Bacillary dysentery: mechanisms and treatment

Citrulline and kynurenine to tryptophan ratio: potential EED (environmental enteric dysfunction) biomarkers in acute watery diarrhea among children in Bangladesh

Two emerging biomarkers of environmental enteric dysfunction (EED) include plasma citrulline (CIT), and the kynurenine (KYN): tryptophan (TRP)/ (KT) ratio. We sought to investigate the plasma concentration of CIT and KT ratio among the children having dehydrating diarrhea and examine associations between concentrations of CIT and KT ratio with concurrent factors. For this analysis, we used cross-sectional data from a total of 102, 6-36 months old male children who suffered from non-cholera acute watery diarrhea and had some dehydration admitted to an urban diarrheal hospital, in Bangladesh. CIT, TRP, and KYN concentrations were determined at enrollment from plasma samples using ELIZA. At enrollment, the mean plasma CIT concentration was 864.48 ± 388.55 µmol/L. The mean plasma kynurenine, tryptophan concentrations, and the KT ratio (× 1000) were 6.93 ± 3.08 µmol/L, 33.44 ± 16.39 µmol/L, and 12.12 ± 18.10, respectively. With increasing child age, KYN concentration decreased (coefficient: - 0.26; 95%CI: - 0.49, - 0.04; p = 0.021); with increasing lymphocyte count, CIT concentration decreased (coef.: - 0.01; 95% CI: - 0.02,0.001, p = 0.004); the wasted child had decreased KT ratio (coef.: - 0.6; 95% CI: - 1.18, - 0.02; p = 0.042) after adjusting for potential covariates. The CIT concentration was associated with blood neutrophils (coef.: 0.02; 95% CI: 0.01, 0.03; p < 0.001), lymphocytes (coef.: - 0.02; 95% CI: - 0.03, - 0.02; p < 0.001) and monocyte (coef.: 0.06; 95% CI: 0.01, 0.11; p = 0.021); KYN concentration was negatively associated with basophil (coef.: - 0.62; 95% CI: - 1.23, - 0.01; p = 0.048) after adjusting for age. In addition, total stool output (gm) increased (coef.: 793.84; 95% CI: 187.16, 1400.52; p = 0.011) and also increased duration of hospital stay (hour) (coef.: 22.89; 95% CI: 10.24, 35.54; p = 0.001) with increasing CIT concentration. The morphological changes associated with EED may increase the risk of enteric infection and diarrheal disease among children. Further research is critically needed to better understand the complex mechanisms by which EED biomarkers may impact susceptibility to dehydrating diarrhea in children.

Association between meteorological factors and bacillary dysentery incidence in Chaoyang city, China: an ecological study

OBJECTIVES

To quantify the relationship between meteorological factors and bacillary dysentery incidence.

DESIGN

Ecological study.

SETTING

We collected bacillary dysentery incidences and meteorological data of Chaoyang city from the year 1981 to 2010. The climate in this city was a typical northern temperate continental monsoon. All meteorological factors in this study were divided into 4 latent factors: temperature, humidity, sunshine and airflow. Structural equation modelling was used to analyse the relationship between meteorological factors and the incidence of bacillary dysentery.

MATERIAL

Incidences of bacillary dysentery were obtained from the Center for Disease Control and Prevention of Chaoyang city, and meteorological data were collected from the Bureau of Meteorology in Chaoyang city.

PRIMARY OUTCOME MEASURES

The indexes including χ², root mean square error of approximation (RMSEA), comparative fit index (CFI), standardised root mean square residual (SRMR) and goodness-of-fit index (GFI) were used to evaluate the goodness-of-fit of the theoretical model to the data. The factor loads were used to explore quantitative relationship between bacillary dysentery incidences and meteorological factors.

RESULTS

The goodness-of-fit results of the model showing that RMSEA=0.08, GFI=0.84, CFI=0.88, SRMR=0.06 and the χ² value is 231.95 (p=0.0) with 15 degrees of freedom. Temperature and humidity factors had positive correlations with incidence of bacillary dysentery, with the factor load of 0.59 and 0.78, respectively. Sunshine had a negative correlation with bacillary dysentery incidence, with a factor load of -0.15.

CONCLUSIONS

Humidity and temperature should be given greater consideration in bacillary dysentery prevention measures for northern temperate continental monsoon climates, such as that of Chaoyang.

An environmental Escherichia albertii strain, DM104, induces protective immunity to Shigella dysenteriae in guinea pig eye model

The environmental Escherichia albertii strain DM104, which cross-reacts serologically with Shigella dysenteriae was assessed for pathogenic properties, immunogenicity, and protective efficacy in different animal models to evaluate it as a vaccine candidate against S. dysenteriae, which causes the severe disease, shigellosis. The DM104 isolate was found to be non-invasive and did not produce any entero- or cyto-toxins. The strain also showed negative results in the mouse lethal activity assay. The non-pathogenic DM104 strain gave, however, a high protective efficacy as an ocularly administered vaccine in the guinea pig eye model against S. dysenteriae type 4 challenge. It also induced a high titer of serum IgG against S. dysenteriae type 4 whole cell lysate and lipopolysaccharide. Taken together, all these results indicate a good potential for the use of the DM104 as a live vaccine candidate against shigellosis.

Survival of Salmonella Typhi and Shigella dysenteriae in dehydrated infant formula

Powdered infant formula has previously been linked to the transmission of various bacterial pathogens in infants resulting in life-threatening disease and death. Survival studies of 2 common foodborne pathogens, Salmonella enterica serovar Typhi and Shigella dysenteriae, in powdered infant formula have not been previously studied despite the potentially devastating consequences from ingestion of these organisms, particularly by newborns, in case of a natural or deliberate contamination event. Therefore, to better predict the risk of S. Typhi and S. dysenteriae infection from consumption of infant formula, the present study was undertaken to determine survival of these microorganisms in dry infant formula under varying atmospheric conditions. A 2-strain cocktail of S. Typhi and a 3-strain cocktail of S. dysenteriae were stored for up to 12 wk in dehydrated infant formula in an ambient air or nitrogen atmosphere. Viable counts of S. Typhi at 12 wk in infant formula revealed a 2.9- and 1.69-log decrease in ambient air and nitrogen atmosphere, respectively. Viable counts of S. dysenteriae at 12 wk in infant formula revealed a 0.81- and 0.42-log decrease in ambient air and nitrogen atmosphere, respectively. These results show that S. Typhi and S. dysenteriae can remain viable for prolonged periods of time in powdered infant formula, and the presence of nitrogen enhances survival.

PRACTICAL APPLICATION

Our goal in this work was to study the survival of S. Typhi and S. dysenteriae in dehydrated storage conditions in infant formula. This interest is partially generated by the possibility of using these 2 microorganisms to deliberately contaminate the food supply. The outcome of this study will help us to have a better idea how to respond and react to the risk of deliberate food contamination.

Core-linked LPS expression of Shigella dysenteriae serotype 1 O-antigen in live Salmonella Typhi vaccine vector Ty21a: Preclinical evidence of immunogenicity and protection

Shigella dysenteriae serotype 1 (S. dysenteriae 1) causes severe shigellosis that is typically associated with high mortality. Antibodies against Shigella serotype-specific O-polysaccharide (O-Ps) have been shown to be host protective. In this study, the rfb locus and the rfp gene with their cognate promoter regions were PCR-amplified from S. dysenteriae 1, cloned, and sequenced. Deletion analysis showed that eight rfb ORFs plus rfp are necessary for biosynthesis of this O-Ps. A tandemly-linked rfb-rfp gene cassette was cloned into low copy plasmid pGB2 to create pSd1. Avirulent Salmonella enterica serovar Typhi (S. Typhi) Ty21a harboring pSd1 synthesized S. Typhi 9, 12 LPS as well as typical core-linked S. dysenteriae 1 LPS. Animal immunization studies showed that Ty21a (pSd1) induces protective immunity against high stringency challenge with virulent S. dysenteriae 1 strain 1617. These data further demonstrate the utility of S. Typhi Ty21a as a live, bacterial vaccine delivery system for heterologous O-antigens, supporting the promise of a bifunctional oral vaccine for prevention of shigellosis and typhoid fever.

Parameters underlying successful protection with live attenuated mutants in experimental shigellosis

Because the use of live attenuated mutants of Shigella spp. represents a promising approach to protection against bacillary dysentery (M. E. Etherridge, A. T. M. Shamsul Hoque, and D. A. Sack, Lab. Anim. Sci. 46:61-66, 1996), it becomes essential to rationalize this approach in animal models in order to optimize attenuation of virulence in the vaccine candidates, as well as their route and mode of administration, and to define the correlates of protection. In this study, we have compared three strains of Shigella flexneri 5--the wild-type M90T, an aroC mutant, and a double purE aroC mutant--for their pathogenicity, immunogenicity, and protective capacity. Protection against keratoconjunctivitis, induced by wild-type M90T, was used as the protection read out in guinea pigs that were inoculated either intranasally or intragastrically. Following intranasal immunization, the aroC mutant elicited weak nasal tissue destruction compared to M90T and achieved protection correlated with high levels of local anti-lipopolysaccharide immunoglobulin A (IgA), whereas the purE aroC double mutant, which also elicited weak tissue destruction, was not protective and elicited a low IgA response. Conversely, following intragastric immunization, only the M90T purE aroC double mutant elicited protection compared to both the aroC mutant and the wild-type strain. This mutant caused mild inflammatory destruction, particularly at the level of Peyer's patches, but it persisted much longer within the tissues. This could represent an essential parameter of the protective response that, in this case, did not clearly correlate with high anti-lipopolysaccharide IgA titers.

Shigella infection as observed in the experimentally inoculated domestic pig, Sus scrofa domestica

The domestic pig, Sus scrofa domestica, was investigated as a potential animal model for shigellosis. We examined the effects of pig age, pig breed and antibiotic pretreatment upon Shigella infection. Shigella dysenteriae, and Shigella flexneri (both virulent and avirulent strains) were utilized. Our results indicated that young (4-week-old), conventionally re ared, domestic pigs were routinely, but briefly, colonized (average=3.5+/-2.5 days) following oral or gavage administration ofS. flexneri, as determined by direct rectal cultures. The duration of S. dysenteriae colonization was significantly shorter. Inoculation of younger (2 days) or older (9 weeks) pigs with S. flexneri had no significant effect on infection duration. Similarly, infection of 4-week-old pigs with virulent and avirulent strains of S. flexneri had no effect upon the duration of infection, nor did the use of a swine-passaged S. flexneri isolate. Marked clinical, histopathological (gross and microscopic) and immunoIhistopathological signs of disease were absent in all infections. However, in instances where microscopic histopathological evidence was used to correctly identify infected pigs, tonsillar lesions were the consistently noted criteria. The tonsils are believed to be an important portal of entry for Salmonella choleraesuis, another member of the Enterobacteriaceae and a prevalent pig pathogen. Taken altogether, our results indicate that the domestic pig is unsuitable as a model for shigellosis.

Diarrheal epidemics among Rwandan refugees in 1994. Management and outcome in a field hospital

We describe the clinical course and outcome of Rwandan refugees with cholera-like illness (n = 567) and clinical dysentery (n = 1,062) treated at the Israeli Army field hospital in the disaster region of Goma, Zaire, during the summer of 1994. Vigorous fluid administration was the primary therapy, complemented with antibiotics for patients with presumed Shigella infection. Recovery rates were 94% and 96% for patients with cholera and dysentery, respectively. Mortality was substantially affected by comorbid conditions such as pneumonia and meningitis, which occurred in one-quarter of these patients. Infective, metabolic, and surgical complications (including three cases of intussusception) may have contributed to the deaths. The outcome of patients during diarrheal epidemics of cholera or bacillary dysentery may be favorable, even in disaster settings, if patients are evacuated promptly to medical facilities and appropriate therapy is instituted. We close with general observations on procedures to be followed in future epidemics of diarrheal diseases.

Construction and characterization of genetically-marked bivalent anti-Shigella dysenteriae 1 and anti-Shigella flexneri Y live vaccine candidates

Bivalent vaccine candidates were developed against Shigella dysenteriae 1 and Shigella flexneri, which are among the most frequent causative agents of shigellosis in developing countries. The rfp and rfb gene clusters, which code for S. dysenteriae serotype 1 O-antigen biosynthesis, were inserted into an arsenite resistance minitransposon and randomly integrated into the attenuated S. flexneri aroD serotype Y strain SFL124. Nine recombinant clones that efficiently expressed both homologous and heterologous O-antigens were obtained. Southern blot analysis showed that in one clone the S. dysenteriae 1 genes had integrated into the chromosome, whereas in all the others they had integrated into the virulence plasmid. All recombinant clones exhibited normal growth characteristics, were able to invade and survive within eukaryotic cells to the same extent as the parental strain, and expressed efficiently the recombinant lipopolysaccharide within invaded cells. Immunization of mice with two of the recombinant clones resulted in the production of antibodies specific for both homologous and heterologous O-antigens. The recombinant clones constitute promising vaccine candidates which can readily be distinguished from endemic shigellae by their non-antibiotic resistance marker.

Construction and characterization of a live attenuated vaccine candidate against Shigella dysenteriae type 1

Vaccine candidates against Shigella dysenteriae type 1, which is associated with the most severe cases of bacillary dysentery, were constructed. The rfp and rfb gene clusters, which code for S. dysenteriae 1 O antigen biosynthesis, were randomly integrated into either the chromosome or the virulence plasmid of the rough attenuated Shigella flexneri aroD strain SFL124-27 with a minitransposon carrying an arsenite resistance selection marker. The recombinant clones efficiently expressed the recombinant O antigen, exhibited a normal growth pattern, were able to invade and survive within eukaryotic cells to the same extent as the parental strain, and expressed the recombinant antigen within invaded cells. A clone was selected as the vaccine candidate, which was demonstrated to be immunogenic and safe in animal models, leading to 47% full protection and 53% partial protection against challenge with the wild-type strain.

Significance of the secreted form of IpaC, a 45 kDa protein of Shigella dysenteriae 1, in the invasive process as determined by monoclonal antibodies

Invasion plasmid antigen C (IpaC), a 45 kDa plasmid encoded protein, is associated with the virulence of virulent Shigella spp. In S. dysenteriae type 1 the 45 kDa IpaC protein is secreted to a greater extent into the surrounding medium in comparison to other Shigella spp. Monoclonal antibodies (mAbs) to the secreted form of IpaC protein were raised in this study. Of the four secretory hybrid cells, one (3G4) was found to have a very high antibody titre as determined by ELISA. The specificity of 3G4 was confirmed by immunoblotting of whole cell extract of Escherichia coli strain MC1061 carrying the plasmid pHW756 which synthesizes both the IpaB and C proteins. The effect of the mAbs on plaque formation by virulent Shigella dysenteriae 1 was determined and it was found that the clone 3G4 substantially (55%) reduced plaque formation on HeLa cell monolayer. The epitope specificity of the mAb 3G4 was competitively inhibited by the convalescent phase sera from human, suggesting that the epitope recognized by clone 3G4 was expressed during the natural course of infection and also indicating that the 45 kDa (IpaC) protein in secreted form has a definite role in the invasive process.

Protective ribosomal preparation from Shigella sonnei as a parenteral candidate vaccine

A parenteral Shigella ribosomal vaccine (SRV) was investigated in animals for safety, antibody-inducing capacity, and protective activity. Ribosomal preparations from a Shigella sonnei phase I avirulent strain were obtained and shown to possess chemical, sedimentation, and other properties typical of bacterial ribosomes. No endotoxin contamination was revealed by a ketodeoxyoctonate assay, although the presence of some kind of O antigen was evidenced by serological findings and the high activity of SRV in inducing the O-antibody response and immunological memory in animals. SRV was nontoxic in mice, guinea pigs, and monkeys and induced no local reactions when injected subcutaneously in reasonable doses. Significant protection against a local Shigella infection (Sereny test) was seen in guinea pigs injected with SRV (efficiency index, about 60%) and the specificity of the protection was evident from cross-challenge experiments. The protective efficiency of SRV was especially high in rhesus monkeys challenged orally with virulent Shigella cells (89%, as calculated from the summarized data of several experiments in 71 animals). Protection in monkeys was long lasting and could be demonstrated several months after injection of SRV. An inexpensive technique can be used for the production of SRV on a large scale. The high immunogenicity of SRV is discussed in terms of the amplifying effect of the ribosome, which serves as a delivery system for polysaccharide O antigen. Further study of SRV as a candidate vaccine for humans seems justified by the data obtained.

Nucleotide sequence of the ipaBCD structural genes of Shigella dysenteriae

A 9 kb EcoRI and two PstI fragments from the virulence plasmid of Shigella dysenteriae CG097 were shown to contain all ipa genes by probing with Shigella flexneri ipaB, -C, -D and -A gene probes. The DNA sequences of S. dysenteriae ipaBC genes were very similar to those of S. flexneri M90T and S. flexneri YSH6000, but ipaD differed by 22 codons from that of S. flexneri. The differences in ipaD may account for the different in vitro host specificities shown by S. dysenteriae and S. flexneri. The nucleotide composition of ipa genes revealed an unusually large number of codons that are rarely used in Escherichia coli chromosomal genes, indicating a different origin.

Admission to hospital with gastroenteritis

A prospective study over a one year period examined preadmission illness and its treatment, social characteristics and referral patterns, and inpatient illness progression in 1148 children admitted with a primary diagnosis of gastroenteritis. Admissions were predominantly from socially disadvantaged families: 712 (62%) from social classes IV and V. Approximately a quarter were referred with minimal symptoms, only 12 (1%) with moderate to severe dehydration, and eight (less than 1%) with hypernatraemia. One hundred and ninety two of 1101 (17%) had not seen their general practitioner during the acute illness. One third had received no treatment and one third inappropriate antibiotics, antidiarrhoeals, antiemetics, or changes of milk. Gastroenteritis is a less severe illness than formerly but remains a significant cause of paediatric morbidity. Suboptimal treatment is common. Improved local district hospital and community based resources are needed.

The prognosis of convulsions during childhood shigellosis

We examined the long-term outcome in 111 children who had convulsions during shigellosis and were followed for 3-18 years after the incident. No deaths or persistent motor deficits occurred as sequellae. Poor coordination of fine hand movements were noted in 3.3% of the 92 children who had no pre-existing neurological abnormality. Only 1 child developed epilepsy by the age of 8 years. Of the children 15.7% had recurrent febrile seizures. The only risk factor identified for febrile seizures following convulsions in shigellosis was a previous history (P less than 0.01). These observations suggest that convulsions in shigellosis have a favourable prognosis, and do not necessitate long-term follow up.

Expression of Shiga toxin epitopes in E. coli immunological characterization

Synthetic oligodeoxynucleotides encoding for two peptides corresponding to residues 9-21 and 19-31 in the amino acid sequence of the B subunit of Shiga toxin were prepared and inserted into pTOZ plasmid, in phase with the lacZ gene. The resultant vectors were used for transfection of E. coli. The bacteria containing the recombinant DNA expressed the respective peptides in the form of fusion proteins with beta-galactosidase. The N-terminal region of the Shiga toxin B subunit, containing the two peptides, was previously identified as a relevant epitope of the toxin, leading to the induction of neutralizing antibodies. The present study demonstrates that the bacterial extracts containing the fusion proteins as the products of the recombinant vectors, when used for immunization of rabbits, elicited a humoral immune response which was specific toward the respective peptides. Furthermore, the antibodies cross-reacted with the intact Shiga toxin.

General considerations in the management of typhoid fever and dysentery

Typhoid fever is diagnosed on the basis of isolation of Salmonella typhi from blood, bone marrow, or bile. S. typhi found in stool or urine may reflect chronic asymptomatic carriage. Although antimicrobial therapy may not eliminate carriage, it is effective for the treatment of clinically evident acute disease. Among the drugs currently available, chloramphenicol is the most widely used. Chloramphenicol is effective and inexpensive, but it is associated with a 3% rate of chronic carriage, a high relapse rate, and, in rare cases, aplastic anemia. For these reasons, and because of the emergence of chloramphenicol-resistant strains of S. typhi, alternative drugs need to be considered. Dysentery is characterized by the passage of unformed stools that commonly contain blood and mucus and in which large numbers of leukocytes can be detected on microscopic examination. Invasion of the intestinal epithelium is the distinguishing characteristic, and Shigella sp are the most frequent cause. Although oral rehydration is useful in dehydrated patients, dehydration is not a common problem in acute dysentery, and antimicrobial treatment is indicated for this disease. An antimicrobial agent should be selected on the basis of knowledge of the susceptibility patterns of locally isolated Shigella strains.

Development of an auxotrophic oral live Shigella flexneri vaccine

An oral live attenuated Shigella flexneri vaccine candidate strain was constructed by making it auxotrophic and dependent on aromatic metabolites not available in mammalian tissues. An aroD gene of Escherichia coli K12 strain NK 5131, inactivated by insertion in it of the Tn 10 transposon, was transduced using phage P1 into a virulent S. flexneri serotype Y strain (Sfl 1) isolated from a patient with bacillary dysentery. One of the transductant strains Sfl 114 was found to invade HeLa cells in vitro, to cause plaque formation in HeLa monolayers (i.e. maintain intracellular multiplication in vitro), but to be unable to cause keratoconjunctivitis in guinea-pig eyes. When the strain was fed to Macacca fascicularis monkeys it was well tolerated, excreted for 1-4 days, and found to elicit a local intestinal sIgA and serum IgA, IgM and IgG responses. Monkeys challenged with 100 ID50 dose (1 X 10(11) bacteria) of the virulent parent Sfl 1 strain were completely protected from development of diarrhoea. Coloscopy of the monkeys and the sampling of intestinal biopsies showed that the vaccine protected against the surface epithelial erosions and ulcerations seen in unimmunized monkeys. Killing of invading virulent shigellae apparently took place intracellularly in the mucosa suggesting that cellular immune mechanisms played a role in the elicited host defence. The constructed S. flexneri Sfl 114 strain has the properties of a promising shigella vaccine and will next be the subject of studies with human volunteers.

Analysis and genetic manipulation of Shigella virulence determinants for vaccine development

Shigellosis is a major public health problem in developing countries. Current epidemics of Shigella dysenteriae serotype 1 strains are particularly serious and are characterized by high mortality rates. A high proportion of the isolates are resistant to many of the antibiotics currently in use in these countries, a feature which seriously compromises clinical treatment of the infections. Efficacious vaccines are thus urgently needed. Basic studies on Shigella virulence factors, infections in laboratory models, and host responses has led to the development of several strategies for the production of vaccines. All of these are live oral vaccines involving bacteria capable of at least limited survival in the animal intestine and of carrying selected antigens to the mucosal immune system. One type of vaccine involves non-pathogenic shigellae, attenuated either by introduction of a requirement for aromatic amino acids (aroD) or by loss of the large plasmid that specifies bacterial invasion of the mucosal epithelium. S. dysenteriae 1 strains under development as vaccines need to be engineered to eliminate high level Shiga toxin production, and a rapid and effective method to achieve this was recently elaborated. The second type of vaccine is represented by hybrid strains consisting of a carrier organism, such as an attenuated Salmonella or an Escherichia coli K-12 strain carrying the Shigella invasion plasmid, and the selected foreign antigen that it produces, in all cases so far the Shigella O antigen polysaccharide.

Bacterial gastroenteritis

Acute diarrhea is a major cause of childhood morbidity. Important advances in the understanding of bacterial gastroenteritis have been made in the past two decades. This article reviews the epidemiology, pathogenesis, and methods of diagnosis of bacterial gastroenteritis. Bacterial enteric pathogens common to North America are discussed in more detail.

Gastrointestinal zoonoses

Infectious gastrointestinal diseases affect man and animals throughout the world. Certain etiologic agents (for example, Salmonella spp., Campylobacter jejuni, Yersinia enterocolitica, Cryptosporidia, Strongyloides stercoralis, Echinococcus granulosa) seem to have the potential to be transmitted from pets to people, causing severe disease in the latter. Other agents seem unlikely to be transmitted but may have the potential to be zoonoses. This article discusses proved, suspected, and possible zoonotic agents that may originate from the gastrointestinal tract of dogs and cats.

New evidence on the causes of slave and crew mortality in the Atlantic slave trade

The journals of slave ship surgeons of the 1790s are used to address questions on the relative importance of African conditions versus those on ships, crowding, the effectiveness of Dolben's Act, and the interaction between slave and crew health. In contrast with previous work we find that most slaves who died did so near the middle of the voyage. Crowding was important to health and mortality, but the restrictions of Dolben's Act did little to reduce losses. The crew was largely isolated from patterns of disease among slaves.

New knowledge on pathogenesis of bacterial enteric infections as applied to vaccine development

Images

Infectious diarrhea. Which culprit? What strategy?

The patient with diarrhea is generally looking for prompt relief, not a prolonged diagnostic workup. In many cases effective treatment can be initiated after careful review of the clinical symptoms and of the patient's recent travel or other activities. Stool examination, sigmoidoscopy, or other studies may be necessary for definitive diagnosis or in refractory cases. Drugs are useful to combat many of the causative organisms, but in mild, self-limited infections, supportive therapy may suffice. Indeed, antimotility agents are contraindicated in some types of infectious diarrhea.