Acute Gastroenteritis Viral Gastroenteritis Bacterial Gastroenteritis VIRAL GASTROENTERITIS

Acute Gastroenteritis

• Viral Gastroenteritis • Bacterial Gastroenteritis

VIRAL GASTROENTERITIS

Background • Acute viral gastroenteritis is a common cause of morbidity and mortality worldwide. Conservative estimates put diarrhea in the top 5 causes of deaths worldwide, with most occurring in young children in nonindustrialized countries. In industrialized countries, diarrheal diseases are a significant cause for morbidity across all age groups. Etiologies include bacteria, viruses, parasites, toxins, and drugs. Viruses are responsible for a significant percentage of cases affecting patients of all ages. Viral gastroenteritis ranges from a self-limited watery diarrheal illness (usually < 1 wk) associated with symptoms of nausea, vomiting, anorexia, malaise, or fever, to severe dehydration resulting in hospitalization or even death.

Background • The clinician encounters acute viral gastroenteritis in 3 settings. The first is sporadic gastroenteritis in infants, which most frequently is caused by rotavirus. The second is epidemic gastroenteritis, which occurs either in semiclosed communities (eg, families, institutions, ships, vacation spots) or as a result of classic food-borne or waterborne pathogens. Most of these infections are caused by caliciviruses. The third is sporadic acute gastroenteritis of adults, which most likely is caused by caliciviruses, rotaviruses, astroviruses, or adenoviruses.

Epidemiology • Each year, more than 3. 5 million infants develop acute viral gastroenteritis, resulting in more than 500, 000 office visits, 55, 000 hospitalizations, and 30 deaths. Statistics on sporadic cases of adult viral gastroenteritis are not known; however, food- and water-borne epidemics of viral gastroenteritis are monitored by the US Centers for Disease Control and Prevention (CDC) surveillance programs. The CDC estimates that viruses cause 9. 2 million cases of food-related illness each year (out of a total of 13. 8 million cases from all causes).

• Noroviruses cause approximately 23 million cases of acute gastroenteritis each year and are the leading cause of outbreaks of gastroenteritis. They are responsible for 68 -80% of all outbreaks in industrialized countries. The genus Norovirus, formerly called the Norwalk-like virus, is a member of the family Caliciviridae. • Noroviruses are now recognized to be a common cause of gastroenteritis in new settings, including nursing homes and other health care settings, cruise ships, in other travelers, and in immunocompromised patients. In 2010 -2011, norovirus was transmitted among players and staff of the National Basketball Association

• In March 2012, the CDC reported a rise in foodborne disease outbreaks caused by imported food in 2009 and 2011. Nearly 50% of the outbreaks implicated food that was imported from regions not previously associated with outbreaks (mostly fish and peppers). Approximately 45% percent of the imported foods causing outbreaks came from Asia. • The frequency is seasonal. The highest incidence of rotavirus cases occurs during the months from November to April. Cruise ship outbreaks of noroviruses are more common during the summer months. However, a CDC study by Tate et al demonstrated a decline in the seasonality of rotavirus following the 2006 introduction of the rotavirus vaccine.

• Rotavirus is the most common etiologic agent of health care–acquired diarrhea in pediatric patients. Community- and health care–acquired infections have similar temporal distributions; they are caused by the same viral subtypes; and they affect children of the same age groups. All of the health care–acquired infections with known viral subtypes occurred while the same subtype was still active in the community, suggesting that health care–acquired infections arise from repeated introduction of the community-acquired rotavirus into the hospital setting

International • Acute viral gastroenteritis is a leading cause of infant mortality throughout the world. By age 3 years, virtually all children become infected with the most common agents. Rotavirus causes 2 million hospitalizations and 600, 000 -875, 000 deaths per year. • Noroviruses were attributed to 9 out of the 21 outbreaks of acute gastroenteritis on cruise ships reported to the CDC's Vessel Sanitation Program from January 1, 2002, to December 2, 2002. The occurrence of noroviruses on cruise ships has led to the use of the term "the cruise ship virus" as another name for these viruses. Some illnesses previously attributed to sea sickness are now recognized to be caused by norovirus infections.

Mortality/Morbidity • Severe cases are seen in the elderly, infant, and immunosuppressed populations, including transplant patients. • Rotavirus infantile gastroenteritis is an important cause of infant mortality in the developing world. • In the United States, elderly persons have the highest risk of death from gastroenteritis. • Caliciviruses may kill more people in the United States than do rotaviruses. • Noroviruses are the most common cause of gastroenteritis in nursing homes, and several such outbreaks have resulted in deaths due to aspiration or exacerbation of another chronic disease. Norovirus infections in hospitalized patients are more severe than those seen in otherwise healthy persons. • The CDC reported enteritis deaths more than doubled in the United States, an increase to 17, 000 in 2007 from about 7, 000 in 1999. Adults over 65 years old accounted for 83% of deaths. Clostridium difficile (C difficile) and norovirus were the most common infectious causes of gastroenteritis-associated deaths. Norovirus was associated with about 800 deaths annually, though there were 50% more deaths in years when epidemics were caused by new strains of the virus

Age • Acute viral gastroenteritis occurs throughout life. Severe cases are seen in the very young and in the elderly. Etiology also varies with age. • In infants, most cases are due to rotavirus. • In adults, the most common cause is norovirus. https: //extranet. who. int/sree/Reports? op=vs&path=/WHO_HQ_Repor ts/G 36/PROD/EXT/Foodborne. Disease. Burden

Presentation • The clinical spectrum of acute viral gastroenteritis ranges from asymptomatic infection to severe dehydration and death. Viral gastroenteritis typically presents with short prodrome, with mild fever and vomiting, followed by 1 -4 days of nonbloody, watery diarrhea. Viral gastroenteritis is usually self-limited. • The history should focus on severity and dehydration. The onset, frequency, quantity, and duration of diarrhea and vomiting are important factors in assessing the status. Oral intake, urine output, and weight loss are important considerations. Viruses are the suspected cause of acute gastroenteritis when vomiting is prominent, when the incubation period is longer than 14 hours, and when the entire illness is over in less than 3 days. Travel history (including cruise ships), eating history, and daycare history are important epidemiological factors. • A viral cause should be suspected when the warning signs of bacterial infection (ie, high fever, bloody diarrhea, severe abdominal pain, >6 stools/24 h) are absent and an alternative diagnosis is not suggested by epidemiologic clues from the history (eg, travel, sexual practices, antibiotic use).

• Factors associated with severe and prolonged disease are immunodeficiency and immune suppression, comorbid disease, and malnutrition. • Death results from dehydration and acidosis. • Ruling out other diagnoses is important. Mucus or overt blood in the stool almost always indicates bacterial or parasitic infection. • In 1982, the Kaplan criteria were established to distinguish outbreaks due to norovirus from outbreaks of bacterial etiology. The criteria are highly specific (99%) and moderately sensitive (68%). The 4 criteria indicative of an outbreak due to norovirus are as follows: • Vomiting in 50% of affected persons in the outbreak • Mean incubation period of 24 -48 hours • Mean duration of illness of 12 -60 hours • Lack of identification of a bacterial pathogen in stool culture

Physical Examination • The physical examination can be helpful in determining the etiology of gastroenteritis and in assessing the presence and degree of dehydration. • Temperature, blood pressure and pulse, and body weight can provide evidence of severity of the condition. • Temperature may be slightly elevated. High fever suggests bacterial infection. Tachycardia, thready pulse, and hypotension suggest severe dehydration. • The degree of weight loss may be related to dehydration and the duration of the diarrhea. • The mucous membranes and the skin should be examined carefully. Dry mouth, no tears, skin tenting, dry skin, and capillary refill are all signs of dehydration. • The mental status in elderly patients and infants may be abnormal, especially when blood pressure and circulation are compromised. • The abdominal examination may demonstrate mild tenderness. Severe abdominal pain and tenderness suggest bacterial infection or an abdominal emergency.

Etiology Sporadic infantile viral gastroenteritis • Group A rotavirus causes 25 -65% of severe infantile gastroenteritis worldwide. Acute infections with group C are quite frequent in the United States and worldwide. • After rotavirus, the most important cause of acute infantile gastroenteritis probably is calicivirus infection. Seroepidemiologic studies have shown that antibodies to caliciviruses are present in 50 -90% of children younger than 2 years in Kuwait, Italy, Kenya, China, London, and South Africa. Using broadly reactive reverse-transcription polymerase chain reaction for calicivirus to study stool specimens from children with acute gastroenteritis, studies have found these viruses in 7 -22% of cases. • Astrovirus infection is associated with 2 -9% of cases of infantile gastroenteritis worldwide, making it the third most frequent cause after rotavirus and calicivirus. The burden of astrovirus disease in developing countries might be especially high. • Researchers have recognized for a long time that certain enteric adenoviruses are an important cause of infantile gastroenteritis. Studies confirm that they cause 2 -6% of cases.

Epidemic viral gastroenteritis • Most cases of epidemic viral gastroenteritis in adults and children are caused by the caliciviruses. Some examples include Norovirus (formerly called Norwalk-like viruses) • Modern molecular diagnostic techniques, such as broadly reactive reverse-transcription polymerase chain reaction, have linked these viruses to epidemics associated with oysters, contaminated community water supplies, restaurant food, hospital patients and staff, day care facilities, nursing homes, college dormitories, military ships, cruise ships, and vacation spots. Rotavirus and astrovirus also may cause epidemics of viral gastroenteritis. Modern molecular diagnostic techniques, such as broadly reactive reverse-transcription polymerase chain reaction, have linked these viruses to epidemics associated with oysters, contaminated community water supplies, restaurant food, hospital patients and staff, day care facilities, nursing homes, college dormitories, military ships, cruise ships, and vacation spots. Rotavirus and astrovirus also may cause epidemics of viral gastroenteritis.

Sporadic adult viral gastroenteritis • Few studies have examined the causes of sporadic cases of adult viral gastroenteritis. Seroepidemiologic evidence suggests that the etiologies are (in descending order of frequency) caliciviruses, non– group A rotavirus, astrovirus, and adenovirus.

DDx • • • Amebiasis Appendicitis Bacterial Gastroenteritis Campylobacter Infections Clostridium Difficile Colitis Escherichia Coli Infections Food Poisoning Giardiasis Peritonitis and Abdominal Sepsis Salmonellosis Shigellosis

Work. Up • In most cases that fit the clinical features of viral gastroenteritis, lab tests are not indicated. • If bacterial or protozoal infection is suspected, stool studies for occult blood, WBC count, microscopy for protozoa, Clostridium difficile toxin, Giardia lamblia by enzyme immunoassay (EIA), or bacterial culture may be indicated. Diagnosis of rotavirus infection • Rapid antigen testing of the stool, either by EIA (>98% sensitivity and specificity) or latex agglutination tests (less sensitive and specific as compared to EIA), is used to aid in the diagnosis of rotavirus infection.

Medical Care In 1996, the American Academy of Pediatrics formulated and published practice guidelines for the management of acute gastroenteritis in children. Use the following parameters to assess the degree of dehydration: blood pressure, pulse, heart rate, skin turgor, fontanelle, mucous membranes, eyes, extremities, mental status, urine output, and thirst. • The treatment of rotavirus diarrhea is based primarily on replacing fluids and electrolytes, as directed by the estimated degree of dehydration. • Oral rehydration therapy is recommended for preventing and treating early dehydration and continued replacement therapy for ongoing loses. • Shock, severe dehydration, and decreased consciousness require intravenous therapy. • Age-appropriate diets should be continued in children with diarrhea who are not dehydrated. When mild-tomoderately dehydrated children are rehydrated, resume age-appropriate diet. • Administering antiemetics and antidiarrheal agents to small children is not recommended. • Several studies have shown that antirotavirus immunoglobulin, as pooled gamma globulin, bovine colostrum, or human milk, may decrease frequency and duration of diarrhea. • Small studies have suggested that zinc supplements may reduce the severity and duration of illness.

Probiotics are nonpathogenic live microorganisms that provide beneficial effects on the health of the host. In recent years, probiotics have entered mainstream medical practice, as a decrease in the severity and duration of infectious gastroenteritis has been shown in some strains. • Probiotics help to improve the balance of the intestinal microflora, although the exact mechanism of action is incompletely understood. Hypothesized mechanisms include suppression of growth or invasion by pathogenic bacteria, improvement of intestinal barrier function, and effects on immune function. • Literature shows a statistically significant, but clinically moderate, benefit for some strains, mainly in infants and young children, in the treatment of acute watery diarrhea, especially in rotavirus gastroenteritis. • Until further data are available, only those organisms that have been clinically tested can be reasonably recommended, Lactobacillus casei GG and S boulardii being the most reported. Limited data and modest expected benefit must be explained to patients.

BACTERIAL GASTROENTERITIS

Background • Bacterial gastroenteritis is a very common disorder. It has many causes, can range from mild to severe, and usually manifests with symptoms of vomiting, diarrhea, and abdominal discomfort. Other causes of some of these symptoms include viral infections, improper diet, malabsorption syndromes, various enteropathies, and inflammatory bowel disease. • Bacterial gastroenteritis is usually self-limited, but improper management of an acute infection can lead to a protracted course. By far, the most common complication is dehydration.

Epidemiology • Bacterial gastroenteritis is a very common problem in primary care and emergency department settings, especially in children younger than 5 years. Diarrhea accounts for as many as 5% of pediatric office visits and 10% of hospitalizations in this age group. • Very often, gastroenteritis is underreported in the adult population. Each year, gastroenteritis in adults accounts for 8 million doctor visits and 250, 000 hospitalizations. Episodes of gastroenteritis do not occur at random but usually take place in outbreaks. Traveler's diarrhea affects 20 -50% of people traveling from industrialized to developing countries. • From 2000 to 2009, the number of hospitalized patients with any Clostridium difficile infection (CDI) discharge diagnoses more than doubled, from approximately 139, 000 to 336, 600, and the number with a primary CDI diagnosis more than tripled, from 33, 000 to 111, 000. • Yersinia species infect children younger than 1 year almost exclusively, and Aeromonas species are a significant cause of bacterial gastroenteritis in young children. Very young children are particularly susceptible to secondary dehydration and malabsorption.

• As a cause of enteric infections, 6 different mechanisms of action of 6 different varieties of E coli have been reported. • Enterotoxigenic E coli (ETEC) is a cause of traveler's diarrhea. • Enteropathogenic E coli (EPEC) is a cause of childhood diarrhea. • Enteroinvasive E coli (EIEC) causes a Shigella -like dysentery. • Enterohemorrhagic E coli (EHEC) causes hemorrhagic colitis or hemolytic-uremic syndrome (HUS). • Enteroaggregative E coli (EAgg. EC) is primarily associated with persistent diarrhea in children in developing countries, and enteroadherent E coli(EAEC) is a cause of childhood diarrhea and traveler's diarrhea in Mexico and North Africa. • ETEC, EPEC, EAgg. EC, and EAEC colonize the small bowel, and EIEC and EHEC preferentially colonize the large bowel prior to causing diarrhea. • Shiga toxin–producing E coli (STEC) is among the most common causes of foodborne diseases. This organism is responsible for several GI illnesses, including nonbloody and bloody diarrhea. Patients with these diseases, especially children, may be affected by neurologic and renal complications, including HUS. • Strains of STEC serotype O 157 -H 7 have caused numerous outbreaks and sporadic cases of bloody diarrhea and HUS.

Presentation • Diarrhea is defined as daily stools with a mass greater than 15 g/kg for children younger than 2 years and greater than 200 g for children 2 years or older. Adult stool patterns vary from 1 stool every 3 days to 3 stools per day; therefore, consider individual stool patterns. • Consistency, color, volume, and frequency are very important in determining whether the stool source is from the small or large bowel. Table 1, below, outlines these characteristics and demonstrates that an index of suspicion can be generated easily for a specific set of organisms.

Systemic symptoms • Associated systemic symptoms can guide empiric therapy. Some enteric infections have characteristic systemic symptoms, whereas the associated systemic features of others do not occur reliably. • The characteristics of symptom onset and symptom duration can narrow the differential diagnosis of the organism. The onset of symptoms within 6 hours of exposure to the bacterial source indicates a preformed toxin, probably produced by a species of Staphylococcus or Bacillus.

Food-borne bacteria Particular foods are associated with certain bacteria. Ingestion of raw or contaminated food, particularly raw milk and meat, is a common cause of bacterial gastroenteritis. The following list outlines organisms that cause food poisoning: • Dairy - Campylobacter, Salmonella, Listeria, and Staphylococcus species • Eggs - Salmonella species • Meats - C perfringens and Salmonella, Aeromonas, Campylobacter, and. Staphylococcus species • Ground beef - Enterohemorrhagic E coli • Poultry - Campylobacter species • Pork - C perfringens and Y enterocolitica • Seafood - Aeromonas, Plesiomonas, Vibrio species, and astrovirus • Oysters - Plesiomonas and Vibrio species and calicivirus • Vegetables - Aeromonas species and C perfringens • Alfalfa sprouts - Enterohemorrhagic E coli and Salmonella species • Fried rice - Bacillus species • Custards, mayonnaise - Staphylococcus species A study by Calbo et al reported a foodborne nosocomial outbreak due to extended-spectrum β-lactamase (ESBL)– producing Klebsiella pneumoniae. This may be the first reported hospital outbreak that provides evidence that food can be a transmission vector for ESBL K pneumoniae.

Water-borne bacteria • Water is a major reservoir for many organisms that cause diarrhea. Swimming pools have been associated with outbreaks of Shigella organisms, and Aeromonas species are associated with exposure to the marine environment. Animal-borne bacteria • Animals can transmit particular bacteria. Exposure to young dogs or cats is associated with Campylobacter transmission. Exposure to turtles is associated with Salmonella transmission.

Travel-associated infections • Travel history is an important and useful clue in determining bacterial etiology. Enterotoxigenic E coli is the leading cause of traveler's diarrhea. Rotavirus, Shigella, Salmonella, and Campylobacter species are prevalent worldwide and need to be considered, regardless of specific travel history. • The risk of contracting diarrhea while traveling is the highest in Africa. Travel to Portugal, Spain, and Eastern European countries is also associated with a relatively high risk. Organisms associated with travel to particular locations are as follows: • Nonspecific - Enterotoxigenic E coli and Aeromonas, Giardia, Plesiomonas, Salmonella, and Shigella species • Developing tropics - C perfringens • Africa - Entamoeba species and Vibrio cholerae • Americas (South and Central) - Entamoeba species and V cholerae • Asia - V cholerae • Australia - Yersinia species • Canada - Yersinia species • Europe - Yersinia species • India - Entamoeba species and V cholerae • Japan - V parahaemolyticus • Mexico - Aeromonas, Entamoeba, Plesiomonas, and Yersinia species • New Guinea - Clostridium species

Bacteria associated with preexisting conditions • Preexisting medical conditions can predispose patients to infections with particular organisms. The following list outlines such medical conditions and their associated organisms: • C difficile - Hospitalization with antibiotic administration • Plesiomonas species - Liver diseases or malignancy • Salmonella species - Intestinal dysmotility, malnutrition, achlorhydria, hemolytic anemia (especially sickle cell disease), immunosuppression, and malaria • Rotavirus - Hospitalization • Giardia species - Agammaglobulinemia, chronic pancreatitis, achlorhydria, and cystic fibrosis • Cryptosporidia - Immunocompromise and immunosuppression Outbreaks • Outbreaks are caused by particular bacteria, including enterohemorrhagic E coli O 157: H 7, Listeria monocytogenes, C perfringens, and Salmonella species.

Physical Examination • Dehydration is the primary cause of morbidity and mortality in cases of gastroenteritis. Assess every patient for signs, symptoms, and severity of dehydration. Lethargy, depressed consciousness, dry mucous membranes, sunken eyes, poor skin turgor, and delayed capillary refill should raise the suspicion for dehydration. • Malnutrition is typically a sign of a chronic process. Reduced muscle and fat mass is found. This is usually due to the development of secondary carbohydrate intolerance. • Abdominal pain is a common symptom in gastroenteritis. Nonspecific, nonfocal abdominal pain and cramping are common with some organisms. This pain usually does not increase with palpation. Focal abdominal pain worsened by palpation, rebound tenderness, or guarding should alert the clinician to possible complications or to another noninfectious gastrointestinal diagnosis. • Borborygmi, defined as a significant increase in peristaltic activity with small bowel diarrhea, can cause an audible and/or palpable increase in bowel activity. • Perianal erythema results from many stools causing a constantly wet area. Failure to properly dry the buttocks and perianal area results in erythema and skin breakdown.

DDx • Colovesical fistula • Cholera • Diverticulitis • Food allergies • Food poisoning • Gardnerella • Viral gastroenteritis • Giardiasis • Isosporiasis • Lower gastrointestinal bleeding • Meckel diverticulum • Microsporidiosis • Salmonellosis • Shigellosis • Short-bowel syndrome • Ulcerative colitis

Work. Up • A stool p. H of 5. 5 or below or the presence of reducing substances indicates carbohydrate intolerance. This is usually transient in nature. • Enteroinvasive infections of the large bowel cause leukocytes, predominantly neutrophils, to accumulate in the lumen wich are then shed into stool. Absence of fecal leukocytes does not eliminate the possibility of enteroinvasive organisms; however, the presence of fecal leukocytes eliminates consideration of enterotoxigenic E coli, Vibrio species, and viruses. Shigella characteristically causes marked bandemia with variable total WBC count. • Examine any exudate found in the stool for leukocytes. Such exudates are highly suggestive of inflammatory bowel disease, which could be infectious or of another origin. • Antilisteriolysin O (ALLO) is positive during the convalescent phase of bacterial gastroenteritis and when invasive disease has occurred. Procedures • Identification of pseudomembranes in the colon by direct visualization is diagnostic for C difficile; however, the yield may be low.

Medical Care • Because most infectious diarrhea is self-limited, medical care is primarily supportive in nature. Oral rehydration therapy is the cornerstone of diarrhea treatment, especially for small bowel infections that produce a large volume of watery stool output. Studies confirm that early refeeding hastens recovery. Many commercial oral rehydration formulas are available and have been designed to promote optimal absorption of nutrients. • Young infants and neonates are at high risk for secondary complications and require close monitoring, as do older individuals. • Consider intravenous rehydration when oral rehydration is unsuccessful. Particular attention must be paid to repletion of potassium as needed • Live Lactobacillus GG and heat-killed Lactobacillus LB reduce the duration of diarrhea in children when they are added to oral rehydration solution. • Antimicrobial therapy is indicated for some bacterial gastroenteritis infections. However, many conditions are self-limited and do not require therapy. • Antimotility agents are not indicated routinely for infectious diarrhea (except for refractory cases of Cryptosporidium infection).

• Although some claim that changes in dietary regimen are not necessary, improper diet can result in prolonged recovery or development of carbohydrate malabsorption, especially if the acute episode is overshadowed by an undiagnosed chronic bacterial or malabsorption syndrome. • Thus, a prolonged course of diarrhea should prompt investigation of complicating factors. Results from tests such as stool acidity and reducing substances can indicate carbohydrate malabsorption. Failure to recognize this complication can result in significant rapid weight loss with wasting of fat and muscle mass. Dietary considerations • The BRAT diet (ie, bananas, rice, applesauce, toast) has been recommended for years in cases of gastroenteritis. This diet is adequate during early convalescence, but, as the patient tolerates solid food, advance the diet to provide adequate protein and caloric intake. • Introduce lean meats and clear fluids as soon as possible. Dairy products are said to be better absorbed when given with proteins or complex carbohydrates. • When feeding lactose-containing dairy products, carefully monitor the patient for signs of malabsorption. • Breast milk contains many substances that promote bowel growth and antagonize bacteria; thus, continue breastfeeding throughout the illness for infants.

• Avoidance of undercooked meats and seafood, as well as contaminated water supplies, when traveling may help to reduce the risk of transmission of food and water-borne infectious causes of gastroenteritis and associated symptoms. Vaccines • Salmonella typhi vaccine is recommended for travelers to countries with a high incidence of this infection, persons with intimate exposure to a documented typhoid fever carrier, and workers with frequent exposure to these bacteria. Live attenuated, killed whole-cell, and capsular polysaccharide vaccines are available. • Vibrio vaccine is available but only protects 50% of immunized persons for 3 -6 months. It is not indicated for widespread use.

• In February 2006, the US Food and Drug Administration (FDA) approved an oral vaccine for rotavirus (Rota. Teq) for use in infants. On Feb 21, 2006, the American Academy of Pediatrics (AAP) and the Advisory Committee on Immunization Practices (ACIP) recommended that Rota. Teq be part of regularly scheduled childhood immunizations. The vaccine is administered in a 3 -dose series starting between ages 6 and 12 weeks and ending before age 32 weeks. • Clinical trials of Rota. Teq demonstrated prevention of 74% of all rotavirus gastroenteritis cases, of nearly all severe rotavirus gastroenteritis cases, and of nearly all hospitalizations. A previously marketed rotavirus vaccine (Rota. Shield) was associated with intussusception, but Rota. Teq did not show an increased risk compared with placebo in clinical trials. • In April 2008, the FDA approved Rotarix, another oral vaccine, for prevention of rotavirus gastroenteritis. It is currently recommended that Rotarix be administered in 2 separate doses to patients between ages 6 and 24 weeks. Rotarix was efficacious in a large study, which showed that it protected patients with severe rotavirus gastroenteritis and also decreased the rate of severe diarrhea or gastroenteritis from any cause.

Campylobacter species • Erythromycin may shorten illness duration and shedding; delaying therapy beyond 4 days from onset of symptoms appears to produce no clinical benefit E coli • Antibiotic treatment appears to increase the likelihood of developing HUS. Consider antibiotics if diarrhea is moderate or severe. Trimethoprim-sulfamethoxazole is a first-line drug, but a parenteral second-generation or third-generation cephalosporin for systemic complications should be used. Salmonella species • Antibiotic treatment prolongs the carrier state and is associated with relapse; thus, treatment is not indicated for nontyphoid, uncomplicated diarrhea. Consider treatment for infants younger than 3 months and for high-risk patients, such as patients who are immunocompromised or who have sickle cell disease. • Ampicillin is recommended for drug-sensitive strains. Trimethoprim-sulfamethoxazole, fluoroquinolones, or third-generation cephalosporins (fluoroquinolones are not recommended for use in children) are also acceptable alternatives. S typhimurium T 104 is a multidrug-resistant organism. Sensitivities from the cultured specimens are important to guide therapy. Shigella species • Antibiotic treatment may shorten illness duration and shedding but does not prevent complications. Most mild infections will recover without antibiotics. Moderate to severe cases should be treated with antibiotics. Ampicillin is preferred for drug-sensitive strains. For ampicillin-resistant strains or in cases of penicillin allergy, trimethoprim-sulfamethoxazole is the drug of choice, although resistance does occur. Fluoroquinolones may be considered in patients with highly resistant organisms.

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