This document summarizes how online data sources like search queries and social media posts can be used to track disease outbreaks and epidemics in real time. It provides examples of how Google Flu Trends and Google Dengue Trends use search data from 28 countries and 39 languages to monitor influenza and dengue fever trends. It also discusses other tools like HealthMap that track outbreaks by crawling online news sources and social media. While these new approaches show promise, the document notes they still have limitations like uneven internet access and a lack of verified truth data.