Is influenza-like illness a useful concept and an appropriate test of influenza vaccine effectiveness?

Abstract

The working diagnosis of ILI presumes influenza may be involved until proven otherwise. Health care workers would benefit by renaming the WHO and CDC ILI symptoms and signs as "acute respiratory illness" and also using the WHO acute severe respiratory illness definition if the illness is severe and meets this criterion. This renaming would shift attention to identify the viral and bacterial pathogens in cases and epidemics, identify new pathogens, implement vaccination plans appropriate to the identified pathogens, and estimate workload during the viral season. Randomised controlled trials testing the effectiveness of influenza vaccine require all participants to be assessed by a gold standard (RT-PCR). ILI has no role in measuring influenza vaccine effectiveness. ILI is well established in the literature and in the operational definition of many surveillance databases and its imprecise definition may be inhibiting progress in research and treatment. The current ILI definition could with benefit be renamed "acute respiratory illness," with additional definitions for "severe acute respiratory illness" (SARI) with RT-PCR testing for pathogens to facilitate prevention and treatment.

Do we have enough evidence how seasonal influenza is transmitted and can be prevented in hospitals to implement a comprehensive policy?

“…Screening will be a major undertaking. In a review of testing individuals with Influenza-Like Illness (ILI), Influenza A was detected in less than <25% in many studies (and often <5-7%) and Influenza B <5%, and when comprehensively tested up to 20 respiratory viruses and some bacteria may be detected [54]. Asymptomatic individuals need screening as an average 16% will test positive for Influenza during epidemics.…”

Analysis of household data on influenza epidemic with Bayesian hierarchical model

“…Also, the identification of influenza cases relies on subjects with influenza seeking for medical consultation which may also contribute to the lower secondary attack rate. The use of clinical definition also introduces another source of variation, since virus such as parainfluenza virus, adenovirus, coronavirus, respiratory syncytial virus, bacteria, and other untypable virus may also cause ILI [47]. These underlying variations in the causative agent for ILI may contribute to the deviation between the predicted and observed number of cases presented in Fig.…”

Improving Outcomes in Patients Receiving Dialysis: The Peer Kidney Care Initiative

“…Noninfluenza viruses that can infect the upper and lower respiratory tracts, such as rhinovirus, adenovirus, respiratory syncytial virus, parainfluenza virus, and human metapneumovirus, may contribute to morbidity and lead to hospitalizations for infection. Data suggest that substantially ,50%, perhaps as low as 25%-30%, of ILIs may be due to true influenza (18,19). ILIs may, in part, explain a less intuitive link between seasonality and hospitalization, and perhaps even with the patterns of death in incident patients.…”