Accuracy of Diagnosis of Intestinal Helminth Parasites, and Relative Prevalence of Necator Americanus and Ancylostoma Duodenale Infections at the Komfo Anokye Teaching Hospital, Kumasi.
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Date
2009-08-14
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Abstract
There is a growing concern that stool reports from the Komfo Anokye Teaching Hospital (KATH) parasitology laboratory are frequently negative for intestinal helminth parasites.
Over the years the wet mount technique has been the only method used at the KATH laboratory for diagnosis of intestinal parasites. The study evaluated the diagnostic sensitivity of the traditional direct wet mount technique using the formol-ether concentration as the gold standard method. After approval from the Committee on Human Research, Publications and Ethics, School of Medical Sciences, Kwame Nkrumah University of Science and Technology and Komfo Anokye Teaching Hospital, Kumasi, and with the permission of the hospital management, 2000 stool samples were collected from out-patients who visited the KATH parasitology laboratory between May and October, 2008 to do stool routine examination. Each stool sample was processed within 2 hours after collection using the direct saline wet mount, Kato-Katz and formol-ether concentration methods in accordance with standard protocols.
All hookworm positive stool samples were cultured using the modified Harada-Mori test-tube technique and the isolated hookworm filariform larvae were identified by their morphological features in accordance with established criteria.
Formol-ether concentration, gave the highest overall prevalence of 11.1% of helminth parasites made up of hookworm (2.9%), Dicrocoelium dendriticum (2.1%), Strongyloides stercoralis (2.1%), Schistosoma mansoni (1.8%), Hymenolepis nana (1.4%), Taenia species (0.6%) and Trichuris trichiura (0.1%). The direct wet mount and Kato-Katz detected total prevalence of 3.2% and 5.1% respectively. Direct wet mount was found to be 29.3% sensitive.
Kato-Katz showed good agreement with the ether concentration for detection of hookworms, T. trichiura and S. mansoni infections (99.1% sensitivity; 95.0% CI, 97.1%-100%, with positive and negative predictive values of 100% (95% CI, 100%-100%) and 99.5% (95% CI, 99.0%-100%), respectively.
Interestingly, no Ascaris lumbricoides eggs were detected using any of the three methods employed. EPG (eggs per gram) of feces counted by Kato-Katz method showed that most patients (89.9%) harboured low intensity infections of the parasites found.
All 58 (100%) hookworm positive cases were identified as Necator americanus.
This study reconfirmed reports that the direct wet mount has low sensitivity.
It is recommended that stool samples that are negative for parasites by the wet mount method should be re-examined using the formol-ether concentration technique as the confirmatory test. This approach will improve the detection of helminths from stool specimens for accurate diagnosis of intestinal helminth infections, for effective management of patients and ultimately improve the quality of life of individuals in the communities.
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A thesis submitted to the Department of Clinical Microbiology in partial fulfillment of the requirements for the award of the Master of Philosophy degree (Mphil) in Clinical Microbiology.