Presentation (CTI)

OBJECTIVES: Macrolides are widely used to treat Bordetella pertussis, yet macrolide-resistant B. pertussis (MRBP) strains are increasingly reported globally, with prevalence estimates ranging from 4.4% to 90%. MRBP infections are associated with more severe clinical disease and require alternative antibiotic therapy. Delayed detection can prolong inappropriate treatment and increases likelihood of ongoing transmission. Debate continues regarding which patients should undergo MRBP testing. This study compared infection burden, severity, mortality, epidemic peak timing, and inappropriate treatment across three diagnostic strategies: (1) testing all confirmed pertussis cases; (2) testing only severe cases; and (3) no MRBP testing.
METHODS: A Susceptible - Exposed - Infected - Recovered (SEIR) model was constructed to simulate pertussis transmission in Australia. Parameters included transmission probabilities, reproductive coefficient, age-specific severity and mortality, and demographic data from the Australian Bureau of Statistics. We modelled MRBP prevalence scenarios of 4.4%, 30%, 60%, and 90%, with five simulations per scenario, assessing trends and differences in outcomes across strategies over 12 months.
RESULTS: Incremental benefits of MRBP testing increased as prevalence rose, plateauing around 60%. Compared with Testing None, Testing All reduced infections by 10% (9-11%) at 4.4% prevalence, increasing to 47% (45-48%) at 60% and 90% prevalence. Testing Severe yielded smaller reductions: 3% (-1-5%) at 4.4% to 13% (12-13%) at 60%. Testing All delayed the epidemic peak by 5-6 weeks at ≥ 60% prevalence, whereas Testing Severe delayed it by 1 week. Across all scenarios, Testing All resulted in the lowest proportion of inappropriate treatment. No meaningful differences in severity or mortality were observed between strategies.
CONCLUSIONS: Routine MRBP testing for pertussis becomes important as MRBP prevalence rises in Asia-Pacific. Comprehensive testing may reduce transmission, delay outbreak peaks, and improve treatment appropriateness. Future work should evaluate implementation feasibility and economic impact to inform policy.