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. 2021 Jan;15(1):56-63.
doi: 10.1111/irv.12779. Epub 2020 Jul 12.

Determining the seasonality of respiratory syncytial virus in Slovenia

Eva Grilc  1 , Katarina Prosenc Trilar  2 , Jaro Lajovic  3 , Maja Sočan  1
Affiliations

Determining the seasonality of respiratory syncytial virus in Slovenia

Eva Grilc et al. Influenza Other Respir Viruses. 2021 Jan.

Abstract

Background: In Slovenia, the respiratory syncytial virus (RSV) surveillance is based on national laboratory data. The weeks with more than 10% of samples tested positive compose RSV epidemic season. The use of real-time multiplex PCR, which identifies other respiratory pathogens in parallel with RSV, caused more testing but the percentage of RSV positives lowered. The 10% threshold was reached with delay, which raised concern about its suitability for defining RSV seasonality.

Methods: To describe the seasonality of RSV, the onset, offset and duration of the RSV epidemic season across 10 years (from week 40, 2008/2009 to week 39, 2017/2018), four calculative methods were deployed including moving epidemic method, MEM, and epidemiological parameters were compared.

Results: In 10 years, 10 969 (12%) out of 90 264 samples tested positive for RSV. The number of tested samples increased remarkably from the first to last season with a drop in the percentage of positive samples from 23% to 10%. The onset of RSV epidemic varied considerably regardless of the calculative method used (from 10 to 13 weeks). The unevenness in the RSV epidemic season end was also observed. The average duration of RSV epidemic season was the shortest when moving epidemic method has been used (15.7 weeks) and longest with ≥3% method (22.9 weeks).

Conclusion: The ≥3% calculative method could be used as an early warning of the RSV season. However, ≥7% calculative method was found to be reliable enough to define the epidemiological parameters of an ongoing season and to support public health response. The potential of the moving epidemic method should be further explored.

Keywords: MEM; RSV; season threshold; seasonality; surveillance.

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Conflict of interest statement

Dr Grilc E has nothing to disclose.

Figures

Figure 1
Figure 1
Number of samples tested negative or positive for RSV from Week 40/2008 to Week 39/2018, Slovenia
Figure 2
Figure 2
The onset and offset weeks of RSV seasons according to different calculative methods
See this image and copyright information in PMC

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