Rifaximin, a Nonabsorbed Oral Antibiotic, Prevents Shigellosis after Experimental Challenge

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1 MAJOR ARTICLE Rifaximin, a Nonabsorbed Oral Antibiotic, Prevents Shigellosis after Experimental Challenge David N. Taylor, 1,2 Robin McKenzie, 1 Anna Durbin, 1 Colleen Carpenter, 1 Christophe B. Atzinger, 1 Robert Haake, 2 and A. Louis Bourgeois 1 1 Center for Immunization Research, Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; and 2 Salix Pharmaceuticals, Morrisville, North Carolina Background. This double-blind, placebo-controlled study was conducted to assess the efficacy of the nonabsorbed oral antibiotic rifaximin to prevent shigellosis in volunteers challenged with Shigella flexneri. Methods. Volunteers were randomized to receive either prophylactic rifaximin (200 mg 3 times daily for 3 days; n p 15) or placebo ( n p 10) on days 0, 1, and 2. On day 1, volunteers were challenged with 1500 colony- forming units of S. flexneri 2a strain 2457T given orally in sodium bicarbonate buffer. Results. The incidence of diarrhea was 0 with rifaximin, compared with 60% with placebo ( P p.001). The median time to onset of diarrhea was 78.5 h with placebo ( P!.001 ). The incidence of dysentery was 0 for rifaximin and 10% for placebo ( P p.4). The incidence of colonization with Shigella was 0 with rifaximin, compared with 50% with placebo ( P!.005). A significant serum or mucosal immune response after challenge by at least 1 indicator (immunoglobulin A titer, immunoglobulin G titer, and immunoglobulin A antibody secreting cell count) was 0 with rifaximin and 80% with placebo ( P!.001). Conclusions. Rifaximin was effective and well tolerated, compared with placebo, in preventing shigellosis in this double-blind study of volunteers challenged with S. flexneri 2a. Travelers diarrhea affects 20% 50% of persons traveling from developed to developing countries [1 3]. Preventing it could reduce the personal and economic consequences associated with loss of vacation time and work time and, theoretically, reduce the risk of rare but potentially serious sequelae, such as reactive arthritis [4], Guillain-Barré syndrome [5], and postinfectious irritable bowel syndrome [6, 7]. These potential benefits notwithstanding, preventative strategies have not been widely adopted. Attempts at prevention through advising travelers about dietary practices have not been effective [8]. Although oral antibiotics have proved to be highly effective in preventing travelers diarrhea, their use for chemoprophylaxis is generally discouraged because of the risk of adverse effects, the potential for inducing antibiotic resistance, and the potential for en- Received 19 October 2005; accepted 23 December 2005; electronically published 22 March 2006 Reprints or correspondence: Dr. David N. Taylor, Salix Pharmaceuticals, 1700 Perimeter Park Dr., Morrisville, NC (david.taylor@salix.com). Clinical Infectious Diseases 2006; 42: by the Infectious Diseases Society of America. All rights reserved /2006/ $15.00 couraging overgrowth of organisms such as Clostridium difficile [9, 10]. The availability of rifaximin, an oral nonabsorbed antibiotic introduced in 2004 in the United States for the treatment of travelers diarrhea, has renewed interest in chemoprophylaxis of travelers diarrhea. Rifaximin is well tolerated [11], does not appear to induce resistance in enteric flora during repeated dosing [12], and has not been associated with clinically relevant resistance during 18 years of use in treating enteric infections in Italy. Rifaximin was effective both in the treatment of travelers diarrhea caused primarily by diarrheagenic strains of Escherichia coli [11, 13, 14] and in the prevention of travelers diarrhea in Mexico, where enterotoxigenic E. coli and enteroaggregative E. coli are the major pathogens [15]. These data suggest that rifaximin is effective at preventing travelers diarrhea in an area of the world where diarrheagenic E. coli is a common cause of travelers diarrhea. Whether rifaximin is similarly effective at preventing travelers diarrhea caused by invasive pathogens, such as Shigella, Salmonella, and Campylobacter species, has not been reported to date. Shigella species cause disease by invading the intestinal mucosal epi- Rifaximin for Prevention of Shigellosis CID 2006:42 (1 May) 1283

2 thelial cells, within whose intracellular environment the microbe is protected from host humoral and cellular immune responses and from antibiotics in the intestinal lumen [16]. The use of minimally absorbed oral antibiotics (such as rifaximin) prophylactically or early in the course of infection has been suggested as a means of protecting against shigellosis by eradicating Shigella species before the organisms enter the protective intracellular environment of colonic epithelial cells [17]. This study was conducted to assess the efficacy of rifaximin in the prevention of shigellosis in volunteers challenged with Shigella flexneri. The S. flexneri 2a strain 2457T has been extensively and safely used for challenge studies to evaluate new drugs and vaccines [18]. The results reported here indicate that rifaximin was highly effective in preventing shigellosis in the challenge model and suggest that rifaximin prophylaxis may be effective in preventing travelers diarrhea due to invasive, as well as noninvasive, bacterial pathogens. METHODS Volunteers Healthy men and women ages years old from the greater Baltimore metropolitan area were eligible to enroll in the study. Women could enroll only if they were not pregnant or lactating and if they either were not physiologically capable of bearing children or agreed to use effective contraception throughout the study. Exclusion criteria included the presence of a significant medical (including psychiatric) condition at screening; abnormal stool pattern or bowel habits (e.g.,!3 stools per week, 12 stools per day, or frequent liquid/loose stools); vaccination against Shigella or Shigella challenge within 3 years before the study; travel to a country where Shigella infection is endemic within 2 years before the study; regular use of laxatives, antacids, or other agents to lower stomach acidity; and use of broadspectrum antibiotics within 7 days before Shigella challenge or proton pump inhibitors or histamine 2 receptor blockers within 24 h before the first dose of study medication in the current study. All volunteers provided written informed consent. Procedures The protocol for this randomized, double-blind, placebo-controlled study (Salix Pharmaceuticals protocol RFID2001) was approved by the Committee on Human Research at the Johns Hopkins Bloomberg School of Public Health and by the Johns Hopkins University School of Medicine General Clinical Research Center inpatient research unit. Funding for this trial was provided under a clinical study agreement between Johns Hopkins Bloomberg School of Public Health (Baltimore, MD) and Salix Pharmaceuticals (Morrisville, NC). The trial was carried out in full compliance with good clinical practices guidelines. The study comprised a screening visit occurring before randomization; a randomized, double-blind inpatient phase, during which study medication was administered and volunteers were challenged with S. flexneri in the research ward; and a follow-up visit that occurred after discharge from the research ward and 14 days after challenge with S. flexneri. Volunteers who were determined during the screening phase to meet eligibility criteria were randomized 3:2 on the first day of the inpatient phase (day 0) to receive either prophylactic rifaximin (200 mg 3 times daily for 3 days, for a total of 9 doses) or placebo with 100 ml of water. Study medication was taken with meals in the research ward on study days 0, 1, and 2. Approximately 90 min after the morning (fourth) dose of study medication on day 1, volunteers were challenged with 1500 cfu of S. flexneri 2a strain 2457T given orally in sodium bicarbonate buffer (2 g per dose for a total of 150 ml). S. flexneri was supplied to the clinical site from a master cell bank that was fermented and vialed under good manufacturing practices conditions by the Bioproduction Facility of the Walter Reed Army Institute of Research. Volunteers remained in the research ward for a minimum of 5 days after challenge with S. flexneri. At the onset of diarrhea (as defined below) or on day 6, whichever occurred first, volunteers began a 3-day course of ciprofloxacin (500 mg administered orally twice daily) to eradicate infection with Shigella species. Volunteers were eligible for discharge from the research ward after ciprofloxacin treatment was initiated, provided they felt well, clinical assessments were completed, and 2 cultures of stool yielded results negative for Shigella species. Throughout the study, volunteers were monitored for and queried about adverse events, defined as any untoward medical occurrences, regardless of their suspected cause. Vital signs were measured at least every 8 h during the inpatient phase and every 4 h if diarrhea developed. Clinical laboratory tests (including blood chemistry analysis, hematological testing, and urinalysis) were undertaken at screening and at the follow-up visit. The incidence of adverse events, as well as vital signs and clinical laboratory test results, were summarized with descriptive statistics, but no hypothesis testing was undertaken for these measures. Measures and End Points Efficacy. Each day from day 0 through the day of discharge, study personnel collected all stools and assessed them for weight, consistency, and gross blood, and volunteers rated signs and symptoms associated with shigellosis. Stools of grade 3 or higher were considered to be diarrheic. Study personnel graded stools on a 5-point scale: 1 p firm, formed; 2 p soft, formed; 3 p viscous, opaque liquid or semiliquid assuming the shape of the container; 4 p watery, nonviscous, opaque liquid assuming the shape of the container; 5 p clear or translucent, watery or mucoid liquid assuming the shape of the container. Volunteers rated shigellosis signs and symptoms of abdominal 1284 CID 2006:42 (1 May) Taylor et al.

3 pain or cramps, nausea, emesis, excessive gas or flatulence, fecal urgency, anorexia, fever ( 38 C), and tenesmus on a 4-point scale ( 0 p none; 1 p mild, present, but not affecting normal daily activity; 2 p moderate, present, and causing a change in normal activity; 3 p severe, present, and preventing normal activity). The primary efficacy end point was the percentage of volunteers who developed diarrhea during the inpatient phase. Diarrhea was defined as passage of 2 grade 3 5 stools weighing 200 g within a 48-h period plus the presence of at least 1 symptom or sign of enteric illness (i.e., abdominal pain or cramps, confirmed blood in the stool, nausea, emesis, excessive gas or flatulence, fecal urgency, anorexia, fever [temperature, 38 C], and tenesmus) or passage of 1 grade 3 5 stool weighing 300 g plus the presence of at least 1 symptom or sign of enteric illness. Other efficacy end points included the percentage of volunteers who developed dysentery (defined as the presence of gross blood in a grade 3 5 stool on at least 2 occasions) during the inpatient phase; the times from S. flexneri challenge to a diagnosis of diarrhea or dysentery; severity of diarrhea as measured by weight (in grams) and number of grade 3 5 stools before and after ciprofloxacin treatment, duration of diarrhea, highest recorded temperature, and number of stools with blood; and severity of diarrhea as measured on a 4-point scale (severe, 10 grade 3 5 stools or 1000 g of grade 3 5 stools within a 24-h period; moderate, 4 9 grade 3 5 stools or g of grade 3 5 stools within a 24-h period; mild, 2 grade 3 5 stools totaling 200 g or 1 grade 3 5 stool totaling 300 g within a 48-h period and not meeting the definitions for moderate or severe diarrhea; or none). Differences between treatment s were compared by Fisher s exact test for the incidences of diarrhea and dysentery; the Wilcoxon rank sum test for median values for stool output (weight in grams and number of grade 3 5 stools), duration, highest recorded temperature, and stools with blood; and the Cochran-Mantel-Haenszel test for diarrhea severity and severity of shigellosis signs and symptoms. The median times to onset of diarrhea and dysentery were estimated with Kaplan-Meier survival analysis methodology and compared between treatment s with the log rank test. Microbiological testing. Each day from day 0 through the day that volunteers were discharged from the research ward, 1 morning stool and 1 afternoon stool (or, if stools were not available, rectal swabs) were cultured for both the qualitative and quantitative detection of Shigella species on Hektoen enteric agar. Nonfermenting colonies recovered on this media were evaluated and determined to be Shigella species by standard biochemical and immunological methods [13]. The incidence of intestinal colonization with Shigella species was compared between s with Fisher s exact test. The MIC of rifaximin for the challenge strain of S. flexneri 2a 2457T was 2 mg/ml (Zhi-Dong Jiang, personal communication). S. flexneri strain 2457T is highly susceptible to ciprofloxacin, with a MIC of!1 mg/ml. Immunological testing. On days 0, 8, and 14, blood samples were obtained for determination of S. flexneri 2a lipopolysaccharide antigen specific serum IgA and IgG immune responses by ELISA, and mucosal antigen specific IgA antibody secreting cell responses were assessed using the enzymelinked immunospot technique (days 0 and 8 only) [19]. A 4- fold increase in antibody titer was considered to be a significant serum antibody immune response, whereas the detection of 5 antibody-secreting cells specific for 2a lipopolysaccharide per 10 6 PBMCs after challenge was considered to be indicative of a significant mucosal IgA response to S. flexneri. Differences in the proportions of subjects with a significant immune response on at least 1 test were tested for statistical significance with Fisher s exact test. Differences in geometric mean titers between s were determined using the Wilcoxon rank sum test. RESULTS Sample population. Twenty-five volunteers were enrolled in the trial (15 in the rifaximin and 10 in the placebo ). All volunteers completed the study and were included in efficacy and tolerability analyses. In the rifaximin, approximately one-half of the volunteers (53.3%) were female, and 80% were black; the mean age ( SD) was years. In the placebo, 30% of volunteers were female and 90% were black; the mean age ( SD) was years. Volunteers were randomized into 3 cohorts because of space limitations on the research ward. The first 8 volunteers received an inoculum of 1497 cfu, the second cohort of 8 volunteers Table 1. Number of subjects receiving rifaximin or placebo who developed clinical symptoms, colonization, and immune responses following challenge with Shigella flexneri 2a. Symptom Rifaximin (n p 15) Placebo (n p 10) P Moderate to severe diarrhea Dysentery Severity of diarrhea None 15 2!.05 Mild 0 2!.05 Moderate 0 3!.05 Severe 0 3!.05 Fever (temperature, 38 C) 0 4!.05 Colonization with Shigella species a 0 5!.005 Immune response to Shigella species 0 8!.001 a Peak shedding levels for the 5 subjects in the placebo passing 3 Shigella species in their stool before ciprofloxacin treatment were 1 10, , 1 10, 4 10, and 3 10 cfu per g of stool. Rifaximin for Prevention of Shigellosis CID 2006:42 (1 May) 1285

4 Table 2. Severity of signs and symptoms of shigellosis in subjects treated with rifaximin or placebo. Sign or symptom Rifaximin (n p 15) Placebo (n p 10) Grade 3 5 stool output, median g (range) Before Cpfx treatment 0 (0 490) a (0 798) After Cpfx treatment 0 ( ) (0 2446) Grade 3 5 stools, median no. (range) Before Cpfx treatment 0 (0 3.0) 2.0 (.0 7.0) After Cpfx treatment 0 (0 1.0) 3.5 (0 19.0) Duration of diarrhea, median h (range) 0 (0 0) 70.7 ( ) Highest recorded temperature, median C (range) 37.5 ( ) 37.8 ( ) Bloody stools, no. of subjects 0 1 Diarrhea severity None 14 (93.3) 4 (40) Mild 1 (6.7) 1 (10) Moderate 0 3 (30) Severe 0 2 (20) Abdominal pain or cramps None 9 (60) 2 (20) Mild 4 (26.7) 2 (20) Moderate 2 (13.3) 1 (10) Severe 0 5 (50) Nausea None 14 (93.3) 8 (80) Moderate 1 (6.7) 2 (20) Emesis None 14 (93.3) 10 (100) Mild 1 (6.7) 0 Excessive gas/flatulence None 8 (53.3) 0 Mild 5 (33.3) 4 (40) Moderate 2 (13.3) 4 (40) Severe 0 2 (20) Fecal urgency None 15 (100) 4 (40) Moderate 0 2 (20) Severe 0 4 (40) Anorexia None 12 (80) 4 (40) Mild 1 (6.7) 2 (20) Moderate 2 (13.3) 2 (20) Severe 0 2 (20) Fever None 15 (100) 6 (60) Mild 0 1 (10) Moderate 0 2 (20) Severe 0 1 (10) Tenesmus None 15 (100) 6 (60) Mild 0 2 (20) Moderate 0 1 (10) Severe 0 1 (10) NOTE. Data are no. (%) of subjects, unless otherwise indicated. Cpfx, ciprofloxacin. a One person in the rifaximin had 490 g of loose stool but did not meet the definition of diarrhea, because these stools were not passed within a 24-h period. received an inoculum of 1449 cfu, and the third cohort of 9 volunteers received an inoculum of 1588 cfu. The results of the 3 cohorts were pooled for all analyses. Efficacy. The incidence of diarrhea was 0 in the rifaximin, compared with 60% in the placebo ( P p.001) (table 1). The median time to onset of diarrhea was 78.5 h in the placebo ( P!.001). The incidence of dysentery was 0 in the rifaximin and 10% in the placebo ( P p.4; table 1). Diarrhea occurred in 1 of 3 control subjects receiving the 1497-cfu inoculum, 2 of 3 control subjects receiving the 1449-cfu inoculum, and 3 of 4 control subjects receiving the 1588-cfu inoculum. Patients in the rifaximin had no or minimal signs and symptoms of shigellosis, whereas most of the placebo had mild to severe signs and symptoms (table 2). Mean ratings for individual signs and symptoms of shigellosis were higher for placebo-treated volunteers than for rifaximin-treated volunteers, including weight and number of grade 3 5 stools; duration of diarrhea; number of stools with blood; diarrhea severity; and severity of abdominal cramps, excessive gas or flatulence, fecal urgency, anorexia, fever, and tenesmus (P!.05 for all comparisons). Colonization. The incidence of colonization with Shigella species was 0 in the rifaximin, compared with 50% in the placebo ( P!.005; table 1). The peak levels of fecal shedding for the 5 placebo recipients who were found to be colonized with S. flexneri after challenge were , , 1 10, 4 10, and 3 10 cfu/g of stool, respectively (data not shown). Fecal coliforms were recoverable from samples from all subjects receiving rifaximin until the subjects received ciprofloxacin at the end of the trial. Fecal coliforms were not recoverable during the 3 days that the subjects received ciprofloxacin. Immune response. The incidence of a significant systemic or local mucosal immune response, as determined by at least 1 indicator (serum IgA titer, IgG titer, or IgA antibody secreting cell count), was 0 in the rifaximin and 80% in the placebo ( P!.001; table 1). Geometric mean IgA titers remained stable in the rifaximin (23.0 on day 0, 24.9 on day 8, and 24.2 on day 14), whereas they increased markedly in the placebo (22.6 on day 0, 26.9 on day 8, and 91.7 on day 14) (table 3). IgA antibody secreting cells were not detected on days 0 or 8 in the rifaximin but increased significantly from day 0 to day 8 in the placebo. The pattern of results with IgG titers was similar to that for IgA titers (table 3). DISCUSSION The oral antibiotic rifaximin was effective, compared with placebo, in preventing shigellosis in this randomized, double-blind study of volunteers challenged with S. flexneri 2a. In the given prophylactic rifaximin, no volunteer developed diarrhea 1286 CID 2006:42 (1 May) Taylor et al.

5 Table 3. Antibody response to Shigella flexneri 2a lipopolysaccharide among subjects who received rifaximin prophylaxis or rifaximin placebo before oral challenge with S. flexneri 2a strain (2457T). Response, time point Rifaximin Placebo IgA Day 0 No. of subjects tested 10 6 Geometric mean titer SD Day 8 Geometric mean titer SD Day 14 Geometric mean titer SD IgA antibody secreting cells Day 0 Geometric mean titer SD Day 8 Geometric mean titer SD IgG Day 0 No. of subjects tested 10 6 Geometric mean titer SD Day 8 Geometric mean titer SD Day 14 Geometric mean titer SD NOTE. On day 1, 10 of 15 volunteers in the rifaximin and 6 of 10 subjects in the placebo were tested for IgA and IgG serum antibodies to S. flexneri 2a lipopolysaccharide. or dysentery, became colonized with Shigella species, or demonstrated an S. flexneri specific immune response after challenge. In contrast, in the given placebo, 60% developed diarrhea, 10% developed dysentery, 50% became colonized with Shigella species, and 80% demonstrated an S. flexneri specific immune response. Rifaximin was well tolerated and caused minimal changes in fecal coliforms. Rifaximin demonstrated prophylactic efficacy in this study with the same dosage regimen used for the treatment of acute travelers diarrhea (200 mg administered 3 times daily) [11, 13, 14]. These data extend other research demonstrating the usefulness of rifaximin in the prophylaxis of diarrheal illness. In a double-blind, placebo-controlled study in which 209 US adults were randomized within 72 h after their arrival in Mexico to receive rifaximin or placebo for 2 weeks, rifaximin significantly protected against the occurrence of diarrhea, compared with placebo [15]. The diarrhea attack rate for the rifaximin was 15%, compared with 54% for placebo (72% protective efficacy). Minimal changes in coliform flora were found during P rifaximin therapy, and the incidence of adverse events did not differ between volunteers treated with rifaximin and those treated with placebo. Besides preventing clinical illness in the current study, rifaximin prevented subclinical infection, as demonstrated by the lack of an S. flexneri specific humoral immune response in rifaximin-treated volunteers, compared with the robust response in placebo-treated volunteers. Protective immunity to shigellosis appears to involve both systemic and mucosal humoral immune responses targeted to the serotype-specific structure of Shigella species lipopolysaccharide [16, 20]. In the placebo after challenge with S. flexneri, marked elevations in 2a-specific IgA antibody secreting cells and serum IgA titers were noted, indicating that both antigen-specific systemic and local intestinal antibody responses were induced in these subjects. In contrast, among volunteers given prophylactic rifaximin, neither serum IgA or IgG titers nor numbers of IgA antibody secreting cells became elevated. The data from this study demonstrate the efficacy of rifaximin in the prevention of shigellosis and suggest that it may be effective in preventing traveler s diarrhea caused by both invasive and noninvasive bacterial pathogens. These results should not be extrapolated to acute treatment of shigellosis, for which the efficacy of rifaximin has not been established. Given the small number of Shigella-infected patients in the travelers diarrhea treatment study, additional research is warranted before conclusions about the efficacy of rifaximin in the acute treatment of Shigella infection can be drawn. The results of this study should be interpreted in the context of the relatively small sample size and the characteristics of the study sample, which comprised healthy volunteers, the majority of whom were aged years. The degree to which the results can be generalized to the larger community and to at-risk persons, including young children and elderly individuals, is not known. Results of this study would be complemented by the demonstration of prophylactic efficacy of rifaximin in a placebo-controlled prevention study among travelers to an area in which shigellosis is hyperendemic. In clinical studies undertaken a decade or more ago, prophylactic therapy with bioavailable antibiotics effectively prevented shigellosis among individuals exposed to Shigella species [21, 22]. However, prophylactic antibiotic therapy is infrequently used for diarrheal syndromes, including shigellosis, because of concerns about adverse effects, drug interactions, and the potential for inducing bacterial resistance [23]. Rifaximin appears to overcome these concerns. Rifaximin has been demonstrated to be effective, compared with placebo, in the prevention of shigellosis and travelers diarrhea, has a favorable adverse event profile with no known clinically relevant drug interactions, and has not been associated with clinically relevant drug resistance; these are attributes that are cause for reeval- Rifaximin for Prevention of Shigellosis CID 2006:42 (1 May) 1287

6 uating the role of prophylactic antibiotic therapy in diarrheal illness. Shigellosis is often spread by person-to-person transmission [24]. Epidemics can be seen in areas of poor sanitation and crowding, and they have been well documented in day care centers, nursing homes, and custodial institutions for prisoners and mentally handicapped individuals. Shigella species also have potential as a bioweapon. Outbreaks are difficult to control, and antibiotic prophylaxis could be used as a strategy to prevent secondary transmission of Shigella species [25, 26]. Rifaximin is potentially important in this regard, because it can be given orally and is well tolerated. Acknowledgments We thank Dr. Larry Hale for providing the challenge strain; Arlene Bloom for coordinating the study; Barbara DeNearing, Ruval Comendador, LaNisha Burke, George Gomes, and the nursing staff of the Johns Hopkins University School of Medicine General Clinical Research Center for their assistance in conducting this research; and Dr. Jane Saiers for assistance with writing the manuscript. Financial support. Salix Pharmaceuticals and the National Institutes of Health (RR-00052). Potential conflicts of interest. R.H. and D.N.T. are currently employed by Salix Pharmaceuticals, which manufactures rifaximin in the United States. Salix Pharmaceuticals funded in part the study and participated in the data analysis through a third party. All other authors: no conflicts. References 1. Brewster SJ, Taylor DN. Epidemiology of travelers diarrhea. In: Keystone JS, Kozarsky PE, Freedman DO, Nothdurft HD, Connor BA, eds. Travel medicine. 1st ed. New York: Mosby, Elsevier Limited, 2004: Steffen R, Tornieporth N, Costa Clemens SA, et al. Epidemiology of travelers diarrhea: details of a global survey. J Travel Med 2004; 11: Steffen R. Epidemiologic studies of travelers diarrhea, severe gastrointestinal infections, and cholera. Rev Infect Dis 1986; 8(suppl 2): S Rees JR, Pannier MA, McNees A, et al. Persistent diarrhea, arthritis, and other complications of enteric infections: a pilot survey based on California FoodNet surveillance, Clin Infect Dis 2004; 38(suppl 3):S Rees JH, Soudain SE, Gregson NA, et al. Campylobacter jejuni infection and Guillain-Barré syndrome. N Engl J Med 1995; 333: Taylor DN, Connor BA, Shlim DR. Chronic diarrhea in the returned traveler. Med Clin North Am 1999; 83: Okhuysen PC, Jiang ZD, Carlin L, et al. Post-diarrhea chronic intestinal symptoms and irritable bowel syndrome in North American travelers to Mexico. Am J Gastroenterol 2004; 99: Peltola H, Gorbach SL. Travelers diarrhea. Epidemiology and clinical aspects. In: DuPont HL, Steffen R, eds. Textbook of travel medicine and health. 2nd ed. Hamilton, Canada: BC Decker, 2001: Rendi-Wagner P, Kollaritsch H. Drug prophylaxis for travelers diarrhea. Clin Infect Dis 2002; 34: Ericsson CD. Travelers diarrhoea. Int J Antimicrob Agents 2003; 21: Steffen R, Sack DA, Riopel L, et al. Therapy of travelers diarrhea with rifaximin on various continents. Am J Gastroenterol 2003; 98: DuPont HL, Jiang ZD. Influence of rifaximin treatment on the susceptibility of intestinal gram-negative flora and enterococci. Clin Microbiol Infect 2004; 10: DuPont HL, Jiang ZD, Ericsson CD, et al. Rifaximin versus ciprofloxacin for the treatment of traveler s diarrhea: a randomized, doubleblind clinical trial. Clin Infect Dis 2001; 33: DuPont HL, Ericsson CD, Mathewson JJ, et al. Rifaximin: an unabsorbed antimicrobial in the therapy of travelers diarrhea. Digestion 1998; 59: DuPont HL, Jiang ZD, Okhuysen P, et al. A randomized, double-blind, placebo-controlled trial of rifaximin to prevent travelers diarrhea. Ann Intern Med 2005; 142: Phalipon A, Sansonetti PJ. Shigellosis: innate mechanisms of inflammatory destruction of the intestinal epithelium, adaptive immune response, and vaccine development. Crit Rev Immunol 2003; 23: Taylor DN. Poorly absorbed antibiotics for the treatment of traveler s diarrhea. Clin Infect Dis 2005; 41(Suppl 8):S DuPont HL, Levine MM, Hornick RB, Formal SB. Inoculum size in shigellosis and implications for expected mode of transmission. J Infect Dis 1989; 159: Coster TS, Hoge CW, VanDeVerg LL, et al. Vaccination against shigellosis with attenuated Shigella flexneri 2a strain SC602. Infect Immun 1999; 67: Jennison AV, Verma NK. Shigella flexneri infection: pathogenesis and vaccine development. FEMS Microbiol Rev 2004; 28: Shanks GD, Ragama OB, Aleman GM, et al. Azithromycin prophylaxis prevents epidemic dysentery. Trans R Soc Trop Med Hyg 1996; 90: Ben-Yehuda O, Cohen D, Alkan M, et al. Doxycycline prophylaxis for shigellosis. Arch Intern Med 1990; 150: Ericsson CD, Kollaritsch H. Prophylactic use of drugs. In: DuPont HL, Steffen R, eds. Textbook of travel medicine and health. 2nd ed. Hamilton, Canada: BC Decker, 2001: Gupta A, Polyak CS, Bishop RD, Sobel J, Mintz ED. Laboratory-confirmed shigellosis in the United States, : epidemiologictrends and patterns. Clin Infect Dis 2004; 38: Mahoney FJ, Farley TA, Burbank DF, Leslie NH, McFarland LM. Evaluation of an intervention program for the control of an outbreak of shigellosis among institutionalized persons. J Infect Dis 1993; 168: Mahoney FJ, Farley TA, Moriniere BJ, Winsor DK, Silberman RL, McFarland LM. Evaluation of an intervention program in the control of an urban outbreak of shigellosis. Am J Prev Med 1991; 7: CID 2006:42 (1 May) Taylor et al.