Abstract
Influenza is associated with severe illness, death, and economic burden. Sentinel surveillance systems have a central role in the community since they support public health interventions. This study aimed to describe and compare the influenza-coded primary care consultations with the reference index of influenza activity used in Portugal, General Practitioners Sentinel Network, from 2012 to 2017. An ecological time-series study was conducted using weekly R80-coded primary care consultations (according to the International Classification of Primary Care-2), weekly influenza-like illness (ILI) incidence rates from the General Practitioners Sentinel Network and Goldstein Index (GI). Good accordance between these three indicators was observed in the characterization of influenza activity regarding to start and length of the epidemic period, intensity of influenza activity, and influenza peak. A high correlation (>0.75) was obtained between weekly ILI incidence rates and weekly number of R80-coded primary care consultations during all five studied seasons. In 3 out of 5 seasons this correlation increased when weekly ILI incidence rates were multiplied for the percentage of influenza positive cases. A cross-correlation between weekly ILI incidence rates and the weekly number of R80-coded primary care consultations revealed that there was no lag between the rate curves of influenza incidence and the number of consultations in the 2012/13 and 2013/14 seasons. In the last three seasons, the weekly influenza incidence rates detected the influenza epidemic peak for about a week earlier. In the last season, the GI anticipated the detection of influenza peak for about a two-week period. Sentinel networks are fundamental elements in influenza surveillance that integrate clinical and virological data but often lack representativeness and are not able to provide regional and age groups estimates. Given the good correlation between weekly ILI incidence rate and weekly number of R80 consultations, primary care consultation coding system may be used to complement influenza surveillance data, namely, to monitor regional influenza activity. In the future, it would be interesting to analyse concurrent implementation of both surveillance systems with the integration of all available information.
Highlights
Influenza is a serious public health problem associated with severe illness and death in highrisk populations
Data used on the analysis provided from National Influenza Surveillance System (General Practitioners Sentinel Network) and primary care consultations registries
For the five studied influenza seasons, characterization of influenza activity, regarding to start and length of epidemic, epidemic peak and intensity, was similar when comparing the number of R80-coded primary care consultations and the weekly influenza-like illness (ILI) incidence rate estimated by General Practitioners Sentinel Network or the Goldstein Index (GI)
Summary
Influenza is a serious public health problem associated with severe illness and death in highrisk populations. Sentinel surveillance systems for medical practices are recognized to be the most efficient way to perform influenza surveillance [7]. Sentinel surveillance aims to promptly identify and monitor influenza activity in the community, presenting a central role in support of public health interventions [5,8,9]. Since 1989 to present, the Portuguese General Practitioners Sentinel Network (Rede Médicos Sentinela) has provided weekly influenza-like illness (ILI) rate estimates. This network is part of the National Influenza Surveillance System, which integrates epidemiological and virological components [10]
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