Screening of Strongyloides stercoralis infection in high-risk patients in Khuzestan Province, Southwestern Iran

Abstract

Background: Strongyloidiasis, one of the neglected tropical diseases (NTDs), can be fatal in immunocompromised patients. Available data on Strongyloides stercoralis infection in high-risk patients in Iran are limited. The aim of the present study was to determine the prevalence of S. stercoralis infection and associated risk factors among high-risk patients as well as to evaluate the sensitivity of the diagnostic tests used in the diagnose of S. stercoralis infection.

Methods: This cross-sectional study was performed from 2019 to 2020 among 300 high-risk patients in Khuzestan Province, southwestern Iran. Patients with autoimmune diseases, uncontrolled diabetes, HIV/AIDS, cancer, organ transplant, hematological malignancy, asthma and chronic obstructive pulmonary disease (COPD) were examined using direct smear examination, formalin-ether concentration, Baermann funnel technique, agar plate culture, and ELISA test. Since agar plate culture was considered the reference diagnostic test, culture-positive samples were confirmed by PCR amplification and the sequencing of the nuclear 18S rDNA (SSU) hypervariable region (HVRIV) of the parasite.

Results: The prevalence of S. stercoralis infection was 1%, 1.3%, 2%, 2.7%, and 8.7% using direct smear examination, formalin-ether concentration, Baermann funnel technique, agar plate culture, and ELISA test, respectively. All culture-positive samples were confirmed by SSU-PCR. According to the results, the most sensitive test was ELISA, with 100% sensitivity, followed by the Baermann funnel technique with the sensitivity of 75%. Direct smear examination, formalin-ether concentration technique, and Baermann funnel technique had the highest PPV (100%) while the ELISA test had the highest NPV (100%). Significant eosinophilia was observed in the patients whose culture test was positive (7/8; P < 0.05). In the present study, the majority of the positive cases by the agar plate culture had a history of prolonged exposure to soil and of asthma and COPD and were > 60 years old.

Conclusions: Given that the ELISA test had the highest NPV, the screening of all high-risk patients for S. stercoralis infection in endemic areas is recommended prior to starting corticosteroid therapy with the ELISA test. The results indicate the importance of paying attention to patients with unknown eosinophilia in endemic areas. Ivermectin should be available to strongyloidiasis patients in the endemic areas.

Keywords: Corticosteroid; High-risk patients; Iran; Risk factors; Strongyloides stercoralis; Strongyloidiasis.

Fig. 1

Map of Iran. Khuzestan Province, highlighted in dark orange, based on the map of Iran in [16]. Map of Khuzestan Province with studied counties highlighted in dark red

Fig. 2

Adult female Strongyloides stercoralis worm, rhabditiform larvae, and ova collected from an agar plate culture of an infected patient examined in this study

Fig. 3

The ROC curves show the comparison between the agar plate culture and other tests used. FECT formalin-ether concentration technique. The ELISA ROC had an AUC (area under the curve) of 0.955 with 100% sensitivity, the Baermann funnel technique had an AUC of 0.875 with 70% sensitivity, the formalin-ether concentration ROC had an AUC of 0.750 with 50% sensitivity, and the direct smear examination ROC had an AUC of 0.688 with 37.5% sensitivity

Fig. 4

PCR amplification of a 712-bp fragment of the nuclear 18S rDNA (SSU) hypervariable region (HVRIV) of Strongyloides stercoralis from larvae in feces of high-risk patients from Khuzestan Province, Iran. Lane M: 100-bp DNA ladder RTU (CinnaGen, Iran); lanes 1–8: positive samples; lanes 9, 10: positive controls; lane 11: negative control