Evaluating the effect of targeted strategies as control tools for hypervirulent meningococcal C outbreaks: a case...

Area of Science:

• Epidemiology
• Mathematical modeling
• Public health

Background:

• Invasive meningococcal disease (IMD) is a significant cause of meningitis and sepsis, primarily caused by *Neisseria meningitidis*.
• A 2015-16 outbreak in Tuscany, Italy, involved 62 cases of IMD due to serogroup C meningococci (MenC), specifically the hyperinvasive ST-11(cc-11) strain.
• Understanding outbreak dynamics and intervention effectiveness is critical for controlling meningococcal disease.

Purpose of the Study:

• To estimate key epidemiological parameters of the 2015-16 MenC outbreak in Tuscany.
• To assess the impact and effectiveness of control interventions implemented during the outbreak.
• To inform future strategies for controlling meningococcal outbreaks.

Main Methods:

• Development of a susceptible-carrier-susceptible individual-based model simulating MenC transmission.
• Incorporation of transmission dynamics across various settings: households, schools, and community.
• Utilisation of detailed epidemiological data from the Tuscany outbreak and information on control measures.

Main Results:

• The estimated outbreak reproduction number (R_e) was 1.35, indicating sustained transmission.
• The probability of developing IMD from a new MenC carriage episode was estimated at 4.6 per 1,000 (95% CI: 1.8-12.2).
• Interventions including chemoprophylaxis and both contact and age-targeted vaccination significantly reduced R_e and controlled the outbreak; case-based interventions alone were insufficient.

Conclusions:

• Widespread reactive vaccination is essential for controlling outbreaks caused by highly transmissible MenC strains.
• Age-targeted vaccination campaigns can improve the effectiveness and efficiency of outbreak control measures.
• Findings provide a basis for developing guidelines to manage future meningococcal outbreaks caused by hypervirulent strains.