Mycoplasma pneumoniae and Chlamydia pneumoniae are important atypical pathogens responsible for respiratory infections in children, most commonly presenting as bronchitis or community-acquired pneumonia. This review discusses epidemiology, clinical features and diagnostics of these organisms as described in the literature between 2015 and 2025, and both pathogens are most commonly observed in school-aged children and teenagers. However, recent studies have reported a resurgence of M. pneumoniae after relaxation of COVID-19 restrictions, including an increase in younger children. Clinically, these infections usually manifest as a viral-like illness with a chronic dry cough and mild systemic symptoms, and cannot be differentiated based on examination or routine laboratory testing, because co-infections are common and may contribute to increased severity or obscure the clinical picture. Diagnostics have shifted towards PCR, which enables earlier and more accurate detection compared to traditional serology, the latter of which is hampered by a delayed antibody response and possible cross-reactivity, therefore early recognition is essential for management. Macrolides remain first-line therapy, but increasing macrolide resistance has emerged, particularly in some Asian areas, and a better understanding of local epidemiology and use of molecular diagnostics may help clinicians more effectively target therapy and avoid unnecessary antibiotics.

mycoplasma pneumoniae, chlamydia pneumoniae, pediatric bronchitis, atypical pneumonia.

Centers for Disease Control and Prevention. (2025). Clinical overview of Chlamydia pneumoniae infection. https://www.cdc.gov/cpneumoniae/hcp/clinical-overview/index.html

Waites, K. B., & Talkington, D. F. (2004). Mycoplasma pneumoniae and its role as a human pathogen. Clinical Microbiology Reviews, 17(4), 697–728. https://doi.org/10.1128/CMR.17.4.697-728.2004

Jain, S., Williams, D. J., Arnold, S. R., Ampofo, K., Bramley, A. M., Reed, C., Stockmann, C., Anderson, E. J., Grijalva, C. G., Self, W. H., Zhu, Y., Patel, A., Chappell, J. D., Kaufman, L., McCullers, J. A., Hymas, A. L., Thapa, K., McNary, L., Rampersad, A., ... Finelli, L. (2015). Community-acquired pneumonia requiring hospitalization among U.S. children. New England Journal of Medicine, 372(9), 835–845. https://doi.org/10.1056/NEJMoa1405870

Kim, K., Jung, S., Kim, M., Park, S., Yang, H. J., & Lee, E. (2022). Global trends in the proportion of macrolide-resistant Mycoplasma pneumoniae infections: A systematic review and meta-analysis. JAMA Network Open, 5(7), e2220949. https://doi.org/10.1001/jamanetworkopen.2022.20949

Waites, K. B., Ratliff, A., Crabb, D. M., Xiao, L., Qin, X., Selvarangan, R., Tang, Y. W., Zheng, X., Dien Bard, J., Hong, T., Prichard, M., Brooks, E., Dallas, S., Duffy, L., Mixon, E., Fowler, K. B., & Atkinson, T. P. (2019). Macrolide-resistant Mycoplasma pneumoniae in the United States as determined from a national surveillance program. Journal of Clinical Microbiology, 57(11), e00968-19. https://doi.org/10.1128/JCM.00968-19

Omori, R., Nakata, Y., Tessmer, H. L., Suzuki, S., & Shibayama, K. (2015). The determinant of periodicity in Mycoplasma pneumoniae incidence: An insight from mathematical modelling. Scientific Reports, 5, Article 14473. https://doi.org/10.1038/srep14473

Meyer Sauteur, P. M., Beeton, M. L., & European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Study Group for Mycoplasma and Chlamydia Infections (ESGMAC), and the ESGMAC Mycoplasma pneumoniae Surveillance (MAPS) study group. (2024). Mycoplasma pneumoniae: Delayed re-emergence after COVID-19 pandemic restrictions. The Lancet Microbe, 5(2), e100–e101. https://doi.org/10.1016/S2666-5247(23)00344-0

Edens, C., Clopper, B. R., DeVies, J., Benitez, A., McKeever, E. R., Johns, D., Wolff, B., Selvarangan, R., Schuster, J. E., Weinberg, G. A., Szilagyi, P. G., Dawood, F. S., Radhakrishnan, L., Quigley, C., Sahni, L. C., Halasa, N., Stewart, L. S., McMorrow, M. L., Whitaker, B., ... Diaz, M. (2024). Notes from the field: Reemergence of Mycoplasma pneumoniae infections in children and adolescents after the COVID-19 pandemic, United States, 2018–2024. Morbidity and Mortality Weekly Report, 73(7), 149–151. https://doi.org/10.15585/mmwr.mm7307a3

Nordholm, A. C., Søborg, B., Jokelainen, P., Lauenborg Møller, K., Flink Sørensen, L., Grove Krause, T., Anker Uldum, S., & Emborg, H.-D. (2024). Mycoplasma pneumoniae epidemic in Denmark, October to December, 2023. Eurosurveillance, 29(2), Article 2300707. https://doi.org/10.2807/1560-7917.ES.2024.29.2.2300707

Diaz, M. H., Hersh, A. L., Olson, J., Shah, S. S., Hall, M., & Edens, C. (2025, June 26). Mycoplasma pneumoniae infections in hospitalized children — United States, 2018–2024. Morbidity and Mortality Weekly Report, 74(23), 394–400. https://doi.org/10.15585/mmwr.mm7423a1

Edouard, S., Boughammoura, H., Colson, P., La Scola, B., Fournier, P., & Fenollar, F. (2024). Large-scale outbreak of Mycoplasma pneumoniae infection, Marseille, France, 2023–2024. Emerging Infectious Diseases, 30(7), 1481–1484. https://doi.org/10.3201/eid3007.240315

Alves, M. S., da Silva Cariolano, M., dos Santos Ferreira, H. L., Sousa de Abreu Silva, E., Felipe, K. K. P., Monteiro, S. G., de Sousa, E. M., Abreu, A. G., Campbell, L. A., Rosenfeld, M. E., Hirata, M. H., Hirata, R. D. C., Bastos, G. M., de Paula Abreu Silva, I. C., & Lima-Neto, L. G. (2020). High frequency of Chlamydia pneumoniae and risk factors in children with acute respiratory infection. Brazilian Journal of Microbiology, 51(2), 629–636. https://doi.org/10.1007/s42770-020-00229-w

Han, H. Y., Moon, J. U., Rhim, J. W., Kang, H. M., Lee, S. J., & Yang, E. A. (2023). Surge of Chlamydia pneumoniae pneumonia in children hospitalized with community-acquired pneumonia at a single center in Korea in 2016. Journal of Infection and Chemotherapy, 29(5), 453–457. https://doi.org/10.1016/j.jiac.2023.01.012

Merida Vieyra, J., De Colsa Ranero, A., Palacios Reyes, D., Murata, C., & Aquino Andrade, A. (2023). Chlamydophila pneumoniae-associated community-acquired pneumonia in paediatric patients of a tertiary care hospital in Mexico: Molecular diagnostic and clinical insights. Scientific Reports, 13, Article 21477. https://doi.org/10.1038/s41598-023-48701-5

Shim, J. Y. (2020). Current perspectives on atypical pneumonia in children. Clinical and Experimental Pediatrics, 63(12), 469–476. https://doi.org/10.3345/cep.2019.00360

Edouard, S., Attamna, R., Million, M., Boschi, C., Delerce, J., Caputo, A., & Colson, P. (2025). Significant rise of Chlamydia pneumoniae infection in 2024 in Marseille, France. International Journal of Infectious Diseases, 155, Article 107897. https://doi.org/10.1016/j.ijid.2025.107897

Ma, R., Zhang, Y., Wang, Y., Liu, Y., Ba, C., & Zhang, M. (2025). Epidemiological and clinical analysis of 291 children diagnosed with Chlamydia pneumoniae pneumonia: A 10-year retrospective study in Shijiazhuang, China. Frontiers in Pediatrics, 13, 1681564. https://doi.org/10.3389/fped.2025.1681564

Chen, J. R., & Zhou, X. F. (2020). A retrospective survey of Chlamydia pneumoniae infection rates in paediatric patients from a single centre in Wuxi, China. The Journal of international medical research, 48(10), 300060520961720. https://doi.org/10.1177/0300060520961720

Gao, L., & Sun, Y. (2024). Laboratory diagnosis and treatment of Mycoplasma pneumoniae infection in children: a review. Annals of medicine, 56(1), 2386636. https://doi.org/10.1080/07853890.2024.2386636

Merișescu, M. M., Jugulete, G., Dijmărescu, I., Dragomirescu, A. O., & Răduț, L. M. (2025). The clinical profile of pediatric M. pneumoniae infections in the context of a new post-pandemic wave. Microorganisms, 13(5), Article 1152. https://doi.org/10.3390/microorganisms13051152

Nguyen, A. D., Stamm, D. R., & Stankewicz, H. A. (2025). Atypical bacterial pneumonia. In StatPearls [Internet]. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK532239/

Morrissey, I., Salman, H., Bakker, S., Farrell, D., Bébéar, C. M., & Ridgway, G. (2002). Serial passage of Chlamydia spp. in sub-inhibitory fluoroquinolone concentrations. Journal of Antimicrobial Chemotherapy, 49(5), 757–761. https://doi.org/10.1093/jac/dkf031

Zhou, Y., Yan, Z., Zhou, S., Li, W., Yang, H., Chen, H., Deng, Z., Zeng, Q., Sun, P., & Wu, Y. (2024). ERA-CRISPR/Cas12a-based, fast and specific diagnostic detection for Chlamydia pneumoniae. Frontiers in Cellular and Infection Microbiology, 14, Article 1477422.