Ethiopia is one of the hotspot areas for hookworm and other STHs in the world (20–22). Thus, an integrated hookworm prevention and control measure is needed. Appropriate diagnosis is one of the most important tools in fighting of the disease. It is recommended to use Kato-Katz, FEC and MacMaster methods for the detection of human soil transmitted helminthes (STHs) including hookworms. All of these and other techniques rely on visual examination of a small sample of stool to determine the presence and number of the parasite’s ova with different sensitivities especially in low transmission areas (23, 24). It is clear that they are helpful in the disease diagnosis; however, they may not be equally sensitive and could also have their own limitations. For instance, DWMM is solely used in almost all health care facilities in Ethiopia and other developing countries due to its low cost, and easy procedure. Nevertheless, it is undoubtedly known that the sensitivity of DWMM is poor (25, 26). In spite of this, there are little studies that have evaluated the clinical sensitivity of DWMM compared to other microscopical techniques for the diagnosis of intestinal parasitosis including Hookworm infection.
The present study evaluated the performance of five types of stool examination methods (TFT, MM, FEC, KK, and DWMM) for hookworm diagnosis using their composite as a gold standard method. It has confirmed that DWMM has poor sensitivity. On the other hand, Test Tube Flotation technique was found to be a more sensitive, cheaper, and easier to apply in the routine practices of hookworm identification. It was reported that both of the sensitivity and diagnostic accuracy of this method was 100%. This is almost three times more sensitive than the commonly used DWMM (37%). Low sensitivity of DWMM might be related with the use of only small amount of the stool sample (only 2 mg of stool is used in DWMM compared to about 4 gm for Test Tube Flotation technique). Moreover, the presence of large stool debris materials in the DWMM may conceal the parasitic ova. The sensitivity of DWMM in this study (37%) is similar with other studies done in Ethiopia (25, 27). This suggests that DWMM has resulted in around 63% false negative reports during hookworm diagnosis. This substantially underestimates the prevalence of hookworm infection. Moreover, it has a great impact in the control and elimination programs of hookworm and other soil transmitted helminthes infections. Thus, this study may encourage using TFT as a confirmatory test for hookworm infection in order to break the transmission cycle and ultimately reduce its morbidity and mortality.
The finding of the present study also demonstrated that MM is the second most sensitive test with a sensitivity and diagnostic accuracy of 68.7%, 80%, respectively. Even though it is one of the most recommended diagnosis methods for soil transmitted helminthes by World Health Organization, its sensitivity is lower by about 33% compared to TFT in the current study. Formol ether concentration technique and KK were also ranked as the third (44.3%) and fourth (38.2%) sensitive tests, respectively in this study. However, this is lower than the previous study carried out in Gondar in which their sensitivities were reported from 69-72.4% (27). The observed differences in the sensitivities among different studies could be due to the infection intensity variation. Moreover, it might be related with the difference in the skill of the laboratory personnel. The observation of lower sensitivity of MM, KK and FEC than TFT from the current study indicates that another better diagnostic tool is necessary during patient diagnosis, monitoring and evaluation of hookworm infection following intervention.
According to the current study, the sensitivity of most of the stool examination methods increases when more eggs are excreted in stool. FEC, KK, and DWMM identified hookworm from only 22%, 2.6%, and 3.9% of the light infections, respectively. However, DWMM, KK, and FEC have detected the parasite from 97, 100, 100 percents of moderately infected study participants, respectively. This may suggest that they will most likely not to miss the moderate-to-heavy intensity of hookworm infections, which is mostly associated with morbidity (28, 29). Hence, these three techniques will be able to diagnose those individuals who are in the highest need of treatment. Nonetheless, their inability to detect light infections properly may make them to have insignificant role in the evaluation of hookworm infection following MDA. Thus, TFT might be taken as the best method over the other available diagnosis methods.
The specificity of all of the stool examination methods described in this study was 100%, and this is in line with findings of a study done in Gondar which revealed that DWMM, FEC and KK had greater than 97% of sensitivity (27). The current study also analyzed the level of agreement of the various types of hookworm diagnosis methods with composite reference standard. The reproducibility of the TFT compared to CRS had a perfect agreement (Agreement = 100%, kappa = 1).This indicates that the TFT is 100% as sensitive as the gold standard technique for the disease diagnosis. Next to TFT, MacMaster showed moderate agreement (agreement = 80%, kappa = 0.67), followed by Formol Ether concentration, and Kato-Katz technique. Importantly, DWMM showed the lowest (Agreement = 60%, kappa = 0.30) and this may suggest its little role in the diseases diagnosis. Generally, this study found an encouraging outcome and implies that TFT could be the most preferred technique for hookworm infection detection.
Limitation
There is no any similar study conducted so far. As a result, this has made difficulties in making rigorous discussions on this finding.