Defining the diagnosis of cryptosporidiosis

Abstract

The prominent role of Cryptosporidium species in the aetiology of childhood diarrhoea, mortality, and long-term sequelae has been highlighted by large-scale studies across multiple countries,1Khalil IA Troeger C Rao PC et al.Morbidity, mortality, and long-term consequences associated with diarrhoea from Cryptosporidium infection in children younger than 5 years: a meta-analyses study.Lancet Glob Health. 2018; 6: e758-e768Summary Full Text Full Text PDF PubMed Scopus (108) Google Scholar, 2Levine MM Nasrin D Acácio S et al.Diarrhoeal disease and subsequent risk of death in infants and children residing in low-income and middle-income countries: analysis of the GEMS case-control study and 12-month GEMS-1A follow-on study.Lancet Glob Health. 2020; 8: e204-e214Summary Full Text Full Text PDF PubMed Scopus (31) Google Scholar providing the stimulus for ongoing, concerted efforts in drug discovery to provide effective, affordable treatment, especially for individuals with compromised immune systems due to malnourishment or HIV.3Abubakar I Aliyu SH Arumugam C Hunter PR Usman NK Prevention and treatment of cryptosporidiosis in immunocompromised patients.Cochrane Database Syst Rev. 2007; 1CD004932Google Scholar However, if suitable treatment modalities are forthcoming, then there needs to be a decision regarding who to treat and when. No clinical gold-standard diagnostic test exists for acute cryptosporidiosis—of which the principle symptoms are profuse watery diarrhoea and abdominal pain—so accessible and accurate diagnostic tests are still required. Preventive interventions to interrupt faecal-oral transmission, or transmission via contaminated food or water, are also necessary. In The Lancet Infectious Diseases, Øystein Johansen and colleagues4Johansen ØH Abdissa A Zangenberg M et al.Performance and operational feasibility of two diagnostic tests for cryptosporidiosis in children (CRYPTO-POC): a clinical, prospective, diagnostic accuracy study.Lancet Infect Dis. 2020; (published online Dec 3.)https://doi.org/10.1016/S1473-3099(20)30556-9Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar report, to our knowledge, the first adequately powered, prospective, diagnostic accuracy study for cryptosporidiosis in children with diarrhoea who presented for health care in a low-income setting. Using a case-control study design, the authors present the highly satisfactory accuracy of two tests for the diagnosis of cryptosporidiosis; one for use in clinical settings and already provisioned for tuberculosis diagnosis, using light-emitting diode fluorescence microscopy and auramine-phenol staining (LED-AP), and the other a near-patient immunochromatographic lateral-flow test strip (Cryptosporidium EZ VUE; TECHLAB, Blacksburg, VA, USA). We were surprised and encouraged to see markedly similar sensitivities and specificities of these two tests compared with a composite reference standard comprising quantitative immunofluorescent antibody test (qIFAT), ELISA, and quantitative PCR (qPCR). LED-AP had a sensitivity for cryptosporidiosis of 88% (95% CI 79–94) and a specificity of 99% (98–99); the lateral-flow test strip had a sensitivity of 89% (79–94) and a specificity of 99% (97–99). Diagnostic tests for cryptosporidiosis have contrasting attributes (appendix);5Garcia LS Diagnostic medical parasitology. ASM Press, Sterling, VA2007Google Scholar uniquely, the EZ VUE lateral-flow test strip can be stored at room temperature, unlike many other near-patient tests. Our previous experience with immunochromatographic point-of-care tests for cryptosporidiosis has not been so favourable, as also reported by others.6Roellig DM Yoder JS Madison-Antenucci S et al.Community laboratory testing for Cryptosporidium: multicenter study retesting public health surveillance stool samples positive for Cryptosporidium by rapid cartridge assay with direct fluorescent antibody testing.PLoS One. 2017; 12e0169915Crossref PubMed Scopus (13) Google Scholar, 7Chalmers RM Campbell BM Crouch N Charlett A Davies AP Comparison of diagnostic sensitivity and specificity of seven Cryptosporidium assays used in the UK.J Med Microbiol. 2011; 60: 1598-1604Crossref PubMed Scopus (81) Google Scholar Refining the diagnosis of acute cryptosporidiosis is valuable as oocyst shedding can persist after diarrhoea ceases, and asymptomatic carriage can occur as recognised by Johansen and colleagues, who calculated quantitative cutoff values for association of test positivity with diarrhoea. These were reported to be 2·3 × 105 DNA copies per g of wet stool for qPCR, and 725 oocysts per g for qIFAT. These cutoff values provide useful interpretative data for highly sensitive tests in endemic settings. The limitations of the study by Johansen and colleagues include using just 48 h as the diarrhoea-free period for controls, which might have led to misclassification in terms of case or control status; symptoms can relapse and remit, and oocysts are shed for several days or sometimes weeks by recuperating patients. The effect of other gastrointestinal pathogens was not investigated, yet the possibility of mixed infections would be quite high, especially for pathogens with similar transmission routes (eg, Giardia spp). Importantly, although many laboratories are provisioned with LED-AP, it is immensely frustrating that the lateral-flow test strip showing improved performance for a point-of-care diagnostic test is not yet commercially available. A test and treat approach is only effective if the pathogens to treat are known, and can be reliably and accurately detected; Johansen and colleagues present a practical way of doing this for Cryptosporidium spp. Establishing the role of asymptomatic carriers in Cryptosporidium spp transmission would clarify whether inclusion of close contacts in a test and treat strategy would limit spread further and improve outcomes. Furthermore, investigation of the role of subclinical Cryptosporidium spp infections in intestinal inflammation and malnutrition associated with environmental enteric dysfunction,8Marie C Ali A Chandwe K Petri Jr, WA Kelly P Pathophysiology of environmental enteric dysfunction and its impact on oral vaccine efficacy.Mucosal Immunol. 2018; 11: 1290-1298Crossref PubMed Scopus (14) Google Scholar requires sensitive detection and redefining of the diagnosis of cryptosporidiosis. We declare no competing interests. Download .pdf (.27 MB) Help with pdf files Supplementary appendix Performance and operational feasibility of two diagnostic tests for cryptosporidiosis in children (CRYPTO-POC): a clinical, prospective, diagnostic accuracy studyLED-AP has high sensitivity and specificity for cryptosporidiosis and should be considered as a dual-use technology that can be easily integrated with existing laboratory infrastructures in low-resource settings. The lateral-flow test strip has similar sensitivity and specificity and provides an alternative that does not require microscopy, although purchase cost of the test strip is unknown as it is not yet available on the market. Full-Text PDF Open Access

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