Diagnostic Methods for Cryptosporidiosis in Low- and Middle-Income Countries: A Systematic Narrative Review

BACKGROUND: Cryptosporidiosis is a major cause of diarrheal disease in low- and middle-income countries (LMICs), yet access to diagnostic testing is limited. Evidence on the diagnostic accuracy and operational feasibility of available tests is fragmented. We therefore systematically reviewed studies reporting on accuracy and feasibility of cryptosporidiosis diagnostic methods in LMICs. METHODS: Following PRISMA guidelines, we systematically identified studies by searching databases and additional sources, screened abstracts, and publications using predefined inclusion criteria and assessed methodological quality using the QUADAS-2 tool. RESULTS: Of 1687 unique records, 51 met our inclusion criteria. Most studies were conducted in Asia (49%) and Africa (45%), with 55% evaluating Cryptosporidium testing conducted consecutively near the point of care. Quality of reporting was poor overall, particularly regarding reference standards used for accuracy calculations. Few studies included sufficiently large sample sizes. Sensitivity of modified acid-fast stains was generally reported as low and varied widely across studies. The reported sensitivity of immunochromatographic lateral flow tests was 50-89% against PCR or quantitative assays, with specificities of 89-100%. Auramine fluorescence microscopy showed promising sensitivity and specificity, including in a prospective clinical diagnostic accuracy study. Only 5 studies (11%) addressed operational feasibility, of which 4 lacked original data and 1 evaluated total test turnaround times and cost-per-test calculations. CONCLUSIONS: Methodological flaws and poor reporting limit the validity of many LMIC studies for cryptosporidiosis diagnostics, leaving substantial evidence gaps. Well-designed, adequately powered studies are needed to evaluate the diagnostic accuracy and operational feasibility of near-patient tests in these settings.