it is estimated that 3.5 billion people are affected , and 450 million are ill as a result of these infections , the majority being children . in ethiopia , however , there are difficulties in estimating the exact burden of parasitic infections in the country . although there are several factors that make estimating the number and burden of intestinal parasitic infections difficult , lack of accurate diagnostic tools is the major one [ 39 ] . although several diagnostic methods such as kato - katz and formol - ether concentration ( fec ) techniques are available , direct wet mount is the commonly used as a reliable diagnosis method for the diagnosis of intestinal parasitic infections generally in africa and particularly in ethiopia [ 1013 ] . however , low sensitivity of the direct wet mount technique has been reported in the detection of low - intensity infection elsewhere . this shows that the use of direct wet mount as a confirmatory test will significantly increase misdiagnosis of intestinal helminth infections . the reliable diagnosis of intestinal parasitic infections requires a more rapid , easy , and sensitive method . therefore , this study aimed to evaluate the operational characteristics ( sensitivity and negative predictive value ( npv ) ) of wet mount , fec , and kato - katz techniques in intestinal parasitic infection endemic locality of ethiopia . a cross - sectional study was conducted in atse fasil elementary school from march 10 to june 30 , 2008 in northwest ethiopia , latitude of 12.55 ( 12330 n ) , a longitude of 37.43 ( 372532 e ) , and an elevation of 1,994 meters above sea level . students who had no history of antihelmenthic drug administration in the two weeks prior to screening , absence of any other serious chronic infection , and had ability to give stool samples were included in the study . students were provided with plastic stool cups and asked to bring approximately 3  gm of fresh stool of their own . approximately 41.7  mg and 20  mg of the stool specimen were used to prepare a single kato - katz thick smear and wet mount preparation , respectively . all the samples were processed in the temporally established laboratory except the kato - katz smear count of the common helminthes , which was done at the laboratory of the university of gondar . the egg per gram of faeces ( epgs ) counts for hookworm were done immediately in the temporary laboratory . the kato - thick smear counts for all the common helminthes except for hookworm were done at the laboratory of university of gondar . before starting the actual work , the specimens were also checked for serial number , quantity , and procedures of collection .   to eliminate observer bias , each stool sample was examined immediately in the temporary laboratory by two experienced laboratory technicians . the technicians were not told about the health and other status of the study participants . in cases where the results were discordant , the results of the third expert reader were considered the final result . since a  gold standard test is not available for detection of intestinal parasites , the operational characteristics ( sensitivity and npv ) were estimated using the combined results from the three methods as diagnostic sensitivities , npv , and kappa were determined for the various tests to evaluate their operational characteristics . the study protocol was reviewed and approved by the ethical review committee of the department of medical laboratory technology , university of gondar . written informed consent was obtained from all study participants and mothers / caretakers of students under 18 who participated in the study after explaining the purpose and objective of the study . students who were positive for intestinal parasites were treated based on the recommended drug regimen at azezo clinic , gondar . a total of 354 students aged 519 years participated in the study ; 146 ( 53.9% ) and 125 ( 46.1% ) were males and females , respectively . the prevalences of intestinal parasites using single wet mount , fec , and kato - katz thick smear techniques were 38.4% , 57.1% , and 59% , respectively ( table 1 ) . the detection rate when two techniques used at a time was 69.8% ( for kato - thick and fec ) , 61% ( for wet mount and fec ) , and 68% ( for wet mount and kato - thick smear technique ) . the detection rate was 72.9% ( 258/354 ) when all the three techniques were used together . the overall prevalence of schistosoma mansoni , ascaris lumbricoides , trichuris trichiura , and hookworm infections was 43.5% , 28.8% , 18.1% , and 8.2% , respectively ( table 2 ) .   among the 354 study participants diagnosed 209 the sensitivity and npv of kato - katz are 81.0% ( confidence interval ( ci ) = 0.7930.810 ) and 66.2% ( ci = 0.630.622 ) , respectively ( table 1 ) . the fec detected 56 negative samples that were positive by the gold standard , indicating 78.3% ( ci = 0.7660.783 ) and 63.2% ( ci = 0.60363 ) sensitivity and npv , respectively ( table 1 ) . as compared to single fec , single kato - katz detected 53 , 83 , 56 , and 95 cases of ascaris lumbricoides , schistosoma mansoni , trichuris trichiura , and hook worm , respectively ( table 3 ) , indicating substantial (  = 0.80 ) , moderate (  = 0.58 ) , and moderate (  = 0.59 )  agreement between the fec and kato - katz for the diagnosis of ascaris lumbricoides , schistosoma mansoni and trichuris trichiura , respectively ( table 3 ) . furthermore , kato - katz detects 113 cases that were negative by a single wet mount ( table 4 ) . the  agreement between the wet mount and kato - katz methods for the diagnosis of ascaris lumbricoides and hook worm was substantial (  = 0.61 for ascaris lumbricoides ,  = 0.65 for hookworm ) ( table 4 ) . a single kato - katz had significantly lower detection capacity than the fec method in diagnosing hookworm . this poor performance of the kato - katz in detecting hookworm infection is explained by the following facts . first , hookworm has lower egg laying capacity , more likely to be missed by kato - katz . second , hookworm eggs disappear due to glycerin when long time delays occur between kato - katz smear preparation and microscopic examination . furthermore , unlike fec , small amount of fecal material is processed in kato - katz technique . the chance of detecting hookworm infection by kato - katz from small amount of faecal material is suggested to be lower [ 20 , 21 ] . therefore , small amount of fecal material used in kato - katz technique may be the reason for lower detection capacity of kato - katz . the finding of the present study showed that , as compared to the kato - katz and fec techniques , direct wet mount exhibited very low sensitivity for the detection of ascaris lumbricoides , schistosoma mansoni , trichuris trichiura and hookworm . the use of direct wet mount alone as an indicator of intestinal parasitic infections is also suggested to be insufficient by other studies . however , in most laboratories in ethiopia , the direct wet mount is the preferred stool parasitological detection technique . this shows that , since the use of direct wet mount as a confirmatory test will significantly increase misdiagnosis of intestinal helminth infections , the use of another diagnosing method is mandatory to decrease the consequences caused in the community due to intestinal helminth infections . as compared to fec and direct wet mount techniques , the kato - katz exhibited high sensitivity for the detection of schistosoma mansoni , trichuris trichiura , and ascaris lumbricoides . this shows that the use of the kato - katz as a confirmatory test for schistosoma mansoni , trichuris trichiura , and ascaris lumbricoides will reduce the morbidity and mortality caused by these parasites by reducing misdiagnosis . however , lack of previous similar study makes difficulty in making rigorous discussion on this finding . in conclusion , the present study revealed that kato - katz technique and fec methods showed a better sensitivity than the traditional direct wet mount method . therefore , the employment of fec technique as a confirmatory test in routine laboratory examination of stool and kato - katz in epidemiological studies will significantly aid in accurate determination and management of parasitic infections in the community .
objective . 
 the aim of this study was to evaluate the operational characteristics ( sensitivity and negative predictive value ( npv ) ) of wet mount , formol - ether concentration ( fec ) , and kato - katz techniques for the determination of intestinal parasitic infections . method . 
 a total of 354 faecal specimens were collected from students in northwest ethiopia and screened with kato - katz , wet mount , and fec for the presence of intestinal parasitic infection . since 
 a gold standard test is not available for detection of intestinal parasites , the combined results from the three methods were used as diagnostic gold standard . 
 result . 
 the prevalences of intestinal parasites using the single wet mount , fec , and kato - katz thick smear techniques were 38.4% , 57.1% , and 59% , respectively . taking the combined results of three techniques as a standard test for intestinal parasitic infection , the sensitivity and negative predictive value of kato - katz is 81.0% ( confidence interval ( ci )  =  0.7930.810 ) and 66.2% ( ci  =  0.630.622 ) , respectively . 
 the fec detected 56 negative samples that were positive by the gold standard , indicating 78.3% ( ci  =  0.7660.783 ) and 63.2% ( ci  =  0.60363 ) sensitivity and npv , respectively . 
 furthermore , kato - katz detects 113 cases that were negative by a single wet mount . 
 the  agreement between the wet mount and kato - katz methods for the diagnosis of ascaris lumbricoides and hookworm was substantial (  = 0.61 for ascaris lumbricoides ,  = 0.65 for hookworm ) .