Overview of patients
Of 9342 children hospitalized with pneumonia (1752, 1803, 1849, 1885, and 2053) from 1st Jan 2014 to 31st Dec 2018, 593 (6.35%) patients with S/L-PP were enrolled in this study. Among them 398 patients were boys and the rest were girls. The male to female ratio was about 2:1. The age of the patients with S/L-PP ranged from 1 year to 13 years (7.4±3.1years). The percent of patients with S/L-PP among patients with pneumonia each year was 4.91% (86/1752), 5.44% (98/1803), 6.22% (115/1849), 7.27% (137/1885) and 7.65% (157/2053) respectively from 2014 to 2018. The annual incidence of S/L-PP increased with time over the study period (table 1). The duration of fever and cough were 4.6±2.1 days and 10.6±8.7 days respectively. 28.50% (169/593) patients had a gasping and 35.08% (208/593) patients had pulmonary crackles at onset. There were 25.13% (149/593) patients with extrapulmonary manifestations including erythematous maculopapular rash, liver and kidney function lesions, and neurological complications. Only a few patients had pleural effusion. The duration of hospital stay was 15.5±3.1 days. There were 64.59% (383/593) patients with abnormal WBCs, 11.64% (69/593) patients with abnormal ESR and 24.96% (148/593) patients with abnormal CRP. 59 (9.95%) bacteria were identified by blood culture and sputum culture, while the rest of the pathogens were identified by other methods.
Pathogens distribution over time
Table 1 summarized pathogens distribution over time including M. pneumoniae, RSV, CP, IFA, PIVS, ADV, COX, LP, IFB, S.pneumoniae, Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P.aeruginosa), Escherichia coli (E.coli), Klebsiella pneumoniae (K.pneumoniae), and showed the positive rate of M.pneumoniae increases over time. The number of patients infected by M.pneumoniae was 43, 67, 96 106, and 117 respectively each year during the study period, and the positive rate of M.pneumoniae between the groups over time was significantly different (p<0.05). But no significant differences in the positive rate for other pathogens between the groups over time were found (p>0.05).
Age distribution of pathogens
Table 2 summarized the distribution of pathogens with age group and showed that the positive rate of M.pneumoniae increased with ages. Significant differences were observed in the positive rate of M.pneumoniae between the age groups (p<0.05). However, no significant differences were found in the positive rate of other pathogens between the age groups (p>0.05).
Sex distribution of pathogens
Significant differences were not observed for M. pneumoniae and S.pneumoniae between male patients and female patients (p>0.05). 18 patients were positive for IFB including 6 male patients and 12 female ones. Female patients displayed significantly higher positive rate for IFB (p<0.05). No significant difference was observed for the other pathogens between sex groups (p>0.05). (supplemental table 1).
Seasonal distribution of pathogens
In general, the seasonality profile of each individual pathogen was diverse. However, we did not observe a distinct pattern for the pathogens. (supplemental table 2).
Mixed infection types of pathogens
Co-infections with multiple pathogens were common. There were 91 patients in whom 2 or more pathogens were positive, representing 15.34% of the patients, and the types of co-infection were complex. These data indicated that 18.88% (81/429) of the children with M.pneumoniae infections were co-infected with other pathogens. 2.53% (15 /593) patients showed infection with 3 pathogens or more. (Table 3)
Association between pathogens and patients’ demographic and clinical characteristics
Table 4 summarized the patients’ demographic and clinical information found in association with pathogens infection. The patients were divided into 10 groups according to pathogens. Patients with co-infections were excluded. Since the sample size was too small to obtain significance in some statistical analyses, only M. pneumoniae and S.pneumoniae were included in the statistical analyses. M.pneumoniae was statistically associated with extrapulmonary manifestations (p<0.05). S.pneumoniae was statistically associated with abnormal WBCs and CRPs (p<0.05). (Table 5)