Worldwide prevalence of emerging parasite Blastocystis in immunocompromised patients: A systematic review and meta-analysis

Blastocystis and Giardia duodenalis infection in a male prison in Spain

Background

General conditions in a prison may facilitate water- or food-borne infections.

Methods

Detection of intestinal parasites was achieved in 471 male prison inmates by standard microscopic procedures on their stool samples. Positive samples were processed by PCR amplification of a 600-bp fragment of the Blastocystis SSU rRNA gene and partial sequences of the Giardia duodenalis bg genes. Identification of subtypes/genotypes was based on Sanger sequencing methods.

Results

Blastocystis was found in 7.9 % (37/471) and G. duodenalis was found in 2.1 % (10/471). Out of the 37 Blastocystis positive samples, 54 % (20/37) were successfully subtyped, allowing the identification of the subtypes ST3 (50 %), ST1 (25 %), ST2 (15 %), ST4 (5 %) and ST6 (5 %). Out of 10 G. duodenalis positive samples, 50 % (5/10) were successfully genotyped, allowing the identification of genotypes A (80 %) and B (20 %).

Conclusions

The predominance of ST3 within the prison inmates, together with its low intra-ST genetic variability, reflected inter-human transmission with spatial stability. The G. duodenalis distribution is not wide enough to consider the possibility of a generalized transmission via contaminated water or food. Personal hygiene practices among male prison inmates may be an important measure to prevent the transmission.

Genetic Diversity and Prevalence of Blastocystis Subtypes in Alborz Province, Iran: A Molecular Epidemiological Study

The primary objective of this study was to evaluate the genetic diversity of Blastocystis. Additionally, it aimed to explore, for the first time in Iran, the potential association between Blastocystis infection and ABO blood groups. Another focus was to examine the relationship between Blastocystis subtypes and blood groups, an often overlooked risk factor, within the population of Alborz Province, Iran. 450 stool samples were collected from diagnostic facilities across Alborz Province between June 2022 and April 2024. The presence of Blastocystis was confirmed in 64 out of 450 samples (14.22%) using the Nested PCR-RFLP technique. Among the 64 positive samples, nine (2%) were classified as indeterminate. Two distinct Blastocystis subtypes were identified in 55 isolates, accounting for 12.22% of the total samples. ST1 was detected in 44 isolates (9.77%), rendering it the most prevalent subtype, while ST3 was identified in 11 isolates (2.44%). Phylogenetic trees were constructed using sequencing data and compared against genotypes available in GenBank. Significant differences between infected and non-infected individuals were observed regarding educational attainment, marital status, and blood type (p < 0.05). A significant association was found between ABO blood groups and the prevalence of Blastocystis infection (p = 0.019). However, when examining the correlation between Blastocystis subtypes (ST1 and ST3) and ABO blood groups, no significant overall association was observed. Nonetheless, specific associations were found for blood groups O+ and B-, with subtype ST1 being more prevalent in these groups.

Epidemiology of Blastocystis in farm animals: A review

Blastocystis is a ubiquitous gastrointestinal protozoan parasite found both in humans and animals. The purpose of this review is to look at the prevalence and genetic diversity of Blastocystis in farm animals, including cattle, sheep, goats, pigs, and poultry, and discuss the potential evidence of transmission between animals and humans, as well as highlight the related risk factors and public health significance. Significant differences have been found in the prevalence of Blastocystis in different hosts worldwide. The global prevalence of Blastocystis infection was 13.6 % in cattle (1219/8961), 15.9 % in sheep (675/4233), 31.7 % in goats (837/2640), 44.57 % in pigs (2589/5808), and 26.29 % in poultry (892/3392). Blastocystis is mainly transmitted through fecal-oral routes. The existence of the same subtypes of the parasite in both animals and humans indicates potential zoonotic transmission. Subtypes ST10 (43.39 %) and ST14 (19.99 %) were most frequently found in cattle, sheep, and goats, while ST5 (62.57 %) was predominantly observed in pigs, and ST6 (16 %) and ST7 (36.6 %) were commonly recorded in poultry. Analysis of risk factors suggests that age, sex, close contact with animals, geographical location, farm management system, and season were the significant risk factors reported in many studies. Although epidemiology and subtype distribution of Blastocystis in different hosts have been described in several studies, understanding the possible transmission pathway from farm animals to humans and the public health impacts of Blastocystis requires more extensive studies.

Serum metabolism-transcriptomics investigated into the immunity of whey protein isolate-galacto-oligosaccharide conjugates after dynamic high-pressure microfluidics pretreatment

The objective of this study was to investigate the immunomodulatory effects of whey protein isolate (WPI)-galacto-oligosaccharide conjugates following dynamic high-pressure microfluidics pretreatment (DHPM) in cyclophosphamide-induced immunosuppressed mice. DHPM facilitated the conjugation of WPI and galacto-oligosaccharide, and inhibited the generation of fluorescent advanced glycation end products (AGEs) and pentosidine. The conjugates demonstrated a significant immune recovery effect on CTX-induced immunosuppressed mice, as evidenced by the enhancement of IgG antibody levels (from 3.5 to 4.1) and the reduction of the levels of immunosuppressive effector factors TGF-β (from 148.1 to 111.2) and IFN-γ (from 34.4 to 17.9). Furthermore, the conjugates exhibited a notable ability to repair histological lesion in the spleen of CTX-induced immunosuppressed mice. Spleen transcriptomics revealed that the Marco, Klrc3 and Cd209b genes were associated with the immune enhancement activity of the conjugates. Metabolomic analysis identified arginine biosynthesis, sphingolipid metabolism, alanine, aspartate and glutamate metabolism, and phenylalanine, tyrosine and tryptophan biosynthesis as key pathways in the immune enhancement activity of the conjugates. Metabolomics combined with transcriptomics indicated the importance of macrophage activation in the restoration of immunosuppressed mice's immunity by the conjugates. Therefore, the improvement in immunity observed with WPI-galacto-oligosaccharide conjugates may be related to the activation of macrophages.

Prevalence and subtyping of Blastocystis sp. in ruminants in Southwestern, Iran

Blastocystis is the most common gastrointestinal protozoan parasite of humans and many vertebrates. This study was carried out to investigate the prevalence and determination subtype (ST) of Blastocystis in domestic ruminants of Shahrekord County, southwestern Iran. In this descriptive cross-sectional study, 330 ruminant fecal samples (107 cows, 115 sheep, and 108 goats) were evaluated by parasitological methods (direct wet mount microscopic examination and formalin-ether concentration), Giemsa staining, In vitro xenic culture (The modified Dobell and Laidlaw culture method), polymerase chain reaction, and sequencing from 2018 to 2019, then data were analyzed using SPSS software version 21. The overall Blastocystis positive in ruminants was 14.2% and the frequency of Blastocystis sp. in cattle, sheep, and goats were 0.93%, 17.4%, and 24.1% respectively. Molecular diagnosis techniques revealed that ruminants were infected with four STs (genotypes) of Blastocystis including ST5(21.3%), ST7(2.1%), ST10(17.1%) and ST14(57.4%). Also, the STs identified in cows were ST10, and the observed STs in sheep were ST5 (40%), ST7 (3%), ST10 (5%), ST14 (45%), and one unknown subspecies. Goats were infected by ST5 (7.7%), ST10 (23.1%), and ST14 (69.2%). In this study, ST14 was identified as the most common subtype of Blastocystis sp. that was not common between humans and livestock, meanwhile, ST5 and ST7 are common between humans and animals accounted 21.3% and 2.1% of the positive cases, respectively, and reinforces the hypothesis that ruminants are reservoirs of blastocystosis in humans.

Food and Drinking Water as Sources of Pathogenic Protozoans: An Update

This narrative review was aimed at collecting updated knowledge on the risk factors, illnesses caused, and measures for the prevention of protozoan infections transmitted by food and drinking water. Reports screened dated from 2019 to the present and regarded global prevalence in food handlers, occurrence in food and drinking water, impact on human health, and recently reported outbreaks and cases of severe infections attributable to the dietary route. Cryptosporidium spp., Cyclospora cayetanensis, Entamoeba histolytica, and Cystoisospora belli were the protozoans most frequently involved in recently reported waterborne and foodborne outbreaks and cases. Blastocystis hominis was reported to be the most widespread intestinal protozoan in humans, and two case reports indicated its pathogenic potential. Dientamoeba fragilis, Endolimax nana, and Pentatrichomonas hominis are also frequent but still require further investigation on their ability to cause illness. A progressive improvement in surveillance of protozoan infections and infection sources took place in developed countries where the implementation of reporting systems and the application of molecular diagnostic methods led to an enhanced capacity to identify epidemiological links and improve the prevention of foodborne and waterborne protozoan infections.

Chronic urticaria associated with Blastocystis hominis infection

Urticaria is a skin rash with several etiologic factors, including infectious agents. Blastocystis hominis is an intestinal protozoan parasite that has been linked to urticaria and skin lesions. The aim of this work was to investigate the association between B. hominis infection and chronic urticaria. In a case-control study, stool samples were obtained from 94 patients with chronic urticaria as case group and 285 healthy individuals as control group. Urticaria activity score 7 (UAS7) was used to score the severity of urticaria, classified as mild, moderate and intense. All stool samples underwent routine stool examinations, as well as polymerase chain reaction (PCR) for the detection of B. hominis. Molecular detection was carried out using the small subunit ribosomal RNA (SSU-rRNA) gene and the parasite subtypes were determined by sequencing. The rate of B. hominis infection was 21.3% (20 out of 94) and 17.2% (49 out of 285) between the case and control groups, respectively (p = 0.463). Three subtypes of B. hominis, including ST-1, ST-2 and ST-3, were detected in the case and control groups (ST-1 = 30% vs. 8.3%, ST-2 = 40% vs. 25% and ST-3 = 30% vs. 66.6% in the case and control group, respectively), which was statistically significant (p = 0.00001). However, no statistical differences were found between the severity of the urticaria and the B. hominis subtypes (p = 0.533). This study revealed a higher prevalence (but not significant) of B. hominis infection among patients with urticaria than healthy individuals. However, the results did not find a significant association between the subtypes of B. hominis and the severity of urticaria.

Prevalence of Blastocystis sp. in Morocco: Comparative assessment of three diagnostic methods and characterization of parasite forms in Jones' culture medium

Blastocystosis is an infection caused by Blastocystis sp., which colonizes the digestive tract of various hosts, including humans, although its pathogenicity is debated. It is crucial to detect and distinguish the different forms of Blastocystis to understand better its impact on human health and its epidemiological evolution. This study evaluated three diagnostic methods on 105 stool samples: direct examination, culture in Jones' medium, and conventional PCR. PCR is considered the gold standard and revealed a high prevalence of Blastocystis (67.62%) compared to direct examination (20.95%) and culture in Jones' medium (51.43%). Although the sensitivity of direct examination and culture was 31% and 76.1%, respectively, their specificity was 100%. No significant risk factors were identified. A statistically significant association was observed between Blastocystis infection and abdominal pain. Microscopic analysis revealed various morphological forms. Molecular diagnosis is an essential tool to determine the true prevalence of Blastocystis, and studying the different forms of this microorganism will contribute to a better understanding of its biological cycle and, therefore, the impact of this emerging infection on human health.

Gastrointestinal Pathogens in Multi-Infected Individuals: A Cluster Analysis of Interaction

Indigenous people live in remote areas of Colombia. Multiple infections with bacteria, protozoa and/or helminths are common, as well as colonization in various forms. This study focused on the question of whether and to what extent various pathogens interact with each other. Therefore, a mathematical approach was retrospectively applied to PCR-based data of 244 stool samples, collected in two datasets. A stable cluster solution of the pathogens assessed was determined, and a unique configuration between Blastocystis hominis/Campylobacter spp./Giardia lamblia forming cluster 1 and Dientaemoeba fragilis was verified. A pathogen density-dependent interplay appeared between the B. hominis/Campylobacter spp./G. lamblia cluster, D. fragilis and Ascaris lumbricoides. The applied mathematical approach demonstrated that co-infections with parasites of questionable pathological relevance such as B. hominis and D. fragilis can be of diagnostic relevance due to their ability to promote or repress other pathogens. With the increasing availability of highly sensitive multiplexed molecular diagnostic approaches even in resource-limited settings, where multiple colonization of infection events with enteric pathogens in parallel are common, the importance of interpreting whole pathogen patterns rather than just individual pathogen detection may become more and more relevant.

Systematic Review and Meta-Analysis: Epidemiology of Human Blastocystis spp. Infection in Malaysia

Blastocystis spp. is a unicellular enteric protozoan parasite in humans with a controversial role in disease etiology. It is common in developing countries among immunocompromised patients and people who have close contact with animals. In this study, we have systematically reviewed previous studies on the distribution and genotypes of human Blastocystis infection in Peninsular Malaysia. Studies examining the prevalence of Blastocystis in diverse demographics, including rural, urban, comorbid conditions, and high-risk populations, were taken into consideration. The infection has been reported in nine states; the total percentage of infection was 17.8% (1671/9397), with the most cases in Pahang (27.3%) and the least in Johor (3.4%). Molecular studies revealed the presence of six subtypes: ST1, ST2, ST3, ST4, ST5, and ST6. ST3 was reported as the predominant subtype in all the states, with a prevalence of 54.7% (338/618). The findings provide greater clarity on the epidemiology of Blastocystis in Malaysia, which will help in policy making towards planning and strategizing control measures against the parasite.

Phylogenetic relationship of nonmammalian and avian Blastocystis isolates and conventional subtypes

Blastocystis is an intestinal protist commonly identified in human and animal feces. At present, there are 28 proposed subtypes (STs) identified based on the small subunit rRNA gene, 13 of which are found in both humans and animals. In general, nonmammalian and avian groups are infected by the nonmammalian and avian subtypes (NMASTs). However, NMASTs were also isolated from mammalian hosts, suggesting possible cross-contamination and transmission from nonmammalian and avian hosts to other animals and, potentially, humans. Thus, this study determined the possible relationship between NMAST sequences and conventional STs to provide new insights into Blastocystis classification, identification, and epidemiological significance. Phylogenetic trees were constructed using three statistical models, namely, Maximum Likelihood, Neighbor Joining, and Maximum Parsimony, based on the 30 NMAST sequences. The NMAST sequences formed groups clustered closely with other NMAST subtrees. Most sequences of nonmammalian and avian isolates formed distinct monophyletic clades based on their NMAST classification, with some clustering with mammalian and avian STs. These results indicate the close relationship between Blastocystis isolated from mammalian and avian hosts and nonmammalian and avian hosts.

Supplementary Information

The online version contains supplementary material available at (10.1007/s12639-022-01554-7).

Prevalence and Associated Factors of Blastocystis sp. Infection in Patients with Gastrointestinal Symptoms in Spain: A Case-Control Study

Blastocystis sp. is known to be the most prevalent parasite in fecal samples of humans worldwide. In the present report, a case-control study (1:9.89 (≈10)) was performed, by analyzing data from 3682 patients who attended a public hospital in the northern area of Spain showing gastrointestinal symptoms. Diagnosis was performed in human fecal samples by means of optical microscopy. The prevalence of Blastocystis sp. in patients with gastrointestinal symptoms was 9.18% (338/3682). Most of the Blastocystis sp.-infected patients tested negative for protozoa and helminths, and were underweight and foreign-born (26.4%), mainly from Africa and Central/South America. Gastrointestinal symptoms, such as abdominal pain, anorexia, halitosis, plus relative eosinophilia, as well as co-infections with pathogenic bacteria were associated with Blastocystis sp. infection. Both type 2 diabetes and treatment with immunosuppressive medicines at the time of Blastocystis sp. detection were associated with a higher proportion of infected patients. This is the first case-control study of Blastocystis sp. in humans in northern Spain and may contribute to surveillance and intervention strategies by public health authorities.

Molecular identification and subtype analysis of Blastocystis in captive Asiatic black bears (Ursus thibetanus) in China’s Heilongjiang and Fujian provinces

Blastocystis sp. is the most isolated enteric protozoan in parasitological surveys of humans. A substantial percentage of human infections is attributed to zoonotic transmissions. However, the contribution of each animal source to human infections with blastocystis is not yet fully understood. This study thus aimed to determine the infection rates and subtype distributions of Blastocystis sp. in captive Asiatic black bears (Ursus thibetanus) in China’s Heilongjiang and Fujian provinces. A total of 218 fresh fecal specimens were collected from captive Asiatic black bears in Heilongjiang (n = 36) and Fujian (n = 182) between May 2015 and December 2017. Genomic DNA was extracted from each sample and then examined for Blastocystis through SSU rRNA gene amplicon-based sequencing. A phylogenetic tree based on the Blastocystis positive sequences was reconstructed using the Mega X program. Eleven percent (24/218) of the animals had Blastocystis and six Blastocystis subtypes, including ST4 (n = 14), ST10 (n = 3), ST1 (n = 2), ST2 (n = 1), ST5 (n = 1), and ST12 (n = 1) were identified. A total of 14 representative sequences, including seven sequences that have been described previously and seven novel sequences comprising ST10 (n = 2), ST5 (n = 1), and ST4 (n = 4), were obtained from the six subtypes of Blastocystis. This study is the first to report the presence of Blastocystis in captive Asiatic black bears in Fujian, China. It provides baseline data for controlling and preventing Blastocystis infection in farm communities. Zoonotic infections in bears with ST1, ST2, ST4, ST5, ST10, and ST14 should be considered potential public health threats. The novel ST sequences of Blastocystis generated in this study provide novel insights into the genotypic variation within the Blastocystis sp.

Frequency, spatial distribution, and genetic diversity of Blastocystis among referred individuals to a clinical laboratory: First report of subtype 9 in Brazil

The enteric protist Blastocystis has a worldwide distribution, however its prevalence in the human population is still underestimated, especially in developing countries where proper diagnosis is not performed in the routine of clinical laboratories. In this study, we aimed to assess the frequency, genetic diversity, and spatial distribution of Blastocystis isolates detected in fecal samples referred to a clinical laboratory for routine examination in inner São Paulo State, Brazil. A total of 348 leftover stool samples available for disposal from female and male individuals with age ranging from 3 months to 88 years were analyzed by both microscopic examination and PCR/sequencing of the SSU rRNA gene. The overall frequency of Blastocystis sp. was 31% (108/348), including 20.1% (70/348) and 31% (108/348) by microscopic examination and PCR/sequencing, respectively. Significant association was found only between Blastocystis infection and age, since the highest rate of positive samples was detected among 5-9 years old individuals (p < 0.0001). In addition, spatial distribution revealed a wide distribution of the positive samples, however they were densely concentrated in more populated areas. Seven subtypes were identified, namely ST1 (40.7%), ST2 (9.2%), ST3 (45.3%), ST4 (0.9%), ST6 (1.8%), ST7 (0.9%) and ST9 (0.9%). The intra-subtype analysis revealed a total of 25 different alleles previously reported. Here, the findings lead us to highlight the following aspects: (1) the identification of a ST9 isolate is a relevant finding since it is considered a very rare subtype in human infections as well as this is the first report in Brazil; (2) the high frequency of Blastocystis in fecal samples submitted for examination in a clinical laboratory points to the need to consider its search in routine parasitological examinations, (3) the spatial distribution of Blastocystis infection was not homogeneous but concentrated in more populated areas where the access for population to diagnostic services in healthcare is likely to be easier and, (4) the genetic variability of Blastocystis isolates suggests exposure of inhabitants living in inner municipalities to different sources of contamination involving anthroponotic and zoonotic transmission pathways.

Evaluation of association with subtypes and alleles of Blastocystis with chronic spontaneous urticaria

Blastocystis is a single-celled parasite commonly found in humans and its pathogenic role is still controversial. In recent years, some studies have suggested that Blastocystis may be a possible agent of gastrointestinal and dermatological symptoms such as acute or chronic urticaria, angioedema, rash, itch, palmoplantar, and diffuse pruritus. We aimed to investigate whether there is a relationship between Blastocystis subtypes and alleles in patients with chronic spontaneous urticaria (CSU) as a case-control study. In this study, stool samples were collected from patients with CSU (n=135) and healthy individuals (n=54). The presence of Blastocystis was investigated using the direct saline smear, Lugol's iodine staining, trichrome staining, Jones' medium culture and PCR assays in stool samples and subtypes (STs) were determined by sequencing according to DNA barcoding. The presence of Blastocystis was identified in 30.4% (64/210) the stool samples, including 31.9% (43/135) of the patients with CSU and 14.8% (8/54) of the control group. Moreover, it was found statistically significant the presence of Blastocystis in terms of both groups (p<0.018). ST3 was detected in 45.9% and 62.5 % as the most prevalent subtype the patients with CSU and the control group, respectively. ST1 (18.9%), ST2 (27%) and ST7 (8.1%) was identified in the patients with CSU group. There was no statistically significant correlation between Blastocystis subtypes and both the groups (p<0.240, p<0.323). Allele 4 for ST1; alleles 9, 10, 11 and 12 for ST2; alleles 34, 36 and 38 for ST3; alleles 41 and 101 for ST7 were detected. Allele 34 (ST3) was found significant in the patients with CSU as compared with control group (p<0.020). Moreover, statistically significant association was found between total IgE value and the certain subtypes (ST2 and ST3) (p<0.0001). As a result of this study, the presence of Blastocystis ST3 allele 34 significantly associated with chronic spontaneous urticaria was revealed.

The neglected role of Blastocystis sp. and Giardia lamblia in development of irritable bowel syndrome: A systematic review and meta-analysis

The possible role of Blastocystis sp. and Giardia lamblia infections in the development of irritable bowel syndrome (IBS) has long been controversial. In this study, we conducted a systematic review and meta-analysis to investigate whether these protozoan infections are associated with IBS development. We systematically searched international databases for all studies that reported these protozoa in IBS patients published by May 10, 2021. Studies were included in the review if they were observational studies with confirmed patients with IBS (in case-control and cross-sectional studies) or parasitic infections (cohort studies) with an appropriate control group. Pooled odds ratios (ORs) and 95% confidence intervals were estimated using a random-effects meta-analysis model for included studies. A total of 32 papers (42 datasets), including 29 papers (31 datasets) for Blastocystis sp./IBS and 11 papers (11 datasets) for G. lamblia/IBS met the eligibility criteria. Our results indicated that the individuals with Blastocystis sp. infection were significantly at a higher risk of IBS development (OR, 1.78; 95%CI, 1.29-2.44). Moreover, cohort studies indicated a significant positive association between G. lamblia infection and IBS risk (OR, 5.47; 95%CI, 4.23-7.08); while an increasing but no statistically significant risk was observed in case-control studies (OR, 1.19; 95%CI, 0.75-1.87). Our findings suggested that Blastocystis sp. and G. lamblia infections are associated with the increased risk of developing IBS. Despite these results, further studies are needed to determine the effect of these protozoa on IBS development.

Molecular Diversity of Giardia duodenalis, Cryptosporidium spp., and Blastocystis sp. in Symptomatic and Asymptomatic Schoolchildren in Zambézia Province (Mozambique)

Infections by the protist enteroparasites Giardia duodenalis, Cryptosporidium spp., and, to a much lesser extent, Blastocystis sp. are common causes of childhood diarrhoea in low-income countries. This molecular epidemiological study assesses the frequency and molecular diversity of these pathogens in faecal samples from asymptomatic schoolchildren (n = 807) and symptomatic children seeking medical attention (n = 286) in Zambézia province, Mozambique. Detection and molecular characterisation of pathogens was conducted by polymerase chain reaction (PCR)-based methods coupled with Sanger sequencing. Giardia duodenalis was the most prevalent enteric parasite found [41.7%, 95% confidence interval (CI): 38.8‒44.7%], followed by Blastocystis sp. (14.1%, 95% CI: 12.1‒16.3%), and Cryptosporidium spp. (1.6%, 95% CI: 0.9‒2.5%). Sequence analyses revealed the presence of assemblages A (7.0%, 3/43) and B (88.4%, 38/43) within G. duodenalis-positive children. Four Cryptosporidium species were detected, including C. hominis (30.8%; 4/13), C. parvum (30.8%, 4/13), C. felis (30.8%, 4/13), and C. viatorum (7.6%, 1/13). Four Blastocystis subtypes were also identified including ST1 (22.7%; 35/154), ST2 (22.7%; 35/154), ST3 (45.5%; 70/154), and ST4 (9.1%; 14/154). Most of the genotyped samples were from asymptomatic children. This is the first report of C. viatorum and Blastocystis ST4 in Mozambique. Molecular data indicate that anthropic and zoonotic transmission (the latter at an unknown rate) are important spread pathways of diarrhoea-causing pathogens in Mozambique.

Blastocystis species and Gastrointestinal Symptoms in Peruvian Adults Attended in a Public Hospital

The objective of this study was to evaluate the role of Blastocystis sp. in gastrointestinal symptoms reported by adult patients in a Peruvian hospital. A case-control 3:1 study was performed at the outpatient clinic. Direct stool examinations were done. One hundred sixty patients were included, 40 cases and 120 controls. Positivity to Blastocystis sp. was associated with dyspepsia (P <0.001), bloating (P <0.001) and abdominal pain (P = 0.03) in patients attending our hospital outpatient clinic.