Google Flu Trends: correlation with emergency department influenza rates and crowding metrics.
BACKGROUND
Google Flu Trends (GFT) is a novel Internet-based influenza surveillance system that uses search engine query data to estimate influenza activity and is available in near real time. This study assesses the temporal correlation of city GFT data to cases of influenza and standard crowding indices from an inner-city emergency department (ED).


METHODS
This study was performed during a 21-month period (from January 2009 through October 2010) at an urban academic hospital with physically and administratively separate adult and pediatric EDs. We collected weekly data from GFT for Baltimore, Maryland; ED Centers for Disease Control and Prevention-reported standardized influenzalike illness (ILI) data; laboratory-confirmed influenza data; and ED crowding indices (patient volume, number of patients who left without being seen, waiting room time, and length of stay for admitted and discharged patients). Pediatric and adult data were analyzed separately using cross-correlation with GFT.


RESULTS
GFT correlated with both number of positive influenza test results (adult ED, r = 0.876; pediatric ED, r = 0.718) and number of ED patients presenting with ILI (adult ED, r = 0.885; pediatric ED, r = 0.652). Pediatric but not adult crowding measures, such as total ED volume (r = 0.649) and leaving without being seen (r = 0.641), also had good correlation with GFT. Adult crowding measures for low-acuity patients, such as waiting room time (r = 0.421) and length of stay for discharged patients (r = 0.548), had moderate correlation with GFT.


CONCLUSIONS
City-level GFT shows strong correlation with influenza cases and ED ILI visits, validating its use as an ED surveillance tool. GFT correlated with several pediatric ED crowding measures and those for low-acuity adult patients.
Department of Emergency Medicine, Johns Hopkins University, Baltimore, Maryland, USA. adugas1@jhmi.edu
Andrea Freyer
AF
Dugas
Yu-Hsiang
YH
Hsieh
Scott R
SR
Levin
Jesse M
JM
Pines
Darren P
DP
Mareiniss
Amir
A
Mohareb
Charlotte A
CA
Gaydos
Trish M
TM
Perl
Richard E
RE
Rothman
D000046:Academic Medical Centers; D000293:Adolescent; D000328:Adult; D015142:Baltimore / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology*; D020407:Internet / Q000706:statistics & numerical data*; D008297:Male; D011159:Population Surveillance / Q000379:methods*; D012189:Retrospective Studies