January 13, 2012 — Trends in the volume of cases reported early through informal sources — such as the HealthMap news media and Twitter — correlated well with officially reported case data in an analysis of the 2010 cholera outbreak in Haiti, new research suggests.
Rumi Chunara, PhD, research fellow in pediatrics from the Children's Hospital Boston at Harvard Medical School in Massachusetts, and colleagues published their findings in the January 2012 issue of the American Journal of Tropical Medicine and Hygiene.
The authors note that "[i]n the early days of a disease outbreak, clinicians, public health officials, and policy makers need rapidly available data to plan a response to an impending epidemic" and that "[d]ata collected and reported through official public health institutions is often not available for weeks..."
Dr. Chunara and colleagues report that theirs is the first study to demonstrate the use of informal social and news media "to gain early insight into an evolving epidemic." They state that this provides an opportunity "for the implementation of more timely and effective interventions."
In this study, the authors evaluated trends in volume of cases reported through 3 sources: HealthMap (a Web site that monitors news of outbreaks around the world) and Twitter, both of which are considered "informal," and data from a government body, the Haitian Ministry of Public Health (Ministère de la Santé Publique et de la Population [MSPP]), which were considered "official."
They examined the data from 3 periods: during the initial phase of the outbreak (October 20, 2010 -November 3, 2010), around the timing of Hurricane Tomas (November 3, 2010 - December 1, 2010), and 100 days from the start of the outbreak.
In the first period, there were 995 HealthMap alerts about the outbreak and 65,728 cholera-related tweets, and in the period of influence by Hurricane Tomas, there were 2248 HealthMap alerts and 84,992 tweets. In total, the researchers captured 188,819 tweets and 4697 HealthMap primary alerts from the period lasting 100 days after the initial upsurge of the outbreak. These data significantly correlated with the "official" MSPP case volume, but were available up to 2 weeks earlier.
The authors also demonstrated the potential use of each of these 3 sources in estimating a key epidemic parameter, the effective reproductive number, by creating epidemic curves from the cumulative volume of informal data and MSPP-reported case burden.
The estimates of effective reproductive number for the initial period ranged from 1.54 to 6.89 (informal sources) and from 1.27 to 3.72 (official sources). During the period of Hurricane Tomas, the effective reproductive numbers were nearly overlapping, ranging from 1.04 to 1.51 (informal sources) and 1.06 to 1.73 (official sources).
"Near real-time estimates of epidemic activity may provide valuable insights into the trajectory of an infectious disease outbreak, help project the spread of an epidemic, and provide guidance on the magnitude of control measures needed," the authors note. They add that "the methods and data types presented here can be extended to other diseases and to other metrics of disease activity." However, they also add that "[i]nformal data sources may contain biases that should be considered."
The study was supported by a grant from Google.org, the National Library of Medicine, the National Institutes of Health, and the National Institute of Allergy and Infectious Diseases. The authors have disclosed no relevant financial relationships.
Am J Trop Med Hyg . 2012;86:39-45. Abstract
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