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Presentations at the 49th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Houston, Texas, Oct/Nov 2000
By Lin Chen, MD
Updates on travelers’ diarrhea were reviewed by Drs. H. DuPont, C. Ericsson, B. Connor, and D. Taylor at a symposium at the 49th Annual Meeting of the American Society of Tropical Medicine and Hygiene. Currently, the etiology of travelers’ diarrhea (TD) is attributed to bacteria in 85%, parasites in 5-15%, and viruses in less than 5%. Enterotoxigenic E. coli, (ETEC)
Shigella, Salmonella, and enterohemorrhagic E. coli occur more frequently in the summer, while Campylobacter and viral pathogens occur more frequently in the winter. Illness occurs more frequently during the first week of travel, and in children 0-2 years of age as well as young adults. Other risk factors include achlorhydria, hypochlorhydria, the use of H2 blockers or proton pump inhibitors, blood group O, location of food consumption, tap water, alcohol, and swimming. Rainy season increases the risk for TD (Dupont).
Food and water precautions remain the primary prevention in TD. Nevertheless, Lactobacillus appears to provide 62% protection compared to placebo.
Current and future approaches to symptomatic and antimicrobial therapy of TD were discussed by Dr. Dupont. Bismuth has antisecretory and antimicrobial effects and leads to 50% decrease in stool volume. Antimotility agents can cause up to 80% reduction in stool by slowing down the intestinal transit. An oral antisecretory drug, Zaldaride, which works as a calmodulin inhibitor, is being investigated for use by travelers. Proveri (Normal Stool Formula), a chloride channel inhibitor, is available commercially and can be used in AIDS-associated diarrhea as well as in TD. Racecadotul, an enkephaline inhibitor, is being studied in adults and children with acute diarrhea.
Newer antibiotics being evaluated for the treatment of TD include azithromycin, pivamdinicillin, and rifaximin. Studies are being conducted in Mexico, Jamaica, Guatemala, and Kenya on rifaximin. In countries where the risk for TD is high, empiric treatment is recommended with levofloxacin 500 mg/d for three days (or ciprofloxacin 500 mg b.i.d.). In Thailand and Barcelona, Spain, where Campylobacter exhibit a high rate of resistance to fluoroquinolones, azithromycin is recommended as empiric treatment for TD. The adult dose is 500 mg on day #1, and 250 mg on days #2 and #3 p.r.n. The pediatric dose is 10 mg/kg on day #1, and 5 mg/kg on days #2 and #3 p.r.n. Furazolidine at 7.5 mg/kg/d may also be used in children.
Dr. Conner discussed chronic diarrhea in the returning traveler. It is estimated that 3-10% of travelers develop diarrhea lasting longer than two weeks, and that up to 3% of travelers have persistent diarrhea lasting longer than 30 days. Etiologies include infections, postinfectious gut damage, malabsorption, unmasking of preexisting gastrointestinal problem such as inflammatory bowel disease, celiac sprue, irritable bowel syndrome, and colon cancer, and the remainder are unknown. It was noted that the empiric treatment of TD with antibiotics correlated with a decrease in the cases of tropical sprue. Evaluation of patients with chronic diarrhea includes antibiotic trials, elimination diets (of lactose, gluten, fat), antispasmodics such as 5HT3 antagonists, antidiarrheal agents, fiber, and cultured Lactobacillus. Gliadin antibody and tissue transglutamine antibodies are suggested for evaluation of sprue.
Finally, Dr. Taylor discussed vaccines for the prevention of TD. Various Shigella vaccines are being developed. These include a live attenuated vaccine (SC602), S. flexeneri 2a vaccine (SC 603), S. sonnei WRSSI vaccine, and a S. dysenteriae/1csa/stxA mutant. Vaccines against ETEC include the inactivated whole cell plus CT toxoid and a recombinant CS6. A Campylobacter inactivated whole cell with mucosal adjuvant is being developed.
Additional abstracts of interest to our readers are:
Abstract #60. Typhoid fever in travelers: Who should we vaccinate? Steinberg EB, et al. All cases of S. typhi infection reported to the U.S. Center for Disease Control (CDC) and Prevention’s National Typhoid Fever Surveillance System between 1994-1999 were reviewed. A total of 1166 laboratory-confirmed cases were reported, with 29% from California and 24% from New York. The median age was 22. A total of 26% were children younger than 10 years old; 73% of infections were acquired abroad. Six countries accounted for 70% of these infections: India (30%), Pakistan (13%), Mexico (10%), Bangladesh (6%), Haiti (6%), and the Philippines (5%). Of the travelers who reported their reason for travel, 77% of cases were visiting family, 14% were immigrants to the United States, 9% were tourists, and 3% were business travelers. Sixty-eight percent of travelers stayed less than six weeks abroad. Vaccination should be considered for the high-risk travelers, even for short-term travel, travelers to the Indian subcontinent, for children, and persons visiting family. (See Mileno MD. Travel Medicine Advisor Update 2000;10:47-48.)
Abstract #291. Duration of shedding of Cyclospora oocysts in U.S. citizens. Eberhard ML, et al. The CDC studied symptomatic but untreated subjects in two outbreaks of Cyclospora cayetanensis in 1999. Oocyst shedding persisted for 6.5-8.5 weeks from the time of exposure. All three subjects reported malaise, fatigue, nausea, and intermittent diarrhea throughout the time of shedding. Diarrhea abated rapidly after the cessation of oocyst shedding, but fatigue persisted.
Abstract #306. Three-year surveillance of acute diarrhea in U.S. military personnel in Thailand: Role of Campylobacter jejuni/coli in disease severity and clinical outcome. Tribble D, et al. Clinical and microbiologic data collected on U.S. military personnel presenting with acute diarrhea in Thailand from 1995, 1998, 1999 showed Campylobacter jujuni/coli to be the most commonly isolated pathogen (33%). Nontyphoidal Salmonella spp. were isolated in 21%, ETEC 11%, multiple bacterial isolates in 20%, and no isolates in 32%. Campylobacter isolates presented more frequently with fever, headaches, myalgias, abdominal cramps, and decreased ability to work. Initial antibiotic used in 1995 and 1998 was a fluoroquinolone in more than 98% of patients, whereas in 1999 azithromycin was used in 30%. FQ resistance was more than 85% during all three years. Infections caused by Campylobacter spp. were characterized by delayed recoveries and higher failures.
Abstract #309. Enterotoxigenic Escherichia coli as a cause of diarrhea among Mexican and U.S. adults in Mexico. Bouckenooghe AR, et al. Stool samples were obtained from resident Mexicans and U.S. travelers presenting with acute diarrhea in Guadalajara, Mexico. The most common pathogen was ETEC in both groups (10.9% vs 18.9%). Shigella was more common in the U.S. travelers (2.3% vs 0.4% of Mexicans). Entamoeba histolytica was more commonly identified in the Mexicans (3.7% vs 0% in U.S. travelers). Symptoms were milder and duration shorter in the Mexican residents.
Abstract #549. Emergence of resistant fecal flora in healthy persons during travel to Guadalajara, Mexico. Huang DB, et al. Thirty-nine healthy students from the United States were studied for development of resistant fecal flora. Stool specimens were obtained upon their arrival to Guadalajara, Mexico, and then weekly for three weeks. None of the subjects took prophylactic or therapeutic medications for TD. Increased growth of aerobic bacteria and trimethoprim-resistant bacteria (predominantly E. coli) were noted over the course of this study. The isolated E. coli were also resistant to ampicillin (44%), chloramphenicol (39%), doxycycline (89%), erythromycin (100%), and furazolidone (72%). Travel to a developing country appears to be a risk in acquiring antibiotic-resistant fecal flora.
Abstract #553. Natural history of enteroaggregative Escherichia coli infection among U.S. travelers in Mexico. Adachi JA, et al. Forty U.S. travelers to Guadalajara, Mexico, collected stool samples upon arrival and weekly for four weeks. Enteroaggregative E. coli (EAEC) colonization was identified in five asymptomatic subjects. By the fourth week, EAEC was identified in 16 subjects. Fewer EAEC infections were associated with diarrhea compared with ETEC infections.
Abstract #303. Surveillance of epidemic and sporadic cholera-like disease occurrence throughout Indonesia including the emergence of Vibrio cholerae 0139 serotype 1993-1999. Corwin AL, et al.
Abstract #307. Prevalence of infection with waterborne pathogens: A seroepidemiologic study in children 6-36 months old, San Juan Sacatepequez, Guatemala. Steinberg EB, et al.
Abstract #308. Surveillance for bacterial diarrheal disease in rural western Kenya, 1997-1999. Brooks JT, et al.
Abstract #541. A comparison of three transport mediums for recovery of intestinal parasites. Van CT, et al.
Abstract #551. Antibiotic treatment for traveler’s diarrhea: A meta-analysis of published reports. De Bruyn G, et al.
Abstract #557. Prevalence of Shigella spp. and the re-emergence of Shigella dysenteriae in Indonesia. Subekti DS, et al.
Abstract #668. Detection of Cyclospora cayetanensis DNA by PCR in experimentally contaminated raspberries and blackberries. Da Silva AJ, et al.