title: A case study of the New York City 2012-2013 influenza season with daily geocoded Twitter data from temporal and spatiotemporal perspectives.
abstract: BACKGROUND
  Twitter has shown some usefulness in predicting influenza cases on a weekly basis in multiple countries and on different geographic scales. Recently, Broniatowski and colleagues suggested Twitter's relevance at the city-level for New York City. Here, we look to dive deeper into the case of New York City by analyzing daily Twitter data from temporal and spatiotemporal perspectives. Also, through manual coding of all tweets, we look to gain qualitative insights that can help direct future automated searches.
  
  
  OBJECTIVE
  The intent of the study was first to validate the temporal predictive strength of daily Twitter data for influenza-like illness emergency department (ILI-ED) visits during the New York City 2012-2013 influenza season against other available and established datasets (Google search query, or GSQ), and second, to examine the spatial distribution and the spread of geocoded tweets as proxies for potential cases.
  
  
  METHODS
  From the Twitter Streaming API, 2972 tweets were collected in the New York City region matching the keywords "flu", "influenza", "gripe", and "high fever". The tweets were categorized according to the scheme developed by Lamb et al. A new fourth category was added as an evaluator guess for the probability of the subject(s) being sick to account for strength of confidence in the validity of the statement. Temporal correlations were made for tweets against daily ILI-ED visits and daily GSQ volume. The best models were used for linear regression for forecasting ILI visits. A weighted, retrospective Poisson model with SaTScan software (n=1484), and vector map were used for spatiotemporal analysis.
  
  
  RESULTS
  Infection-related tweets (R=.763) correlated better than GSQ time series (R=.683) for the same keywords and had a lower mean average percent error (8.4 vs 11.8) for ILI-ED visit prediction in January, the most volatile month of flu. SaTScan identified primary outbreak cluster of high-probability infection tweets with a 2.74 relative risk ratio compared to medium-probability infection tweets at P=.001 in Northern Brooklyn, in a radius that includes Barclay's Center and the Atlantic Avenue Terminal.
  
  
  CONCLUSIONS
  While others have looked at weekly regional tweets, this study is the first to stress test Twitter for daily city-level data for New York City. Extraction of personal testimonies of infection-related tweets suggests Twitter's strength both qualitatively and quantitatively for ILI-ED prediction compared to alternative daily datasets mixed with awareness-based data such as GSQ. Additionally, granular Twitter data provide important spatiotemporal insights. A tweet vector-map may be useful for visualization of city-level spread when local gold standard data are otherwise unavailable.
authors.affiliation: Children's Hospital Informatics Program, Boston Children's Hospital, Boston, MA, United States. ruchit.nagar@yale.edu.
authors.forename: Ruchit
authors.identifier: http://orcid.org/0000-0002-9461-8121
authors.initials: R
authors.lastname: Nagar
authors.forename: Qingyu
authors.identifier: http://orcid.org/0000-0002-7542-8402
authors.initials: Q
authors.lastname: Yuan
authors.forename: Clark C
authors.identifier: http://orcid.org/0000-0002-6281-219X
authors.initials: CC
authors.lastname: Freifeld
authors.forename: Mauricio
authors.identifier: http://orcid.org/0000-0002-4206-418X
authors.initials: M
authors.lastname: Santillana
authors.forename: Aaron
authors.identifier: http://orcid.org/0000-0001-9787-4465
authors.initials: A
authors.lastname: Nojima
authors.forename: Rumi
authors.identifier: http://orcid.org/0000-0002-5346-7259
authors.initials: R
authors.lastname: Chunara
authors.forename: John S
authors.identifier: http://orcid.org/0000-0001-8568-5317
authors.initials: JS
authors.lastname: Brownstein
mesh_terms: D057218:Blogging / Q000706:statistics & numerical data*; D004196:Disease Outbreaks; D062305:Geographic Mapping; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D020407:Internet; D009519:New York City / Q000453:epidemiology; D011446:Prospective Studies; D012189:Retrospective Studies; D062211:Spatio-Temporal Analysis
keywords: Google Flu Trends; New York City; Twitter; influenza; infodemiology; mHealth; medical informatics; social media, natural language processing; spatiotemporal