Part IV Section 6-B

Probiotics

Robert Vasquez, MD, PhD,

SUNY-Downstate medical Center

Zvi Weizman, MD

Ben-Gurion University of the Negev

Beer-Sheva, Israel

Pretest Questions:

Q1) Probiotics is (are):

a) a philosophical system of beliefs that advocates the fundamental importance of all life on earth.

b) the use bacterial preparations that impart beneficial effects on the health of the host when orally consumed .

c) orthopedic devices that are actually stronger than their natural counterparts.

d) A Japanese philosophy that includes dietary principles involving "whole" foods cooked in prescribed ways.

Q2) The normal intestinal microflora:

a) synthesizes some vitamin K for host needs

b) aids in the digestion of carbohydrates

c) helps to prevent colonization of intestinal mucosa by pathogenic organisms

d) primes the immune system

e) all of the above.

Q3) The major etiology of acute diarrhea in children in the U.S. is:

a) viral

b) bacterial

c) protozoan

d) antibiotic use

Q4) True or False. The G.I. microflora is first established at 6 months of age but is easy to permanently modify throughout life.

Q5) True or False. The use of antibiotics has been shown to dramatically decrease the time-course of most bacterially caused diarrhea.

Facilitator's Preparation:

The facilitator(s) is referred to the following sources for additional information:

Salminen SJ, Gueimonde M., Isolauri E. Probiotics that Modify Disease Risk. J Nutrition. 2005; 135: 1294-1298. A very recent review of the use of probiotics in the prevention and/or treatment of many diseases and conditions. This review is especially useful for illustrating different outcomes with different probiotic species.

Vanderhoof, J.A., and R.J. Young. Probiotics in Pediatrics. 2005. Pediatrics 109; 956-958. A short, concise review of the use of probiotics in the prevention and treatment of pediatric conditions with a special emphasis on their use in diarrheal illnesses.

Van Niel, C.W.,C. Feudtner, M.M., Garrison and D.A. Christakis. 2005. Lactobacillus Therapy for Acute Infectious Diarrhea in Children: A Meta-Analysis. 2002. Pediatrics 109; 678-684. This paper is fantastic for summarizing the state of the field of probiotics in acute pediatric diarrhea as of 2002.

Vanderhoof, J.A., and R.J. Young. Probiotics in Pediatrics. 2005. Pediatrics 109; 956-958.

Weizman Z, Ghaleb Asli, and Ahmed Alsheikh. Effect of a Probiotic Infant Formula on Infections in Child Care Centers: Comparison of Two Probiotic Agents Pediatrics. 2005; 115: 5 - 9. This recent paper demonstrated that probiotics were effective in preventing episodes of acute diarrhea in a pediatric population at high risk, namely in a daycare setting.

In addition, the facilitator should review the modules on acute and chronic diarrhea for an overview of the topic.

Objectives:

On completion of this module, residents and physicians will be able to:

1. Gain an understanding of probiotics.

2. Recognize the importance of normal intestinal microflora in health and disease.

3. Be familiar with current thoughts on the establishment and maintenance of intestinal microflora.

4. Appreciate the primary causes of and standard treatments for diarrhea in the pediatric population.

5. Develop a model that incorporates the appropriate use of probiotics in the prevention and treatment of pediatric diarrhea.

Summary:

This module is designed to familiarize the student/resident with the impact of diarrheal disease in the pediatric population. It reviews common causes acute and chronic diarrhea in the pediatric population as well as the etiologies, signs and symptoms and recommended treatments for common diarrheal illnesses. This module also presents information on the role of the intestinal microflora in health and disease states and summarizes recent evidence that strongly suggests that probiotic agents are a safe and effective means for treating and preventing many cases of diarrhea in the pediatric population.

Background:

Diarrhea is one of the most frequently encountered problems encountered in the pediatrics setting. In the U.S., diarrhea is a contributing factor in approximately 12% of hospitalizations and 300 deaths per year (CDC statistics, 2004). Currently in the U.S., within the population under 3 years of age, the incidence of acute diarrhea is approximately 1.3 episodes per child per year, and this rate is double for children who attend day care (Bentley et al.,2001).

Worldwide, the situation is much worse, with acute diarrheal illness being the leading cause of childhood morbidity and mortality, resulting in more than 3 million deaths (WHO statistics, 2003). Diarrhea is somewhat difficult to define and depends on the individual bowel habits of the individual. However, a strict clinical definition is excessive daily stool volume more than approximately 10ml/kg/day. However, in actual practice, daily stool volumes are usually not available, so the diagnosis of diarrhea is based on the history. Clinically, one should suspect diarrhea if the patient is experiencing more than 3 watery or liquid bowel movements per day. Acute diarrhea is defined as diarrhea lasting under 2 weeks. Chronic diarrhea is defined as diarrhea lasting for more than 2 weeks.

Diarrhea can be subdivided by its physiological mechanism or its etiology. Mechanistically, diarrhea may be a) secretory or b) osmotic.

Secretory diarrhea may result from infectious causes or inflammation and is characterized by watery stools with a relatively high electrolyte count that persists even during fasting. The most commonly cited example, though extreme and rare in the developed world, is cholera, which results in a severe secretory diarrhea, marked by huge volumes of watery stools. In the developed world, a more common cause of secretory diarrhea is inflammatory bowel disease.

Osmotic diarrhea most commonly results from malabsorption, dietary intake or intestinal injury and is characterized by stools that have a relatively low electrolyte content. Osmotic diarrhea tends to resolve when oral intake is eliminated. Diarrhea may also be classified as to etiology: whether it is infectious or non-infectious or inflammatory or non-inflammatory.

"Probiotics" is a term used to describe use bacterial preparations that impart beneficial effects on the health of the host when orally consumed . Often these agents contain active bacteria which are part of the normal host flora.

The G.I. microflora aid in the digestion of carbohydrates and some bacterial species synthesize vitamin K. In addition, the colonization of the gut by these "good" bacteria is believed to hinder the attachment and colonization of the intestinal mucosa by pathogenic bacteria and also is thought to play a role in priming the host immune system.

Case Studies

1. The case of Lynne K: An Introduction To "Probiotics"

Lynne K is a 4 year old girl is brought to the pediatrician's office by her mother for diarrhea. Lynne has had 2 days of frequent (6-10 per day), watery stools. Mrs. K reports that the stools do not appear black nor do they contain bright red blood. The child had two episodes of vomiting 2 days ago. Her mom reports that she has been running low-grade fevers for the last 2 days, with the highest reading being 100.8 F. Lynne is in day care and has 3 similar episodes of diarrhea in the last year. The mother tells you that the childcare workers in the center where her daughter attends have reported that several children have had similar symptoms in the last 2 weeks.

On physical exam, Lynne appears in no distress. She is febrile at this time and pulse, blood pressure and respiration are within normal limits. She appears to be slightly dehydrated based on slightly dry mucous membranes and slightly decreased skin turgor. Examination of the abdomen reveals it to be soft.

Q1. Mrs. K asks "Is it true that that your intestines actually have lots of bacteria living in them?"

A1. The intestinal microflora is the collection of bacteria that colonize the GI tract. The bacterial content is highest in the mouth and pharynx and colon. There are probably hundreds if not thousands of bacterial species, which compose this flora- many of which have not been cultured or identified. During fetal development, the GI tract is essentially sterile. The flora is established during the birthing process when the child swallows secretions during delivery, and the gut becomes colonized within the first 12 hours of life. As a result, and individuals GI microflora is remarkably similar to the microflora of her mother's vagina, which is normally colonized by the mother's intestinal flora (Adlerberth, 1999 as cited in Vanderhoof and Young, 2002). In addition, breast-fed infants appear to have a gut microflora that is richer in probiotic organisms and contains fewer pathogenic organisms and also have a lower incidence of infectious diarrhea than their bottle-fed counterparts (Mackie et al., 1999; Loez-Alaarcon et al., 1997).

Q2. She then asks you, 'what do these bacteria do".

A2. You explain that bacteria that colonize the GI tract have many functions that are important and beneficial to the host. The resident bacteria serve to prevent colonization of the GI tract by pathogenic organisms by competing with these organisms for colonization, competing for nutrients and by secreting agents that may be bacteriostatic or bacteriocidal to other organisms. In addition, some species of bacteria help in the digestion of certain nutrients and secrete vitamins (e.g. Vit K). In addition, the GI microflora appears to play a very important role in priming the immune system of the host.

Q3. She then asks "is this microflora the same throughout one's life or does it change with what one eats ?".

A3. You tell her that for the most part, the GI microflora appears to be pretty constant and not easily changed after the first year or so of life. Many possible explanations for this observation have been proposed, including the difficulties of recolonizing intestinal mucosa and the bacteriostatic and bacteriocidal nature of some of the resident flora. In addition, it appears that many probiotic species may not replicate very well in the G.I. environment so long term alteration is difficult.

Q4. The mother then states that she read reports about probiotics- things like yogurt- that are supposed to be good for treating diarrhea. She asks you to explain what probiotics are and whether or not there is any truth to these statements.

A4. You explain that probiotics are viable nonpathogenic bacteria that colonize the intestine and modify the microflora with beneficial effects for the host. This idea is hardly new. People have routinely used bacteria for hundreds of years in substances such as yogurts and cheeses. In fact, several common foods contain probiotic agents (see Figure 1 for pictures of some examples). One of the most well studied probiotic agents is the bacterial genus Lactobacillus that is a normal component of the GI microflora and is frequently found in yogurt and fermented dairy products. Other probiotic agents include Bifidobacterium (infantis, longum and breve) and the yeast, Saccharomyces boulardi . In many parts of the world, it is well accepted that Lactobacillus is a safe and effective means of preventing and treating infectious diarrhea and antibiotic-associated diarrhea; however, health professionals in the U.S. do not routinely recommend Lactobacillus (Elemer et al., 1996).

Figure 1: Examples of probiotic foods.

Caption: Buttermilk

Q5. Being a big user of Google and other search engines as well as a science enthusiast, the mother asks whether there are well conducted studies that indicate that probiotics are useful in the treatment and/or prevention of diarrheal illness?

A5. Table 1 presents a selected handful of recent studies that have been performed to examine the efficacy and safety of using probiotics in the treatment and prevention of infectious diarrhea in the pediatrics population. Most studies have concluded that probiotic agents are safe and effective in the treatment and, though less well-studied, the prevention of infectious diarrhea in children. For example, a meta-analysis conducted by Van Niel et al. (2002) concluded that Lactobacillus is a safe and effective treatment for infectious diarrhea caused by a variety of pathogens in children. In addition, a recently published study by Weizman (2005) showed that the use of probiotic agents significantly reduced the incidence of acute diarrheal illness in children in a daycare setting.

Table 1: Summary of some of the Recent Studies on Probiotics- This table contains a brief outline of a few of the recent studies of probiotic agents in the treatment or prevention of diarrheal illness in the pediatric population. The student or resident should familiarize herself with the different probiotic agents used and the overall trends in these studies.

TEACHING CAPTION: This table provides a sampling of recent papers in the literature investigating the use of probiotic agents in the treatment and/or prevention of various diseases or conditions. This is an active area of investigation.

Q6. The mother thanks you for all of the information and asks whether you recommend that she give her child probiotics. What do you tell her?

A6. In terms of standards of care, the American Academy of Pediatrics does not recommend the use of probiotics in the treatment or prevention of acute diarrheal illness. However, you tell the mother that if she wished to incorporate foods high in probiotics such as low fat yogurt with live active cultures or tofu, you would not think this a bad idea. In addition to the potential probiotics benefit, you tell her that low fat dairy products are good sources of calcium and proteins.

So, you close the consultation by recommending that the child be given oral rehydration and begin feeding her as soon as she will tolerate solid foods. You tell the mother to contact you if her daughter's symptoms persist for more than a week or worsen or if she is unable to maintain adequate fluid intake. She and her daughter thank you and leave the office.

Case Number 2: Charlie, the "Costly Cure"

Mrs. W brings her 5 year old son, Charlie, to your office because the child has been suffering from diarrhea for the past 3 days. You had seen the child in your office 18 days previously for a sore throat that upon culture was determined to be Group A Streptococcus. You prescribed a 10 day course of amoxicillin. Mrs. W says that Charlie finished the prescribed course, even after the sore throat resolved with 2 days of treatment. According to mom, the child was feeling well until 3 days ago, when she reported having abdominal cramps and frequent loose stools.

Charlie is eating well and his abdominal symptoms are not causing limitations to daily activity other than the need to have frequent bowel movements. The mother became concerned yesterday when she noticed that one of her son's stools looked very dark and had a particular foul smell. She describes the stool as very soft, but not liquid, very dark in color and very foul smelling. On examination, the child appears well. His temperature and vital signs are normal. The abdomen is soft, non-distended and slightly tender to deep palpation in the left and right lower quadrants. The mother has brought in a stool sample, which you send for microscopic examination and culture and Clostridium difficile toxin.

Q7. Mrs. W asks, "do antibiotics cause diarrhea? And if so, "How?

A7. You explain that antibiotics can indeed cause diarrhea. Since antibiotics are relatively blunt therapies, killing classes of bacteria rather than selecting just pathogenic organisms, the intestinal microflora is often disrupted, leading to diarrhea. In most cases, the diarrhea results from undigested carbohydrates normally digested by bacteria in the flora passing into the distal colon, producing an osmotic type diarrhea. The diarrhea is usually self-limited. However, in some cases, the use of antibiotics may result in the overgrowth of pathogenic organisms such as Clostridium dificile, a normal low-level component of the GI microflora. This organism can lead to pseudomembranous colitis, a serious and potentially life-threatening condition.

The antibiotics most implicated in C. dificile infection are clindamycin, cephalosporins (especially 2nd and 3rd generation), metronidazole and ampicillin (referenced in Louie and Meddings, 2004). These antibiotics kill off anaerobes, and since the major component of the normal GI flora are anaerobes, especially Bacteriodes species, the colon is left open to colonization by nasty bugs.

Q8. Mrs. W then tells you that she read that she has heard that eating yogurt can help prevent diarrhea when one is taking antibiotics. She asks if this is true.

A8. Repeat answer to Q4.

Q9. The mother is very interested in these good bacteria and ask, "are there other diseases that may be prevented or treated with probiotics?"

A9. the data her are not so clear but this is a very active area of research. There have been studies that suggest that probiotics may be useful in immune modulation. One such study found that probiotics decreased the incidence of severe respiratory infections in children with cystic fibrosis (Guarino, 1998). Other studies have looked at the effects of probiotics on inflammatory disorders of the GI tract. One such study showed benefits of using Lactobacillus GG in children with Crohn's disease (Gupta et al, 2003). Other large scale trials are currently underway to investigate the role of probiotics in the treatment of inflammatory bowel disease. Other recent studies have indicated that Lactobacillus may reduce the incidence of milk allergy (Kalliomaki et al., 2001) and eczema (Isolauri et al., 2000). Another area where probiotics are currently being investigated is in the prevention of necrotizing enterocolitis in very low birth weight infants. Recently, Lin et al. (2005) showed a significant reduction in the incidence of this potentially fatal disease using a commercially formulated probiotic agent called Infloran (contains L. acidophilus and B. infantis). In addition, a report from a recent Nutrition Symposium summarized by Salminen et al. (2005) reviews many of the recent studies of the use of probiotics in the treatment and prevention of several gastrointestinal and immune system disorders. This report also reports that different probiotic bacteria have appeared to have different efficacies in the treatment and prevention of different diseases.

Q10. Mom then asks, "do we know how these probiotics work"?

A10. As of now, the answer is no. There is a great deal of speculation that probiotics may prevent diarrhea by colonizing the intestinal mucosa and competing with pathogenic agents, or that these agents have direct bacteriocidal or immuno-modulating activity.

Q11. Mom is fascinated by all of this new information and she asks you why she hasn't had a doctor tell her this information before now. She asks whether or not probiotics are or should be integrated into clinical practice?

A11. The American Academy of Pediatrics currently does not recommend the use of probiotic agents in the treatment or prevention of acute diarrhea in the pediatric population. However, while more study is warranted, a growing body of evidence suggests that probiotic agents are safe and effective in the treatment of acute infectious diarrhea and the prevention of antibiotic-associated diarrhea and may be beneficial as prophylaxis in children at high risk for developing infectious diarrhea (e.g. children in day care). Further studies concerning which agents are particularly helpful, as well as elucidation of the mechanism(s) by which probiotics function, and any potential adverse effects of long-term use are needed. However, all studies published to date indicate that probiotics have an excellent safety profile, and it is possible that guidelines may change in the near future. In an extensive review of the literature, only one paper reported significant complications from the use of probiotics, and this was case studies of 2 children who suffered from severe immune impairment and serious illnesses who developed sepsis following treatment with probiotic agents (Land et al., 2005). These authors state that the safety profile of probiotics is excellent.

Q12. She then asks you if probiotic agents are currently available.

A12. Yes, they are. There are commercial preparations such as Infloran that are available. In addition, probiotic-enhanced formula is being used in several countries. In addition, yogurt and other fermented dairy products contain cultures of probiotic bacteria, though usually in smaller numbers than used in most studies. You also tell her that there are commercially available preparations containing specific probiotic agents but that you are not endorsing their use. A few examples are show in Table 2.

Q13. She then asks "what you are going to do for Charlie now?"

A13. You say, I am going to send the stool specimen for a test for Clostridium difficile, and the results should be available in the next day or two." Based on clinical evidence, you decide to not start metronidazole, the treatment for C. difficile, and tell Mom to use oral rehydration salts, monitor Charlie's fluid intake. Let him eat real foods avoiding highly osmotic ones like fruit juice. And, yes, you do encourage yogurt consumption with an acknowledgement that that it cannot hurt and may help.

Summary:

This module is designed to familiarize the student/resident with the impact of diarrheal disease in the pediatric population. It reviews common causes of acute and chronic diarrhea in the pediatric population as well as the etiologies, signs and symptoms and recommended treatments for common diarrheal illnesses. This module also presents information on the role of the intestinal microflora in health and disease states and summarizes recent evidence that strongly suggests that probiotic agents are a safe and effective means for treating and preventing many cases of diarrhea in the pediatric population.

Post-test Questions:

Q1) T or F. Diarrheal illnesses place a large burden on the healthcare system and

collectively is a major cause or contributor to mortality in the pediatric population

worldwide?

Q2) T or F. Bottle fed infants have fewer episodes of diarrhea than breast fed infants.

Q3) T or F. Antibiotics should be used in nearly all cases of diarrhea when the cause is

known to be a bacterial agent?

Q4) T or F. Probiotic agents have so far demonstrated an excellent safety profile.

Q5) The proposed mechanism(s) through which probiotics may aid in the treatment and

prevention of diarrhea include:

a) colonizing the intestinal mucosa and competing with pathogens

b) direct bacteriocidal activity

c) immunomodulatory activity

d) a and b

e) all of the above

References:

Arvola, T., K. Laiho, S. Torkkeli, H. Mykkanen, S. Salminen, L. Maunula and E. Isolauri. Prophylactic Lactoacillus GG Reduces Antibiotic-Associated Diarrhea in Children with Respiratory Infections: A Randomized Study. 1999. Pediatrics 104: 5 1-4.

Adlerberth I. Establishment of a normal intestinal microflora in the newborn infant. In: Hanson LA, ed. Probiotics, Other Nutritional Factors, and Intestinal Microflora. Philadelphia, PA: Lippincott-Raven;1999 :63 -78.

Belmont D, Lifshitz C, Lawson M. Pediatric Gastroenterology and Clinical Nutrition, 2001. ReMedical Publishing, London U.K.

Elmer GW, Surawicz CM, McFarland LV. Biotherapeutic agents. A neglected modality for the treatment and prevention of selected intestinal and vaginal infections. JAMA.1996; 275 :870 -876

Gorbach SL, Chang TW, Goldin BR. Successful treatment of relapsing Clostridium difficile colitis with Lactobacillus GG. Lancet.1987; 26 :1519.

Guandalini S, Pensabene L, Abu Zikri M, et al. Lactobacillus GG administered in oral rehydration solution to children with acute diarrhoea. A multicenter European trial. J Pediatr Gastroenterol Nutr.2000; 30 :54 -60.

Gupta P, Andrew H, Kirschner BS, Guandalini S. Is Lactobacillus GG helpful in children with Crohn's disease? Results of a preliminary, open-label study. J Pediatr Gastroenterol Nutr.2000; 31 :453 -457.

Isolauri E, Arvola T, Moilanen E, Salminen S. Probiotics in the management of atopic eczema. Clin Exp Allergy.2000; 30 :1604 -1610

Isolauri E, Juntunen M, Rautanen T, Sillanaukee P, Koivula T. A human Lactobacillus strain (Lactobacillus casei sp strain GG) promotes recovery from acute diarrhea in children. Pediatrics.1991; 88 :90 -97.

Kalliomaki M, Salminen S, Arvilommi H, Kero P, Koskinen P, Isolauri E. Probiotics in primary prevention of atopic disease: a randomised placebo-controlled trial. Lancet.2001; 357 :1076 -1079.

Kliegman, R.M and R.E. Willoughby. Prevention of Necrotizing Enterocolitis with Probiotics. 2005. Pediatrics 115; 171-172.

Land, M.H., K. Rouster-Stevens, C.R. Woods, M.L Cannon. Lactobacillus Sepsis Asscociated with Probiotics Therapy. 2005. Pediatrics 115:178-181.

Lin, H-C, B-H Su, A-C Chen, T-W Lin, C-H Tsai, T-F Yeh and W Oh. Oral Probiotics Reduce the Incidence and Severity of Necrotizing Enterocolitis in Very Low Birth Weight Infants. 2005. Pediatrics 115: 1-4

Lopez-Alacron M, Villalpando S, Fajardo A. Breast feeding lowers the frequency and duration of acute respiratory infections and diarrhea in infants under six months of age. J Nutr. 1997; 127:436-443.

MackieRI, Sghir A, Gaskins HR. Developmental microbial ecology of the neonatal gastrointestinal tract. Am J Clinic Nutr. 1999; 69: 1035s-1045s.

McFarland LV, Surawicz CM, Greenberg RN, et al. A randomized placebo-controlled trial of Saccharomyces boulardii in combination with standard antibiotics for Clostridium difficile disease. JAMA.1994; 271 :1913 -1918.

McFarland LV, Surawicz CM, Greenberg RN, et al. Prevention of ß -Lactam-Associated diarrhea by Saccharomyces boulardii compared with placebo. Am J Gastroenterol.1995; 90 :439 -448.

Pavia AT, Nichols CR, Green DP, et al. Hemolytic-uremic syndrome during an outbreak of Escherichia coli O157:H7 infections in institutions for mentally retarded persons: clinical and epidemiologic observations. J Pediatr.1990; 116 :544 -551.

Salminen SJ, Gueimonde M., Isolauri E. Probiotics that Modify Disease Risk. J Nutrition. 2005; 135: 1294-1298.

Simakachorn N, Pichaipat V, Rithipornpaisarn P, Kongkaew C, Tongpradit P, Varavithya W. Clinical evaluation of the addition of lyophilized, heat-killed Lactobacillus acidophilus LB to oral rehydration therapy in the treatment of acute diarrhea in children. J Pediatr Gastroenterol Nutr.2000; 30 :68 -72

Vanderhoof JA, Whitney DB, Antonson DL, Hanner TL, Lupo JV, Young RJ. Lactobacillus GG in the prevention of antibiotic-associated diarrhea in children. J Pediatr.1999; 135 :564 -568.

Vanderhoof, J.A., and R.J. Young. Probiotics in Pediatrics. 2005. Pediatrics 109; 956-958.

Van Niel, C.W.,C. Feudtner, M.M., Garrison and D.A. Christakis. Lactobacillus Therapy for Acute Infectious Diarrhea in Children: A Meta-Analysis. 2002. Pediatrics 109; 678-684

Van Niel C.W. Probiotics: Not Just for Treatment Anymore. 2005. Pediatrics 115; 174-177.

Weizman Z, Ghaleb Asli, and Ahmed Alsheikh. Effect of a Probiotic Infant Formula on Infections in Child Care Centers: Comparison of Two Probiotic Agents

Pediatrics. 2005; 115: 5 - 9.

Wong CS, Jelacic S, Habeeb RL, Watkins SL, Tarr PI. The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med.2000; 342 :1930 -1936

Annotated Answers

A1. The answer is b. Probiotics are compounds that contain bacteria that may be beneficial to the host. Often these agents contain active bacteria which are part of the normal host flora.

A2. The answer is e - all of the above. Bacteria that comprise the G.I. microflora aid in the digestion of carbohydrates and some bacterial species synthesize vitamin K. In addition, the colonization of the gut by these "good" bacteria is believed to hinder the attachment and colonization of the intestinal mucosa by pathogenic bacteria and also is thought to play a role in priming the host immune system.

A3. The answer is a - viral. While all of the possible answers are causes of diarrhea in pediatric population, by far, the most common cause of causative agents are viruses. In the U.S., the most common cause of acute diarrhea is rotavirus.

A4. The answer is False. The intestinal microflora is established during early infancy, and is initially dependent on the mother's microflora, mode of birth, the birth environment and early feeding practices. However, most studies have indicated that later in life, the microflora is difficult to permamently alter.

A5. The answer is False. While there are indications for the use of antibiotics in the treatment of some types of bacterially- caused diarrhea, in many instances, the use of antibiotics does not significantly decrease the time-course or severity of symptoms of acute diarrheal illness.