Mycoplasma pneumoniae in hospitalized children: 20-year study finds age shift and post-COVID resurgence

Mycoplasma pneumoniae, an atypical bacterium that lacks a cell wall and is a major cause of childhood respiratory illness, has shown remarkably stable behavior over two decades of hospital surveillance in eastern China, according to a retrospective study published in the Egyptian Pediatric Association Gazette. Researchers at Children’s Hospital of Soochow University reviewed 51,399 respiratory specimens collected from children under 18 years of age who were hospitalized with respiratory tract infections between October 2005 and December 2025. Of these, 16,086 specimens tested positive for the pathogen, yielding an overall positivity rate of 31.3 percent.

The analysis revealed a cyclical epidemic pattern, with positivity rates peaking roughly every 3 to 5 years. After remaining near 30 percent in the early years of the study, detection rates surged above 45 percent during 2008 to 2009, 2013, and 2016. The researchers note that these recurring waves are considered a characteristic feature of the pathogen’s epidemiology, likely shaped by host susceptibility and transmission dynamics rather than a single seasonal driver.

Age emerged as the most consistent factor influencing infection risk. Positivity rose steadily with age across the entire two-decade window: children aged 7 years or older had the highest rate at 51.73 percent, followed by those aged 3 to 7 years at 41.04 percent, children aged 1 to 3 years at 34.13 percent, infants aged 6 to 12 months at 24.80 percent, and infants younger than 6 months at 12.97 percent. This gradient held steady across all calendar periods, suggesting that the underlying susceptibility structure of the population remained intact even as epidemic intensity fluctuated.

Despite that stability in relative risk, the composition of positive cases shifted noticeably over time. Younger children under 3 years accounted for a larger share of detections in the early study years, while the contribution of older children grew progressively. In the most recent period, 2021 to 2025, children aged 3 years and older made up a substantially larger proportion of positive cases than in earlier intervals, indicating a long-term redistribution of infections toward school-aged groups.

The COVID-19 pandemic left a clear imprint on these patterns. During 2020 to 2022, positivity fell to between 22.42 and 25.58 percent, among the lowest levels recorded across the entire observation period, and the decline was evident in every age category. The absolute drop was largest among older children: in those older than 7 years, positivity fell from 67.49 percent before the pandemic to 42.49 percent during it, while in children aged 3 to 7 years it decreased from 54.36 percent to 26.74 percent. Younger children also showed reduced positivity, though the magnitude of change was smaller.

After the pandemic, the pathogen rebounded. In 2023, positivity climbed to 45.16 percent, approaching the peak levels seen in pre-pandemic epidemic years such as 2009, 2013, and 2016, before declining again in 2024 and 2025. The rebound was concentrated among children aged 3 years and older, whose positivity approached but did not fully reach pre-pandemic levels, while no comparable increase was observed among children younger than 3 years. The authors attribute this pattern to the accumulation of a large susceptible population during the years when strict public health measures, including social distancing, isolation, and mask wearing, suppressed transmission and delayed the anticipated epidemic peak that would otherwise have been expected around 2020 to 2021 based on the regular cycle.

Seasonality also shaped the infection landscape. Across the full study period, positivity was highest in summer at 36.55 percent and autumn at 34.29 percent, and lower in winter at 27.07 percent and spring at 27.06 percent. However, this pattern changed in recent years: summer remained a peak season at 33.76 percent in the most recent five-year period, but autumn positivity declined to 26.41 percent and no longer represented the highest seasonal peak, suggesting a modification of the traditional seasonal distribution.

The pandemic also disrupted seasonal patterns. Before 2020, positivity was clearly elevated in summer at 39.46 percent and autumn at 40.71 percent compared with winter at 29.37 percent and spring at 30.43 percent. During the pandemic years, overall positivity was uniformly low across all seasons and the typical variation became less pronounced. In the post-pandemic period, seasonal variation partially re-emerged, with summer positivity rising to 35.38 percent and approaching pre-pandemic levels, while autumn positivity reached only 26.51 percent and did not show a comparable recovery, leaving summer as the predominant peak season.

Sex-stratified analysis showed that female patients consistently had higher positivity than males throughout the study period, at 35.47 percent compared with 28.61 percent, a difference the authors report as statistically significant. The gap remained stable across calendar years and pandemic phases, and the researchers did not emphasize it further in subsequent analyses, noting that sex-specific patterns in the literature are inconsistent across settings and may reflect social and healthcare utilization factors rather than intrinsic biological differences.

The study has limitations that the authors acknowledge. It is observational and derives positivity rates from tested specimens rather than population-based incidence, which may introduce sampling bias. The diagnostic criteria relied partly on single IgM results, which may slightly overestimate positive cases, although the case definition required consistent respiratory clinical manifestations in combination with laboratory evidence. The interval between paired serum samples for IgG testing was limited to approximately 7 days, shorter than the optimal 10 to 14 day window for detecting fourfold titer rises, potentially reducing serological sensitivity. Data came from a single region, and clinical characteristics, co-infections, and changes in testing practices over time were not analyzed in detail. The authors conclude that sustained long-term surveillance remains essential to inform clinical preparedness and public health strategies as the pathogen’s epidemic cycles, age distribution, and seasonal behavior continue to evolve.

Subject of Research: Long-term epidemiology of Mycoplasma pneumoniae infection among hospitalized children

Article Title: Twenty-year epidemiological trends of Mycoplasma pneumoniae infection among hospitalized children: age shift and post-COVID resurgence

Article References: Wang, Z., Sun, H., Shen, Q., Hua, S., Ma, Y., He, Y., Dong, H., Zhang, X., Hao, C., & Gu, W. (2026). Twenty-year epidemiological trends of Mycoplasma pneumoniae infection among hospitalized children: age shift and post-COVID resurgence. Egyptian Pediatric Association Gazette, 74(1), Article 114. https://doi.org/10.1186/s43054-026-00614-4

Image Credits: AI Generated

DOI: 10.1186/s43054-026-00614-4

Keywords: Mycoplasma pneumoniae, pediatric respiratory infection, epidemiology, COVID-19 pandemic, age distribution, seasonality, retrospective study, Suzhou, serology, PCR, disease surveillance, community-acquired pneumonia