Monitoring COVID-19 and Influenza: The Added Value of a Severe Acute Respiratory Infection Surveillance System in Portugal.

Background: Severe acute respiratory infections (SARI) surveillance is recommended to assess the severity of respiratory infections disease. In 2021, the National Institute of Health Doutor Ricardo Jorge, in collaboration with two general hospitals, implemented a SARI sentinel surveillance system based on electronic health registries. We describe its application in the 2021/2022 season and compare the evolution of SARI cases with the COVID-19 and influenza activity in two regions of Portugal. Methods: The main outcome of interest was the weekly incidence of patients hospitalized due to SARI, reported within the surveillance system. SARI cases were defined as patients containing ICD-10 codes for influenza-like illness, cardiovascular diagnosis, respiratory diagnosis, and respiratory infection in their primary admission diagnosis. Independent variables included weekly COVID-19 and influenza incidence in the North and Lisbon and Tagus Valley regions. Pearson and cross-correlations between SARI cases, COVID-19 incidence and influenza incidence were estimated. Results: A high correlation between SARI cases or hospitalizations due to respiratory infection and COVID-19 incidence was obtained (ρ = 0.78 and ρ = 0.82, respectively). SARI cases detected the COVID-19 epidemic peak a week earlier. A weak correlation was observed between SARI and influenza cases (ρ = -0.20). However, if restricted to hospitalizations due to cardiovascular diagnosis, a moderate correlation was observed (ρ = 0.37). Moreover, hospitalizations due to cardiovascular diagnosis detected the increase of influenza epidemic activity a week earlier. Conclusion: In the 2021/2022 season, the Portuguese SARI sentinel surveillance system pilot was able to early detect the COVID-19 epidemic peak and the increase of influenza activity. Although cardiovascular manifestations associated with influenza infection are known, more seasons of surveillance are needed, to confirm the potential use of cardiovascular hospitalizations as an indicator of influenza activity.

Resurgence of Respiratory Syncytial Virus in Children: An Out-of-Season Epidemic in Portugal.

INTRODUCTION: An out-of-season increase in respiratory syncytial virus (RSV) incidence was observed in Portugal from June 2021 onwards, revealing a continuing surge in cases throughout 2021/2022 autumn/winter. We aimed to describe this out-of-season epidemic and define its epidemic period, by analysing RSV incidence from week 40 of 2020 (2020-W40) to week 18 of 2022 (2022-W18). MATERIAL AND METHODS: Surveillance data on weekly RSV laboratory confirmed cases, in Portugal, was used to monitor RSV incidence using CUSUM test methodology for count data. RESULTS: In 2021-W23, the CUSUM score identified a significant increase in the risk of RSV. By that time, the percentage of RSV positive tests rose from 1% in 2021-W22 (3/265) to 6% in 2021-W23 (18/298). Despite a sharp decrease in RSV incidence on 2021-W33 and on 2022-W02, the CUSUM score stayed over the limit up to 2022-W07, indicating that the RSV activity remained at an epidemic level. Distinct peaks of RSV cases were observed between 2021-W30 and 2021-W32 (average of 77 RSV cases per week) and between 2021-W39 and 2021-W41 (average of 79 RSV cases per week) with positivity rates around 60%. CONCLUSION: An out-of-season RSV epidemic was identified, with a longer epidemic period compared with previous seasons. Possible reasons include relaxation of COVID-19 physical distancing measures and a greater proportion of population susceptible to disease. As several factors may change the pattern of RSV activity, countries should implement year-round surveillance RSV surveillance systems. These findings might have an impact on public health planning regarding future RSV surges, namely, on the palivizumab prophylaxis period for high-risk infants.

SARS-CoV-2 seroprevalence in Portugal following the third epidemic wave: results of the second National Serological Survey (ISN2COVID-19).

BACKGROUND: Integrated approaches to surveillance of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection are important for public health actions. The 2nd National Serological Survey (ISN2COVID-19) aimed to characterize the extent of SARS-CoV-2 infection and vaccine-induced response in the Portuguese population following the third epidemic wave and the launch of the vaccination campaign. METHODS: A cross-sectional study was performed using data on 8463 Portuguese 1-79 years of age, collected in February and March, 2021. SARS-CoV-2 IgM and IgG (anti-nucleoprotein and anti-spike) antibodies were determined in serum samples using Abbott Architect chemiluminescent microparticle assays. Post-infection and vaccine-induced seroprevalence with 95% confidence intervals (95%CI) were estimated in the overall sample and stratified by population characteristics. RESULTS: The estimated seroprevalence was 15.5% (95%CI:14.6-16.5%), of which 13.5% (95%CI: 12.6-14.4%) was attributable to natural infection and 2.0% (95%CI:1.7-2.4%) to vaccination. The lowest seroprevelence was observed in persons aged 70-79 years (8.9% 95%CI:6.8-11.6), while seroprevalence in children (14.3%; 95%CI:11.5-17.6%) and adolescents (12.9%; 95%CI:10.5-15.7%) was similar to that of persons aged between 20 and 69 years. Of seropositive individuals, 22.6% (95%CI:19.7-25.9%) did not report any symptoms in 6 months prior to interview. Of persons with completed vaccination (2-doses), 98.6% (95%CI: 93.0-99.7%) had specific IgG (anti-S) antibodies. CONCLUSIONS: After the third epidemic wave, the post-infection SARS-CoV-2 seroprevalence was 1.7 times higher than the cumulative incidence based on PCR-testing, but was higher (2.7 times) in children may be due to the high proportion of asymptomatic and mild infections.