Influenza Epidemic Thresholds for Turkey Using the Moving Epidemic Methods: A Ten-Season Analysis

Background

The Moving Epidemic Method (MEM) is the ECDC/WHO-Europe standard for establishing influenza epidemic thresholds and intensity levels. Despite over a decade of sentinel surveillance, no MEM analysis has been published for Turkey or any country within the WHO Western Asia influenza transmission zone. It is aimed to establish MEM-derived thresholds for Turkey and assess concordance with WHO regional transmission zones.

Methods

Weekly influenza positivity rates from FluNet sentinel surveillance covering ten seasons (2013/2014–2024/2025, excluding COVID-19 pandemic seasons) were analysed using the mem R package with cross-validated optimized slope parameter. Turkey’s average epidemic curve and thresholds were compared with Western Asia (excluding Turkey) and South West Europe zones using Pearson’s r, Spearman’s ρ, Lin’s concordance correlation coefficient (CCC), root mean square deviation, and mean absolute difference.

Results

The epidemic threshold was 10.59% positivity, with intensity thresholds at 42.56% (medium), 60.92% (high), and 71.38% (very high). Cross-validated sensitivity was 0.77, specificity 0.88, and Matthews correlation coefficient 0.65. Turkey’s average curve showed higher concordance with Western Asia (CCC=0.890; RMSD=4.22pp) than South West Europe (CCC=0.672; RMSD=12.48pp), despite similar Pearson correlations (0.922 vs 0.939).

Conclusions

This first MEM application for Turkey and the Western Asia zone establishes operational epidemic thresholds suitable for routine surveillance integration. From an epidemiological timing perspective, Turkey’s influenza patterns show closer resemblance to Western Asia than South West Europe, though transmission zone classification incorporates multiple additional factors beyond epidemic curve dynamics. These thresholds can strengthen seasonal preparedness planning and real-time intensity monitoring.

Key messages

• This is the first MEM-based influenza threshold analysis for Turkey and the WHO Western Asia transmission zone, establishing operational epidemic intensity levels.

• Turkey’s influenza epidemic timing patterns more closely resemble Western Asia than South West Europe, offering one epidemiological lens supporting its zone classification.