A total of 1322 neonates hospitalized with LRTIs in Children's Hospital of Soochow University, China, from Jan 2011 to Dec 2014 were selected for this observational retrospective study. To be included in this study, patients had to be aged less 29 days and be hospitalized for LRTIs during the study period. LRTI was defined as the presence of at least three of the following signs and symptoms: cough, tachypnea, chest retractions, abnormal auscultatory findings (wheezing or crackles), and radiologic evidence indicative of lower respiratory tract infection. The exclusion criteria were: neonates with a vertical infection (i.e., an infection transmitted from mother to child) or infection acquired during delivery. The study was approved by the Ethics Committee of Children's Hospital of Soochow University.

Patient demographic data, laboratory and radiographic reports were collected and reviewed. Laboratory data including peripheral white blood cell count, neutrophil and lymphocyte proportions, C-reactive protein (CRP), serology for MP, and nasopharyngeal specimens for viral testing were recorded and further analyzed.

Specific IgM and IgG antibodies against MP were detected in serum samples of patients in the acute phase of MP (on admission) and convalescent phase (on discharge), using a commercial ELISA kit (Serion ELISA classic MP IgG/IgM, Institute Virion/Serion, Würzburg, Germany) according to the manufacturer's instructions. The presence of IgM in the convalescent phase was used as criteria of current MP infection.

Nasopharyngeal secretions were collected from each study participant within 24h after admission by a lab technician as previously described. Briefly, an aseptic plastic sputum catheter was inserted into the nostril to a depth of about 7–8cm until reaching the pharynx. Approximately 2mL of nasopharyngeal secretions was collected by applying negative pressure. The sample was mixed with 4–8mL PBS, and centrifuged for 10min at 300–500rpm. The supernatant was discarded and the pellet was mixed with 4–8mL PBS and centrifuged for an additional 10min. The specimens were centrifuged and were stored at −80°C until tested.

All nasopharyngeal swabs were tested by immunofluorescence for antigen detection of seven common viruses, including respiratory syncytial virus (RSV), adenovirus (ADV), influenza viruses (IV) A and B, and parainfluenza viruses (PIV) 1, 2 and 3.

We used n (%) for categorical variables and median (range) for continuous variables with non-normal distribution or mean (SD) for those with normal distribution. We assessed differences in categorical variables with the χ2 test. We calculated 95% CI for differences in medians with an exact test. SPSS (version 17.0) software was used for all statistical analysis. Multivariate logistic regression analysis was used to analyze variables associated with detection of MP.

A total of 1322 neonates hospitalized with LRTIs were included in this study. Of those, MP was identified in 89 (6.7%) patients, with RSV in 255 (19.3%) cases, 59 (4.7%) with IV-A, 13 (1.0%) with PIV-3, 9 (0.7%) with IV-B, and 8 (0.6%) with ADV. Multi-viruses were identified in 36 (2.7%) patients. Among the 89 patients with MP infection, 16 patients (17.8%) were co-infected with RSV, and one (1.1%) was co-infected with influenza A.

Age ranged from 1 day to 28 days with a median of 22 days. The male to female ratio was 1.15:1. The birth weight ranged from 2150 to 4000g with a median of 3450g. Gestational age ranged from 33 to 41 weeks with a median of 37 weeks.

The age distribution of MP infection in neonates is shown in Fig. 1. Three (3.4%) cases were aged 1–7 days, 11 (12.4%) 8–14 days, 28 (31.5%) 15–21 days, and 47 (52.8%) were aged 22–28 days. Thus, the incidence of MP infection in neonates increases with age.

Fig. 1.

The age distribution of Mycoplasma pneumoniae infection in neonates.

(0.03MB).

The monthly distribution of MP infection in neonates is shown in Fig. 2. MP infection peaked in spring (from March through May) and winter (from December through February), which involved 30 cases (33.7%) in spring, and 28 (31.5%) cases in winter, respectively, compared with 16 cases (18.0%) in summer (June to August), and 15 (16.9%) in autumn (from September to November). The prevalence of MP infection was higher during winter and spring, and lower in summer and autumn.

Fig. 2.

The seasonal distribution of Mycoplasma pneumoniae infection in neonates.

(0.05MB).

The main clinical features of the patients with MP infection are shown in Table 1. Eighty-one (91.0%) patients had cough. Dyspnea or tachypnea was observed in 47 (52.8%) patients, wheezing in 9 (10.1%), and fever (temperature, >38°C) in 43 (48.3%) patients. Mean WBC counts were 11.2±3.2×109L–1; CRP were >10mg/mL in eight (9.0%) patients. Liver enzyme, alanine aminotransferase level was above the upper limit of normality in seven (7.9%) patients.

Chest radiographs of all patients were available for review. Peribronchial infiltration and perihilar infiltration were observed in 81 (91.0%) children. Homogenous consolidation was present in seven (7.9%) patients. None of the patients presented with pleural effusion.

Demographic and clinical characteristics from Table 1 were compared between neonates with MP infection (n=89) and those with non-MP infection (n=1233). From this univariate analysis, three predictor variables, namelyage, fever (temperature≥38°C) and tachypnea were evaluated in a logistic regression model: compared to non-MP cases MP cases were older (median of 22 days vs 14 days), had more fever (48.3% vs 13.5%), and less tachypnea (52.8% vs 63.2%) (see Table 2 for statistics).

Overall, three (3.4%) out of 89 patients with MP infection required supplemental oxygen. None required mechanical ventilation. The median length of hospital stay was seven (4–12) days. Duration of follow-up was one month for 83 children. None of the patients had residual pulmonary disease.

The clinical characteristics of MP, RSV, and multi-viruses infection are shown in Table 3. The median age was 22 days for MP patients, 17 days for RSV patients, and 18 days for multi-viruses patients. Fever was more common in children with MP than either RSV or multi-viruses infection (both p<0.01). Tachypnea and oxygen supplementation were more often present in children with RSV than with MP infection (both p<0.01). The median length of hospital stay was longer in children with RSV and multi-viruses infection than for those with MP infection (both p<0.01).