3.1 Study population
From January 1, 2018, to December 31, 2023, a total of 211,600 patients with acute respiratory tract infections (ARTI) were collected from Renmin Hospital of Wuhan University. Among them, 48, 542 cases did not meet the inclusion criteria, leaving a total of 163,058 cases included in the study, with an average age of 4.25 2.91 years. This included 93,575 males and 69,483 females. Among the included cases, 121,384 underwent MP specific IgM antibody testing on blood specimens, while 41,674 (including nasal swabs, nasopharyngeal swabs, sputum, and bronchoalveolar lavage fluid) underwent MP nucleic acid testing. A total of 49,936 cases tested positive for MP (45,602 positive for MP-IgM and 4,334 positive for MP-DNA), resulting in an overall positive rate of 30.62%. The specific process is detailed in Fig.1.
3.2 Seasonal and Annual Trends of MP Infections
From 2018 to 2023, the annual positive rates of MP among ARTI patients were 45.92%, 32.23%, 22.84%, 16.22%, 16.26%, and 42.93%, respectively. The differences in positive rates between each year were statistically significant (P<0.001). Throughout the entire study period, the highest positive rate was observed in autumn (35.13%), while the lowest was in spring (26.28%). The comparison of MP positive rates among seasons showed statistically significant differences (P<0.001). Between 2018 and 2019, spring and summer were the seasonal peaks, with positive rates of 50.24% and 49.20%, and 35.23% and 35.86%, respectively. In January 2020, the positive rate peaked at 27.39%, followed by a decline in February, reaching its lowest point in March (6.38%), gradually increasing in April, and maintaining a relatively stable level thereafter. In 2021 and 2022, the highest positive rates were observed in summer, with rates of 17.79% and 21.51%, respectively. However, in 2023, the highest number of MP cases sent for testing occurred in autumn and winter, consistent with the MP positive rates. Particularly, in late autumn and early winter, the monthly positive rates were 72.32% and 65.35%, respectively. The differences in seasonal positive rates each year were statistically significant (P<0.001). The specific distribution of monthly, seasonal, and annual MP infections during the study period is illustrated in Fig.2, and the detailed numerical values are provided in Table 1.
3.3 Age-related Characteristics and Temporal Trends of MP Infections
The 163,058 ARTI patients were divided into three age groups, with the positive rate for each age group: infants (21,436 cases, accounting for 25.32%), pre-school children (19,570 cases, accounting for 34.87%), and school-age children (8,930 cases, accounting for 40.09%). Among these, the school-age children group had the highest MP infection rate. The results for each age group are shown in Table 1. Further stratifying by detection time into three periods: 2018-2019, 2020-2022, and 2023, pre-school and school-age children were more common in all three years. The number of MP positive patients and the positive rates for each year group are shown in Fig.3. It's noteworthy that the positive rate increased with the age of the patients. Furthermore, we observed a linear relationship between the MP infection rates among patients aged 1 to 12 months throughout the months of the year, as depicted in Fig.4.
3.4 Gender Differences in MP Infection Positive Rates
Of the 49,936 confirmed infection cases, there were 23,726 females with an average positive rate of 34.15%, and 26,210 males with a positive rate of 28.01%. Despite a higher number of males being tested, the positive rate among females was significantly higher than that of males, with a statistically significant difference between the two groups (p < 0.001). Over the six years from 2018 to 2023, the positive rate among females was consistently higher than that of male patients, with rates of 50.71%, 36.68%, 25.66%, 19.17%, 18.46%, and 46.45%, respectively. The gender differences over the six-year period were statistically significant (p < 0.001). For specific numerical values, please refer to Table 1.
3.5 Prevalence and Patterns of Coinfections in MP Patients
In cases of MP infection, 7,126 cases were found to have at least one concurrent infection with another pathogen, with an overall positive rate of 14.27%. The yearly positive rates were 18.62%, 18.30%, 8.06%, 5.32%, 13.10%, and 12.98%, respectively, with statistically significant differences between the years (P<0.001). Among the 7,126 coinfected cases, 5,085 were found to have at least one concurrent viral infection (71.36%), while 2,041 were found to have at least one concurrent bacterial infection (28.64%). The study found that younger children were more likely to have coinfections with other pathogens, with infants (48.98%) > pre-school children (37.29%) > school-age children (13.74%), with statistically significant differences between age groups (P<0.001). The rate of coinfection was similar between genders (14.25% for males, 14.29% for females, P=0.914).
Among MP coinfections with viruses, the most commonly detected virus was influenza virus (IFV) (1,933 cases, accounting for 38.01%), followed by respiratory syncytial virus (RSV) (1,545 cases, accounting for 30.38%), human parainfluenza Virus (HPIV) (738 cases, accounting for 14.51%), human rhinovirus (HRV) (424 cases, accounting for 8.34%), human adenovirus (HAdV) (286 cases, accounting for 5.62%), human metapneumovirus (HMPV) (72 cases, accounting for 1.42%), human coronavirus (HCoV) (71 cases, accounting for 1.40%), and human bocavirus (HBoV) (16 cases, accounting for 0.31%). Genetic typing analysis of IFV showed that influenza B virus (FluB) predominated, accounting for 89.91% of all genetically analyzed cases, while influenza A virus (FluA) accounted for 10.09%. Among FluA coinfected patients, 66 cases of coinfection with influenza A subtype H3N2 (H3N2) were found, with no cases of coinfection with influenza A subtype H1N1 (H1N1) detected. Further age-specific analysis revealed that the top two viruses in all three age groups were IFV and RSV (42.10% and 34.53% for infants, 34.04% and 27.93% for pre-school children, 33.68% and 21.50% for school-age children, respectively), while the third-ranked virus in school-age children was HRV (16.84%). The pattern of virus coinfection was generally similar between infants and pre-school children (with HCoV > HMPV for preschool children), as shown in Fig.5.
Among MP coinfections with bacteria, the most commonly detected was Chlamydia pneumoniae (C.pneumoniae, CP) (1,286 cases, accounting for 63.01%), followed by Haemophilus influenzae (H.influenzae, Hi) (297 cases, accounting for 14.55%), Streptococcus pneumoniae (S.pneumoniae, Sp) (273 cases, accounting for 13.38%), Staphylococcus aureus (S.aureus, Sa) (81 cases, accounting for 3.97%), Acinetobacter baumannii (A.baumannii, Ab) (25 cases, accounting for 1.22%), Methicillin-Resistant Staphylococcus aureus (MRSA) (23 cases, accounting for 1.13%), Klebsiella pneumoniae (K.pneumoniae, Kp) (14 cases, accounting for 0.69%), Legionella pneumophila (L.pneumophila, Lp) (14 cases, accounting for 0.69%), Pseudomonas aeruginosa (P.aeruginosa, Pa) (12 cases, accounting for 0.59%), Coxiella burnetii (Coxiella burnetii, Cox) (7 cases, accounting for 0.34%), Escherichia coli (E.coli) (6 cases, accounting for 0.29%), Mycobacterium tuberculosis (M.tuberculosis, MTB) (2 cases, accounting for 0.10%), and Stenotrophomonas maltophilia (Stenotrophomonas maltophilia, Sm) (1 case, accounting for 0.05%). Further age-specific analysis showed that among the top three coinfection bacteria in all three age groups were C.pneumoniae, H.influenzae, and S.pneumoniae, albeit with slightly different orderings. In pre-school children, the order was C.pneumoniae > S.pneumoniae > H.influenzae. The ranking of coinfection patterns with other bacteria varied across different age groups, as shown in Fig.5.
Among the MP positive patients, 5,775 cases had single pathogen infections, while 641 cases exhibited coinfections involving at least two pathogens. The most common coinfection patterns with viruses were MP, HPIV and HAdV. The most common coinfection patterns with bacteria were MP, H. influenzae and S. pneumoniae. The most common coinfection patterns with bacterial and viruses were MP, RSV and C. pneumoniae. In addition, there were 64 cases with coinfections involving at least three pathogens. Among them, 7 cases involved MP mixed with 4 other pathogens, and 2 cases involved MP mixed with 5 other pathogens. The specific distribution and mutual relationships of coinfection pathogens can be found in Fig.6.