The role of Blastocystis hominis as a possible intestinal pathogen in travellers

Blastocystis hominis: A Pathogenic Parasite

Background: Blastocystis hominis is recognized as a common intestinal parasite. Some studies have reported the effect of phenotypic, serologic, and biochemical indices on the parasites’ pathogenic characteristics. Objectives: This study aimed to introduce B. hominis as a pathogen, trying to change views about this parasite and introduce it as a parasite important in medical sciences. Methods: An open-ended, language-restricted (English) search was conducted in MEDLINE (PubMed), CINAHL, Scopus, and the Cochrane Library databases (from 1990 to 2018) using specific search criteria to identify Blastocystis spp. Results: The search of the literature retrieved 158 published articles on Blastocystis spp. Among these articles, the ones related to the pathogenicity of B. hominis were selected for further investigations. Results obtained in this study showed that the number of articles within five-year periods had an increasing trend. Also, studies of B. hominis have mainly investigated its pathogenic characteristics, accounting for 37.34% of the studies. Conclusions: This study showed comprehensive reasons for proving the pathogenesis of the parasite. It is hoped that further studies would fill the existing gaps regarding this parasite and identify its true identity as a medically important parasite.

Surveillance of enteropathogenic bacteria, protozoa and helminths in travellers returning from the tropics

Diarrhoea is a frequent symptom associated with travelling to tropical regions, but the cause is often not found. Epidemiology was assessed including up-to-date real-time PCR approaches.We analysed datasets of 528 patients who presented at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Germany, between 2006 and 2010 for screening purposes or because of diarrhoea. Stool samples were obtained and investigated by microscopy, bacterial culture, two PCR assays targeting Entamoeba histolytica, Entamoeba dispar, Giardia duodenalis, and Cryptosporidium parvum, or Salmonella spp., Shigella/EIEC spp., Campylobacter jejuni, and Yersinia spp.Among patients with gastrointestinal symptoms, 51% tested positive for bacteria or parasites, of which 66% had a known enteropathogenic potential. In patients without diarrhoea, 53% (n = 80) were positive, and 33% of these cases harboured agents of pathogenic potential. Association with clinical symptoms was primarily found for bacterial infections. Blastocystis hominis, however, was more frequent in asymptomatic than in symptomatic travellers.In conclusion, the study stresses the etiological relevance of bacterial gastroenteritis in travellers returning from the tropics, the need for molecular approaches to increase diagnostic sensitivity and demonstrates that asymptomatic carriage of enteropathogens after prolonged stays in the tropics is similarly frequent compared with symptomatic infections in travellers.

Blastocystis in Swiss children: a practical approach

Blastocystis is a parasite with a worldwide distribution and a varying prevalence in different countries. The pleomorphic nature of the protozoon and the lack of understanding a possible pathogenesis have led to confusion regarding its clinical significance. The aim of the study was to shed light on clinical characteristics of pediatric patients in Swiss children with a positive stool sample for Blastocystis, in order to provide recommendations for a practical approach for the clinician to know whom, when, and how to test. This is a retrospective study of pediatric patients, whose stool has been tested positive for Blastocystis in the last 10 years in northern Switzerland. A total of 4047 stool samples, belonging to 1887 different patients, were analyzed; 240 stool samples (of 160 patients) were tested positive for Blastocystis. On average, 2.2 (CI 1.98-2.35) stool samples per patient were analyzed, of which 1.48 (CI 1.36-1.61) were positive for Blastocystis. In 63% abdominal pain was the leading symptom, while in 17.5% it was an accidental finding without symptoms. There was a high significance in correlation of abdominal pain and chronicity (p < 0.0001) but none in diarrhea (p = 0.082) nor nausea/vomiting or other symptoms and chronicity. Followed by Entamoeba coli (8%), 26.3% of the patients with Blastocystis had a co-infection with another parasite, mostly Endolimax nana (13%).Conclusion: Carriage of Blastocystis is common; therefore, only children/teenagers at risk for a symptomatic Blastocystis infection should be tested. There is a good correlation between Blastocystis and chronic abdominal pain. Children with abdominal symptoms persisting over 4 weeks should have two different stool samples analyzed. No screening after travels/immigration is recommended.What is Known:• Blastocystis has a worldwide distribution.• The clinical significance is unclear.What is New:• Based on retrospective data, we recommend to only test children/teenagers with chronic abdominal pain for Blastocystis.• Two different stool samples should be examined by microscopy; serological investigations are not warranted.

Parasites in Human Stool: To Ignore or Not To Ignore?

Human stool contains a myriad of microorganisms, of which the vast majority are nonpathogenic and represent an important component of the healthy microbiome. The increasing use of molecular techniques has allowed the rapid identification of bacteria, viruses and parasites in human stool. This review focuses on the 3 main classes of parasite responsible for human disease, helminths, protozoa and ectoparasites, and highlights the importance of differentiating between pathogenic and nonpathogenic parasites.

Carriage of Blastocystis spp. in travellers - A prospective longitudinal study

INTRODUCTION

A lack of prospective and longitudinal data on pre- and post-travel carriage of Blastocystis spp. complicates interpretation of a positive test post-travel. Therefore we studied dynamics of Blastocystis carriage in a cohort of Dutch travellers.

METHODS

From the prospective, multicentre COMBAT study among 2001 Dutch travellers, a subset of 491 travellers was selected based on travel destination to 7 subregions (70 or 71 travellers each). Faecal samples taken directly before and after travel were screened for Blastocystis with qPCR, followed, when positive, by sequence analysis to determine subtypes.

RESULTS

After exclusion of 12 samples with missing samples or inhibited qPCR-reactions, stool samples of 479 travellers were analysed. Before travel, 174 of them (36.3%) carried Blastocystis and in most of these, the same subtype was persistently carried. However, in 48/174 of those travellers (27.6%; CI95 20.8-36.6%) no Blastocystis or a different subtype was detected in the post-travel sample, indicating loss of Blastocystis during travel. Only 26 (5.4%; CI95 3.7%-8.0%) of all travellers acquired Blastocystis, including two individuals that were already positive for Blastocystis before travel but acquired a different subtype during travel.

DISCUSSION

This study shows that Blastocystis carriage in travellers is highly dynamic. The observed acquisition and loss of Blastocystis could either be travel-related or reflect the natural course of Blastocystis carriage. We demonstrate that the majority of Blastocystis detected in post-travel samples were already carried before travel.

Epidemiology and Prevalence of Blastocystis spp. in North Cyprus

AbstractThis study was conducted to investigate the prevalence of Blastocystis spp. and its subtypes (STs) in North Cyprus; and to evaluate the presence of this parasite and its STs with respect to demographic, socioeconomic, and epidemiological factors, as well as gastrointestinal symptoms. Stool samples were collected from 230 volunteers. Each participant also filled out a questionnaire. The samples were examined microscopically by native-Lugol and trichrome methods and further tested by polymerase chain reaction (PCR) and sequencing. Prevalence of Blastocystis spp. infection was found to be 10.5%, 10.5%, and 27.8%, by direct microscopy, trichrome method, and PCR, respectively. No other parasites were detected in the specimens except Giardia spp. (n = 2; 0.8%) and Entamoeba coli (n = 1; 0.4%). The most common Blastocystis STs were ST3 (20; 31.2%), ST2 (18; 28.2%), ST1 (8; 12.5%), and ST4 (7; 11%); whereas other STs were identified as ST6 (3; 4.7%), ST7 (2; 3.2%), and non-ST (6; 9.4%). Presence of Blastocystis spp. and its STs was not significantly related to any of the demographic, socioeconomic, and epidemiological factors. Furthermore, no significant association of Blastocystis spp. and its STs with gastrointestinal symptoms was found. This study is the first investigation of the epidemiology of Blastocystis spp. in North Cyprus. Distribution of Blastocystis spp. and its STs among demographic, socioeconomic, and epidemiological factors showed complete homogeneity. Presence of the parasite and its STs was not significantly related with the gastrointestinal symptoms among symptomatic and asymptomatic individuals. These findings suggest that Blastocystis spp. may be part of the intestinal flora in humans.

[Blastocystis spp.: Advances, controversies and future challenges]

Blastocystis spp. is the most common protozoan detected in human stool samples. In developing countries, infection rates are higher than 20%. The presence of this parasite in the feces of several host species suggests its zoonotic potential. The clinical relevance and the pathogenic role of Blastocystis spp. in the intestinal tract remain unclear. There are several clinical reports that recognize it as the etiologic agent of several intestinal disorders such as diarrhea, inflammatory bowel disease and ulcerative colitis, although the pathogenicity of this parasite has not been proved yet. This wide range of clinical manifestations could be related to the genetic diversity exhibited by this parasite.

Diagnosis and subtype analysis of Blastocystis sp. in 442 patients in a hospital setting in the Netherlands

Background

Blastocystis sp. are among the most commonly observed intestinal parasites in routine clinical parasitology. Blastocystis in humans consists of at least 9 genetic subtypes. Different subtypes of Blastocystis may be associated with differences in pathogenicity and symptomatology.

Methods

Advanced microscopy on two samples and sequence-confirmed PCR on a third sample from the same individual were used for Blastocystis diagnosis and subtype analyses on routine clinical samples in a university hospital.

Results

With a combined gold standard of sequence-confirmed PCR and positive advanced microscopy, 107 out of 442 (24.2%) patients were diagnosed with Blastocystis. infection, which is a high frequency of detection in comparison to previous reports from industrialized countries. The sensitivity of microscopy and sequence-confirmed PCR was 99.1% (106/107) and 96.3% (103/107), respectively.

Among 103 typable samples, subtype 3 was most abundant (n = 43, 42%), followed by subtypes 1 and 2 (both n = 23, 22%), subtype 4 (n = 12, 12%), and single samples with subtypes 6 (1%) and subtype 7 (1%). The prevalence of Blastocystis infection was 38% in patients from the Department of Tropical Medicine and 18% in patients from other departments.

Conclusions

A high prevalence of Blastocystis infection was found with both advanced microscopy and sequence-confirmed PCR in our patient population. Most cases were caused by subtypes ST1, ST2, ST3 and ST4. A significantly higher prevalence was found among patients with a history of recent travel to tropical countries.

HIV and intestinal parasite co-infections among a Chinese population: an immunological profile

BACKGROUND

Parasite infections often result in a switch of the human body's predominant immune reaction from T-helper 1 (Th1)-type to Th2-type. Hence, parasite infections are widely expected to accelerate the progression of human immunodeficiency virus (HIV) infections to acquired immunodeficiency syndrome (AIDS). In the People's Republic of China, both parasitic diseases and AIDS are epidemic in certain rural areas, and co-infections are relatively common. However, no population-based studies have yet investigated the frequency of HIV and parasite co-infections, and its effects on immune responses. We studied (1) the immune status of an HIV-infected population, and (2) the effect of co-infection of HIV and intestinal parasites on selected parameters of the human immune system.

METHODS

A total of 309 HIV-infected individuals were recruited and compared to an age-matched and sex-matched control group of 315 local HIV-negative individuals. Questionnaires were administered to all participants to obtain information on sociodemographic characteristics, sanitation habits, family income, and recent clinical manifestations. Two consecutive stool samples and 10 ml samples of venous blood were also collected from each individual for the diagnosis of parasite infections and quantitative measurements of selected cytokines and CD4+ T-lymphocytes, respectively.

RESULTS

During the study period, 79 HIV-infected individuals were not under highly active antiretroviral therapy (HAART) and were thus included in our analysis; the prevalence of intestinal helminth infections was 6.3% and that of protozoa was 22.8%. The most common protozoan infections were Blastocystis hominis (B. hominis) (13.9%) and Cryptosporidium spp. (10.1%). The prevalence of Cryptosporidium spp. in HIV-infected individuals was significantly higher than that in HIV negative individuals (P < 0.05). Compared to the non-co-infected population, no significant difference was found for any of the measured immunological indicators (P > 0.05). However, the following trends were observed: IFN-γ levels were lower, but the IL-4 level was higher, in the population co-infected with HIV and helminths. In the population co-infected with HIV and B. hominis, the IL-2 level was higher. The population co-infected with HIV and Cryptosporidium spp. had markedly lower CD4+ T-lymphocyte counts.

CONCLUSION

According to the immunologic profile, co-infection with helminths is disadvantageous to HIV-infected individuals. It was associated with a shift in the Th1/Th2 balance in the same direction as that caused by the virus itself, which might indicate an acceleration of the progress from an HIV infection to AIDS. Co-infection with Cryptosporidium spp. was not associated with a significant change in immune factors but co-infection with Cryptosporidium spp. was associated with a reduced level of CD4 + T-lymphocytes, confirming the opportunistic nature of such infections. Co-infection with B. hominis, on the other hand, was associated with an antagonistic shift in the immunological profile compared to an HIV infection.

Blastocystis subtypes in symptomatic and asymptomatic family members and pets and response to therapy

BACKGROUND

Blastocystis is a common, enteric parasite. The pathogenicity of the organism is uncertain, but subtypes (ST) 1 and 3 have been reported more likely to cause irritable bowel-like symptoms.

AIMS

We treated symptomatic patients positive for Blastocystis with conventional therapy and analysed 16 small-subunit (SSU) rDNA to assess clearance and carriage rates and ST prevalence of the parasite in the asymptomatic household members.

METHODS

In a longitudinal, prospective case study, 11 symptomatic patients positive for Blastocystis underwent outpatient clinical assessment to exclude other diagnoses before 14 days of either metronidazole 400 mg three times daily or trimethoprim/sulfamethoxazole 160/800 mg twice-daily therapy. Faecal specimens were collected from patients at baseline, day 15, 28 and 56 after therapy and from 17 family members and eight pets at day 15. Specimens were analysed using faecal smear, culture and polymerase chain reaction analysis of 16SSU rDNA.

RESULTS

No patient cleared the organism following therapy. ST 1 (45%), 3 (36%), 4 (36%) and 6 (9%) were found in the symptomatic Blastocystis patients, and ST identified before and after therapy were identical in each individual. All household contacts were positive for Blastocystis and 16/17 (94%) contacts showed identical Blastocystis ST to the symptomatic family member. All pets were positive for Blastocystis with polymerase chain reaction testing, 7/8 (88%) demonstrating ST concordance with the symptomatic Blastocystis patients.

CONCLUSIONS

Conventional therapy is ineffective for symptomatic Blastocystis infection. The high prevalence of Blastocystis infection within households suggested transmission between humans and their pets. Subtyping analysis of SSU rDNA alone in Blastocystis does not appear to predict pathogenicity.

New insights on classification, identification, and clinical relevance of Blastocystis spp

SUMMARY

Blastocystis is an unusual enteric protozoan parasite of humans and many animals. It has a worldwide distribution and is often the most commonly isolated organism in parasitological surveys. The parasite has been described since the early 1900s, but only in the last decade or so have there been significant advances in our understanding of Blastocystis biology. However, the pleomorphic nature of the parasite and the lack of standardization in techniques have led to confusion and, in some cases, misinterpretation of data. This has hindered laboratory diagnosis and efforts to understand its mode of reproduction, life cycle, prevalence, and pathogenesis. Accumulating epidemiological, in vivo, and in vitro data strongly suggest that Blastocystis is a pathogen. Many genotypes exist in nature, and recent observations indicate that humans are, in reality, hosts to numerous zoonotic genotypes. Such genetic diversity has led to a suggestion that previously conflicting observations on the pathogenesis of Blastocystis are due to pathogenic and nonpathogenic genotypes. Recent epidemiological, animal infection, and in vitro host-Blastocystis interaction studies suggest that this may indeed be the case. This review focuses on such recent advances and also provides updates on laboratory and clinical aspects of Blastocystis spp.

Treatment options for the eradication of intestinal protozoa

Pathogenic intestinal protozoa are responsible for clinically important infections in both the developed and the developing world. These organisms are responsible for both acute and chronic diarrhea, and Entamoeba histolytica, which affects the colon, can spread to involve the liver. Many of these pathogens, particularly the intracellular protozoa that predominantly affect the small intestine, produce their most devastating effects in patients with HIV/AIDS and other forms of immune deficiency. There are also various intestinal protozoa that do not seem to have any adverse effects on humans and can, therefore, be regarded as harmless commensal organisms. Although treatment has been available for several decades for giardiasis, isosporiasis and amoebiasis, until recently there have been no effective remedies for infection with intestinal coccidia--Cryptosporidium, Microsporidium and Cyclospora species. Cyclospora respond well to co-trimoxazole, microsporidia respond variably to albendazole, and cryptosporidia can often be eradicated by nitazoxanide. In chronically infected HIV-positive patients, treatment with multidrug regimens usually results in rapid resolution of the diarrhea and, in many instances, eradication of the parasite.

Epidemiology of Blastocystis hominis and other intestinal parasites in a Vietnamese female immigrant population in southern Taiwan

There has been a rapid increase in cross-border female marriage immigrants in Taiwan. In this study, 1,434 Vietnamese female marriage immigrants arriving between July 1998 and June 2001 were examined for intestinal parasites. Most (77.9%) of these women were 20-29 years of age. The prevalence of intestinal parasite infection was 37.7%, and the trend increased from 1999 to 2001 (statistically significant, p < 0.0001), but decreased among age subgroups (p < 0.0001). Among the 20 species of intestinal parasites found in this study, 10 species (27.8%) were transmitted via the fecal-oral route, 5 (14.6%) via the soil-mediated route, and 5 (0.7%) by food-borne infection. The prevalence of blastocystosis (20.4%) and hookworm (9.7%) remained high among this population. The results provide unprecedented information on intestinal parasitic infection among these immigrants in southern Taiwan and recommend that appropriate health care be given after parasite infection is confirmed in these migrant communities.

No correlation between clinical symptoms and Blastocystis hominis in immunocompetent individuals

Abstract Background and Aim: Previous reports regarding the clinical significance and pathogenicity of Blastocystis hominis have been contradictory. The aim of this study was to examine the association between Blastocystis and gastrointestinal symptoms in immunocompetent individuals.

METHODS

We monitored over 2800 healthy people for a period of 15 months, and took stool specimens during both asymptomatic periods and during periods of gastrointestinal symptoms.

RESULTS

After exclusion of individuals who had simultaneous identification of other fecal pathogens, we compared the proportions of asymptomatic versus symptomatic individuals positive for Blastocystis and found no significant difference (P = 0.5). Symptom status did not correlate with parasite abundance. We found that some individuals were likely to have Blastocystis detected during both asymptomatic and symptomatic periods, possibly suggesting carriage of the organism.

CONCLUSION

In conclusion, we found no correlation between clinical symptoms and the presence or absence of Blastocystis among this healthy cohort.

Blastocystis hominis and travelers

B. hominis is a unicellular protozoan commonly identified in stool specimens of travelers who have returned from tropical countries. It has a world-wide distribution, and infection is more common in developing countries compared to industrialized nations. Clinical features of illness which have been attributed to Blastocystis include nausea, anorexia, abdominal pain, flatulence and acute or chronic diarrhea. The preferred method of diagnosis is a permanently stained smear of an unconcentrated stool specimen. The presence of B. hominis in stool specimens of symptomatic travelers should prompt clinicians to search for other unrecognized co-pathogens. Due to controversy regarding the pathogenicity of B. hominis in humans, clinicians are often faced with the dilemma of whether or not they should offer treatment for B. hominis infection in returned travelers. The most commonly used drugs for treatment include metronidazole and trimethoprim-sulfamethoxazole (TMP-SMX), when treatment is deemed necessary. Prevention in travelers should focus on food and water precautions as the organism is transmitted by the fecal-oral route.

Changing patterns in intestinal parasitic infections among Southeast Asian laborers in Taiwan

In order to determine whether there are changing patterns in intestinal parasitic infections among foreign laborers in North Taiwan, one fecal specimen was obtained from each of 1,569 laborers and examined by the formalin-ethyl acetate sedimentation technique. The prevalence of intestinal parasitic infections was 8.2%. Females (11.7%) had a significantly higher prevalence than males (6.9%), although there was no significant difference between Filipinos (7.7%), Thais (8.3%) and Indonesians (12.5%). Blastocystis hominis (3.4%) had the highest prevalence among the nine species of parasites detected. The significantly higher prevalence of B. hominis in the entry examination indicates an increasing trend in incoming Southeast Asian laborers. In addition, the prevalence of soil-transmitted helminth infections has become extremely low. Female laborers had a significantly higher positive rate. Although Opisthorchis viverrini/Clonorchis sinensis remains prevalent among Thais, the positive rate was also significantly reduced. These epidemiological patterns are different from those observed in previous studies and may be attributed to the long-term and constant movement of the foreign laborers.

Hematological effects of Blastocystis hominis infection in male foreign workers in Taiwan

Blastocystis hominis found in stool specimens has been the most frequently identified parasite among foreign workers from Southeast Asia in Taiwan since 1992. The prevalence of B. hominis was 14.1% in this study. In their quarantine physical examinations, 121 male Thai workers were examined hematologically and screened for stool parasites using the merthiolate-iodine-formaldehyde concentration method. Hematological values were compared in workers with and without a B. hominis infection. Multiple regressions were used to adjust for age. Those infected with any parasite other than B. hominis were excluded from further analysis. The workers infected with B. hominis had a lower leukocyte count (6.5+/-0.4 X 10(3)/microl) than those who were not (7.4+/-0.2 X 10(3)/microl). This was mainly caused by a reduced neutrophil count (3.2+/-0.4 vs 4.2+/-0.2 X 10(3)/microl). Hemoglobin (13.9+/-0.3 vs 14.5+/-0.1 g/dl) and hematocrit (41.4+/-0.6 vs 42.9+/-0.2%) were also reduced in B. hominis-positive workers.

A placebo-controlled treatment trial of Blastocystis hominis infection with metronidazole

Blastocystis hominis, previously considered a harmless yeast, is now classified as a protozoan inhabiting the human intestinal tract. The pathogenicity of B. hominis remains controversial and is currently the subject of extensive debate.1- 5 As a result of the uncertainty surrounding the pathogenic role of B. hominis, large-scale treatment trials of B. hominis infection have so far been lacking. In spite of this, several drugs have been reported to be active against the parasite.6-8 The present study was carried out in order to evaluate the efficacy of metronidazole treatment in inducing clinical remission and parasitologic eradication in immunocompetent individuals with B. hominis as the only evident cause of diarrhea.

Recent advances in Blastocystis hominis research: hot spots in terra incognita

Despite being discovered more than 80 years ago, progress in Blastocystis research has been gradual and challenging, due to the small number of laboratories currently working on this protozoan parasite. To date, the morphology of Blastocystis hominis has been extensively studied by light and electron microscopy but all other aspects of its biology remain little explored areas. However, the availability of numerous and varied molecular tools and their application to the study of Blastocystis has brought us closer to understanding its biology. The purpose of this review is to describe and discuss recent advances in B. hominis research, with particular focus on new, and sometimes controversial, information that has shed light on its genetic heterogeneity, taxonomic links, mode of transmission, in vitro culture and pathogenesis. We also discuss recent observations that B. hominis has the capacity to undergo programmed cell death; a phenomenon similarly reported for many other unicellular organisms. There are still many gaps in our knowledge of this parasite. Although there is a growing body of evidence suggesting that B. hominis can be pathogenic under specific conditions, there are also other studies that indicated otherwise. Indeed, more studies are warranted before this controversial issue can be resolved. There is an urgent need for the identification and/or development of an animal model so that questions on its pathogenesis can be better answered. Another area that requires attention is the development of methods for the transfection of foreign/altered genes into B. hominis in order to facilitate genetic experiments.

Infectious causes of chronic diarrhea

Chronic diarrhea can be seen in association with specific pathogens, usually parasites and occasionally some bacteria. This article reviews pathogens causing chronic diarrhea in immunocompetent individuals and provides a rational diagnostic approach.

Diarrhea in the returned traveler

Diarrhea in the returned traveler is a common problem that can be caused by a number of different pathogens. A history of the patient's travel and exposures, the duration of illness, the response to prior treatment, and the clinical syndrome can help to establish a good etiologic differential diagnosis on which further therapy can be based. Many of these patients can be treated empirically with antibiotics, either a fluoroquinolone or azithromycin, without further microbiologic evaluation. Those patients with severe or persistent disease or comorbid illnesses, or those who have failed empiric therapy, should undergo further microbiologic evaluation with directed stool cultures and ova and parasite screening. For those patients with negative evaluations, further empiric therapy may be warranted if syndromes are suggestive of specific agents of infection, such as by Giardia or Cyclospora species. Other patients may require endoscopic evaluation to exclude diagnoses such as tropical sprue or inflammatory bowel disease.

Multiyear prospective study of intestinal parasitism in a cohort of Peace Corps volunteers in Guatemala

We conducted a prospective, longitudinal study in a cohort of 36 Peace Corps volunteers (PCVs) in Guatemala to study the incidence and natural history of intestinal parasitic infections during the PCVs' >2-year overseas stay. PCVs collected stool specimens at least monthly and when ill with gastrointestinal symptoms. Of the 1,168 specimens tested, 453 (38.8%) were positive for at least one parasite and 48 (4.1%) were positive for a pathogenic parasite. A median interval of 187 days (range, 14 to 752 days) elapsed before the first documented parasitic infection, and the median intervals from arrival until subsequent infections (e.g., second or third) were >300 days. The PCVs had 116 episodes of infection with 11 parasites, including up to 4 episodes per PCV with specific nonpathogens and Blastocystis hominis. The incidence, in episodes per 100 person-years, was highest for B. hominis (65), followed by Entamoeba coli (31), Cryptosporidium parvum (17), and Entamoeba hartmanni (17). The PCVs' B. hominis episodes lasted 6,809 person-days (28.7% of the 23,689 person-days in the study), the E. coli episodes lasted 2,055 person-days (8.7%), and each of the other types of episodes lasted <2% of the person-days in the study. Gastrointestinal symptoms were somewhat more common and more persistent, but not significantly so, in association with pathogen episodes than with B. hominis and nonpathogen episodes. Although infections with pathogenic parasites could account for only a minority of the PCVs' diarrheal episodes, the continued acquisition of parasitic infections throughout the PCVs' >2-year stay in Guatemala suggests that PCVs repeatedly had fecal exposures and thus were at risk for infections with both parasitic and nonparasitic pathogens throughout their overseas service.

Additional investigations fail to alter the diagnosis of irritable bowel syndrome in subjects fulfilling the Rome criteria

OBJECTIVE

Irritable bowel syndrome (IBS) is diagnosed by the presence of a constellation of symptoms fulfilling the Manning or Rome Criteria, after exclusion of organic disease. To exclude other diagnoses that might contribute to the abdominal pain or bowel symptoms experienced by subjects with IBS, numerous screening algorithms have been advocated, incorporating lactose hydrogen breath tests, thyroid function tests, fecal ova and parasite determination, and colonic endoscopy/radiography. The utility of these tests in uncovering alternative diagnoses, other than IBS, was examined in 1452 patients.

METHODS

Data were combined from two large multinational studies of IBS patients. All patients exhibited symptoms meeting the Rome criteria for IBS for at least 6 months before study entry. If prior evaluation had been > 2 yr previously, patients underwent colonic endoscopy/radiography at study entry. In addition, thyroid function tests, fecal ova and parasite determination, and a lactose hydrogen breath test were performed.

RESULTS

Lactose malabsorption was diagnosed in 23% (256/1122) of patients. Colonic abnormalities were detected in 2% (7/306) of patients; in four patients, colonic inflammation (n = 3) or obstruction (n = 1) may have contributed to symptoms of abdominal pain or altered bowel habits. Abnormal thyroid-stimulating hormone levels were detected in 6% (67/1209) of patients, of whom half were hypothyroid and half were hyperthyroid. Positive fecal ova and parasite tests were noted in 2% (19/1154) of patients.

CONCLUSIONS

Examination of screening tests in 1452 patients with an established history of IBS revealed an incidence of lactose malabsorption comparable to that in the general U.S. population and a low incidence of thyroid dysfunction, ova and parasite infestation, or colonic pathology. The limited detection rates, added costs, and inconvenience of these tests suggest that their routine use in the diagnostic evaluation of established IBS patients should be scrutinized.

Prevalence and clinical relevance of Blastocystis hominis in diverse patient cohorts

The pathogenicity of Blastocystis hominis is extensively debated in the medical literature. Therefore, we did a prevalence study to investigate the association between the presence of several intestinal parasites and gastrointestinal symptoms in diverse patient cohorts. The study population consisted of 1216 adults, including immunocompromised patients, institutionalized psychiatric or elder subjects, immigrants from developing countries, travellers to developing tropical countries and controls. Several variables for each risk group were considered. Stools specimens, collected in triplicate, were processed by the same technicians. Clinical data about each subject were provided by standardized questionnaires. The presence of gastrointestinal symptoms were related to the presence of any parasite. In addition, on the basis of microbiological results, five subgroups of subjects were evaluated. The results showed a high prevalence of parasites in all the risk groups. Immunocompromised status, recent arrival from developing countries and the presence of behavioural aberrations were significantly related to presence of parasites. B. hominis was the parasite most frequently detected in each studied group. B. hominis showed a significant correlation with gastrointestinal symptoms only when detected in the group including subjects with a severe immunodepression. Immunodepression seems to be a factor of primary importance of the pathogenic role of B. hominis.