What proportion of influenza infections are associated with febrile illness : a systematic review

Abstract

Background Human infected with influenza virus commonly present with fever and cough. However, it is documented in the literature that a proportion of people with influenza infection remained afebrile or even asymptomatic. Understanding of the prevalence of febrile illness among people infected with influenza (the febrile proportion) could guide the public health response to influenza epidemics and pandemics.

Methods A systematic review was conducted by a search of relevant articles published in peer-review journals using PubMed and Google. Two different approaches were adopted in the synthesis of the febrile proportion.

Results Nine studies were included in the systematic review. The febrile proportion of influenza infection was estimated to lie between 32% and 83%, with the most plausible values in the range of approximately 50%. Pandemic and pre-pandemic strain of influenza A H1N1 subtype may have a higher febrile proportion than influenza A H3N2 subtype and influenza B. The febrile proportion among children was also higher than adults.

Conclusion This systematic review consolidated evidence on the febrile proportion in influenza infection. Attributes were identified to be potentially associated with higher febrile proportion. These preliminary findings provide interesting hypothesis for future research and provide opportunities for changes in the public health response to influenza epidemics and pandemics, with particular implications for the use of body temperature screening at national borders.