chain reaction testing of stool samples suggested that symptomatic infection can exist even when sufficient quantities of the organism do not exist for identification through direct microscopy. diagnosis-by-exclusion: some physicians diagnose blastocystis infection by excluding all other causes, such as infection with other organisms, food intolerances, colon cancer, etc. this method can be time-consuming and expensive, requiring many tests such as endoscopy and colonoscopy. disregarding blastocystis : in the early to mid-1990s, some us physicians suggested all findings of blastocystis are insignificant. no recent publications expressing this opinion could be found. not clinically available the following diagnostic methods are not routinely available to patients. researchers have reported that they are more reliable at detecting infection, and in some cases can provide the physician with information to help determine whether blastocystis infection is the cause of the patient's symptoms: serum antibody testing: a 1993 research study performed by the nih with united states patients suggested that it was possible to distinguish symptomatic and asymptomatic infection with blastocystis using serum antibody testing. the study used blood samples to measure the patient's immune reaction to chemicals present on the surface of the blastocystis cell. it found that patients diagnosed with symptomatic blastocystis infection exhibited a much higher immune response than controls who had blastocystis infection but no symptoms. the study was repeated in 2003 at ain shams university in egypt with egyptian patients with equivalent results. fecal antibody testing: a 2003 study at ain shams university in egypt indicated that patients symptomatically infected could be distinguished with a fecal antibody test. the study compared patients diagnosed with symptomatic blastocystis infection to controls who had blastocystis infection but no symptoms. in the group with symptoms, iga antibodies to blastocystis were detected in fecal specimens that were not present in the healthy control group. stool culture: culturing has been shown to be a more reliable method of identifying infection. in 2006, researchers reported the ability to distinguish between disease causing and non-disease causing isolates of blastocystis using stool culture. blastocystis cultured from patients who were sick and diagnosed with blastocystis infection produced large, highly adhesive amoeboid forms in culture. these cells were absent in blastocystis cultures from healthy controls. subsequent genetic analysis showed the blastocystis from healthy controls was genetically distinct from that found in patients with symptoms. protozoal culture is unavailable in most countries due to the cost and lack of trained staff able to perform protozoal culture. genetic analysis of isolates: researchers have used techniques which allow the dna of blastocystis to be isolated from fecal specimens. this method has been reported to be more reliable at detecting blastocystis in symptomatic patients than stool culture. this method also allows the species group of blastocystis to be identified. research is continuing into which species groups are associated with symptomatic (see genetics and symptoms) blastocystosis. immuno-fluorescence (ifa) stain: an ifa stain causes blastocystis cells to glow when viewed under a microscope, making the diagnostic method more reliable. ifa stains are in use for giardia and cryptosporidium for both diagnostic purposes and water quality testing. a 1991 paper from the nih described the laboratory development of one such stain. however, no company currently offers this stain commercially. classification reports conflict regarding whether blastocystis causes disease in humans. these reports resulted in a brief debate in medical journals in the early 1990s between some physicians in the united states who believed that blastocystis was harmless, and physicians in the united states and overseas who believed it could cause disease. at the time, it was common practice to identify all blastocystis from humans as blastocystis hominis, while blastocystis from animals was identified differently (e.g. blastocystis ratti from rats). research performed since then has shown that the concept of blastocystis hominis as a unique species of blastocystis infecting humans is not supported by microbiological findings. although one species group associated with primates was found, it was also discovered that humans can acquire infection from any one of nine species groups of blastocystis which are also carried by cattle, pigs, rodents, chickens, pheasants, monkeys, dogs, and other animals. research has suggested that some types produce few or no symptoms, while others produce illness and intestinal inflammation. researchers have suggested conflicting reports may be due to the practice of naming all blastocystis from humans blastocystis hominis and have proposed discontinuing the use of that term. a standard naming system for blastocystis organisms from humans and animals has been proposed which names blastocystis isolates according to the genetic identity of the blastocystis organism rather than the host. the naming system used identifies all isolates as blastocystis sp. subtype nn where nn is a number from 1 to 9 indicating the species group of the blastocystis organism. the identification of the species can not be performed with a microscope at this time, because the different species look alike. identification requires equipment for genetic analysis that is common in microbiology laboratories, but not available to most physicians. some new scientific papers have begun using the standard naming system. treatment there is a lack of scientific study to support the efficacy of any particular treatment. an additional review published in 2009 made a similar conclusion, noting that because the diagnostics in use have been unreliable, it has been impossible to determine whether a drug has eradicated the infection, or just made the patient feel better. historical reports, such as one from 1916, note difficulty associated with eradication of blastocystis from patients, describing it as "an infection that is hard to get rid of." a 1999 in vitro study from pakistan found 40% of isolates are resistant to common antiprotozoal drugs. a study of isolates from patients diagnosed with ibs found 40% of isolates resistant to metronidazole and 32% resistant to furazolidone. drugs reported in studies to be effective in eradicating blastocystis infection have included metronidazole, trimethoprim, tmp-smx (only trimethoprim is active with sulphamethoxazole demonstrating no activity), tetracycline, doxycycline, nitazoxanide, pentamidine, paromomycin and iodoquinol. iodoquinol has been found to be less effective in practice than in-vitro. miconazole and quinacrine have been reported as effective agents against blastocystis growth in-vitro. rifaximin, and albendazole have shown promise as has ivermectin which demonstrated high effectiveness against blastocystis hominis isolates in an in vitro study. there is also evidence that the probiotic yeast saccharomyces boulardii, and the plant mallotus oppositifolius may be effective against blastocystis infections. physicians have described the successful use of a variety of discontinued antiprotozoals in treatment of blastocystis infection. emetine was reported as successful in cases in early 20th century with british soldiers who contracted blastocystis infection while serving in egypt. in vitro testing showed emetine was more effective than metronidazole or furazolidone. emetine is available in the united states through special arrangement with the center for disease control. clioquinol (entero-vioform) was noted as successful in treatment of blastocystis infection but removed from the market following an adverse event in japan. stovarsol and narsenol, two arsenic-based antiprotozoals, were reported to be effective against the infection. carbarsone was available as an anti-infective compound in the united states as late as 1991, and was suggested as a possible treatment. the reduction in the availability of antiprotozoal drugs has been noted as a complicating factor in treatment of other protozoal infections. for example, in australia, production of diloxanide furoate ended in 2003, paromomycin is available under special access provisions, and the availability of iodoquinol is limited. epidemiology percentage of stool samples from us states found to contain various protozoa in 1987 and 2000 number of stool samples from canadian lab found to contain various protozoa in 2005 like other protozoal infections, the prevalence of blastocystis infection varies depending on the area investigated and the population selected. a number of different species groups of blastocystis infect humans, with some being reported to cause disease while others do not. to date, surveys have not distinguished between different types of blastocystis in humans, so the significance of findings may be difficult to evaluate. developing countries have been reported to have higher incidences, but recent studies suggest that symptomatic infection with blastocystis may be prevalent in certain industrialized countries, as well. a study on parasites in stool samples in the united states during 2000 found blastocystosis to be the most common parasitic infection in the population, occurring in 23% of individuals. a canadian study of samples received in 2005 identified blastocystis as the most prevalent protozoal infection identified. a study in pakistan identified blastocystis infection in 7% of the general population and 46% of patients with irritable bowel syndrome. the study used stool culture for identification. a 2014 study of samples from 93 children from the senegal river basin found that 100% of the population was infected with blastocystis. other animals experimental infection in immunocompetent and immunocompromised mice has produced intestinal inflammation, altered bowel habits, lethargy, and death. chronic diarrhea has been reported in non-human higher primates. research while many enteric protists are the subject of research, blastocystis is unusual in that basic questions concerning how it should be diagnosed and treated and how it causes disease remain unsettled. the following groups have ongoing research programs directed at these questions: country organization year established research focus research singapore national university of singapore 1991 co-culture, pathogenesis tan singh malaysia university of malaya 1996 ultrastructure, pathogenicity kumar united states blastocystis research foundation 2006 phylogenetics, pathogenicity, treatment article denmark statens serum institut 2006 diagnostics stensvold cr