Inter-institutional laboratory standardization for SARS-CoV-2 surveillance through wastewater-based epidemiology applied to Mexico City.

Objectives: Wastewater-based surveillance applied to SARS-CoV-2 viral load quantification for COVID-19 has become one of the most relevant complementary tools in epidemiologic prevention programs worldwide. However, this valuable decision-making tool still requires fine-tuning to produce comparable results between laboratories, especially when applied to the surveillance of megacities.

Methods: Six laboratories across Mexico and one from the United States executed an interlaboratory study to set up a singular standardized protocol considering method cost, installed infrastructure, materials available, and supply availability for SARS-CoV-2 quantification from five Mexico City sampling sites across this megacity.

Results: Comparable data from processing outcomes in the Mexican laboratories and in the external international laboratory serve as a validating data source. The Bland-Altman comparison showed consistency, with cycle threshold values within ±1.96 SD of SARS-CoV-2 genetic copies for the standard curve quantification, with a mismatch of two laboratories. In addition, MS2 bacteriophage recovery rates varied between 35% and 67% among all participating laboratories. Finally, the efficiency of viral genetic material recovered from all participating laboratories varied between 65% and 93% for the participating laboratories.

Conclusion: This work lays the foundation for extensive and continuous wastewater-based surveillance application across independent Mexican laboratories in a time- and resource-effective manner.