Abstract

INTRODUCTION

Globally, intestinal parasitic infections (IPIs) are one of the main causes of human morbidity and mortality especially in developing countries in which public health standards are not as high as in developed countries. IPIs are associated with climate conditions, poor sanitation and economic variables, lack of access to potable water, improper food and cultural habits¹1. Mehraj V, Hatcher J, Akhtar S, Rafique G, Beg MA. Prevalence and factors associated with intestinal parasitic infection among children in an urban slum of Karachi. PLoS One. 2008;3:e3680.

2. Östan I, Kilimcioğlu AA, Girginkardeşler N, Özyurt BC, Limoncu ME, Ok ÜZ. Health inequities: lower socio-economic conditions and higher incidences of intestinal parasites. BMC Public Health. 2007;7:342.^-33. Pullan RL, Brooker SJ. The global limits and population at risk of soil-transmitted helminth infections in 2010. Parasit Vectors. 2012;5:81.. The most important protozoan etiologic agents of IPIs are Entamoeba histolytica (affecting 50 million people), Giardia lamblia (affecting 200 million people), and also Cryptosporidium spp., Cyclospora cayetanensis, Cystoisospora belli and Microsporidia spp. in immune compromised patients⁴4. Pham Duc P, Nguyen-Viet H, Hattendorf J, Zinsstag J, Dac Cam P, Odermatt P. Risk factors for Entamoeba histolytica infection in an agricultural community in Hanam province, Vietnam. Parasit Vectors. 2011;4:102.

5. Yason JA, Rivera WL. Genotyping of Giardia duodenalis isolates among residents of slum area in Manila, Philippines. Parasitol Res. 2007;101:681-7.^-66. Paboriboune P, Phoumindr N, Borel E, Sourinphoumy K, Phaxayaseng S, Luangkhot E, et al. Intestinal parasitic infections in HIV-infected patients, Lao People's Democratic Republic. PloS one. 2014;9:e91452..

The soil-transmitted helminths (STH) Ascaris lumbricoides, Trichuris trichiura, and hookworms are the most common causes of IPIs and affect more than 2 billion people worldwide⁷7. Kaliappan SP, George S, Francis MR, Kattula D, Sarkar R, Minz S, et al. Prevalence and clustering of soil-transmitted helminth infections in a tribal area in southern India. Trop Med Int Health. 2013;18:1452-62.. Other common helminths in IPIs are Enterobius vermicularies, Strongyloides stercoralis, Taenia spp., Schistosoma mansoni and Hymenolepis nana⁸8. Mamo H. Intestinal parasitic infections among prison inmates and tobacco farm workers in Shewa Robit, north-central Ethiopia. PloS One. 2014;9:e99559..

IPIs can cause diarrhea, abdominal pain, nausea and vomiting, bloating and weight loss. In addition, the rate of disability adjusted life years (DALYs) resulting from IPIs is approximately 39 million, indicating a substantial economic burden of these infections⁹9. Stephenson LS, Latham MC, Ottesen EA. Malnutrition and parasitic helminth infections. Parasitology. 2000;121 Suppl:S23-38.. The effects of IPIs on children are: (i) growth disorders¹⁰10. Crompton DW, Nesheim MC. Nutritional impact of intestinal helminthiasis during the human life cycle. Annu Rev Nutr. 2002;22:35-59.

11. Muniz-Junqueira MI, Queiróz EF. Relationship between protein-energy malnutrition, vitamin A, and parasitoses in children living in Brasília. Rev Soc Bras Med Trop. 2002;35:133-42.^-1212. Moktar N, Al-Mekhlafi HM, Azlin M, Nor Aini U, Shaik A, Sa'iah A, et al. Malnutrition and soil-transmitted helminthiasis among Orang Asli children in Selangor, Malaysia. Asia Pac J Clin Nutr 2004;13:S122., (ii) vitamin A deficiency¹³13. Al-Mekhlafi HM, Surin J, Sallam AA, Abdullah AW, Mahdy MA. Giardiasis and poor vitamin A status among aboriginal school children in rural Malaysia. Am J Trop Med Hyg. 2010;83:523-7.^,1414. Mahalanabis D, Simpson TW, Chakraborty ML, Ganguli C, Bhattacharjee AK, Mukherjee KL. Malabsorption of water miscible vitamin A in children with giardiasis and ascariasis. Am J Clin Nutr. 1979;32:313-8., (iii) iron deficiency anemia¹⁵15. Stoltzfus RJ, Chwaya HM, Montresor A, Albonico M, Savioli L, Tielsch JM. Malaria, hookworms and recent fever are related to anemia and iron status indicators in 0-to 5-y old Zanzibari children and these relationships change with age. J Nutr. 2000;130:1724-33.^,1616. Ngui R, Ishak S, Chuen CS, Mahmud R, Lim YA. Prevalence and risk factors of intestinal parasitism in rural and remote West Malaysia. PLoS Negl Trop Dis. 2011;5:e974. and (iv) poor educational performance¹⁷17. Nokes C, Bundy DA. Does helminth infection affect mental processing and educational achievement? Parasitol Today. 1994;10:14-8.^,1818. Ahmed A, Al-Mekhlafi HM, Azam MN, Ithoi I, Al-Adhroey AH, Abdulsalam AM, et al. Soil-transmitted helminthiasis: a critical but neglected factor influencing school participation of Aboriginal children in rural Malaysia. Parasitology. 2012;139:802-8.. In addition, IPIs can result in severe complications in immune compromised patients such as those with HIV, transplant recipients and hemodialysis patients¹⁹19. Huang DB, Chappell C, Okhuysen PC. Cryptosporidiosis in children. Semin Pediatr Infect Dis. 2004;15:253-9.^,2020. Omrani VF, Fallahi Sh, Rostami A, Siyadatpanah A, Barzgarpour G, Mehravar S, et al. Prevalence of intestinal parasite infections and associated clinical symptoms among patients with end-stage renal disease undergoing hemodialysis. Infection. 2015;43:537-44..

Gastrointestinal disorders refer to diseases involving the gastrointestinal tract such as the ones compromising the stomach, small and large intestines and rectum. They are associated to many symptoms such as diarrhea, abdominal/stomach pain, nausea and vomiting, weight loss, indigestion/dyspepsia, bloating and constipation. It has been shown that intestinal parasites have a high prevalence in patients with gastrointestinal disorders and are related to the above mentioned symptoms²¹21. Haghighi A, Khorashad AS, Mojarad EN, Kazemi B, Nejad MR, Rasti S. Frequency of enteric protozoan parasites among patients with gastrointestinal complaints in medical centers of Zahedan, Iran. Trans R Soc Trop Med Hyg. 2009;103:452-4.

22. Moosavi A, Haghighi A, Mojarad EN, Zayeri F, Alebouyeh M, Khazan H, et al. Genetic variability of Blastocystis sp. isolated from symptomatic and asymptomatic individuals in Iran. Parasitol Res. 2012;111:2311-5.

23. Qadri SM, al-Okaili GA, al-Dayel F. Clinical significance of Blastocystis hominis. J Clin Microbiol. 1989;27:2407-9.^-2424. Abdulsalam AM, Ithoi I, Al-Mekhlafi HM, Khan AH, Ahmed A, Surin J, et al. Prevalence, predictors and clinical significance of Blastocystis sp. in Sebha, Libya. Parasit Vectors. 2013;6:86..

In Iran, despite a sustained improvement of the sanitary conditions that has happened during the last three decades, IPIs are still highly prevalent, especially among rural communities and small towns where residents survive thanks to agriculture and pastoral culture²⁰20. Omrani VF, Fallahi Sh, Rostami A, Siyadatpanah A, Barzgarpour G, Mehravar S, et al. Prevalence of intestinal parasite infections and associated clinical symptoms among patients with end-stage renal disease undergoing hemodialysis. Infection. 2015;43:537-44..

The main purpose of this study was to assess the prevalence and clinical manifestations of IPIs in patients with gastrointestinal disorders in Nahavand County, Western Iran, and investigate the association of IPIs with socio-demographic factors.

MATERIAL AND METHODS

Study areas

This cross sectional study was carried out from April to September 2014 in Nahavand County, (34°14'N, 48°14'E), Western Iran. The average annual rainfall in the area is 376 mm and the average temperature ranges from -0.5 to 25.6 ^ºC.

Population, studied variables and ethical issues

The Nahavand County has 196 villages and the population is estimated at 181,711 people in 112,297 families²⁵25. Statistical Centre of Iran. Summary and statistical report of the 2012 population and housing census. Islamic Republic of Iran: Population census commission Hamadan province; Population census commission Nahavand County : 24 October-13 November 2011. [cited 2015 Nov 28]. Available from: http://www.amar.org.ir/english/Census-2011.
http://www.amar.org.ir/english/Census-20... . The majority of inhabitants are farmers and ranchers especially those living in rural areas and small towns around the Nahavand city.

The study population was composed of individuals with gastrointestinal disorders who presented one or more symptoms (abdominal pain, diarrhea, dysenteric diarrhea, crumping, nausea and vomiting, constipation) and were referred to medical laboratories in the Nahavand County. In order to calculate the sample size, we used a reference prevalence of 27% in patients with gastrointestinal disorders, a 95% level of confidence and 5% of marginal error²¹21. Haghighi A, Khorashad AS, Mojarad EN, Kazemi B, Nejad MR, Rasti S. Frequency of enteric protozoan parasites among patients with gastrointestinal complaints in medical centers of Zahedan, Iran. Trans R Soc Trop Med Hyg. 2009;103:452-4.. The sample size required was 1,038 people, but for more accuracy 1,301 samples were collected.

A written consent was obtained from each participant, and then the participants were asked to respond to a questionnaire containing basic individual information (sex, age, residence), socio-demographic data (education, occupation), health status (water supply, contact with domestic animal and soil) and clinical symptoms such as abdominal pain (defined as a diffuse pain in the abdominal cavity), bloating (any abnormal general swelling or fullness), diarrhea (at least three loose or liquid stools per day), stomach pain (cramps or a dull abdominal ache), nausea and vomiting (the sensation or act of forcible and frequent emptying of the stomach) was filled by each participant. The study has enrolled individuals with gastrointestinal disorders that did not use any anti-parasitic drugs for one week prior to the study, and agreed to participate.

All the procedures were approved by the Ethics Committee of the Shahid Beheshti University of Medical Science (SBMU), Iran, before the beginning of the study. All the study participants were informed about the procedures and written informed consents were obtained from all of them prior to the sample collection.

Fecal sample collection and analysis

In this study, a simple random sampling technique was used. All the participants were given a clean and dry plastic collector, pre-labeled with their name and an identification number. Collected samples were sent to the medical laboratory located at the Ayatollah Alimoradian hospital, as soon as possible. All the samples were physically examined and screened for intestinal parasites by the following methods: I. Direct smear using the normal saline (0.85% NaCl solution), II. Lugol's iodine staining, III. Formalin-ether concentration technique, IV. Modified Ziehl-Neelsen acid-fast technique for the detection of Cryptosporidium spp. oocysts, V. Trichrome staining technique for the detection of intestinal protozoa such as Giardia lamblia and Entamoeba histolytica²⁶26. World Health Organization. Basic laboratory methods in medical parasitology. Geneva: WHO; 1991.^,2727. Henriksen SA, Pohlenz JF. Staining of cryptosporidia by a modified Ziehl-Neelsen technique. Acta Vet Scand. 1981;22:594-6.. Prepared slides were examined under light microscopy (Zeiss, Germany) with 10×, 40× and 100× magnification.

Statistical analysis

Data analysis was carried out using the Statistical Package for the Social Sciences software version₁₆ (SPSS, Chicago, IL, USA). For the descriptive data, frequencies and percentages were used to describe the characteristics of the participants, including the prevalence of IPIs according to the residence, education, occupation, age and gender. The Pearson's Chi-square (Chi2) test and the Fisher's exact test were used for comparison of proportions of IPIs between different subgroups and odds ratios (OR) and 95% confidence intervals (CI) were used to associate the variables. A p value < 0.05 was considered statistically significant. A logistic regression was used to identify a potential contribution of each of the variables for the acquisition of intestinal parasite infections.

RESULTS

Socio-demographic characteristics

A total of 1,301 participants (52.4% male, 47.6% female) aged 22 days-90 years with a mean age of 26.31 ± 22.22 were enrolled in this study. Six hundred and eighty-three subjects (52.5%) lived in rural areas and 618 subjects (47.5%) lived in urban areas. Six hundred and eighteen (47.5%) had access to clean treated potable water and 683 (52.5%) used untreated water (river, well, rain). Four hundred and eighty-five participants (37.3%) reported a frequent contact with domestic animals or soil. The percentage of participants categorized as government employees, farmer, student, house wife, other and children < 17 years old were 7.5%, 11.4%, 8.2%, 20.1%, 12.8% and 40%, respectively.

Prevalence and distribution of intestinal parasitic infections

Overall, 32.2% (419/1,301) of the participants were infected with at least one intestinal parasite species. The prevalence rate among males (231/682 cases; 33.9%) was slightly higher than in females (188/619 cases; 30.4%). The most common IP was Blastocystis sp. (350 participants, 26.9%), followed by Entamoeba coli (38 participants, 2.92%), Giardia lamblia (30 participants, 2.3%) and Cryptosporidium spp. (17 participants, 1.3%). The prevalence of other IPs is presented in Table 1.

Three hundred and fifty nine participants (27.6%) were infected with a single parasite and in 60 cases (4.6%) polyparasitism was observed. The prevalence of intestinal helminths in this study (5 cases, 0.38%) was significantly lower than intestinal protozoa (416 cases, 32%) (p < 0.001).

Risk factors for intestinal parasitic infections (IPIs)

The results of the univariate analysis to evaluate the risk factors associated to IPIs and socio-demographic, environmental and personal hygiene factors are presented in Table 2. Among the selected socio-demographic variables, some were significantly associated to IPIs: educational status (p = 0.001), contact with domestic animals and soil (p = 0.02), age above 15 years (p = 0.001) and seasons (p = 0.001). However, regarding other socio-demographic characteristics such as sex, residence, water supply, and occupation, they did not show any association with the finding of parasites (Table 2). Moreover, according to the period of the year (season), it was observed that the prevalence of IPIs in July, August and September was significantly higher than in April, May and June (p = 0.001).

Using a binary logistic regression analysis, variables such as age, sex, residence, educational level, occupation, contact with domestic animals and soil, as well as the water supply status were added to the model. Then, we used a forward logistic regression to perform the analysis. Among the added variables, only the age (OR = 2.07; CI _95% = 1.4-2.8; p < 0.001) and the seasons (OR = 1.16; CI _95% = 1.28-2.13; p < 0.001) were identified as major socio-demographic determinants of IPIs.

Clinical features associated to IPIs

Concerning clinical characteristics, the presence of IPIs was significantly associated to diarrhea (OR = 1.57; CI _95% = 1.24-1.98; p < 0.001), dysentery (OR = 1.94; CI _95% = 1.03-3.6; p < 0.04) and constipation (OR= 0.298; CI 95%= 0.141-0.633; p < 0.001). The frequencies of other clinical characteristics including the presence of abdominal pain, nausea and vomiting, stomach pain and bloating did not show significant differences between parasite-infected and non-infected participants (Table 3). According to these data diarrheic disease may result from IPs in patients with gastrointestinal disorders.

DISCUSSION

The results of the present study have indicated that approximately one third of patients with gastrointestinal disorders were infected with one or more IPs. This rate is slightly higher than the results of a previous study conducted in similar populations in Zahedan, where the prevalence of IPIs was 27.3%²¹21. Haghighi A, Khorashad AS, Mojarad EN, Kazemi B, Nejad MR, Rasti S. Frequency of enteric protozoan parasites among patients with gastrointestinal complaints in medical centers of Zahedan, Iran. Trans R Soc Trop Med Hyg. 2009;103:452-4..

Climate differences and thriving in agriculture and animal husbandry in Nahavand County might be responsible for the higher prevalence of IPs in this region compared to Zahedan. However, our subsequent study in a different region of Iran has shown a prevalence of 10% for IPs in patients with gastrointestinal disorders²⁸28. Zebardast N, Gharavi MJ, Abadi A, Tabaei SJ, Yeganeh F, Khazan H, et al. Frequency of intestinal parasites in patients with gastrointestinal disorders, in different parts of Iran during 2012-2013. Int J Enteric Pathog. 2015;3:e22682.. The differences of results can be attributed to peculiarities of the studied regions. Zahedan and Nahavand have poorer hygiene conditions and lower socio-economic status compared to the areas studied by Zebardast et al²⁸28. Zebardast N, Gharavi MJ, Abadi A, Tabaei SJ, Yeganeh F, Khazan H, et al. Frequency of intestinal parasites in patients with gastrointestinal disorders, in different parts of Iran during 2012-2013. Int J Enteric Pathog. 2015;3:e22682.. It is well established that providing a basic infrastructure and suitable education are effective tools to decrease the prevalence of IPIs²⁹29. Ngui R, Lim YA, Chong Kin L, Sek Chuen C, Jaffar S. Association between anaemia, iron deficiency anaemia, neglected parasitic infections and socioeconomic factors in rural children of West Malaysia. PLoS Negl Trop Dis. 2012;6:e1550.. In Iran, some areas located at the western, southern and eastern regions of the country are less developed in comparison with areas close to the capital and people live in traditional-built houses, although using untreated water from wells or rivers.

The findings of our study showed that protozoan infections (32%) were more common compared to helminth ones (0.38%). In recent years, there has been a decrease in the incidence of intestinal helminth infections such as ascariasis, strongyloidiasis and hookworm infections in Iran²⁰20. Omrani VF, Fallahi Sh, Rostami A, Siyadatpanah A, Barzgarpour G, Mehravar S, et al. Prevalence of intestinal parasite infections and associated clinical symptoms among patients with end-stage renal disease undergoing hemodialysis. Infection. 2015;43:537-44.^,3030. Rokni M. The present status of human helminthic diseases in Iran. Ann Trop Med Parasitol. 2008;102:283-95.. This decline is probably due to general improvements in sanitation in Iran. However, some helminth parasites with direct fecal-oral transmission, such as Hymenolepis nana and Enterobius vermicularis remain common in many parts of the country³⁰30. Rokni M. The present status of human helminthic diseases in Iran. Ann Trop Med Parasitol. 2008;102:283-95.. In addition, among the five cases of helminth infections that were found in this study, Hymenolepis nana and Enterobius vermicularis were observed in one and three cases, respectively. Moreover, other authors in Iran and other countries have also found higher frequencies of protozoan compared to helminth infections³¹31. Sharif M, Daryani A, Kia E, Rezaei F, Nasiri M, Nasrolahei M. Prevalence of intestinal parasites among food handlers of Sari, northern Iran. Rev Inst Med Trop Sao Paulo. 2015;57:139-44.

32. Colli CM, Mizutani AS, Martins VA, Ferreira EC, Gomes ML. Prevalence and risk factors for intestinal parasites in food handlers, southern Brazil. Int J Environ Health Res. 2014;24:450-8.^-3333. Dagnew M, Tiruneh M, Moges F, Tekeste Z. Survey of nasal carriage of Staphylococcus aureus and intestinal parasites among food handlers working at Gondar University, Northwest Ethiopia. BMC Public Health. 2012;12:837..

The findings of the present study showed that Blastocystis sp. was the most common IP. This finding is in agreement with a previous study carried out in a similar population²²22. Moosavi A, Haghighi A, Mojarad EN, Zayeri F, Alebouyeh M, Khazan H, et al. Genetic variability of Blastocystis sp. isolated from symptomatic and asymptomatic individuals in Iran. Parasitol Res. 2012;111:2311-5.. The pathogenicity of Blastocystis is still under debate. Some studies have strongly suggested that it is pathogenic and can be associated to several disorders³⁴34. Tan KS. New insights on classification, identification, and clinical relevance of Blastocystis spp. Clinl Microbiol Rev. 2008;21:639-65.^,3535. Tan KS, Mirza H, Teo JD, Wu B, Macary PA. Current views on the clinical relevance of Blastocystis spp. Curr Infect Dis Rep. 2010;12:28-35., whereas other studies have reported that it is a commensal organism rather than a pathogenic one, and it is probably not responsible for clinical symptoms³⁵35. Tan KS, Mirza H, Teo JD, Wu B, Macary PA. Current views on the clinical relevance of Blastocystis spp. Curr Infect Dis Rep. 2010;12:28-35.^,3636. Scanlan PD, Stensvold CR. Blastocystis: getting to grips with our guileful guest. Trends Parasitol. 2013;29:523-9., The Centers for Disease Control and Prevention (CDC) suggests that Blastocystis treatment is necessary when there are no other causes for the occurrence of diarrhea or gastrointestinal disorders³⁷37. Centers for Disease Control and Prevention Blastocystis hominis: laboratory identification of parasites of public health concern. [cited 2015 Apr 15]. Available from: http://www.cdc.gov/dpdx/blastocystis/tx.html.
http://www.cdc.gov/dpdx/blastocystis/tx.... . Previous clinical studies have shown that abdominal pain and diarrhea are two of the main symptoms among Blastocystis-positive patients²²22. Moosavi A, Haghighi A, Mojarad EN, Zayeri F, Alebouyeh M, Khazan H, et al. Genetic variability of Blastocystis sp. isolated from symptomatic and asymptomatic individuals in Iran. Parasitol Res. 2012;111:2311-5.^,3434. Tan KS. New insights on classification, identification, and clinical relevance of Blastocystis spp. Clinl Microbiol Rev. 2008;21:639-65.. Excepting for Blastocystis, Giardia lamblia (2.3%) and Cryptosporidium spp. (1.3%) were the most pathogenic protozoan parasites. In a recently published study that has been carried out in Iran, 4.73%, 2.30% and 0.06% of the studied population had Blastocystis, Giardia lamblia and Cryptosporidium spp., respectively²⁸28. Zebardast N, Gharavi MJ, Abadi A, Tabaei SJ, Yeganeh F, Khazan H, et al. Frequency of intestinal parasites in patients with gastrointestinal disorders, in different parts of Iran during 2012-2013. Int J Enteric Pathog. 2015;3:e22682.. These zoonotic protozoa are a great threat to public health in Iran. They can be transmitted through contaminated water and food. Animal wastes and farming practices are important sources of water and food contamination. Thus it is necessary to keep animals away from water and food sources that are used by humans.

Considering the symptoms, the results of our study have shown that there was a significant association between the presence of IPs and the finding of diarrheal stools. Diarrhea is one of the most reported symptoms due to IPs. Entamoeba histolytica can be the cause of severe dysentery, colitis, constipation, tenesmus and extra-intestinal complications³⁸38. Pritt BS, Clark CG. Amebiasis. Mayo Clin Proc. 2008;83:1154-9.. Giardia lamblia is responsible for acute diarrhea, steatorrhea and malabsorption³⁹39. Ortega YR, Adam RD. Giardia: overview and update. Clin Infect Dis. 1997;25:545-9.. Cryptosporidium spp. infections has been increasingly recognized as a cause of diarrhea in both immune competent and immune compromised patients, as well as in children¹⁹19. Huang DB, Chappell C, Okhuysen PC. Cryptosporidiosis in children. Semin Pediatr Infect Dis. 2004;15:253-9.^,2020. Omrani VF, Fallahi Sh, Rostami A, Siyadatpanah A, Barzgarpour G, Mehravar S, et al. Prevalence of intestinal parasite infections and associated clinical symptoms among patients with end-stage renal disease undergoing hemodialysis. Infection. 2015;43:537-44.. Although in our study, most of referred participant were infected with nonpathogenic protozoan parasites.

In this study, the described clinical symptoms are common complications induced by IPIs as well as by bacterial, viral or fungal agents. All the enrolled participants were examined by a physician, but we did not have access to their previous laboratory and medical records that would allow a more accurate interpretation on whether the symptoms were due to IPIs or to bacterial infections and/or malignancies.

Worldwide, previous studies have shown that there are several risk factors associated to the high prevalence and incidence of IPIs including untreated water supply, age, poor sanitation, low family income, low level of education, low level of parental education, eating unpeeled/unwashed vegetables and fruits, contact with livestock or pets and poor personal hygiene⁴⁰40. Choy SH, Al-Mekhlafi HM, Mahdy MA, Nasr NN, Sulaiman M, Lim YA, et al. Prevalence and associated risk factors of Giardia infection among indigenous communities in rural Malaysia. Sci Rep. 2014;4:6909.

41. Muñoz-Antoli C, Pavón A, Marcilla A, Toledo R, Esteban J. Prevalence and risk factors related to intestinal parasites among children in Department of Rio San Juan, Nicaragua. Trans R Soc Trop Med Hyg. 2014;108:774-82.

42. Arani AS, Alaghehbandan R, Akhlaghi L, Shahi M, Lari AR. Prevalence of intestinal parasites in a population in south of Tehran, Iran. Rev Inst Med Trop Sao Paulo. 2008;50:145-9.

43. Wördemann M, Polman K, Menocal Heredia LT, Diaz RJ, Madurga AM, Núñez Fernández FA, et al. Prevalence and risk factors of intestinal parasites in Cuban children. Trop Med Int Health. 2006;11:1813-20.^-4444. Daryani A, Sharif M, Nasrolahei M, Khalilian A, Mohammadi A, Barzegar G. Epidemiological survey of the prevalence of intestinal parasites among schoolchildren in Sari, northern Iran. Trans R Soc Trop Med Hyg. 2012;106:455-9.. In our study, variables such as age above 15 years, low level of education, contact with soil and livestock, as well as the season were considered significant risk factors of IPIs. Results of the current study have shown that adult patients (aged ≥ 15 years) are almost twice as likely to be infected with IPs. Outdoor activities practiced by adults and a higher exposure to sources of IPs may explain the significantly higher prevalence of IPIs among these participants. Moreover, another reason for this finding is the higher prevalence of Blastocystis infections according to the increasing age²³23. Qadri SM, al-Okaili GA, al-Dayel F. Clinical significance of Blastocystis hominis. J Clin Microbiol. 1989;27:2407-9.^,2424. Abdulsalam AM, Ithoi I, Al-Mekhlafi HM, Khan AH, Ahmed A, Surin J, et al. Prevalence, predictors and clinical significance of Blastocystis sp. in Sebha, Libya. Parasit Vectors. 2013;6:86.. In our study, the prevalence of IPIs was slightly higher in males (33.9%) than in females (30.4%), although there was no statistically significant difference (p = 0.197). This result is in agreement with previous studies in Iran²¹21. Haghighi A, Khorashad AS, Mojarad EN, Kazemi B, Nejad MR, Rasti S. Frequency of enteric protozoan parasites among patients with gastrointestinal complaints in medical centers of Zahedan, Iran. Trans R Soc Trop Med Hyg. 2009;103:452-4.^,4444. Daryani A, Sharif M, Nasrolahei M, Khalilian A, Mohammadi A, Barzegar G. Epidemiological survey of the prevalence of intestinal parasites among schoolchildren in Sari, northern Iran. Trans R Soc Trop Med Hyg. 2012;106:455-9.. Our findings have indicated that the season is a significant predictor of IPIs. The Nahavand County is located in a mountainous area (far from the sea) and its weather in summer (July, August and September) is little to moderately warm (20-35 °C), whereas in spring (April, May and June) the weather is colder (10-18 °C). Another explanation to the higher prevalence of IPs during the summer could be the existence of more agricultural practices. This finding is in agreement with previous studies that have indicated that endemic regions have seasonal variations in the prevalence of IPIs⁴⁵45. Miller SA, Rosario CL, Rojas E, Scorza JV. Intestinal parasitic infection and associated symptoms in children attending day care centres in Trujillo, Venezuela. Trop Med Int Health. 2003;8:342-7.

46. Mercado R, Otto J, Pérez M. Variación estacional de las infecciones por protozoos intestinales en pacientes ambulatorios del sector norte de Santiago, Chile: 1995-1996. Bol Chil Parasitol. 1999;54:41-4.^-4747. Nasiri V, Esmailnia K, Karim G, Nasir M, Akhavan O. Intestinal parasitic infections among inhabitants of Karaj City, Tehran province, Iran in 2006-2008. Korean J Parasitol. 2009;47:265-8..

There were some limitations in this study. Firstly, stool samples were collected only once, so that it is likely that the analysis of three consecutive stool samples could have increased the diagnostic sensitivity. Secondly, there is a possibility that some of the participants have decided to take antiparasitic drugs prior to the stool sampling, considering that metronidazole, mebendazole and albendazole can be purchased without prescription in Iran. Thirdly, due to the lack of facilities and financial funding we could not use all the laboratory available techniques, such as the Baerman technique that is used to find larvae of worms including strongyloides or adhesive tape to detect Enterobius vermicularies. The lack of these procedures might explain the absence of helminth infections in this study. In addition, it is likely that the prevalence of some protozoa such as Entamoeba histolytica and Blastocystis could be even higher if culture techniques had been used.

In conclusion, the findings of this study have indicated that IPIs are important causes of gastrointestinal disorders. Moreover, despite a significant reduction in the prevalence of intestinal helminths, the prevalence and incidence of intestinal protozoa are still a major public health concern in Iran. Thus, effective control programs to reduce the prevalence and incidence of IPIs should be considered in public health policies. Considering that the incidence of IPIs are significantly associated to poverty, lower levels of education, poor environmental sanitation, contact with soil and animals, there is an urgent need that these factors are effectively addressed.

ACKNOWLEDGMENTS

This study was part of the M.Sc. thesis of Hamed Kiani and was financially supported by Shahid Beheshti University of Medical Sciences (grant. n^o 13/1285). The corresponding author would like to express his gratitude to the administrators and the staff of the Ayatollah Alimoradian hospital, authorities and personnel of Nahavand Health Care Network and centers, medical laboratories and the research participants for their kind cooperation during the sample collection.

REFERENCES

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