SARS-CoV-2 titers in wastewater are higher than expected from clinically confirmed cases

Fuqing Wu; Amy Xiao; Jianbo Zhang; Xiaoqiong Gu; Wei Lin Lee; Kathryn Kauffman; William Hanage; Mariana Matus; Newsha Ghaeli; Noriko Endo; Claire Duvallet; Katya Moniz; Timothy Erickson; Peter Chai; Janelle Thompson; Eric Alm

sewage could be quantified. Standard curves for all three primer sets showed linear behavior over 6 log units (r 2 ranging from 0.981 to 0.998) using DNA standards (SARS-CoV-2 nucleocapsid gene). We sought to validate our results against other samples, including biobanked samples collected before the first known US case on January 20, which could serve as a relevant negative control. Figure 2 shows estimated viral titer per mL of sewage at the treatment facility over seven different sample dates, with samples from two catchment areas (Southern and Northern) for each date. All four samples from before the first known US SARS-CoV-2 case were negative for virus. In contrast, all 10 samples taken in the range of March 18 -March 25 tested positive (seven out of ten samples hit all the three primers with an average Ct for all samples below 40) for virus by qPCR, using the DNA probes provided by the CDC (11) . For each positive sample, we confirmed the presence of a ~150 bp band after PCR using the S gene primers (data not shown). Thus, our approach is sensitive enough to detect viral titers similar to those currently seen in the treatment facility catchments. Spike-in experiments with purified virus will be needed to establish rigorous limits of detection and are currently underway.