Epidemiological characterization of respiratory tract infections caused by Mycoplasma pneumoniae during epidemic and post- epidemic periods in North China, from 2011 to 2016

Background: Mycoplasma pneumoniae (M. pneumoniae) is a commonly causative pathogen for respiratory tract infections (RTIs) in humans. The epidemiological features of M. pneumoniae infections during post-epidemic, including age distribution and the seasonality of the patients, are not well investigated. Methods: We retrospectively analyzed the clinical data of 7835 consecutive RTIs patients (3852 adults and 3983 children) who visited a teaching hospital, and defined an epidemic (2011-2013) and a post-epidemic period (2014-2016). M. pneumoniae was detected by fluorescence-quantatitive PCR in respiratory samples. Informed consent was obtained by all adults and the legal representatives of patients aged < 18 years, and the study was approved by Institutional Review Board of Beijing Chao-Yang Hospital (project approval number 10-KE-49). Results: The median (IQR) age was 16 (53) years (range < 0-105 years). The M. pneumoniae positive rate was 14.4% (21. 2%, epidemic; 6.7%, post-epidemic), with seasonal peaks from late summer to autumn during epidemic, and from fall to winter during post-epidemic period, which was highest in children aged 7-17 years. In epidemic, no statistical difference was found in the positive rates between children and adults among most months (except February, July and August), neither for the positive rates among age groups (P = 0.801). However, in post-epidemic period, significant differences were observed in the positive rates between children and adults in nearly every month (P<0.05 or P<0.001, except May), as well as in the positive rates among age groups (P<0.001). Most of the older patient admissions and all of ICU admissions occurred during the epidemic. Conclusions: Different patterns of age distribution and seasonality of M. pneumoniae RTIs between epidemic and post-epidemic periods were reported. Our results suggest that M. pneumoniae should be considered as a possible pathogen in pneumonia patients admitted to the ICU in the setting of an epidemic.