title: Determinants of Participants' Follow-Up and Characterization of Representativeness in Flu Near You, A Participatory Disease Surveillance System.
abstract: BACKGROUND
  Flu Near You (FNY) is an Internet-based participatory surveillance system in the United States and Canada that allows volunteers to report influenza-like symptoms using a brief weekly symptom report.
  
  
  OBJECTIVE
  Our objective was to evaluate the representativeness of the FNY population compared with the general population of the United States, explore the demographic and behavioral characteristics associated with FNY's high-participation users, and summarize results from a user survey of a cohort of FNY participants.
  
  
  METHODS
  We compared (1) the representativeness of sex and age groups of FNY participants during the 2014-2015 flu season versus the general US population and (2) the distribution of Human Development Index (HDI) scores of FNY participants versus that of the general US population. We analyzed associations between demographic and behavioral factors and the level of participant follow-up (ie, high vs low). Finally, descriptive statistics of responses from FNY's 2015 and 2016 end-of-season user surveys were calculated.
  
  
  RESULTS
  During the 2014-2015 influenza season, 47,234 unique participants had at least one FNY symptom report that was either self-reported (users) or submitted on their behalf (household members). The proportion of female FNY participants was significantly higher than that of the general US population (n=28,906, 61.2% vs 51.1%, P<.001). Although each age group was represented in the FNY population, the age distribution was significantly different from that of the US population (P<.001). Compared with the US population, FNY had a greater proportion of individuals with HDI >5.0, signaling that the FNY user distribution was more affluent and educated than the US population baseline. We found that high-participation use (ie, higher participation in follow-up symptom reports) was associated with sex (females were 25% less likely than men to be high-participation users), higher HDI, not reporting an influenza-like illness at the first symptom report, older age, and reporting for household members (all differences between high- and low-participation users P<.001). Approximately 10% of FNY users completed an additional survey at the end of the flu season that assessed detailed user characteristics (3217/33,324 in 2015; 4850/44,313 in 2016). Of these users, most identified as being either retired or employed in the health, education, and social services sectors and indicated that they achieved a bachelor's degree or higher.
  
  
  CONCLUSIONS
  The representativeness of the FNY population and characteristics of its high-participation users are consistent with what has been observed in other Internet-based influenza surveillance systems. With targeted recruitment of underrepresented populations, FNY may improve as a complementary system to timely tracking of flu activity, especially in populations that do not seek medical attention and in areas with poor official surveillance data.
authors.affiliation: Computational Health Informatics Program, Boston Children's Hospital, Boston, MA, United States.|Department of Biostatistics, Boston University School of Public Health, Boston, MA, United States.
authors.forename: Kristin
authors.identifier: http://orcid.org/0000-0003-2090-9513
authors.initials: K
authors.lastname: Baltrusaitis
authors.affiliation: Computational Health Informatics Program, Boston Children's Hospital, Boston, MA, United States.|Harvard Medical School, Boston, MA, United States.|Harvard School of Engineering and Applied Sciences, Cambridge, MA, United States.
authors.forename: Mauricio
authors.identifier: http://orcid.org/0000-0002-4206-418X
authors.initials: M
authors.lastname: Santillana
authors.affiliation: Skoll Global Threats Fund, San Francisco, CA, United States.
authors.forename: Adam W
authors.identifier: http://orcid.org/0000-0002-1077-3889
authors.initials: AW
authors.lastname: Crawley
authors.affiliation: The Global Institute of Public Health, New York University, New York, NY, United States.|Computer Science & Engineering, New York University, New York, NY, United States.
authors.forename: Rumi
authors.identifier: http://orcid.org/0000-0002-5346-7259
authors.initials: R
authors.lastname: Chunara
authors.affiliation: Skoll Global Threats Fund, San Francisco, CA, United States.
authors.forename: Mark
authors.identifier: http://orcid.org/0000-0002-5713-8241
authors.initials: M
authors.lastname: Smolinski
authors.affiliation: Computational Health Informatics Program, Boston Children's Hospital, Boston, MA, United States.|Harvard Medical School, Boston, MA, United States.
authors.forename: John S
authors.identifier: http://orcid.org/0000-0001-8568-5317
authors.initials: JS
authors.lastname: Brownstein
keywords: community-based participatory research; crowdsourcing; digital disease detection; influenza, human; public health informatics; public health surveillance