Evaluating analytical approaches for smarter decision-making in faecal contamination monitoring and assessment

Quantification of faecal indicator organism (FIO) is essential for surveillance monitoring, performance compliance and public health interventions. IDEXX's automated FIO detection technique, TECTA^TM, and IDEXX Colilert offer greater efficiency than traditional methods but have not been critically compared across diverse levels of faecal contamination or evaluated against key practical requirements and cost factors. This study compared the use of IDEXX Colilert and TECTA™ for measuring indicative contamination in 785 samples from drinking water, wells, surface water, greywater and a constructed wetland system, collected from Fijian and Indonesian informal settlements. Both methods ranked sample types in the same order in terms of indicative faecal contamination, and at Escherichia coli (E. coli) concentrations between <1-10⁵ CFU or MPN/100 mL (municipal, shallow and deep well samples), both methods were highly correlated. However, at 10²-10⁹ CFU/100 mL (TECTA™) or 10²-10⁶ MPN/100 mL (IDEXX Colilert) E. coli (surface water samples), a moderate positive correlation was observed (R = 0.56, p = 2.2^-13), and a high proportion of samples exceeded the detection limit of the IDEXX Colilert method. Greywater and septic tank samples exhibited total coliform mean values greater than 10⁶ CFU/100 mL, with no correlation between IDEXX Colilert and TECTA™ results. TECTA™ required only one dilution for returning specific E. coli values, ideal for performance compliance and faecal contamination assessments, while IDEXX Colilert often needed two levels of dilution. For surveillance purposes, IDEXX Colilert may be more cost-effective given the higher initial setup costs of TECTA™; however, TECTA™'s faster turnaround times and automated results may offset expenses. This study presents a versatile decision analysis that enables laboratories worldwide to customise method comparisons based on their unique requirements, driving more effective implementation and global standardisation of these methods.