JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
of the 13 patients were from the Southeast U.S. and denied any foreign travel. 19 Despite treatment with thiabendazole as recommended at that time, 11 patients died (85%); and six died within 16 days of the onset of purpura. 19 The authors concluded that Strongyloides stercoralis remained endemic in the Southeast U.S. and could result in fatal hyperinfection syndrome and disseminated strongyloidiasis associated with purpura in patients receiving corticosteroids. 19
and can be improved by examining multiple stool specimens over several days and by specialized stool exams, such as the Baermann concentration. The parasites can be most effectively cultured fromstool specimens on nutrient agar plates. Duodenal aspirates, duodenal string tests (Enterotest®), and duodenal biopsies are also more sensitive than stool examinations; but are more invasive and rarely performed today. Although serological tests are more sensitive than microscopy, they are less specific and can cross-react with antibodies from other parasites, especially other nematodes like Ascaris lumbricoides , filarial worms, and schistosomes. In addition, serological tests may not differentiate between active cases and chronic, quiescent cases with minimal larval output. Since the parasite burden is low between bouts of autoinfection, molecular methods, such as real-time and nested PCR, that detect parasite DNA, are the most sensitive and specific tests for the detection of Strongyloides stercoralis in concentrated stool samples. Molecular testing for strongyloidiasis may not be available locally andwill require consultationwithparasitological references laboratories, such as the Centers for Disease Control and Prevention (CDC) Diagnostic Parasitology Laboratory in Atlanta, Georgia, and the National Institutes of Allergy and Infectious Disease (NIAID) Parasitic Disease Laboratory in Bethesda, Maryland. Table 2 presents the types of diagnostic tests recommended for strongyloidiasis, stratifies them by methodology, and compares their sensitivities if reported.
The Laboratory Diagnosis of Strongyloidiasis
Unlike other nematode infections, peripheral eosinophilia is not a constant finding in strongyloidiasis. Eosinophilia above 5% is typically observed during symptomatic bouts of acute strongyloidiasis and autoinfection. Mild peripheral eosinophilia with elevated IgE levels may also be observed in chronic, quiescent strongyloidiasis. Peripheral eosinophilia is often absent in hyperinfections. The clinical diagnosis of strongyloidiasis may be confirmed by positive laboratory studies including direct microscopy, specialized parasite culture techniques, serological detection of antibodies, andmolecular methods to detect parasite DNA, such as polymerase chain reaction (PCR). The traditional methods used for the diagnosis of strongyloidiasis initially relied on the microscopic identification of larvae in stool, sputum, or duodenal biopsies (Figures 2 and 3). The sensitivities of microscopic diagnoses, however, are low compared to other diagnostic tests
Direct microscopy for larval identification (rhabditiform> occasional filariform)
Larval culture for subsequent microscopic identification
Serological tests for antibodies
Molecular tests for DNA
1. Enzyme-linked
1. Real time-polymerase chain reaction (84.7%) 2. Nested polymerase chain reaction (100%)
1. Iodine-stained fecal
1. After culture by the
specimens x 1 (15.3%)
Harada-Mori filter paper technique (NR) 2. After culture in modified
immunosorbent assay (90%)
2. Iodine-stained fecal
2. Indirect fluorescent assay (NR) 3. Indirect hemagglutination test (NR)
specimens x 3 (≤ 30%)
3. Iodine-stained fecal
nutrient agar plates (93.2%)
specimens x 7 (≤ 100%) 4. Larval identification after concentration in formalin-ethyl acetate x 1 (22%) 5. Direct duodenal aspiration or Enterotest® string test for larval identification (NR) 6. Larval recovery by the Baermann funnel technique (76.6%)
NR : Not reported.
Table 2: Diagnostic Tests for Strongyloidiasis and their Sensitivities (%)
22 J La State Med Soc VOL 170 JANUARY/FEBRUARY 2018
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