Pertussis in infants: alarm lights and amplifiers for persistent community transmission
Authors: Qinghong Meng, Wei Shi, Yahong Hu, Kaihu Yao
Journal: Journal of Infection (2024)

Dear editor, The resurgence of pertussis and the shift in age composition of reported pertussis cases in China were reported recently.1Mengyang G. Yahong H. Qinghong M. Wei S. Kaihu Y. Resurgence and atypical patterns of pertussis in China.J Infect. 2024; 88106140https://doi.org/10.1016/j.jinf.2024.106140Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar, 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; 88106170https://doi.org/10.1016/j.jinf.2024.106170Abstract Full Text Full Text PDF Scopus (2) Google Scholar The data revealed an increase in pertussis cases among older children, and a decrease in the proportion of infant pertussis. 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; 88106170https://doi.org/10.1016/j.jinf.2024.106170Abstract Full Text Full Text PDF Scopus (2) Google Scholar The predominance of infant cases in China before the COVID-19 pandemic was consistent with a recent report from Italy, which showed a significant pertussis outbreak among neonates and young infants, with infants accounting for 88.0% of the 108 reported cases. 3Poeta M. Moracas C. Albano C. Petrarca L. Maglione M. Pierri L. et al.Pertussis outbreak in neonates and young infants across Italy, January to May 2024: implications for vaccination strategies.Eur Surveill. 2024; 29: 2400301https://doi.org/10.2807/1560-7917.ES.2024.29.23.2400301Crossref PubMed Scopus (1) Google Scholar During 2011–2017, infant cases accounted for 64.33% of nationally reported cases and 87.4% of culture-confirmed cases in Beijing Children's Hospital (BCH) from 2013–2014. However, this rate has decreased to 31.17% of nationally reported cases in 2022, 47.8% of BCH culture-confirmed cases in 2023, and 42.6% in the first two months of 2024. 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; 88106170https://doi.org/10.1016/j.jinf.2024.106170Abstract Full Text Full Text PDF Scopus (2) Google Scholar Although Poeta et al. 3Poeta M. Moracas C. Albano C. Petrarca L. Maglione M. Pierri L. et al.Pertussis outbreak in neonates and young infants across Italy, January to May 2024: implications for vaccination strategies.Eur Surveill. 2024; 29: 2400301https://doi.org/10.2807/1560-7917.ES.2024.29.23.2400301Crossref PubMed Scopus (1) Google Scholar did not explicitly state this, we hypothesize that the infant cases they reported exhibit a similar sporadic pattern to our previous observations. Pertussis patients or suspected cases among their close contacts are typically identified only through active surveillance. These cases are often not detected or diagnosed during routine work. Since humans are the only hosts of Bordetella pertussis, it is difficult to achieve sustained community transmission solely based on infant cases. The lifestyle of infants does not support the transmission of this bacterium between infants. However, due to the clinical characteristics of infant cases, they frequently visit the doctor earlier and are more likely to prompt the doctor's vigilance and specimen testing. The infant pertussis cases, therefore, are clear evidence and alarm lights for the persistent community transmission of pertussis. Most other cases, particularly among teenagers and adults who contribute to sustaining transmission, do not seek medical attention due to asymptomatic or mild symptoms. Additionally, many cases are not identified or reported due to missed or incorrect diagnoses. These silent cases are integral to the community transmission of pertussis. Without detecting these cases, the full dynamics of pertussis transmission within the community cannot be accurately understood. Achieving long-term control of pertussis remains a significant challenge. This factor may have contributed to the recent global outbreak of pertussis. On the other hand, infant cases serve as important sources of pertussis community transmission. Previous studies have not been rigorous enough to assume that close contacts who test positive are often the source of infant pertussis infection. However, actively testing close contacts of infants with pertussis often reveals multiple positive results. In fact, a baby can be infected with pertussis from one person, who is likely to have cleared the pathogen from his body by the time the baby gets sick. A study conducted by Shenzhen Children's Hospital examined 617 close household contacts of 270 children with pertussis, with 173 (28.0%) testing positive for pertussis pathogens. These contacts included mothers (34.9%), grandparents (26.2%), fathers (24.7%), siblings (18.3%), and other relatives (15.6%, including uncles, aunts, cousins, etc.).4Xu Z. Wang H.M. Wu X.Y. Guo F.W. Deng J.K. [Clinical epidemiological characteristics of pertussis in children and the status of infection in their close contacts].Zhonghua Yi Xue Za Zhi. 2021; 101: 3650-3654https://doi.org/10.3760/cma.j.cn112137-20210301-00523Crossref PubMed Scopus (4) Google Scholar Infants have increased opportunities for close contact with others, making it more likely for them to transmit the disease to multiple contacts. In this process, mothers are often the first to be infected. Therefore, determining whether the mother is the source of infection for the infant, especially for breastfeeding infants, poses significant challenges. Family members or caregivers who have close contact with pertussis-infected infants may reintroduce the pathogen into the community. In this sense, an infant with pertussis may mark the beginning of multiple community transmission chains, acting as an "amplifier" in the transmission chain (Fig. 1). This underscores the importance of preventing infant infections to control pertussis in the community. This work was supported by the National Natural Science Foundation of China (81973100) and Funding for Reform and Development of Beijing Municipal Health Commission (FRD-2024).