Internet searches on gastrointestinal symptoms predicted a rise in Covid-19 cases weeks later, researchers at Massachusetts General Hospital found, demonstrating a novel early warning system for hot spots of the pandemic disease.

Researchers at the top-ranked hospital in Boston compared search interest in loss of taste and appetite, and diarrhea with the reported incidence of Covid-19 in 15 US states from Jan. 20 to April 20. Using Alphabet Inc.’s Google Trends online tool, they found the volume of searches correlated most strongly with cases in New York, New Jersey, California, Massachusetts and Illinois — states with high disease burden — three to four weeks later.

The research, published in the journal Clinical Gastroenterology and Hepatology, showed that the same approach used to monitor pandemic influenza trends more than a decade ago could be deployed for the coronavirus, the hospital said in a report this month. Patients with Covid-19 often report gastrointestinal symptoms, such as abdominal pain and diarrhea, sparking interest in conducting the study.

“Our data underscore the importance of GI symptoms as a potential harbinger of Covid-19 infection and suggests that Google Trends may be a valuable tool for prediction of pandemics with GI manifestations,” Kyle Staller, a gastroenterologist and the director of Mass General’s gastrointestinal motility laboratory, and colleagues wrote in the study.

Scientists are also testing for traces of the coronavirus in wastewater to identify places where Covid-19 is spreading.