Understanding the unconventional reemergence of M. pneumoniae epidemics during the COVID-19 pandemic.

Since the implementation of coronavirus disease 2019 (COVID-19) restrictions since 2020, the number of Mycoplasma pneumoniae (M. pneumoniae) infections in children has significantly decreased. However, after the end of the COVID pandemic, there has been a notable resurgence in M. pneumoniae infections, which is particularly unusual in terms of both the number of infections and their severity. The purpose of this article is to review the existing evidence and explore theories that underlying the epidemiological shifts of M. pneumoniae following the COVID-19 pandemic, and propose factors contributing to the unconventional resurgence of M. pneumoniae infections. Proposed factors include decline of M. pneumoniae immunity, circulation of different genetic types and emergence of new macrolide-resistant M. pneumoniae (MRMP) variants, immune dysregulation following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and others. Among these factors, the decline in M. pneumoniae immunity and the circulation of different genetic types are considered significant contributors. Further research in bacterial genomics and more robust immunology studies are needed to guide the prevention of M. pneumoniae infections and the allocation of healthcare resources. International cooperation and information sharing are crucial for understanding the epidemiological changes of M. pneumoniae. Further cross-regional collaboration is called to enhance our understanding of the scope of M. pneumoniae outbreaks and facilitate a collective response.