<p><b>OBJECTIVE</b>Symptomatic predictors of
influenza could assess
risks and improve decisions about isolation and
outpatient treatment. To develop such predictors, we undertook a prospective
analysis of
pandemic (H1N1) 2009 and seasonal
influenza (H3N2) in
patients attending
fever clinics.</p><p><b>
METHODS</b>From 1 May 2009 to 1 January 2010, all
adult patients admitted to
fever clinics for suspected
influenza, confirmed by real
time RT-PCR, were enrolled. Predictors of
influenza virus infection were selected with
logistic regression models.
Measures of
sensitivity,
specificity, positive and negative likelihood ratios (LRs) were calculated to identify the best predictors.</p><p><b>RESULTS</b>The clinical features and routine
blood test results of
influenza (H1N1) 2009 and seasonal
influenza were
similar. The positive and negative LRs of current US
CDC influenza-like illness (ILI) criteria were modest in predicting
influenza infection. Our modified clinic predictors improved the
ability of the positive and negative LRs to recognize
pandemic (H1N1) 2009 and seasonal
influenza. The revised criteria are
fever >38 °C accompanied by at least one of the following-
cough,
arthralgia or relative
lymphopenia.</p><p><b>CONCLUSION</b>
Patients with
symptoms and signs that meet the new criteria are likely to have
influenza and timely
antiviral therapy may be appropriate. In addition,
physicians should ascertain if
influenza is circulating within the
community or if there is a contact
history of
influenza and combine this information with the newly developed criteria to clinically
diagnose influenza.</p>