Emergency-room doctors need to know when they’re about to be swamped by a flood of flu patients. According to a new study from Johns Hopkins and George Washington universities, they should turn to Google’s Flu Trends tool, which tracks the frequency of 45 flu-related search queries to offer daily estimates of how bad the flu is in a given place at a given time. Previous studies have shown that Flu Trends data match up well with that collected by official disease control organisations. The problem with the official data is that it takes weeks to reach doctors on the front lines. The study is the first to demonstrate that Google data actually predict, with minimal lag time, when emergency-room traffic is about to rise.