When they’re feeling sick, many people turn to the Internet. They Google their symptoms—headache, chest pain, shortness of breath—hoping to learn more about what’s happening in their bodies.

According to University of Louisville researcher Thomas S. Higgins, Jr., MD, MSPH, those searches could help epidemiologists and public health officials trying to track the spread of infectious diseases, like COVID-19.

In a new study published in the Journal of Medical Internet Research, Higgins and colleagues at Cedars Sinai Medical Center, Indiana University, and Kentuckiana ENT found a correlation between searches for symptoms of the disease and new confirmed cases and deaths.

“Internet searches have the potential to be a great tool for epidemiology and mapping future pandemics,” said Higgins, a clinical assistant professor at the UofL School of Medicine. “How often do you have access to that much data in real-time?”

The researchers studied internet search terms between January 9 and April 6, 2020, when the disease was rapidly spreading and growing into a global pandemic. They collected data from Google Trends, which maps the frequency of search terms over time, and its Chinese equivalent, the Baidu Index (BI).

The data revealed a strong correlation between new COVID-19 cases and an uptick in searches for its symptoms in the hotspots of China, Italy, Spain, and the US states of New York and Washington. The strongest correlations were with the search terms: shortness of breath, anosmia (loss of smell), dysgeusia/ageusia (loss of taste), headache, chest pain and sneezing, with slight variation between countries.

Higgins said the researchers were also able to tie the increased symptom searches to “super spreading” events, including the February Champions league soccer match in Italy. More than 40,000 people attended, and some are believed to have become infected and later spread the virus elsewhere.

Because the virus takes a while to incubate and people might not be tested right away, Higgins said there is some lag-time between infection, internet searches and when the case is confirmed. The study showed a worldwide lag time of 5 days between the upticks in symptom searches and confirmed cases.

“Really, these searches let us peek into the collective mindset of the public, sometimes revealing what’s coming,” he said. “If there’s a spike in searches, it might be an indicator that in a week, we’ll have more cases.”

While Higgins said Internet searches can be a valuable tool for tracking disease spread, he added that there are some limitations. A person might search for symptoms they don’t have, for example, because they heard the term and want to know what it means.

“If we can somehow isolate the noise from everything else, I think this can be extremely helpful,” he said. “It’s not the only tool, but it can be a warning shot for identifying potential and upcoming outbreaks.”