Author(s):
Gonçalves, Paulo 
; Pechirra, Pedro ; Conde, Patrícia ; Nunes, Baltazar ; Guiomar, Raquel
Date: 2011
Persistent ID: http://hdl.handle.net/10400.18/991
Origin: Repositório Científico do Instituto Nacional de Saúde
Subject(s): Infecções Respiratórias; Gripe; Influenza; Vírus Respiratórios; Diagnóstico Diferencial
Description
The National Influenza Reference Laboratory (NIRL) coordinates and performs virological surveillance of Influenza-Like Ilness (ILI), integrated in the Portuguese National Influenza Surveillance Programme (NISP). Despite of this well established surveillance, little is known about the aetiology, virology and clinical aspects of respiratory illness in the country, other than that caused by influenza. National data shows that, during a winter influenza season, 40-70% of ILI cases are not attributed to influenza infection. This will have a significant impact on the estimation of influenza incidence, morbidity and mortality rates. Information on the contribution of other pathogens on the aetiology of ILI is, therefore, necessary. The objective of this preliminary study was to identify other respiratory viruses associated with influenza-like illness and their prevalence in Portugal.
During the 2010/2011 influenza winter season, 1017 cases of influenza-like illness (according to the ICHPPC-II definition) were reported to the NIRL for influenza (FLU) diagnosis, in the context of the NISP. From these, 400 were selected to be additionally tested for other respiratory virus that cause respiratory illness with influenza-like symptoms, including respiratory syncytial virus (RSV) types A and B, human parainfluenza viruses (hPIV) types 1, 2 and 3, human rhinovirus (hRV) and adenovirus (AdV), by real-time PCR. Sample size was set in order to estimate the proportion ILI cases positive for other respiratory virus, considering an expected prevalence of 50% and an abosolute precison of 5% for the 95% confidence interval. The sample was selected with a random simple scheme using the package of statistcial programs SPSS.
22 cases were excluded from the study due to insufficient specimen. Infection with at least one virus was detected in 256 (67.7%) of the 378 ILI cases analysed, the most frequent of which (79.3%) were FLU viruses (43.0% FLU-A, 36.3% FLU-B) and hRV (11.3%). RSV, hPIV-2, hPIV-3 and AdV accounted for less than 8% frequency (3.1% RSV-A, 1.6% RSV-B, 1.2% hPIV-2, 0.4% hPIV-3 and 1.6% AdV). Co-infection of influenza with other respiratory virus was observed in 4 (1.6%) cases.
The high frequency observed for FLU viruses was not unexpected since the recruitment of cases is, in this setting, biased towards the detection of influenza. Still, it is clear that multiple viruses co-circulate with influenza. Their influence on the clinical presentation of ILI will be further analysed.
