CliniCon Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2023

The Diagnosis of Strongyloidiasis in Humans (95059)

Richard Bradbury 1
  1. Federation University, Berwick, VIC, Australia

Strongyloidiasis is predominantly caused by infection with Strongyloides stercoralis intestinal nematodes. The disease remains hyperendemic endemic in many remote northern Australian communities, with local transmission as far south as northern New South Wales, Central South Australia, and the Goldfields of Western Australia.1 Many chronic imported cases in veterans and immigrants remain overlooked.1

Infection may be asymptomatic, or may present with intermittent abdominal pain, eosinophilia, skin rashes, diarrhoea and malnourishment in children.3 Due to its autoinfective lifecycle, infection lasting for many decades may occur.2,3 In immunosuppressed patients, particularly those given corticosteroid therapy, hyperinfection may occur, leading to systemic disease, enteric bacterial sepsis, multi-organ failure and death in the majority of cases.2,3

Low and intermittent larval shedding presents unique challenges for the coprological diagnosis of S. stercoralis.3 Traditional microscopic techniques, including formalin-ethyl acetate sedimentation, have low sensitivity. Agar plate culture or Baermann sedimentation, preferably on multiple stools, are optimal. Molecular techniques, including real time PCR and LAMP have significant advantages in the context of sampling from remote areas, but sensitivity is dependent on DNA extraction methods and appropriate pre-analytical processing.3

The sensitivity and specificity of serological assays varies based on the antigen/s employed. Seroreversion occurs in most patients within 18 months of successful treatment, meaning that a positive Strongyloides serology result indicates current or recent infection.3 Cross-reaction in crude antigen assays are primarily seen with filarial and Schistosoma infections,3 which are not endemic in Australia.  Immunocompromised patients may present as seronegative despite passage of S. stercoralis larvae in their stools.3

The diagnosis of strongyloidiasis requires careful consideration. The choice of laboratory test, or test combinations, should be guided by the clinical history of the patient, the likelihood of infection, the likely clinical impact of a missed diagnosis, and the practicality of suitable specimen collection, preservation and transport being possible. Australian laboratories are encouraged to review their protocols to avoid missing this most important of endemic helminthic diseases.

  1. Shield J, Braat S, Watts M, Robertson G, Beaman M, McLeod J, Baird RW, Hart J, Robson J, Lee R, McKessar S. Seropositivity and geographical distribution of Strongyloides stercoralis in Australia: A study of pathology laboratory data from 2012–2016. PLoS Negl Trop Dis 2021; 15:e0009160.
  2. Page W, Judd JA, Bradbury RS. The unique life cycle of Strongyloides stercoralis and implications for public health action. Trop Med Infect Dis 2018; 3:53.
  3. Buonfrate D, Tamarozzi F, Paradies P, Watts MR, Bradbury RS, Bisoffi Z. The diagnosis of human and companion animal Strongyloides stercoralis infection: Challenges and solutions. A scoping review. Adv Parasitol 2022; 118:1-84.