Using Internet Searches for Influenza Surveillance

Abstract

The Internet is an important source of health information. Thus, the frequency of internet searches may provide information regarding infectious disease activity. As an example, we examine the relationship between searches for influenza and actual influenza occurrence. Using search queries from http://search.yahoo.com, between March 2004 and May 2008, we counted daily unique queries, originating in the U.S. and containing influenza-related search terms. Counts were divided by the total number of searches, and the resulting daily fraction of searches was averaged over the week. We estimated linear models, using searches with one- to ten-week lead times as explanatory variables, to predict the percentage of positive influenza cultures and also deaths due to pneumonia and influenza in the U.S. Using the frequency of searches, our models predicted an increase in positive influenza cultures 1–3 weeks in advance (p < 0.0001) and similar models predicted an increase in mortality from pneumonia and influenza up to five weeks in advance (p < 0.0001). Search-term surveillance may provide an additional tool for disease surveillance.