Interrupted time-series analysis of nationwide surveillance in Thai adult pneumococcal diseases over 14 years: evidence to inform policy in resource-limited countries

Abstract

Background: This study aimed to update the incidence and mortality of pneumococcal diseases and to evaluate the population-level trends in pneumococcal diseases incidence in Thailand, following PCV13 licensure and during the COVID-19 pandemic, in order to generate evidence supporting its inclusion in the National Immunization Program (NIP). Research design and methods: We conducted a quasi-experimental interrupted time-series analysis using sentinel hospital surveillance data from adults aged ≥ 18 years hospitalized with pneumococcal disease in Thailand between 2010 and 2024. Surveillance comprised retrospective passive data collection (2010–July 2023) and prospective active surveillance (August 2023–July 2024), applying consistent case definitions and outcome ascertainment methods throughout. Four epidemiologic periods were predefined based on PCV13 licensure and key phases of the COVID-19 pandemic. Results: Among 2069 hospitalized adults, 61.0% were aged ≥ 65 years. Non-invasive pneumococcal pneumonia (NIPP) accounted for 72.8% of cases, while invasive pneumococcal disease (IPD) comprised 27.2%, with a rising trend over time. The overall in-hospital fatality rate was 23.4%, significantly higher in IPD (31.7%) than in NIPP (20.4%, p < 0.001). The incidence of both IPD and NIPP nearly tripled over the study period. IPD increased from 1.43 to 4.05 per 100,000 population, while NIPP rose from 3.23 to 10.92 per 100,000 population, with a marked increase observed during the recent COVID-19 pandemic period. An increasing trend in macrolide resistance was observed in IPD and NIPP, particularly during the COVID-19 pandemic. Serotype analysis showed that PCV13 covered 79% of all isolates, PCV15 covered up to 79–81%, and PCV20 offered the broadest coverage (up to 95%), particularly for IPD. Conclusions: The burden of pneumococcal diseases in Thailand remains substantial, especially during the recent COVID-19 pandemic. The majority of disease-causing serotypes remained vaccine-type strains. Given that PCV13 or PCV15 inclusion in the Thai adult NIP should be prioritized to reduce the disease burden and antimicrobial-resistant pneumococcal infections. Clinical trial registration: This study was registered with the Thai Clinical Trial Registry (TCTR20230816007).