Influenza causes severe illness and deaths, and global surveillance systems use different clinical
case definitions to identify patients for diagnostic testing. We used data collected during January
2007–July 2010 at hospital-based influenza surveillance sites in western Kenya to calculate
sensitivity, specificity, positive predictive value, and negative predictive value for eight clinical
sign/symptom combinations in hospitalized patients with acute respiratory illnesses, including
severe acute respiratory illness (SARI) (persons aged 2–59 months: cough or difficulty breathing
with an elevated respiratory rate or a danger sign; persons aged o5 years: temperature o38 xC,
difficulty breathing, and cough or sore throat) and influenza-like illness (ILI) (all ages:
temperature o38 xC and cough or sore throat). Overall, 4800 persons aged o2 months were
tested for influenza; 416 (9%) had laboratory-confirmed influenza infections. The symptom
combination of cough with fever (subjective or measured o38 xC) had high sensitivity [87.
0%,
95% confidence interval (CI) 83.
3–88.
9], and ILI had high specificity (70.
0%, 95% CI 68.
6–71.
3).
The case definition combining cough and any fever is a simple, sensitive case definition for
influenza in hospitalized persons of all age groups, whereas the ILI case definition is the most
specific. The SARI case definition did not maximize sensitivity or specificity.