Pertussis in older adults in the developed economies of Asia-Pacific: Is the burden fully recognised?

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Background: Despite being a notifiable disease, burden of pertussis beyond childhood is poorly documented in many countries. Methods and materials: We collated pertussis notification data since 2001 from government websites for six developed economies in Asia-Pacific (Australia/Hong Kong/New Zealand/Singapore/South Korea/Taiwan) to describe the pertussis disease burden in older adults from 60 years of age (YOA) onwards. Results: Australia: Between 2001–2018, cyclic increase in reported pertussis cases was observed every ∼4 years. From 2004, more than 10% of annual reports were in adults ≥60YOA. New Zealand: The notification pattern between 2001–2017 was similar to that of Australia, with cyclic changes in notifications. Since 2005, ∼10% of reported cases were in adults ≥60YOA. Hong Kong: Fewer than 50 pertussis cases were reported annually between 2001–2016. The number of annual cases increased to 110 in 2018. No breakdown by age was available. Taiwan: Data from 2010–2018 were available and showed that <100 pertussis cases were reported annually with no clear trend. No breakdown by age was available. Singapore: Data from 2009 showed that <20–30 pertussis cases were reported annually until 2014 increased significantly, with 80 cases reported in 2016. Before 2011, all cases were in children <5YOA. Cases ≥65YOA were first reported in 2016 (3 cases, 3.8% of all notifications) and rose to 8 cases (10.5%) in 2017. South Korea: Between 2001–2009, ≤21 pertussis cases were reported annually, the majority in infants <1YOA. The number of reported cases in older age groups has slowly increased since 2009. In 2018, the total number of notifications surged to 980. To be noted, despite a 2012 study reporting that seroprevalence of anti-pertussis toxin IgG was highest in adults ≥60YOA, <5% of notified cases were in this age group before 2014. Conclusion: Some sero-epidemiology data suggests that pertussis continues to circulate in the older age groups, even in countries with satisfactory paediatric vaccination coverages. Yet, it remains widely under recognised/diagnosed/reported as shown by the low number of notifications except for Australia and New Zealand. There is a need to raise awareness about the disease and improve surveillance to fully capture pertussis burden in the “overlooked” older adult population.