Heat susceptibility of bacterial enteropathogens. Implications for the prevention of travelers' diarrhea

The heat susceptibility of four bacterial enteropathogens in foods and water was studied to develop effective recommendations for travelers to regions where diarrheal diseases are important health problems. All enteropathogens tested survived well in foods stored at refrigerator temperature (4 degrees C), room temperature (25 degrees C), and 50 degrees C, which is too hot to touch. Tap water had to be heated above 65 degrees C to reliably kill all bacterial enteropathogens. At 13 of the 14 tourist-oriented hotels in four countries, water from the hot water tap did not reach temperatures of 65 degrees C. The implications of this study are that food and water that are too hot to touch may still be contaminated with bacterial enteropathogens. Travelers should be advised that food, water, or beverages are safe only if they have been brought to boiling or near-boiling temperatures prior to consumption.

Shigella

Shigella strains capable of producing illness possess a 140 megadalton plasmid that determines its property of epithelial cell penetration. In the classic presentation, there is a descending intestinal tract infection beginning with the passage of small numbers of large-volume stools and progressing to the passage of many small-volume stools that contain blood and mucus. Shigellae are efficiently transmitted to contacts in person-to-person spread and only 200 viable cells are sufficient to produce illness in susceptible persons. Shigellosis should be suspected in persons with severe diarrhea, in those with fever, when bloody stools are passed, or when stool smears contain many leukocytes. The current treatment of choice is TMP-SMX or, in adults, a quinolone (norfloxacin or ciprofloxacin).

Enzyme immunoassay for the detection of Giardia lamblia

An enzyme immunoassay (EIA) was developed for direct detection of Giardia lamblia antigens in fecal specimens. The EIA was evaluated by testing specimens from 1,331 subjects in the USA and Egypt. For the 353 specimens from human subjects in the USA there was a 97% overall agreement between the results of the EIA and direct microscopic examination, yielding a sensitivity and specificity of 92% and 99% respectively. Due to adverse field conditions the EIA did not perform as well in the specimens collected and tested in Egypt. The sensitivity and specificity for 585 human specimens from Egypt were 74% and 97% respectively.

Illness and reservoirs associated with Giardia lamblia infection in rural Egypt: the case against treatment in developing world environments of high endemicity

A longitudinal investigation of the health effects and reservoirs of Giardia was undertaken during 1984-1985 in 40 households located in the rural Nile Delta region of Egypt. Stool specimens obtained once weekly for six months from 2-4-year-old children were cyst- or trophozoite-positive in 42% of the 724 examined. Only one child remained Giardia-negative during the study. The mean duration of excretion in Giardia-positive children was seven and one-half weeks with a range of one to 17 weeks. Mucus was present in 52% of all stools collected, and fecal leukocytes were observed with surprising frequency in the absence of identifiable pathogens. Clinical symptoms of illness were frequently observed within a month before or after Giardia excretion in stool of children, but a statistical inference of association was not demonstrated. Seventeen per cent of 697 specimens obtained from their mothers were Giardia-positive for a mean duration of four weeks and a range of one to 18 weeks. A total of 962 specimens were collected from 13 species of household livestock. Giardia was detected in 22 specimens from cows, goats, sheep, and one duck. Giardia cysts were detected in three of 899 samples of household drinking water. The ubiquity of the protozoan as well as the failure to show an association between infection and symptomatic illness argue against the administration of Giardia-specific drugs to children in settings where the risk of reinfection is high and for whom intestinal insults are both varied and constant.

Travelers' diarrhea in West Africa and Mexico: fecal transport systems and liquid bismuth subsalicylate for self-therapy

The goals of this study were threefold: to compare the etiology of travelers' diarrhea in West Africa and Mexico, to evaluate two fecal transport systems for the recovery of enteropathogens, and to verify the efficacy of liquid bismuth subsalicylate (BSS) in different locations and under different entrance criteria for disease severity. The study populations consisted of 133 European tourists in West Africa and 112 American students in Mexico who had suffered from travelers' diarrhea. In 60% and 38% of the stool samples at the two study sites, similar proportions of enteropathogens were detected. A two-vial system consisting of Enteric Plus medium and polyvinyl alcohol fixative was slightly superior for identifying enteric pathogens than was a three-vial system with buffered glycerol saline, Cary-Blair medium with campylobacter antibodies, and polyvinyl alcohol fixative. In a parallel, double-blind, randomized trial, BSS significantly shortened disease duration at both study sites.

Test-of-cure stool cultures for traveler's diarrhea

Whether enteropathogens were eradicated or persisted in test-of-cure stool cultures from 251 patients with traveler's diarrhea, the durations of diarrhea were similar within the antimicrobial agent-treated (32 versus 33 h) and placebo-treated (82 versus 96 h) groups. Routine test-of-cure stool cultures can be useful for evaluating treatment failures and for assessing asymptomatic carriage of enteropathogens after treatment, but they are not mandated in the design of placebo-controlled antimicrobial treatment trials in traveler's diarrhea when the focus of the trial is clinical efficacy.

The human health implication of the use of antimicrobial agents in animal feeds

Antimicrobials given in subtherapeutic levels in feed are credited with having contributed to lower cost of meat, milk and eggs. The practice often is associated with the acquisition of resistant enteric flora by the involved animals, and this may in turn contribute to the human reservoir of antimicrobial resistant coliforms and salmonellae. Associated farm workers may transiently acquire resistant flora and on rare occasions develop salmonellosis. Although irrefutable evidence of growth promotant properties of antibiotics in animal feed was provided 30 to 40 years ago, additional studies on mechanisms of the effect are presently needed. It may be possible to identify factors effective in promoting growth without deleterious effects on flora. A national surveillance programme of antimicrobial utilisation (both subtherapeutic and therapeutic) among food producing animals should be established. Molecular epidemiologic research efforts will need to be undertaken to establish whether genetic information of animal origin importantly contributes to the human environmental pool of antimicrobial resistance. In the meantime, it does not appear that the use of drugs as feed additives, while allowing their unrestricted use for therapy in both animals and persons, would favorably influence the problems of antimicrobial resistance of salmonellosis in human populations.

Norwalk virus antigen and antibody response in an adult volunteer study

To better define the optimum timing of specimen collection and identify alternate ways to diagnose Norwalk virus outbreaks, we looked at the timing of the antibody response and virus excretion in a human volunteer study. The Norwalk virus antibody titers and antigen in stool specimens were examined by biotin-avidin immunoassay. Our data suggest that in epidemic situations, convalescent-phase sera could be collected as soon as 13 days after the onset of illness and acute-phase sera could be collected as late as 5 days after onset. Our data also suggest that if sufficient serum samples are collected, convalescent-phase case and control serum samples can be used to identify Norwalk virus outbreaks. Antigen detection was much less sensitive than seroconversion for detecting infection.

Bismuth subsalicylate in the treatment and prevention of diarrheal disease

Bismuth subsalicylate (BSS) has been used for more than 80 years to treat gastrointestinal symptoms although little clinical evidence was available until recently to substantiate its value and possible mechanisms of action. BSS 4.2 g given over 3 1/2 hours was shown to reduce the number of stools passed and favorably alter subjective symptoms in patients with traveler's diarrhea. BSS has also been shown to have beneficial effects on chronic infantile diarrhea. A small but discernible effect has been shown on selected symptoms associated with Norwalk virus-induced gastroenteritis. A liquid preparation, in a dose of 60 ml qid (4.2 g/d), was 62 percent effective in preventing traveler's diarrhea during a three-week period of risk and a tablet formulation (BSS 600 mg qid) was 76 percent effective in preventing experimentally induced enterotoxigenic Escherichia coli diarrhea in volunteers. A tablet formulation (2.1 g/d) was recently shown to be 65 percent effective in preventing traveler's diarrhea during a three-week clinical trial in Mexico. Preliminary evidence suggests that the salicylate moiety exerts antisecretory effects in patients with diarrhea and the bismuth and intestinal hydrolysis products of BSS have direct antimicrobial effects.

Efficacy of trimethoprim-sulfamethoxazole in treatment of acute diarrhea in a Mexican pediatric population

The efficacy of trimethoprim-sulfamethoxazole (TMP-SMX) and placebo were compared in a randomized double-blind study of 141 Mexican children with acute diarrhea. Patients who met specific entry criteria received TMP-SMX or an identical appearing placebo for 5 days. Stools were examined for bacterial, viral, and parasitic pathogens. Enterotoxigenic Escherichia coli were the most commonly isolated pathogens (22% of total). Patients given TMP-SMX had a significantly shorter time to "last illness stool" than did those given placebo, but no difference in number of unformed stools in 5 days was found between treatment groups. However, TMP-SMX significantly shortened the illness in patients with fever or many fecal leukocytes. When stool cultures positive for any bacterial pathogen or for enterotoxigenic E. coli were analyzed as separate groups, a significantly faster recovery was observed in patients given TMP-SMX. TMP-SMX is efficacious in the treatment of Mexican children with diarrhea and culture-proved bacterial infection or when the clinical signs and symptoms suggest bacterial enteritis.

Use of antimicrobial agents in animal feeds: implications for human health

The inclusion of subtherapeutic doses of antimicrobial agents in animal feed is credited for having contributed to lower costs of meat, milk, and eggs. The practice often is associated with the acquisition of resistant enteric flora by the involved animals, a phenomenon that in turn may contribute to the human reservoir of coliforms and salmonellae resistant to antimicrobial agents. Farm workers may transiently acquire resistant intestinal flora and on rare occasions develop salmonellosis. Although irrefutable evidence of the growth-promoting properties of antibiotics in animal feed was provided 30-40 years ago, additional studies--with a focus on mechanisms of the effect--are presently needed. It may be possible to identify factors effective in promoting growth without deleterious effects on the intestinal flora. A national program of surveillance of antimicrobial administration (in both subtherapeutic and therapeutic doses) to food-producing animals should be established. Molecular epidemiologic research efforts must be undertaken to determine whether genetic information of animal origin contributes significantly to the human environmental pool of antimicrobial resistance. In the meantime, it does not appear that the banning of drugs as feed additives, with concomitant unrestricted use of these agents for the treatment of both animals and people, would favorably influence the problems of antimicrobial resistance and salmonellosis in human populations.

Current problems in antimicrobial therapy for bacterial enteric infection

Trimethoprim/sulfamethoxazole is currently considered the treatment of choice for shigellosis and severe travelers' diarrhea. The problem with this combination regimen is inactivity against Campylobacter jejuni strains and other bacterial enteropathogens showing in vitro resistance to the drug. Resistance to trimethoprim/sulfamethoxazole among enteric pathogens has occurred frequently in certain areas of the world. A study of the in vitro susceptibility of enteric bacterial pathogens isolated from multiple countries was recently performed. The minimal inhibitory concentration of ciprofloxacin required to inhibit 90 percent of the 210 bacterial enteropathogens ranged from 0.25 micrograms/ml for C. jejuni to 0.016 micrograms/ml for enterotoxigenic Escherichia coli, Salmonella, and Shigella. In a clinical trial carried out in a United States student population that acquired diarrhea while in Mexico, it was shown that ciprofloxacin was as effective as trimethoprim/sulfamethoxazole and both were significantly (p less than 0.001) more effective than placebo. The average duration of diarrhea was 29 or 20 hours after initiation of treatment with ciprofloxacin or trimethoprim/sulfamethoxazole, respectively, compared with 81 hours in the placebo group. The antimicrobial agents were more efficacious than placebo in treating diarrhea caused by enterotoxigenic E. coli, invasive enteropathogens, and unknown pathogens. Ciprofloxacin and the quinolone derivatives are uniquely suited to the therapy of acute bacterial diarrhea in areas where C. jejuni is commonly found and where trimethoprim/sulfamethoxazole-resistant strains regularly occur.

Prevention of travelers' diarrhea by the tablet formulation of bismuth subsalicylate

Within 48 hours of arrival in Mexico, 182 US students participated in a study to compare the efficacy of two dosages of bismuth subsalicylate (262 mg per tablet) as a prophylactic agent against diarrhea. The students were randomly assigned to receive two tablets (high dose) or one tablet (low dose) of bismuth subsalicylate four times daily or a placebo four times daily during a three-week period. Among these completing the trial, diarrhea (four or more unformed stools in 24 hours or three in eight hours, plus one other symptom) occurred in seven (14%) of 51 receiving the high-dose regimen compared with 15 (24%) of 63 receiving the low-dose regimen and 23 (40%) of 58 in the placebo group. Protection rates were 65% for high-dose and 40% for low-dose bismuth subsalicylate. Diarrhea caused by enterotoxigenic Escherichia coli was found in one student receiving the high-dose regimen, in no students receiving the low-dose regimen, and in seven placebo-treated subjects. Bismuth subsalicylate was well tolerated; the most common side effects were blackening of tongues and stools. Bismuth subsalicylate use in both dosages was associated with tinnitus at a low, clinically insignificant frequency of 1.2 days per 100 days of treatment. The dosage of two tablets of bismuth subsalicylate four times daily (2.1 g/d) appears to be a safe and effective means of reducing the occurrence of travelers' diarrhea among persons at risk for periods up to three weeks.

Rotavirus gastroenteritis

Rotaviruses have proven to be major causes of pediatric diarrheal disease morbidity and mortality worldwide. The past several years have yielded substantial new insights into these viruses, their epidemiology, and the mechanisms of host resistance to them. These insights have in turn resulted in development of several candidate rotavirus vaccine strains, bringing closer the possibility of effective protection of young children from rotavirus disease.

Detection of enteropathogens in fatal and potentially fatal diarrhea in Cairo, Egypt

A 1-year study of the etiology of acute diarrhea complicated by severe (10%) dehydration, active bleeding, shock and cardiovascular collapse, pneumonia, acute renal failure, or seizures in infants under 18 months of age was performed in Cairo, Egypt. Of 145 infants, 19 (13%) died or left the hospital moribund; the remaining 126 patients were classified as having potentially fatal illness. A variety of enteropathogens were identified with approximately equal frequency in the fatal and nonfatal complicated cases as well as in 135 controls with severe uncomplicated diarrhea. The agents most frequently detected in infants with severe diarrhea in this population which were felt to be etiologically important were rotavirus (33%), heat-stable enterotoxin-producing Escherichia coli (20%), heat-labile enterotoxin-producing E. coli (11%), enteropathogenic E. coli (8%), and Salmonella spp. (5%). The high rate of occurrence of Giardia lamblia (35%) probably represented the high carriage rate of the protozoan in this population. Complicated (fatal and potentially fatal) cases differed from control cases in a number of ways: the onset of diarrhea was more sudden, the course was progressive and of greater initial intensity, vomiting occurred more frequently, the patients more often had visited another physician before coming to the hospital, the patients more often had respiratory symptoms and pulmonary abnormalities on auscultation, hypoactive bowel sounds and abdominal distention were more common, as was oliguria, and the patients showed lower mean body weights.

The detection of enteropathogens in acute diarrhea in a family cohort population in rural Egypt

In 8 villages of rural northeastern Egypt, a 2-year study of the etiologic agents associated with episodes of diarrhea was carried out. Stool specimens (3,243) from 3,513 episodes of diarrhea were processed for enteropathogens. The most commonly identified agents in the group with diarrhea were Giardia lamblia (44%), heat stable enterotoxin (ST)-producing enterotoxigenic Escherichia coli (ETEC) (15%), heat labile toxin (LT)-producing ETEC (12%), enteropathogenic E. coli (EPEC) (4%), rotavirus (3%), Shigella (2%) and Salmonella (1%). Isolation rates were increased in cases compared to controls for all agents except G. lamblia and EPEC strains. Rotavirus, Salmonella and ST-producing ETEC were more frequently isolated during cooler months and Shigella and LT-ETEC occurred more commonly in warmer months. Campylobacter, EPEC, Giardia and E. histolytica did not show a discernable seasonal pattern. Rotavirus was primarily associated with diarrhea in infants only. Forty-four percent of children experienced at least 1 bout of rotavirus diarrhea by the age of 3 years. Vomiting was reported in 65% of cases of rotavirus infection. Dehydration was reported in greater than 40% of those with rotavirus-, Salmonella-, Campylobacter-, LT-ETEC- and EPEC-associated illness and in those without an identifiable agent. While rotavirus was implicated in 3% of cases overall, when vomiting or vomiting plus dehydration occurred, rotavirus was identified with a rate of 10% and 12%, respectively. Dysentery was common only in Shigella cases, occurring in 24%. A decrease in occurrence of rotavirus, Campylobacter and possibly EPEC illness was seen in the infants less than 6 months of age who were breast-fed when compared to those who were not.

The relation between production of cytotoxin and clinical features in shigellosis

The relation between in vitro production of HeLa cell cytotoxin by strains of Shigella and clinical symptomatology was determined for 35 travelers from the United States who developed shigellosis in Guadalajara, Mexico. There were 25 patients with Shigella sonnei, eight with Shigella flexneri, one with Shigella boydii, and one with Shigella dysenteriae. These strains were evaluated for in vitro production of cytotoxin. The amount of cytotoxin did not correlate with the number of stools passed, the severity of abdominal pain, or the presence of nausea or vomiting. However, patients with strains of Shigella that produced more cytotoxic activity were more likely to have fever (P less than .02) and occult blood in their stools (P less than .004). The cytotoxicity produced by 30 (86%) strains could not be neutralized with rabbit antiserum to purified, formaldehyde-treated Shiga toxin from S. dysenteriae type 1 strain 60 R; the cytotoxicity of five (14%) of the strains was partially neutralized. When only nonneutralizable cytotoxin was considered, the presence of fecal leukocytes (P less than .04), as well as of occult blood (P less than .002) and fever (P less than .02), correlated with the amount of cytotoxin. The amount of nonneutralizable cytotoxin produced by shigella strains was related to the clinical findings. This cytotoxic activity was infrequently attributable to "Shiga toxin".

Role of a novel antidiarrheal agent, BW942C, alone or in combination with trimethoprim-sulfamethoxazole in the treatment of traveler's diarrhea

The efficacy of BW942C, a novel enkephalinlike pentapeptide antidiarrheal agent, was compared with the efficacy of trimethoprim-sulfamethoxazole (TMP-SMX) and the combination of the two agents in a placebo-controlled trial of the 72-h treatment of acute diarrhea. Subjects with diarrhea but without bloody stools or fever greater than 102 degrees F (38.9 degrees C) were enrolled. Administered to 134 U.S. adults with diarrhea that developed shortly after their arrival in Guadalajara, Mexico, BW942C was more efficacious than TMP-SMX in relieving diarrhea and cramps in the first 12 h of therapy, especially among subjects with diarrhea caused by enterotoxigenic E. coli. In the BW942C treatment group, 25% of subjects eventually took additional therapy because their diarrhea did not respond to BW942C alone. Neurological side effects such as dizziness and light-headedness occurred more frequently among BW942C-treated subjects. Therapy for 3 days with TMP-SMX provided lasting relief comparable with previously reported 5-day therapy. Use of the combination of both agents provided the benefits of prompt relief afforded by BW942C and lasting relief afforded by TMP-SMX. BW942C might prove to be an agent suitable for the treatment of acute diarrhea, with TMP-SMX reserved for treatment of those who do not respond adequately. The empiric use of the combination of BW942C and TMP-SMX appears appropriate for the treatment of severe nondysenteric disease.

Western blot analysis of intestinal secretory immunoglobulin A response to Campylobacter jejuni antigens in patients with naturally acquired Campylobacter enteritis

Secretory immunoglobulin A (sIgA) response at the intestinal mucosa is a primary defense against enteric infections. We sought to determine which antigens of Campylobacter jejuni outer membranes elicited sIgA responses in 8 patients with naturally acquired Campylobacter enteritis using Western blot analysis of fecal extracts. Naturally acquired Campylobacter infection elicited an sIgA response in 7 of 8 patients. Of these 7 patients, 5 had Campylobacter-specific sIgA titers of 1:16 and two had titers of 1:64. The C. jejuni antigens eliciting sIgA production varied, but 5 of 8 patients exhibited reactions to a 63-kilodalton flagellar antigen, and 7 of 8 patients had a reaction with a 58- and a 44-kilodalton antigen of C. jejuni and Campylobacter coli. Reaction with a 14.5- and a 97-kilodalton antigen was observed with the only stool that contained gross blood and mucus. Reactions with Campylobacter antigens were not detected in the fecal extracts of 5 healthy individuals. Identification of the antigens of C. jejuni that elicit an sIgA response may help us to better understand the immunology of Campylobacter enteritis and to identify antigens that are important in vaccine development.