Quantifying infectious disease epidemic risks: A practical approach for seasonal pathogens

Area of Science:

• Epidemiology
• Mathematical Biology
• Public Health

Background:

• Outbreak risk for infectious diseases often depends on the season of pathogen introduction.
• Current methods like Case Epidemic Risk (CER) may be uninformative for seasonal pathogens due to neglecting seasonal transmission limitations.

Purpose of the Study:

• To develop and evaluate a new method for assessing outbreak risks of seasonal pathogens.
• To address the limitations of the Case Epidemic Risk (CER) in scenarios with strong seasonal transmission patterns.

Main Methods:

• Devised an alternative approach: Threshold Epidemic Risk (TER).
• TER calculates the probability of exceeding a threshold number of infections before extinction.
• TER can be calculated numerically for simple models or estimated via simulations for complex models (e.g., host-vector).

Main Results:

• The Case Epidemic Risk (CER) can be close to zero and uninformative when transmission is limited for long periods.
• The Threshold Epidemic Risk (TER) provides more informative and practically relevant risk assessments for seasonal pathogens.
• Demonstrated application using chikungunya virus in northern Italy, highlighting summer transmission suitability.

Conclusions:

• The Threshold Epidemic Risk (TER) is a more robust metric for evaluating outbreak potential of seasonal pathogens.
• This new approach enhances public health policy by enabling better quantification of epidemic risks.
• Accurate risk assessment is crucial for managing infectious diseases with seasonal dynamics.