Epidemiology and Infection

Original Papers

Influenza

What are the most sensitive and specific sign and symptom combinations for influenza in patients hospitalized with acute respiratory illness? Results from western Kenya, January 2007–July 2010

E. L. MURRAYa1, S. KHAGAYIa2, M. OPEa3, G. BIGOGOa4, R. OCHOLAa5, P. MUTHOKAa3, K. NJENGAa4, F. ODHIAMBOa2, D. BURTONa4, K. F. LASERSONa2, R. F. BREIMANa4, D. R. FEIKINa4 and M. A. KATZa5 c1

a1 Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, GA, USA

a2 Kenya Medical Research Institute (KEMRI)/Centers for Disease Control and Prevention, Kenya

a3 Division of Disease Surveillance and Response, Ministry of Public Health and Sanitation, Kenya

a4 International Emerging Infections Program, Global Disease Detection Division, Centers for Disease Control and Prevention, Kenya

a5 Influenza Program, Global Disease Detection Division, Centers for Disease Control and Prevention, Kenya

SUMMARY

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 ≥5 years: temperature ≥38 °C, difficulty breathing, and cough or sore throat) and influenza-like illness (ILI) (all ages: temperature ≥38 °C and cough or sore throat). Overall, 4800 persons aged ≥2 months were tested for influenza; 416 (9%) had laboratory-confirmed influenza infections. The symptom combination of cough with fever (subjective or measured ≥38 °C) 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.

(Received July 01 2011)

(Revised February 13 2012)

(Accepted February 20 2012)

(Online publication March 15 2012)

Key words

  • Influenza;
  • predictive value of tests;
  • respiratory infections;
  • sensitivity and specificity;
  • surveillance

Correspondence:

c1 Author for correspondence: M. A. Katz, M.D., Epidemic-Prone Disease and Surveillance Advisor, Centers for Disease Control and Prevention – Haiti, Unit 3400, Box 68, DPO, AA 34060-068, USA. (Email: katzm@ht.cdc.gov)

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