It is important to understand that infection prevalence cannot be determined from wastewater concentrations of SARS-CoV-2 sequence data at the present time. There are a wide range of factors that affect concentrations measured in wastewater, including the fecal shedding rate of individuals during different stages of infection/disease, the proportion of the population actively shedding viruses into the sewer, sewer transit times, and RNA decay rates. None of these factors are completely understood, and their variability between systems makes inferring prevalence difficult. The greatest barrier to determining prevalence is lack of data on fecal shedding for patients, particularly during the pre-symptomatic period of infection. Therefore, at the present time, data must be interpreted in terms of trends in concentrations within a single system using a defined methodology. This is why establishing a consistent method and sampling longitudinally are so critical to applying wastewater surveillance for SARS-CoV-2.
Communicating Sewage Surveillance for COVID-19
