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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

CSTE Position Statement(s)



Strongyloidiasis is a parasitic disease caused by the soil-transmitted helminth (STH) Strongyloides spp. Strongyloidiasis in humans is mainly caused by Strongyloides stercoralis (S. stercoralis), which is endemic to parts of the United States (U.S.).1,2 Human infection with S. fuelleborni is rarer and has been reported from sub-Saharan Africa and Southeast Asia, and S. fuelleborni subsp. kellyi from Papua New Guinea.3 Unlike infections with other STH (Ascaris lumbricoides, Trichuris trichiura, hookworm, and S. fuelleborni), S. stercoralis can result in chronic, lifelong infection without adequate treatment owing to its autoinfection cycle.3,4

Laboratory Criteria

Confirmatory laboratory evidence:

  • Strongyloides larvae or eggs* detected in stool by ova and parasites exam, OR
  • Strongyloides larvae detected in body tissues or fluid aspirates

Presumptive laboratory evidence:

  • S. stercoralis specific immunoglobulin G (IgG) antibody detected in blood by enzyme-linked immunosorbent assay (ELISA), immunoassay, or monoclonal antibody test

*S. fuelleborni releases eggs rather than larvae into host stool.

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

Criteria to Distinguish a New Case from an Existing Case

A person should be enumerated as a case if not previously enumerated as a case.

Case Classification


Meets presumptive laboratory evidence.


Meets confirmatory laboratory evidence.


  1. Singer R, Xu TH, Herrera LNS, Villar MJ, Faust KM, Hotez PJ, Aiken ARA, Mejia R. (2020). Prevalence of intestinal parasites in a low-income Texas community. Am J Trop Med Hyg 102: 1386–1395.
  2. Russell ES, Gray EB, Marshall RE, Davis S, Beaudoin A, Handali S, McAuliffe I, Davis C, Woodhall D, 2014. Prevalence of Strongyloides stercoralis antibodies among a rural Appalachian population—Kentucky, 2013. Am J Trop Med Hyg 91: 1000–1001.
  3. Centers for Disease Control and Prevention Accessed April 26, 2022
  4. Nutman TB. Human infection with Strongyloides stercoralis and other related Strongyloides species. Parasitology. 2017 Mar;144(3):263-273. doi: 10.1017/S0031182016000834. Epub 2016 May 16. PMID: 27181117; PMCID: PMC5563389.