Monitoring COVID-19 and Influenza: the added-value of a Severe Acute
Respiratory Infection surveillance system in Portugal
Abstract
Background Severe Acute Respiratory Infections (SARI) surveillance is
recommended to assess severity of respiratory infections disease. In
2021, the National Institute of Health Doutor Ricardo Jorge, in
collaboration with two central 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 We identified SARI cases based on ICD-10 codes for
influenza-like illness, cardiovascular diagnosis, respiratory diagnosis
and respiratory infection. Pearson correlation and cross-correlations
between weekly SARI cases, weekly COVID-19 cases and the number of
weekly positive samples for influenza 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). Weekly SARI hospitalizations detected the COVID-19
epidemic peak a week earlier. A weak correlation was observed between
SARI cases and the number of positive samples for influenza (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 5th COVID-19 epidemic wave and the increase
of influenza activity. Establishing complementary virological inpatient
surveillance is vital to aid in understanding the relationship between
respiratory virus epidemics and disease severity.