Given the irregular and often low larval output in uncomplicated infections, the sensitivity of direct stool examination is very poor (12, 27, 59). IFAT result at an antibody dilution of 1 1:80 was virtually 100% specific, with 71% level of Aldicarb sulfone sensitivity. To test the usefulness of the IFAT like a monitoring tool, the changes in specific-antibody titers after treatment in a group of 155 individuals were evaluated. Seroreversion or Aldicarb sulfone a decrease in antibody titer of twofold or more was observed in 60% of the individuals. Response to treatment was directly correlated to the initial antibody titer, and a baseline titer of 1 1:80 was identified as the best predictor of response. In conclusion, a positive IFAT result at an antibody dilution of 1 1:20 is the ideal cutoff for testing. A titer of 1 1:80, with virtually no false-positive result, is a reliable cutoff for any serological assessment of treatment effectiveness and for inclusion in medical trials. Strongyloidiasis is definitely a chronic, soil-transmitted helminthiasis with a worldwide distribution. Current estimations indicate that it affects 30 to 100 million people, but accurate prevalence data are lacking. Although strongyloidiasis is definitely endemic in many tropical and subtropical countries (sub-Saharan Africa, Latin America, Southeast Asia, and Northern Australia), foci of low endemicity will also be reported in temperate climates, such as the Mediterranean coast, Eastern Europe, and the southeastern United States (1, 3, 8, 18, 20, 23, 26, 38, 39, 42, 47, 48, 50, 52, 53). Due to its unique autoinfective cycle, may persist in the sponsor for indefinite periods (21). Most infected individuals are asymptomatic or may present aspecific and intermittent medical symptoms and unexplained eosinophilia (14, 38, 43). However, in instances of immunosuppression, strongyloidiasis may become a disseminated, life-threatening Aldicarb sulfone disease (7, 16, 29, 30, 54). Regrettably, its diagnosis remains a challenge. Given the irregular and often low larval output in uncomplicated infections, the level of sensitivity of direct stool examination is very Vegfa poor (12, 27, 59). Furthermore, currently available antiparasitic medicines do not usually eradicate the illness (27). Consequently, the risk of failing to diagnose the disease is compounded from the hard dedication of treatment effectiveness. Therefore, an enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence antibody test (IFAT) have been developed, with a wide range of reported sensitivities and specificities (19, 40, 55, 56, 57, 58, 60). Assessing the accuracies of serological assays has been limited primarily from the absence of a platinum standard. Therefore, the power of immunoassays both for analysis and for follow-up remains controversial (38, 43, 57). The aim of the present study was to assess the level of sensitivity and specificity of an IFAT for at different antibody titers in order to determine the best cutoff both for a clinical decision and for enrollment in clinical trials. In addition, to test the usefulness of serology as a monitoring tool, changes in specific-antibody titers were measured after treatment in a group of 155 patients over a 4-month follow-up period. MATERIALS AND METHODS Samples used to assess diagnostic sensitivity. Sera were collected from 156 patients in whose stool specimens larvae had been detected. Samples used to assess diagnostic specificity. Unfavorable control sera were obtained from a group of 427 subjects, comprising 229 healthy Italian blood donors and 198 patients admitted to the hospital in medical and pediatric departments for any reason. None of these subjects had a history of travel to high-risk areas or any other known epidemiologic risk factor for contamination. None of them had an eosinophil count of more than 300/l or complained of any cutaneous, gastrointestinal, or respiratory symptom indicative of strongyloidiasis. Samples used to assess cross-reactivity. The sera used to evaluate cross-reactions were obtained from 41 patients with the following other parasitologically confirmed helminth infections: filariasis (11 cases), schistosomiasis (9 cases), hookworm infections (7 cases), toxocariasis (5 cases), ascariasis (5 cases), trichuriasis (3 cases), and contamination (1 case). All of them had multiple (at least five) stool specimens unfavorable for upon direct examination. IFAT for were detected by an IFAT developed and validated at the Centre for Tropical Diseases, Sacro Cuore Hospital, Negrar, Verona, Italy. Briefly, for antigen preparation, intact filariform larvae were obtained from.