The impact of alternative diagnoses on the utility of influenza-like illness case definition to detect the 2009 H1N1 pandemic.
OBJECTIVE
To investigate the impact of excluding cases with alternative diagnoses on the sensitivity and specificity of the Centers for Disease Control and Prevention's (CDC) influenza-like illness (ILI) case definition in detecting the 2009 H1N1 influenza, using Geographic Utilization of Artificial Intelligence in Real-Time for Disease Identification and Alert Notification, a disease surveillance system.


METHODS
Retrospective cross-sectional study design.


METHODS
Emergency department of an urban tertiary care academic medical center.


METHODS
1,233 ED cases, which were tested for respiratory viruses from September 5, 2009 to May 5, 2010.


METHODS
The main outcome measures were positive predictive value, negative predictive value, sensitivity, specificity, and accuracy of the ILI case definition (both including and excluding alternative diagnoses) to detect H1N1.


RESULTS
There was a significant decrease in sensitivity (chi2 = 9.09, p < 0.001) and significant improvement in specificity (chi2 = 179, p < 0.001), after excluding cases with alternative diagnoses.


CONCLUSIONS
When early detection of an influenza epidemic is of prime importance, pursuing alternative diagnoses as part of CDC's ILI case definition may not be warranted for public health reporting due to the significant decrease in sensitivity, in addition to the resources required for detecting these alternative diagnoses.
Department of Emergency Medicine, Rush University, Chicago, Illinois, USA.
Dino P
DP
Rumoro
Jamil D
JD
Bayram
Julio C
JC
Silva
Shital C
SC
Shah
Marilyn M
MM
Hallock
Gillian S
GS
Gibbs
Michael J
MJ
Waddell
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D016133:Polymerase Chain Reaction; D011159:Population Surveillance; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult