Pertussis in the elderly: Plausible amplifiers of persistent community transmission of pertussis in South Korea

Abstract

•The pertussis incidence in Korea shifted from infants to children and the elderly.•The elderly are likely to be a potential contributor to pertussis spread in Korea.•Seroprevalence study across different age groups and regions is needed. Dear Editor, We read with great interest the article by Meng et al.,1Meng Q. Shi W. Hu Y. Yao K. Pertussis in infants: alarm lights and amplifiers for persistent community transmission.J Infect. 2024; 89106219Abstract Full Text Full Text PDF Scopus (1) Google Scholar which reported that infants with pertussis (i.e., age <1 year) are a significant contributor to the community transmission of pertussis. Other studies have also shown that the patient population aged <1 year accounts for a significant proportion of the overall cases of pertussis in China.2Hu Y. Guo M. Yao K. Infections in preschool and school-aged children are driving the recent rise in pertussis in China.J Infect. 2024; 88106170Abstract Full Text Full Text PDF Scopus (5) Google Scholar, 3Mengyang G. Yahong H. Qinghong M. Wei S. Kaihu Y. Resurgence and atypical patterns of pertussis in China.J Infect. 2024; 88106140Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar Pertussis is a vaccine-preventable disease caused by Bordetella pertussis and is highly transmissible through respiratory droplets.2Hu Y. Guo M. Yao K. Infections in preschool and school-aged children are driving the recent rise in pertussis in China.J Infect. 2024; 88106170Abstract Full Text Full Text PDF Scopus (5) Google Scholar, 3Mengyang G. Yahong H. Qinghong M. Wei S. Kaihu Y. Resurgence and atypical patterns of pertussis in China.J Infect. 2024; 88106140Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar The incidence of pertussis is reportedly increasing in the United Kingdom and the United States in 2024. In contrast, no increase in incidence has been reported in East Asia, including Japan, Taiwan, and Singapore, as of July 2024 (Supplementary Figure 1). However, in South Korea, located east of mainland Asia, the notification number for pertussis cases has abruptly increased since October 2023, and the incidence is the highest for school-aged children (Fig. 1A and Supplementary Table 1). In Korea, pertussis outbreaks among kindergarten and school children have been reported in Gyeongsang Province since October 2023 (Supplementary Table 2 and Supplementary Figure 2).4Cho U.J. Kim A.-R. Park H.R. An D.-H. Yang S.-G. Kim Y. Report on the epidemic investigation of the Pertussis outbreak in Gyeongsangnam-do, 2023-2024.Public Health Wkly Rep. 2024; 17: 1143-1157Google Scholar Most cases presented with mild and atypical symptoms (i.e., 4% of patients had whooping cough and 10% presented with paroxysmal cough).4Cho U.J. Kim A.-R. Park H.R. An D.-H. Yang S.-G. Kim Y. Report on the epidemic investigation of the Pertussis outbreak in Gyeongsangnam-do, 2023-2024.Public Health Wkly Rep. 2024; 17: 1143-1157Google Scholar On November 14, 2023, the Korea Disease Control and Prevention Agency (KDCA) implemented enhanced active screening for pertussis suspects (i.e., persistent cough for days) across primary care clinics nationwide, particularly school-aged children, in the regions where outbreaks occurred. In Korea, KDCA has been conducting mandatory nationwide surveillance for pertussis. The national immunization program with the diphtheria/tetanus/pertussis (DTap) vaccine has been performed at 2, 4, and 6 months, between 15 and 18 months, and between 4 and 6 years of age.5Korea Disease Control and Prevention Agency. National Immunization Program for Children; 2024. 〈https://www.kdca.go.kr/contents.es?mid=a30333000000〉 [Accessed 15 July 2024].Google Scholar As a previous study demonstrated that the waning immunity against pertussis was observed after the fourth year of vaccination,6Wendelboe A.M. Rie A.V. Salmaso S. Englund J.A. Duration of immunity against pertussis after natural infection or vaccination.Pediatr Infect Dis J. 2005; 24: S58-S61Crossref Scopus (539) Google Scholar a booster vaccination (Tdap) has been administered to children aged 11–12 years in Korea. Furthermore, additional Tdap vaccination has been introduced for adult women during pregnancy since 2015 to provide passive immunity to the infant (i.e., aged <1 year).7Korea Disease Control and Prevention Agency. Pertussis integrated management guidelines; 2015. 〈https://www.kdca.go.kr/board/board.es?mid=a20507020000&bid=0019&act=view&list_no=138202&tag=&nPage=1〉 [Accessed 15 July 2024].Google Scholar Overall, the age distribution of pertussis patients in Korea gradually shifted from infants to school-aged children and the elderly (Fig. 1B). This may be due to several factors. First, waning immunity of DTap vaccination (complete vaccination rate of 97% for the 4–6-year-old) and relatively lower booster vaccination rate among 11–12 years old (complete vaccination rate of 83%), and the adult (2% in Gyeonggi Province, Korea).8Gyeonggi welfare foundation. Gyeonggi-do health care baseline study: Gyeonggi welfare foundation; 2019.Google Scholar Second, the increased passive immunity of neonates acquired from the maternal Tdap vaccination implemented in 2015 for pregnant women. After this introduction for pregnant women, the proportion of cases accounted for by patients aged <1 year significantly differed between 2015 and 2024 (9% of overall cases) than between 2001 and 2014 (75% of overall cases; Mann-Whitney test, P < 0.001). Third, potential antigenic variation of circulating B. Pertussis strains and possible reduction of vaccine effectiveness.9Mir-Cros A. Moreno-Mingorance A. Martin-Gomez M.T. Codina G. Cornejo-Sánchez T. Rajadell M. et al.Population dynamics and antigenic drift of Bordetella pertussis following whole cell vaccine replacement, Barcelona, Spain, 1986-2015.Emerg Microbes Infect. 2019; 8: 1711-1720Crossref PubMed Scopus (11) Google Scholar Fourth, active case finding for pertussis for the suspected individuals having atypical symptoms in the outbreak-affected regions and age group. One notable feature of the change in pertussis epidemiological trend in Korea is the role of the elderly in the transmission. Compared to the decreased incidence of cases among infants, the incidence among individuals aged >65 years has increased, resulting in this population accounting for >45% of the total cases in 2022 (Fig. 1B). This is in line with the results of a previous seroprevalence study conducted in Korea in 2014 that reported the highest seroprevalence in older adults (age >61 years; positive for 48% among the overall population).10Lee S.Y. Han S.B. Bae E.Y. Kim J.H. Kang J.H. Park Y.J. et al.Pertussis seroprevalence in korean adolescents and adults using anti-pertussis toxin immunoglobulin G.J Korean Med Sci. 2014; 29: 652-656Crossref PubMed Scopus (19) Google Scholar This indicates that the natural pertussis infection was likely endemic among older adults in Korea. Although further household contact study should be performed to corroborate this argument, the elderly population may play a potential amplifying role in pertussis transmission in Korea as the elderly usually care for their grandchildren (i.e., school-aged children). Therefore, the community transmission characteristics for pertussis in Korea differ from those in China, wherein the infant population plays a significant role.1Meng Q. Shi W. Hu Y. Yao K. Pertussis in infants: alarm lights and amplifiers for persistent community transmission.J Infect. 2024; 89106219Abstract Full Text Full Text PDF Scopus (1) Google Scholar In conclusion, Tdap booster dose administration for maternal immunization has been helpful in pertussis control among infants in Korea. While the 2023 Korean immunization guideline recommends either Td or Tdap booster vaccination every 10 years for adults, it has not been fully incorporated into the National Immunization Program. Therefore, the Tdap booster vaccination program is necessary for the adolescents and elderly population to reduce the transmission of pertussis in the community. Additional nationwide surveillance for circulating B. Pertussis strains (i.e., genomic surveillance) and the seroprevalence study across different age groups and regions is needed to determine the exact burden of pertussis. This study did not require institutional review board approval or informed consent because all data used are anonymous and are publicly available on websites. This study was supported by the Government-wide R&D to Advance Infectious Disease Prevention and Control, Republic of Korea (grant number: RS-2023-KH140322) and the Basic Science Research Program through the National Research Foundation of Korea funded by the Korean Ministry of Education (NRF-2020R1I1A3066471).

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