The latest testing of raw sewage at Lake County Special Districts’ four treatment facilities found no presence of the virus that causes COVID-19 at any of the plants late in April, despite the fact that samples earlier in the month confirmed its presence.

Special Districts Administrator Jan Coppinger reported Friday that she received the latest test results from Biobot, a Massachusetts firm that is offering the testing as part of a pro bono program it’s conducting along with MIT, Harvard and Brigham and Women’s Hospital.

The tests are used to detect the presence of SARS-Cov-2, the virus that causes COVID-19. The virus is shed in the stools of infected people.

Sewage testing also has successfully tracked the poliovirus and consumption of drugs such as opioids, according to Dr. Mariana Matus, chief executive officer and cofounder of Biobot.

Biobot is seeking to use wastewater testing to proactively detect outbreaks and help governments and communities to get ahead of public health crises like the COVID-19 pandemic.