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Severe Blastocystis hominis in an elderly man
Iournal of Infection (1996) 33, 57-59
CASE REPORT
Severe Blastocystis homini$ in a n Elderly Man Y. Levy, J. George and Y. Shoenfeld Department of Medicine 'B' and the Unit of Autoimmune Disease Research, Sheba Medical Center, Tel-Hashomer and Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel Accepted for publication 8 March 1996
We describe a unique case of severe Blastocystis hominis infection in an dderly man with severe dehydration, marked leukocytosis and hypoalbuminaemia after antibiotic treatment for right pneumonia. The patient recovered after treatment with metronidazole. This case presentation demonstrates the ability of B. hominis to induce severe gastrointestinal manifestations and general deterioration, particularly in light of the controversy surrounding its possible potential pathogenicity. We believe, therefore that aggressive treatment with metronidazole should be instituted, following demonstration of the parasite in the stools, if diarrhoea is protracted, since it may well be attributed to Blastocystis infection.
Introduction
The patient also complained of fatigue and low grade fever rising up to 38 °C in the evenings. On examination Blastocystis hominis is an anaerobic parasite which m a y he appeared exhausted with blood pressure of 120/ be associated with mild diarrhoea. Herein we describe 80 m m H g while standing and 107/80 m m H g when lying an elderly m a n admitted due to prolonged diarrhoea and down. His temperature was 3 6.8 °C, respirations (16 per general deterioration following antibiotic treatment. minute), his skin turgor was low and few crackles were heard over both lung bases. A grade II systolic m u r m u r was heard over his aortic valve and his abdomen was Case Report mildly and diffusely tender. No enlargement of either the A 74-year-old m a n with a history of non-insulin diabetes liver or the spleen was evident and his rectal examination mellitus controlled with diet, and hypertension was ad- was unrevealing. His blood tests disclosed: haemoglobin 13.4 g/dl, white mitted to our ward due to diarrhoea and general deblood cell count 30 1 3 0 m m 3 (neutrophils 90%, terioration. Five years before his admission he underwent lymphocytes 6%, monocytes 4%), platelet count replacement of the aortic valve (with coronary artery 252 000 m m 3, urea 49 mg/dl, creatinine 1.4 mg/dl, glucbypass grafting) due to aortic stenosis. Three weeks previously he washospitalized due to the ose 182 mg/dl, chloride 110mEq/dl, sodium 1 3 4 m E q / dl, potassium 2.8 mEq/dl, CO2 14 mg/dl, uric acid 8 mg/ appearance of fever and productive cough and a chest X-ray study demonstrated a lobar infiltrate in his right dl, albumin 2.7 g/dl, globulin 2.0 g/dl. Three weeks before his present admission his blood lung base. The patient was treated by intravenous adtests showed: haemoglobin 14.0 g/dl, white cell count of ministration of cefuroxime, resulting in rapid clinical 5 6 5 0 m m 3 with normal differential, platelet count of improvement and was discharged with a re1 5 0 0 0 0 m m 3 albumin 4.3g/dl, urea zigmg/dl, crecommendation to continue treatment with oral ceatinine 1.1mg/dl, potassium 4.1mEq/dl and sodium fnroxime for 10 days. 141 mEq/dl. Two weeks following his previous hospitalization the During hospitalization his blood and stool cultures patient was readmitted d u e to occurrence of diarrhoea (including culture for Clostridium defficile and toxin A) up to five times a day. The stools were mucoid on were negative. Examination of the stools disclosed B. appearance with no evidence of blood yet, they were hominis following which treatment with intravenous accompanied by colicky abdominal pains and nausea. metronidazole 2 g/day was started. Ten days later the patient was discharged after an improvement in his Address correspondence to: Y. Shoenfeld, Department of Medicine 'B' and Autoimmune Research Unit, Sheba Medical Center, Tel-Hashomer condition, disappearance of the diarrhoea and resumption of his appetite. 52621, Israel. 0163-4453/96/040057+03 $12.00/0
© 1996 The British Society for the Study of Infection
58
Y. Levy and J. George Discussion
Blastocystis hominis is an anaerobic parasite. By light microscopic examination, three forms of the parasite can be discerned: vacuolar, granular and ameboid) The vacuolar form is the most prevalent. The size of the parasite is 8 - 1 0 gm and it is transmitted via the faecal-oral route or through contaminated water.2' 3 Controversy exists as to whether B. hominis can cause gastrointestinal complaints either in symptomatic or in asymptomatic patients. ~ In the initial reports the parasite was incriminated as a pathogen being responsible for abdominal pains and diarrhoea, 5-7 however in the recent years it is regarded as pathogenic only in special circumstances such as states of immunosuppression. It should be noted that several reports of diarrhoea epidemics have been described in the literature, which have been associated with the occurrence of the parasite) Different screening studies have shown that it was present in varying frequencies (1-25%) of the either symptomatic or asymptomatic individuals, xz-~3In a very recent study Aucott and Ravidin 14 suggested that the parasite is not a direct cause of the disease, based on following observations:
1. It could be isolated in symptomatic as well as asymptomatic subjects. 2. The parasite was shown to disappear without specific therapy. 3. Its occurrence was demonstrated during diarrhoea and following its disappearance. A recent study reporting follow-up of 120 symptomatic and asymptomatic subjects with B. hominis evidenced continued presence of the parasite, regardless of the clinical course. Eighty percent of the asymptomatic individuals were found to carry the parasite on repetitive stool cultures, while 77% of the symptomatic patients with protracted clinical course continued to have positive stool cultures. Another work ~6 engaged in the follow-up of patients with positive stool cultures of the parasite and gastrointestinal manifestation revealed, on consecutive cultures, the appearance of other pathogens such as Giardia and entameba histolytica serving as more probable aetiologies for the diarrhoea. Miller and Minshew ~7 evaluated hospitalized patients shown to harbour B. hominis, Concluding that other causes for the gastrointestinal complaints could be found including gastrointestinal bleeding, irritable bowel syndrome and medications. There are, however several authors attributing a pathogenic role to the parasite. 3,~s If, indeed such clinical
symptoms and signs exist they consist only of mild to moderate diarrhoea, seldom reaching significant values of 2-3 litres a day. This can sometimes be accompanied by nausea, vomiting, abdominal fullness anorexia, abdominal pains and, rarely, fever. Diarrhoea can be protracted (lasting up to a month) or intermittent, and could sometimes contain abundant eosinophils. The parasite does not enter the intestinal mucosa. 19 When gastrointestinal symptoms do occur they are manifested acutely in patients with malignancies or AIDS, 2° 23 and occasionally, in children where it might be associated with weight loss. 4 Blastocystis is considered pathogenic when the number of parasites in the stools, seen under x 400 magnification field equals or is higher than five. 24 Some authors oppose this definition, stating the pathogenicity is not dependent on the numbers of parasites) 2 Two other studies further establishing the pathogenic nature of the parasite in the gastrointestinal tract, came from the far east. The first, 25 retrospectively demonstrated B. hominis in 17.5% of 19 252 stool samples. In 25.6% of the positives, other parasites were simultaneously apparent and in 79.6% it was either present in large numbers or with other nonpathogenic parasites. Eighteen percent of the patients were treated with metronidazole due to either large number of parasites in the stools or because of recurrent gastrointestinal complaints. All the patients treated were found to have a complete clinical response with no evidence of the parasite in their subsequent stool examinations. In the second study the authors examined 1000 stool samples in children of different ages. The parasite has been isolated in 20.3% of the cases and in 75% of these no other pathogenic parasites have been noted. The clinical picture evidenced among the positive carriers included mild diarrhoea (sometimes recurrent), abdominal pains, nausea, anorexia and malaise. The acceptable treatment of choice for B. hominis consists of metronidazole and other alternative treatment modalities include: cotrimoxasole, ketoconazole and pentamidine)6, 27 In summary, B. hominis can be recovered from the stools of 2-16% of the general population, either in healthy or in those suffering from diarrhoea. The diagnosis is made by correlating the clinical picture with the stool examination and is strongly supported by detecting the parasite in abundant numbers in stool samples with no other demonstrable parasitic pathogens. The patient under discussion was admitted with an impressive clinical picture consisting of general deterioration, marked leukocytosis and rapid development of hypoalbuminaemia. Other presumptive pathogens that could possibly induce these findings were not identified. To our knowledge,
Severe B. Hominis this is the first description so far, in which Blastocystic infection has been associated with a relatively severe clinical course in a patient not being immunosuppressed. Furthermore, no association has yet been noted between the emergence of this infection and antibiotic treatment and it may indeed merit further assessment.
References 1 2ierdtCH, RudeWS, BullBS, ProtozoancharacteristicsofBlastocystis hominis, Am J Clin Pathol 1967; 48: 495-501. 2 Nimri L, Batchoun R. IntestinaI colonization of symptomatic and asymptomatic schoolchildren with Blastocytosis hominis. ] Clin Microbial 1994; 32: 2865-2866. 3 Nimri LR Evidence of an epidemic of Blastocystis hominis infections in preschool children in northern Jordan. J Clin Microbial 1993; 31: 2706-2708. 4 Pedro-Borer J, Auguet I, Rubies-Prat f. Blastocytosis hominis: a controversial enteric protozoon, l Clin Gastroenterol 1992; 14: 8889. 5 Barilari MJ. Blastocytosis horninis (sic). Prensa Med ANent 1924; 11: 854-858. 6 Caderin CC. E1 Blastocytosis hominis coma parasito patogeno dei hombre. Rev Med Trap Parasitol 1937; 3: 207-209. 7 Sangiogri G. Pathogenicity of Blastocytosis hominis. Pathologica 1930; 22: 173-176. 8 Miller JH. The protozoa. In: Braude AI, Davis CE, Fierer, eds. Infectious dseases and medical microbiology. Philadelphia: WB Saunders Co., 1986: 610-625. 9 Smith JW, Bartlett MJ. Intestinal and atrial protozoa. In: Balows A, Hausler WJ, eds Diagnostic procedures for bacterial, mycotic and parasitic i@ctions. Washington, D.C.: American Public Health Association, 1981: 1153-1174. 10 UdkowMP, MarkellEK. Blastocystishominis: Prevalence in asymptomatte versus symptomatic hosts. J Infect Dis 1993; 168:242 244.
59
11 Kappus KD, Lundgren RG, Juranek DD, Roberts JM, Spencer HC. Intestinal parasitism in the United States: update on a continuing problem. Am ] trap Meal Hyg 1994; 50: 705-713. 12 Martin-Sanches AM, Canut-Blasco A, Rodrigues-Hernandez J, Montes-Martinez I, Carcia-Rodriguez JA. Epidemiology and clinical significance of Blastocytosis hominis in different population groups in Salamanca (Spain). Eur] Epiderniol 1992; 8: 553-559. 13 O'Goran MA, Ornestein SR, Proujansky R, Wadowsky RM, Putnam PE, Kocoshis SA. Prevalence and characteristics of Blastocytosis homtnis infection in children. Clin Pediatr (Phila) 1993; 32: 91-96. 14 Aucott IN, Ravidin JI. Amebiasis and "nonpathogenic" intestinal protozoa. Infect Dis Clin North Am 1993; 7: 467-485. 15 Senay, MacPherson D. Blastocystis hominis epidemiology and neutral history. J Infect Dis 1990: 162: 987. 16 Markell EK, Udkow ME BIastocystis hominis: pathogen or fellow traveler.) Am J Trap Med Hyg 1986; 35: 1023. 17 Miller RA, Minshew BH. Blastocystis horninis: An organism in search of disease. Rev Infect Dis 1988; 10: 930. 18 Logar J, Andlovic A, Poljsac-Prijatelj M. Incidence of Blastocystis hominis in patients with diarrhoea. J Infect 1994; 28: 151-154. 19 Zuckerman MJ, Watts MT, Ha I-I, Meriano FV. Blastocytosis hominis infection and intestinal injury. Am ] Med Set 1994; 308: 96-101. 20 Garavelli PL, Orsi P, Seaglione L. Blastocystis hominis infection during AIDS. Lancet 1988; 2: 1364. 21 Carcia LS, Bruuehner DA, Clancy MN. Clinical relevance of Blastocystis hominis. Lancet 1984; 1: 1233-1234, 22 Kain KC, Noble MA, Freeman HI. Epidemiology and clinical features associated with Blastocystis hominis infection. Diagn Microbial Infect Dis 0000; 8: 235-244. 23 Ralston KVI, Winans R, Rodrigues S. Blastocystis hominis: Pathogen or not? Rev lnfect Dis 1989; 11: 661. 24 Zierdt CH. Blastocytosis hominis, a protozoan parasite and intestinal pathogen of human beings. Clin Microbial News 1983; 5: 57. 25 Sheehan DJ, Raucher BG, McKitrick JC. Association of Blastoeystis hominis with signs and symptoms of human disease. J Clin Microbial 1986; 24: 548-550. 26 Zierdt CH, Swan JC, Hosseini J. In vitro response of Blastocystis hominis, to antiprotozoaI drugs, l Protozool 1983; 30: 332-394. 27 Schwartz E, Houston R, Effect of co-trimoxazole on stool recovery of Blastocystis hominis [letter], Lancet 1992; 339: 428-429.
CASE REPORT
Severe Blastocystis homini$ in a n Elderly Man Y. Levy, J. George and Y. Shoenfeld Department of Medicine 'B' and the Unit of Autoimmune Disease Research, Sheba Medical Center, Tel-Hashomer and Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel Accepted for publication 8 March 1996
We describe a unique case of severe Blastocystis hominis infection in an dderly man with severe dehydration, marked leukocytosis and hypoalbuminaemia after antibiotic treatment for right pneumonia. The patient recovered after treatment with metronidazole. This case presentation demonstrates the ability of B. hominis to induce severe gastrointestinal manifestations and general deterioration, particularly in light of the controversy surrounding its possible potential pathogenicity. We believe, therefore that aggressive treatment with metronidazole should be instituted, following demonstration of the parasite in the stools, if diarrhoea is protracted, since it may well be attributed to Blastocystis infection.
Introduction
The patient also complained of fatigue and low grade fever rising up to 38 °C in the evenings. On examination Blastocystis hominis is an anaerobic parasite which m a y he appeared exhausted with blood pressure of 120/ be associated with mild diarrhoea. Herein we describe 80 m m H g while standing and 107/80 m m H g when lying an elderly m a n admitted due to prolonged diarrhoea and down. His temperature was 3 6.8 °C, respirations (16 per general deterioration following antibiotic treatment. minute), his skin turgor was low and few crackles were heard over both lung bases. A grade II systolic m u r m u r was heard over his aortic valve and his abdomen was Case Report mildly and diffusely tender. No enlargement of either the A 74-year-old m a n with a history of non-insulin diabetes liver or the spleen was evident and his rectal examination mellitus controlled with diet, and hypertension was ad- was unrevealing. His blood tests disclosed: haemoglobin 13.4 g/dl, white mitted to our ward due to diarrhoea and general deblood cell count 30 1 3 0 m m 3 (neutrophils 90%, terioration. Five years before his admission he underwent lymphocytes 6%, monocytes 4%), platelet count replacement of the aortic valve (with coronary artery 252 000 m m 3, urea 49 mg/dl, creatinine 1.4 mg/dl, glucbypass grafting) due to aortic stenosis. Three weeks previously he washospitalized due to the ose 182 mg/dl, chloride 110mEq/dl, sodium 1 3 4 m E q / dl, potassium 2.8 mEq/dl, CO2 14 mg/dl, uric acid 8 mg/ appearance of fever and productive cough and a chest X-ray study demonstrated a lobar infiltrate in his right dl, albumin 2.7 g/dl, globulin 2.0 g/dl. Three weeks before his present admission his blood lung base. The patient was treated by intravenous adtests showed: haemoglobin 14.0 g/dl, white cell count of ministration of cefuroxime, resulting in rapid clinical 5 6 5 0 m m 3 with normal differential, platelet count of improvement and was discharged with a re1 5 0 0 0 0 m m 3 albumin 4.3g/dl, urea zigmg/dl, crecommendation to continue treatment with oral ceatinine 1.1mg/dl, potassium 4.1mEq/dl and sodium fnroxime for 10 days. 141 mEq/dl. Two weeks following his previous hospitalization the During hospitalization his blood and stool cultures patient was readmitted d u e to occurrence of diarrhoea (including culture for Clostridium defficile and toxin A) up to five times a day. The stools were mucoid on were negative. Examination of the stools disclosed B. appearance with no evidence of blood yet, they were hominis following which treatment with intravenous accompanied by colicky abdominal pains and nausea. metronidazole 2 g/day was started. Ten days later the patient was discharged after an improvement in his Address correspondence to: Y. Shoenfeld, Department of Medicine 'B' and Autoimmune Research Unit, Sheba Medical Center, Tel-Hashomer condition, disappearance of the diarrhoea and resumption of his appetite. 52621, Israel. 0163-4453/96/040057+03 $12.00/0
© 1996 The British Society for the Study of Infection
58
Y. Levy and J. George Discussion
Blastocystis hominis is an anaerobic parasite. By light microscopic examination, three forms of the parasite can be discerned: vacuolar, granular and ameboid) The vacuolar form is the most prevalent. The size of the parasite is 8 - 1 0 gm and it is transmitted via the faecal-oral route or through contaminated water.2' 3 Controversy exists as to whether B. hominis can cause gastrointestinal complaints either in symptomatic or in asymptomatic patients. ~ In the initial reports the parasite was incriminated as a pathogen being responsible for abdominal pains and diarrhoea, 5-7 however in the recent years it is regarded as pathogenic only in special circumstances such as states of immunosuppression. It should be noted that several reports of diarrhoea epidemics have been described in the literature, which have been associated with the occurrence of the parasite) Different screening studies have shown that it was present in varying frequencies (1-25%) of the either symptomatic or asymptomatic individuals, xz-~3In a very recent study Aucott and Ravidin 14 suggested that the parasite is not a direct cause of the disease, based on following observations:
1. It could be isolated in symptomatic as well as asymptomatic subjects. 2. The parasite was shown to disappear without specific therapy. 3. Its occurrence was demonstrated during diarrhoea and following its disappearance. A recent study reporting follow-up of 120 symptomatic and asymptomatic subjects with B. hominis evidenced continued presence of the parasite, regardless of the clinical course. Eighty percent of the asymptomatic individuals were found to carry the parasite on repetitive stool cultures, while 77% of the symptomatic patients with protracted clinical course continued to have positive stool cultures. Another work ~6 engaged in the follow-up of patients with positive stool cultures of the parasite and gastrointestinal manifestation revealed, on consecutive cultures, the appearance of other pathogens such as Giardia and entameba histolytica serving as more probable aetiologies for the diarrhoea. Miller and Minshew ~7 evaluated hospitalized patients shown to harbour B. hominis, Concluding that other causes for the gastrointestinal complaints could be found including gastrointestinal bleeding, irritable bowel syndrome and medications. There are, however several authors attributing a pathogenic role to the parasite. 3,~s If, indeed such clinical
symptoms and signs exist they consist only of mild to moderate diarrhoea, seldom reaching significant values of 2-3 litres a day. This can sometimes be accompanied by nausea, vomiting, abdominal fullness anorexia, abdominal pains and, rarely, fever. Diarrhoea can be protracted (lasting up to a month) or intermittent, and could sometimes contain abundant eosinophils. The parasite does not enter the intestinal mucosa. 19 When gastrointestinal symptoms do occur they are manifested acutely in patients with malignancies or AIDS, 2° 23 and occasionally, in children where it might be associated with weight loss. 4 Blastocystis is considered pathogenic when the number of parasites in the stools, seen under x 400 magnification field equals or is higher than five. 24 Some authors oppose this definition, stating the pathogenicity is not dependent on the numbers of parasites) 2 Two other studies further establishing the pathogenic nature of the parasite in the gastrointestinal tract, came from the far east. The first, 25 retrospectively demonstrated B. hominis in 17.5% of 19 252 stool samples. In 25.6% of the positives, other parasites were simultaneously apparent and in 79.6% it was either present in large numbers or with other nonpathogenic parasites. Eighteen percent of the patients were treated with metronidazole due to either large number of parasites in the stools or because of recurrent gastrointestinal complaints. All the patients treated were found to have a complete clinical response with no evidence of the parasite in their subsequent stool examinations. In the second study the authors examined 1000 stool samples in children of different ages. The parasite has been isolated in 20.3% of the cases and in 75% of these no other pathogenic parasites have been noted. The clinical picture evidenced among the positive carriers included mild diarrhoea (sometimes recurrent), abdominal pains, nausea, anorexia and malaise. The acceptable treatment of choice for B. hominis consists of metronidazole and other alternative treatment modalities include: cotrimoxasole, ketoconazole and pentamidine)6, 27 In summary, B. hominis can be recovered from the stools of 2-16% of the general population, either in healthy or in those suffering from diarrhoea. The diagnosis is made by correlating the clinical picture with the stool examination and is strongly supported by detecting the parasite in abundant numbers in stool samples with no other demonstrable parasitic pathogens. The patient under discussion was admitted with an impressive clinical picture consisting of general deterioration, marked leukocytosis and rapid development of hypoalbuminaemia. Other presumptive pathogens that could possibly induce these findings were not identified. To our knowledge,
Severe B. Hominis this is the first description so far, in which Blastocystic infection has been associated with a relatively severe clinical course in a patient not being immunosuppressed. Furthermore, no association has yet been noted between the emergence of this infection and antibiotic treatment and it may indeed merit further assessment.
References 1 2ierdtCH, RudeWS, BullBS, ProtozoancharacteristicsofBlastocystis hominis, Am J Clin Pathol 1967; 48: 495-501. 2 Nimri L, Batchoun R. IntestinaI colonization of symptomatic and asymptomatic schoolchildren with Blastocytosis hominis. ] Clin Microbial 1994; 32: 2865-2866. 3 Nimri LR Evidence of an epidemic of Blastocystis hominis infections in preschool children in northern Jordan. J Clin Microbial 1993; 31: 2706-2708. 4 Pedro-Borer J, Auguet I, Rubies-Prat f. Blastocytosis hominis: a controversial enteric protozoon, l Clin Gastroenterol 1992; 14: 8889. 5 Barilari MJ. Blastocytosis horninis (sic). Prensa Med ANent 1924; 11: 854-858. 6 Caderin CC. E1 Blastocytosis hominis coma parasito patogeno dei hombre. Rev Med Trap Parasitol 1937; 3: 207-209. 7 Sangiogri G. Pathogenicity of Blastocytosis hominis. Pathologica 1930; 22: 173-176. 8 Miller JH. The protozoa. In: Braude AI, Davis CE, Fierer, eds. Infectious dseases and medical microbiology. Philadelphia: WB Saunders Co., 1986: 610-625. 9 Smith JW, Bartlett MJ. Intestinal and atrial protozoa. In: Balows A, Hausler WJ, eds Diagnostic procedures for bacterial, mycotic and parasitic i@ctions. Washington, D.C.: American Public Health Association, 1981: 1153-1174. 10 UdkowMP, MarkellEK. Blastocystishominis: Prevalence in asymptomatte versus symptomatic hosts. J Infect Dis 1993; 168:242 244.
59
11 Kappus KD, Lundgren RG, Juranek DD, Roberts JM, Spencer HC. Intestinal parasitism in the United States: update on a continuing problem. Am ] trap Meal Hyg 1994; 50: 705-713. 12 Martin-Sanches AM, Canut-Blasco A, Rodrigues-Hernandez J, Montes-Martinez I, Carcia-Rodriguez JA. Epidemiology and clinical significance of Blastocytosis hominis in different population groups in Salamanca (Spain). Eur] Epiderniol 1992; 8: 553-559. 13 O'Goran MA, Ornestein SR, Proujansky R, Wadowsky RM, Putnam PE, Kocoshis SA. Prevalence and characteristics of Blastocytosis homtnis infection in children. Clin Pediatr (Phila) 1993; 32: 91-96. 14 Aucott IN, Ravidin JI. Amebiasis and "nonpathogenic" intestinal protozoa. Infect Dis Clin North Am 1993; 7: 467-485. 15 Senay, MacPherson D. Blastocystis hominis epidemiology and neutral history. J Infect Dis 1990: 162: 987. 16 Markell EK, Udkow ME BIastocystis hominis: pathogen or fellow traveler.) Am J Trap Med Hyg 1986; 35: 1023. 17 Miller RA, Minshew BH. Blastocystis horninis: An organism in search of disease. Rev Infect Dis 1988; 10: 930. 18 Logar J, Andlovic A, Poljsac-Prijatelj M. Incidence of Blastocystis hominis in patients with diarrhoea. J Infect 1994; 28: 151-154. 19 Zuckerman MJ, Watts MT, Ha I-I, Meriano FV. Blastocytosis hominis infection and intestinal injury. Am ] Med Set 1994; 308: 96-101. 20 Garavelli PL, Orsi P, Seaglione L. Blastocystis hominis infection during AIDS. Lancet 1988; 2: 1364. 21 Carcia LS, Bruuehner DA, Clancy MN. Clinical relevance of Blastocystis hominis. Lancet 1984; 1: 1233-1234, 22 Kain KC, Noble MA, Freeman HI. Epidemiology and clinical features associated with Blastocystis hominis infection. Diagn Microbial Infect Dis 0000; 8: 235-244. 23 Ralston KVI, Winans R, Rodrigues S. Blastocystis hominis: Pathogen or not? Rev lnfect Dis 1989; 11: 661. 24 Zierdt CH. Blastocytosis hominis, a protozoan parasite and intestinal pathogen of human beings. Clin Microbial News 1983; 5: 57. 25 Sheehan DJ, Raucher BG, McKitrick JC. Association of Blastoeystis hominis with signs and symptoms of human disease. J Clin Microbial 1986; 24: 548-550. 26 Zierdt CH, Swan JC, Hosseini J. In vitro response of Blastocystis hominis, to antiprotozoaI drugs, l Protozool 1983; 30: 332-394. 27 Schwartz E, Houston R, Effect of co-trimoxazole on stool recovery of Blastocystis hominis [letter], Lancet 1992; 339: 428-429.