E-Mail IMAGE: San Diego County's primary wastewater treatment plan is located on the coast in the city's Point Loma neighborhood. view more Credit: San Diego County In earlier days of the COVID-19 pandemic, before diagnostic testing was widely available, it was difficult for public health officials to keep track of the infection's spread, or predict where outbreaks were likely to occur. Attempts to get ahead of the virus are still complicated by the fact that people can be infected and spread the virus even without experiencing any symptoms themselves. When studies emerged showing that a person testing positive for COVID-19 -- whether or not they were symptomatic -- shed the virus in their stool, "the sewer seemed like the 'happening' place to look for it," said Smruthi Karthikeyan, PhD, an environmental engineer and postdoctoral researcher at University of California San Diego School of Medicine.