Influenza-like illness criteria were poorly related to laboratory-confirmed influenza in a sentinel surveillance study

J Clin Epidemiol. 2005 Mar;58(3):275-9. doi: 10.1016/j.jclinepi.2004.08.014.


Objective: To analyze the most related clinical data for influenza and the utility of influenza-like illness criteria as the clinical threshold for sampling in an influenza sentinel surveillance over a 3-year period.

Methods: Sentinel physicians collected throat specimens and data from outpatients with acute respiratory infection (< or = 72 hours duration). Laboratory-confirmed influenza infection was compared with independent symptoms and the influenza-like illness criteria, as defined by the Classification Committee of the World Organization of Family Doctors.

Results: From 1934 patients, 359 (18.56%) yielded positive results for influenza viruses. Only 199 (55.4%) of laboratory-confirmed cases fulfilled clinical criteria of influenza-like illness: positive and negative predictive value (PPV and NPV) of 0.36 and 0.88, respectively. Fever, cough, and rhinorrhea individually correlated with influenza infections (PPV: 0.30, 0.20, and 0.20, respectively; NPV: 0.92, 0.87, and 0.85, respectively). Multivariate analysis demonstrated that the correlation of influenza infection with the presence of fever and cough was similar to the correlation between influenza infection and influenza-like illness criteria (odds ratio 2.24 vs. 2.71, respectively).

Conclusion: Influenza-like illness criteria are poorly related to laboratory-confirmed influenza. For early detection of influenza viruses in surveillance systems, a less restrictive clinical criterion (specifically, acute respiratory infection) perhaps should be followed.

Publication types

  • Multicenter Study

MeSH terms

  • Acute Disease
  • Adolescent
  • Adult
  • Age Distribution
  • Aged
  • Aged, 80 and over
  • Child
  • Child, Preschool
  • Cough / virology
  • Family Practice
  • Female
  • Fever / virology
  • Humans
  • Infant
  • Influenza A virus / isolation & purification
  • Influenza B virus / isolation & purification
  • Influenza Vaccines / administration & dosage
  • Influenza, Human / complications
  • Influenza, Human / diagnosis*
  • Influenza, Human / epidemiology*
  • Logistic Models
  • Male
  • Middle Aged
  • Pharynx / virology
  • Respiratory Tract Infections / diagnosis
  • Sentinel Surveillance*
  • Spain / epidemiology


  • Influenza Vaccines