with knives or other utensils that have been used with raw meat.

Parental concerns

Because of the extensive media coverage that often follows outbreaks of enterobacterial infections such as E. coli , many parents associate such infections with eating undercooked meat such as hamburger. It is important, however, that other modes of transmission be considered, such as poorly or infrequently washed hands. Frequent hand washing is encouraged for caregivers and children alike, particularly in settings such as daycares and schools.

Resources

BOOKS

Eisenstein, Barry I., and Dori F. Zaleznik. "Enterobacteriaeae." In Principles and Practice of Infectious Diseases , 5th ed. Edited by Gerald L. Mandell, John E. Bennett, and Raphael Dolin. New York: Churchill Livingstone, 2000.

Rozenberg-Arska, Maja, and Maarten R. Visser. "Enterobacteriaeae." In Infectious Diseases. Edited by Jonathan Cohen et al. New York: Mosby, 2004.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.

WEB SITES

Cuthill, Sara L. " Escherichia coli Infections." eMedicine , October 16, 2003. Available online at http://www.emedicine.com/ped/topic2696.htm (accessed January 6, 2005).

" Escherichia coli O157:H7." Centers for Disease Control and Prevention , January 27, 2004. Available online at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm (accessed January 6, 2005).

Rebecca J. Frey, PhD Stephanie Dionne Sherk