Computer simulation of alternative sampling strategies to estimate risk of infection from Cryptosporidium

Estimation of acceptably safe levels of biological contaminants in drinking water requires fitting a mathematical model to infection rates observed in small samples of human subjects. Because of obvious constraints on exposing human subjects to infective conditions, it is not feasible to compare the utilities of alternative sampling strategies and research designs using data from real experiments. Computer simulation methods were used to generate sample data having known probabilities of infection determined by an exponential or log-linear infectivity model. Experimental conditions that were examined included variations in the total available sample size, strategies for allocating subjects among different test concentrations, and methods for fitting a prediction model to the observed data. Results confirmed that data obtained by exposing most subjects to a concentration that produces an infection rate approximating 50% and calculating the sample regression coefficient for the log-linear model as the average infectivity-to-concentration ratio provided the best estimates of safe concentration. Exposing a single subject to each successively higher test level until an initial infection is observed, and exposing all remaining subjects at that level, or an adjacent log-concentration level is a tactic supported by the empirical results.

Travellers' diarrhoea

Although TD is usually a mild and self-limited illness, 30-50% of travellers from industrialized to less developed countries are affected. Enterotoxigenic E. coli (ETEC) remain the most frequent cause, being identified in 40-70% of cases. TD frequently occurs within the first 2 weeks of arrival in the foreign country. The clinical manifestation is variable, but watery diarrhoea is the most common clinical presentation. Chronic diarrhoea or remitting symptoms after empirical therapy in the returning traveller are indications for a stool culture and a careful search for stool parasites. Since the major precaution against TD is to avoid exposure to the infectious agents, careful selection of food and beverage is crucial. Bismuth subsalicylate has been proven to be safe and effective in the treatment and prophylaxis of TD. The tablet form has removed the inconvenience of previously required luggage space. Doxycycline, trimethoprim/sulphamethoxazole, trimethoprim and the quinolones have been shown to be effective for prevention of diarrhoea. However, side-effects, superinfection, development of antibiotic resistance and easy-to-treat illness may limit the use of these antimicrobial agents to those travellers with concomitant serious medical conditions that would be adversely affected by diarrhoea, or travellers with unaffordable temporary incapacity. A new oral-killed whole-cell and B-subunit cholera toxin vaccine was demonstrated to induce protection against severe ETEC-associated diarrhoea. This is a promising field under investigation. Finally, fluid replacement is the most important aspect of treatment. Patients with moderate to severe TD can be treated with one of the above-mentioned antimicrobial agents for 3-5 days. Selection of the antimicrobial agent is based on the pattern of resistance and the enteric organism prevalent in the geographical area. While TMP-SMX remains active against the strains prevalent in Mexico during summertime, the quinolones represent the choice for the therapy of diarrhoea acquired in the high-risk areas of South America, Africa and Asia.

Treatment of travellers' diarrhoea with fleroxacin: a case study

A double-blind, randomized, placebo-controlled trial was conducted to evaluate the efficacy and safety of fleroxacin for one or two days as treatment for patients with travellers' diarrhoea. A total of 195 patients who were suffering with acute diarrhoea of less than six days' duration were enrolled. One hundred and fifty-one patients, of whom 49 received placebo, 54 received fleroxacin 400 mg for one day and 48 received fleroxacin 400 mg for two days, were included in the analysis of efficacy. The results showed that fleroxacin was significantly superior to placebo, but that there was no significant difference in terms of efficacy between the one- and two-day regimens. Adverse events, particularly minor neuropsychiatric disturbances such as headache and insomnia, were significantly more common amongst patients receiving active treatment. In conclusion, a single dose of fleroxacin 400 mg could be recommended as self-treatment for visitors to high-risk countries who develop travellers' diarrhoea.

Efficacy and toxicity of fleroxacin in the treatment of travelers' diarrhea

The efficacy and safety of fleroxacin in brief self-treatment of travelers' diarrhea were studied. In The Gambia, 195 tourists with acute diarrhea were randomized in a double-blind, controlled trial into three treatment groups: fleroxacin 400 mg for 1 day, fleroxacin 400 mg daily for 2 days, and placebo. Microbiology of stools was assessed only at recruitment. In the fleroxacin-treated groups, stool consistency was normal in 67% and 71% of the volunteers after 48 hours, as compared to 37% in the placebo group (p < 0.01). The time to total relief of diarrhea and of all symptoms was also significantly shorter in fleroxacin-treated patients. Adverse events, particularly slight neuropsychiatric reactions (headache, insomnia) were more frequent in the fleroxacin-treated groups (p < 0.05). There was no statistically significant difference in efficacy and tolerance if fleroxacin was administered for 1 or 2 days. A single dose of fleroxacin 400 mg may be recommended for the self-treatment of travelers' diarrhea.

Zaldaride maleate, an intestinal calmodulin inhibitor, in the therapy of travelers' diarrhea

BACKGROUND

The therapeutic value of zaldaride maleate (Zm), an intestinal calmodulin inhibitor, was examined in patients with travelers' diarrhea, known to be caused by enterotoxigenic Escherichia coli (ETEC) and other bacterial agents.

METHODS

One hundred seventy-six American students acquiring diarrhea in Mexico during the summer of 1991 were given Zm in doses of 5 mg, 10 mg, or 20 mg, or a matching placebo, four times a day for 48 hours.

RESULTS

The duration of diarrhea was reduced by 53% in the group given the 20-mg Zm dose (overall P < 0.01). Curative antibiotics were required post-treatment only in the placebo and 5-mg Zm groups (P < 0.01). The number of unformed stools passed during 0-48 hours of therapy with the highest Zm dose was reduced compared with placebo by 36% for all subjects (P < 0.05), by 39% for ETEC diarrhea (NS), by 45% for those with any bacterial agents (NS), and by 38% for those without an identifiable bacterial agent (NS).

CONCLUSIONS

The fact that a calmodulin inhibitor decreases the severity and duration of travelers' diarrhea has therapeutic implications and suggests that calmodulin and intracellular calcium may serve as mediators of diarrhea in bacterial enteric infection.

Case definitions for paediatric AIDS: the Zambian experience

For the purpose of surveillance of the acquired immunodeficiency syndrome (AIDS) in developing countries, the World Health Organization (WHO) has recommended criteria for the clinical case definition of AIDS in adults and children. In a preliminary examination of children in Zambia a number of patients with obvious AIDS did not fit the published WHO case definition for paediatric AIDS. Based on this the Zambia National AIDS Surveillance Committee designed local criteria for the clinical case definition of paediatric AIDS. We compared the Zambian criteria with the WHO criteria for the diagnosis of paediatric AIDS by studying 134 consecutively admitted children to one of the paediatric wards at the University Teaching Hospital in Lusaka. Twenty-nine of the patients were HIV-1 seropositive and 105 were HIV-1 seronegative. Among the 29 HIV-seropositive patients, the Zambian criteria identified 23, and the WHO criteria identified 20 children as having AIDS. The 105 HIV-seronegative children were classified as having AIDS in 9 cases by the Zambian criteria and in 38 cases by the WHO criteria. These results give the Zambian criteria for the diagnosis of AIDS a sensitivity of 79.3%, a specificity of 91.4% and a positive predictive value of 86.8% compared to a sensitivity of 69%, specificity of 64% and a positive predictive value of 38% for the WHO criteria. The current WHO criteria are inadequate for the diagnosis of paediatric AIDS. The need to refine the WHO criteria for the diagnosis of paediatric AIDS is discussed.

Quinolones in Salmonella typhi infection

The quinolones possess a high degree of in vitro activity against enteric bacteria, including Salmonella. This observation, coupled with the limitations of current antityphoid agents, has resulted in the evaluation of quinolones in the therapy of S. typhi infection, including both enteric fever and chronic intestinal carriage. In open uncontrolled trials, norfloxacin, ciprofloxacin, ofloxacin and pefloxacin have been used successfully to treat more than 200 patients with culture-proven typhoid fever. In comparative clinical trials, ciprofloxacin, ofloxacin, pefloxacin or fleroxacin were equivalent or superior to standard antityphoid therapy. In separate studies, norfloxacin and ciprofloxacin were each effective in eliminating intestinal excretion of S. typhi in chronic carriers. Because of increasing resistance worldwide to conventional antityphoid drugs, and in view of the efficacy of the quinolones in the therapy of both typhoid fever and typhoid intestinal carriage, these drugs may become the treatment of choice for these important enteric infections.

Optimal dosing of trimethoprim-sulfamethoxazole when used with loperamide to treat traveler's diarrhea

To explore the optimal dosing regimen for trimethoprim-sulfamethoxazole (TMP-SMX) when used in combination with loperamide to treat traveler's diarrhea, 190 U.S. adults with acute diarrhea were enrolled in a double-blind, randomized trial in Guadalajara, Mexico. All patients received loperamide (4-mg loading dose; 2 mg after each loose stool, not to exceed 16 mg/day for 3 days) and were randomized to receive a 3-day course of TMP-SMX (160:800 mg twice daily for six doses) (group A), a single large dose of TMP-SMX (320:1,600 mg) (group B), or a large loading dose (320:1,600 mg) followed by standard doses for 3 days (160:800 mg twice daily for five doses) (group C). Patients in group C responded best (P < 0.01), with 75% of subjects recovered from diarrhea in 12 h compared with 34 h (group A) and 33 h (group B). Similar differences in favor of group C were noted in the subset of patients who presented with moderate to severe diarrhea. On average, patients in group C took significantly (P < 0.05) less loperamide (1.2 mg) after the 4-mg loading dose compared with patients in group A (2.4 mg) or group B (2.0 mg). We conclude that the most efficacious treatment of traveler's diarrhea in the interior of Mexico is to take loperamide in usual doses to control symptoms in combination with a single large dose of TMP-SMX, which should then be continued for 3 days in standard doses.

Prelacteal infant feeding practices in rural Egypt

Data collected during a prospective cohort study of infant feeding and health in rural Bilbeis, Egypt, were analysed to define prelacteal infant feeding practices, identify their determinants, and assess whether these practices were predictive of breastfeeding and supplementation patterns and diarrhoea incidence during infancy. Sixty per cent (89/149) of study infants were prelacteally fed sugar-water, teas, or both. Lack of milk in the mother's breast (74 per cent), and maternal exhaustion or illness following labour (29 per cent) were the two most commonly stated reasons for prelacteal feeding. After multivariate adjustment, significantly higher incidence of prelacteal feeding was associated with childbirth during the warmer months [odds ratio (OR): 2.4; 95 per cent confidence interval (CI): 1.1-5.1], birth attendants with modern training (OR: 5.5; 95 per cent CI: 1.7-17.5), and labour lasting > 8 hours (OR: 2.3; 95 per cent CI: 0.1-4.9). Prelacteally fed infants were significantly less likely to be exclusively breastfed in age periods 0-3, 4-7, and 8-11 weeks. Diarrhoea incidence was higher among prelacteally fed infants in age periods 0-11, 12-23, and 36-47 weeks. Indiscriminate practice of prelacteal feeding and early supplementation of breastfeeding need to be discouraged.

Evaluation of new anti-infective drugs for the treatment of antibiotic-associated colitis. Infectious Diseases Society of America and the Food and Drug Administration

Colitis due to Clostridium difficile is diagnosed in 10%-15% of hospitalized patients who develop diarrhea after treatment with antimicrobial drugs. Diagnosis is based on the concurrence of diarrhea, one or more signs or symptoms of enteric intoxication, and stool from which toxigenic C. difficile is isolated or from which its toxins are identified. Clinical trials evaluating therapy may be placebo controlled (for mild disease) or concurrently controlled with an active drug. A randomized, double-blind study design is preferred. Outcome should be assessed by monitoring of the degree of inflammation of the bowel mucosa, the intensity and severity of diarrhea, the duration of illness, changes in stool form, and the eradication of C. difficile or its toxins from stool. Because C. difficile can be a component of the normal gastrointestinal flora, assessment of clinical outcome is paramount.

Evaluation of new anti-infective drugs for the treatment of acute infectious diarrhea. Infectious Diseases Society of America and the Food and Drug Administration

This guideline includes diarrhea causing infantile mortality in which a bacterial pathogen is recovered and for which oral rehydration therapy is an important component of care as well as traveler's diarrhea (with or without recovery of a pathogen). Diarrhea is defined as the passage of three or more unformed stools per day plus--in all patients except infants--one or more signs or symptoms of enteric infection. The preferred study design is prospective and randomized, with an active concurrent control and (when possible) blinding. Placebo-controlled trials may be performed if the severity of disease is judged by the investigator to be mild or moderate. It is desirable that both clinical and microbiological outcome be determined. Microbiological eradication is paramount.

Evaluation of new anti-infective drugs for the treatment of diarrhea caused by Cryptosporidium. Infectious Diseases Society of America and the Food and Drug Administration

Cryptosporidium is a coccidian protozoan that produces symptoms by infesting the small bowel. The illness is characterized by watery stools, anorexia, weight loss, and abdominal pain. Diagnosis is made by visualization of the organisms on microscopic examination of stool. There currently is no approved therapy for this infection. A randomized, double-blind, placebo-controlled study design is recommended. Stratification of patients by age and immune status should be considered. Two stool samples obtained 48 hours to 7 days after completion of therapy should be negative for Cryptosporidium oocysts. Assessment of microbiological outcome is paramount.

Evaluation of new anti-infective drugs for the treatment of typhoid fever. Infectious Diseases Society of America and the Food and Drug Administration

Typhoid fever is an acute febrile illness caused by Salmonella typhi. The evidence of blood-borne infection required for study entry includes clinical signs and symptoms plus confirmation of the presence of S. typhi in blood or other tissues or body fluids. The preferred study design is prospective and randomized with an active concurrent control. It is preferred that the investigator or an evaluator be blinded to therapy. In general, treatment should be administered for 2 weeks until it is demonstrated that a shorter course is as efficacious and as safe. Follow-up cultures of specimens from sites originally shown to be infected with S. typhi should be performed unless the diagnostic procedure places the patient at unnecessary risk.

Evaluation of new anti-infective drugs for the treatment of chronic carriage of Salmonella. Infectious Diseases Society of America and the Food and Drug Administration

The chronic carriage of salmonellae is defined as the shedding of a Salmonella species for > or = 1 year, as documented by an initial positive culture of a stool sample obtained at least 1 month after resolution of the acute illness and repeated positive cultures for at least 1 year. Clinical trials of investigational anti-infective drugs for the treatment of the salmonella carrier state may be conducted with a placebo control or an active concurrent control. A crossover design also may be employed for establishing efficacy. Patients should generally receive therapy for at least 6 weeks. Outcome will be assessed only by microbiological criteria. Determination of the interval required for the suppression of salmonellae and follow-up for 6 months after completion of therapy are recommended.

Evaluation of new anti-infective drugs for the treatment of diarrhea caused by Entamoeba histolytica. Infectious Diseases Society of America and the Food and Drug Administration

Entamoeba histolytica causes colonic infection that ranges from asymptomatic carriage to invasive disease with infection of extraintestinal organs, particularly the liver. The disease occurs in both sporadic and epidemic forms. Diagnosis requires visualization of trophozoites or cysts by microscopic examination of stool, colonic scrapings, or biopsy specimens. Patients with either asymptomatic or symptomatic disease may be eligible for clinical trials. A prospective, randomized, double-blind, placebo-controlled study design is recommended for asymptomatic carriers and an active-concurrent-control study design for symptomatic patients. Final outcome should be assessed 48 hours to 7 days after completion of therapy. Assessment of microbiological outcome is paramount.

Evaluation of new anti-infective drugs for the treatment of gastritis and peptic ulcer disease associated with infection by Helicobacter pylori. Infectious Diseases Society of America and the Food and Drug Administration

Helicobacter pylori is a gram-negative, microaerophilic, spiral bacillus. Infection by this organism is currently believed to be the major cause of type B gastritis. Inflammation and infection may persist for years in the absence of therapeutic intervention. There is currently no approved antimicrobial therapy for gastritis. Clinical investigations have shown that combination regimens including bismuth salts and antimicrobial drugs result in the relief of symptoms, the resolution of histologic evidence of gastritis, the eradication of H. pylori, high rates of ulcer healing, and lower rates of ulcer relapse than have been found with other therapies (antacids and H2 antagonists). A randomized, double-blind, placebo-controlled study design is recommended for evaluation of new therapies. Study participants should have their progress monitored by endoscopy performed at enrollment, at completion of therapy, and 3 months thereafter. Assessment of microbiological outcome is paramount for final evaluation of the patient.

Evaluation of new anti-infective drugs for the treatment of cholera. Infectious Diseases Society of America and the Food and Drug Administration

Cholera is an acute gastrointestinal infection caused by Vibrio cholerae. It is characterized by watery diarrhea that may lead to massive fluid loss, which in turn may result in hypotension, shock, and death within hours. Key to the treatment of cholera is fluid replacement. Anti-infective therapy decreases the severity and duration of diarrhea and the duration of shedding of V. cholerae. Enrolled patients should have diarrhea that is moderate to severe and a culture that ultimately yields V. cholerae. A prospective, randomized, active-controlled clinical trial is preferred. Studies should be double-blinded or evaluator-blinded. The rapidity with which the organism is eliminated from stool may be assessed. Both clinical and microbiological outcome should be determined. Assessment of microbiological eradication is paramount, since fluid replacement may suffice for treatment of signs and symptoms.

Evaluation of new anti-infective drugs for the treatment of diarrhea caused by Giardia lamblia. Infectious Diseases Society of America and the Food and Drug Administration

Giardia lamblia is a flagellate protozoan that produces symptoms by infecting the small bowel and biliary tract in the trophozoite form. Diagnosis is currently established by microscopic visualization of the organism in appropriate intestinal contents (stool, small-bowel contents, or biopsy specimen). Adult patients with diarrhea and one or more enteric symptoms may be enrolled in clinical trials of new drugs for the treatment of giardial disease. A randomized, double-blind, active-concurrent-control design is recommended. Post hoc stratification by age, immune status, chronicity of disease, and ease of establishing diagnosis (organism load) may be performed. Microbiological assessment 48 hours to 7 days after the completion of therapy is paramount for determining final outcome.

Oral aztreonam, a poorly absorbed yet effective therapy for bacterial diarrhea in US travelers to Mexico

OBJECTIVE

To evaluate a poorly absorbed antimicrobial with in vitro activity against all major bacterial enteropathogens in oral therapy for bacterial diarrhea.

DESIGN

One hundred ninety-one US students with diarrhea acquired in Mexico received 100 mg of aztreonam or matching placebo three times a day for 5 days. Stools were cultured for bacterial enteropathogens before and after therapy.

SETTING

We studied US students who acquired diarrhea in Mexico (travelers' diarrhea) in view of the high frequency of bacterial agents in this setting.

MAIN OUTCOME MEASURE

We examined time of clinical recovery, treatment failures, adverse experiences, and microbiologic eradication from stool of the etiologic agent in subjects randomized to receive aztreonam or placebo.

RESULTS

Aztreonam reduced the average duration of diarrhea compared with the placebo: for all cases, by 40 hours (P much less than .01); for those with enterotoxigenic Escherichia coli diarrhea, by 50 hours (P less than .01); for those with shigellosis, by 90 hours (P, not significant [small sample size]); for all bacterial agents, by 57 hours (P much less than .01). Clinical failures during the 5 days of therapy were seen in six patients (6%) receiving aztreonam and 25 (27%) receiving placebo (P less than .01). Pathogen eradication occurred in 95% of those receiving aztreonam and in 70% of those receiving the placebo (P less than .01). All bacterial enteropathogens were susceptible in vitro to aztreonam. The drug was well tolerated.

CONCLUSIONS

Oral aztreonam, which is poorly absorbed, was well tolerated and was an effective therapy for bacterial diarrhea in US adults in Mexico.

Molecular characterization of strains of enteroinvasive Escherichia coli O143, including isolates from a large outbreak in Houston, Texas

A large diarrhea outbreak due to enteroinvasive Escherichia coli (EIEC) serogroup O143 occurring in Houston, Tex., provided the opportunity to investigate aspects of the molecular epidemiology of this and related organisms. This was done by comparing the plasmid patterns and the chromosomal restriction endonuclease digestion patterns by pulsed-field gel electrophoresis (PFGE) of EIEC from the outbreak, other E. coli from the same serogoup (O143), and EIEC isolated from other patients with diarrhea. Among the isolates studied, there was marked restriction fragment length polymorphism. All 3 non-O143 EIEC isolates had very different restriction endonuclease digestion patterns, as did 5 of 5 O143 non-EIEC isolates and 6 of 15 O143 EIEC isolates. Four Houston outbreak O143 EIEC isolates had the same restriction pattern as an O143 EIEC strain isolated 2 months before in Mexico and was nearly identical to another two O143 EIEC Mexican isolates. These related strains also had the same plasmid pattern; however, the presence of only a few plasmid bands, versus the 21 to 30 chromosomal bands seen with PFGE, suggests that plasmid patterns could be a less specific way to distinguish different strains. These results demonstrate that PFGE can distinguish between different E. coli strains of the same serogroup and phenotype. This technique can also identify relatedness within O143 EIEC, and our data suggest the spread of a strain of EIEC from Mexico to Houston, where it caused a large outbreak. PFGE may be useful to study the epidemiology of EIEC.

Antimicrobial therapy of bacterial diarrhea in adult residents of Mexico--lack of an effect

Two clinical trials in adults in Mexico are reported. In the first trial, long-term residents of Mexico with acute fecal leukocyte-positive diarrhea were randomized to receive trimethoprim/sulfamethoxazole (TMP/SMX), clioquinol or a placebo. Neither antimicrobial shortened the illness for all cases or for those with shigellosis or enterotoxigenic Escherichia coli diarrhea. In a second study, US and Mexican students received enoxacin, TMP/SMX or a placebo on a blind random basis. While the placebo-treated subjects with bacterial diarrhea tended to be more ill after treatment than other groups, no statistical differences were seen in treatment groups. These studies cast doubts on the value of antimicrobial drugs for 'invasive' and other forms of bacterial diarrhea in adults living in endemic areas and indicate the importance of a placebo control group when conducting clinical trials in these populations.