Analysis On Surveillance Of Mycoplasma Pneumoniae Infection In Children

Background and aims:Mycoplasma pneumoniae (M. pneumoniae) is an important pathogen causing respiratory tract infection in adults and children. It is one of the most common causes of community acquired pneumonia (CAP). It causes extrapulmonary complications or even life-threatening infections in some patients.In recent years, epidemiological characteristics of M. pneumoniae infection have changed:reports on M. pneumoniae infection in infants and young children increased, M. pneumoniae-induced upper respiratory tract infection (URI) and bronchitis become common, in the last a few years macrolide-resistance M. pneumoniae strains also become common. Further epidemiological studies are needed to find answers to this phenomenon.In recent years, molecular characters’study on M. pneumoniae infection became popular. The methods, like P1 gene typing developed earlier and multiple-locus numbers tandem-repeat analysis (MLVA) developed recently, provided new means for our study.Therefore, by study on M. pneumoniae outbreaks in school children, in fever clinic patients in our hospital and in healthy children without respiratory symptoms, we described clinical characters and molecular characteristics of M. pneumoniae infection and provide epidemiologic data for M. pneumoniae infection prevention and control work.Methods:(1) Study population:we chose the following 3 crowds as the subjects of our study: school children in M. pneumoniae outbreak for school outbreak surveillance of M. pneumoniae infection; patients seeing fever clinic for on-site investigation of M. pneumoniae respiratory tract infection; small surgical operation patients for M. pneumoniae carrying status in healthy children without respiratory symptoms.(2) The clinical data of the subjects were obtained by questionnaire, medical history collection, physical examination and assistant examination.(3) Pharyngeal swab acquisition and DNA detection:after acquisition pharyngeal throat swabs from subjects, we detected M. pneumoniae-DNA by realtime-PCR method. For some objects, we conducted long-time monitoring for M. pneumoniae-DNA in pharyngeal swabs to observe the carrying duration of M. pneumoniae after infection and to observe its relationship with the progression of the disease.(4) Culture and isolation of M. pneumoniae strains:throat swab was inoculated to M. pneumoniae solid medium, and the isolation, liquid culture and PCR validation were carried out.(5) Drug resistance analysis and mutation detection of M. pneumoniae strains: isolated strains were detected and analyzed for macrolide-resistance, and the mutation points were confirmed.(6) Molecular typing of M. pneumoniae strains:all isolates were detected by MLVA molecular genotyping. Parts of strains were also detected by P1 gene typing. The two kinds of molecular genotyping methods were compared. We also explored the significance of MLVA typing in molecular characters in M. pneumoniae infection.Results:(1) Study in two primary schools:we confirmed that M. pneumoniae can cause outbreaks in children in semi closed environment. The infection rates were 30.8% and 31% in the two schools, separately. The forms of M. pneumoniae infection were recessive infection, URI and pneumonia. The percentage of pneumonia was highest. Among different forms of infection, the carrying time of M. pneumoniae was different. The duration of pneumonia was longest, URI the second, and latent infection the shortest. Eighteen M. pneumoniae strains were isolated from the two schools. P1 typing showed all the strains belonged to P1-1 subtype. MLVA typing distinguished the strains into two types (U [5-4-5-7-2] and J [3-4-5-7-2]) from two schools separately. Macrolide-resistance analysis and mutation detection found all the 18 strains were A2063G point mutation macrolide-resistant strains.(2) Study of the M. pneumoniae infection status of patients in clinic:a total of 1025 patients were enrolled. Among them,163 were M. pneumoniae-DNA positive, with the positive rate 15.09%. We found that M. pneumoniae infection tended to occur in children over the age of 5 years, summer and autumn were epidemic seasons, and pneumonia was the most common form of M. pneumoniae infection. Multiple regression analysis found that M. pneumoniae infection was positively correlated with age, severity of disease and multiple siblings, and was negatively correlated with runny nose, nasal symptoms, past history of pneumonia. M. pneumoniae carrying time varied by different parts of M. pneumoniae infection:pneumonia was the longest, bronchitis the second, and URI the shortest. A total of 94 M. pneumoniae strains were isolated from M. pneumoniae-DNA positive patients, with the isolation rate 57.7%. MLVA typing distinguished the strains into 8 types. Except 2 strains, all the other 92 strains (97.9%) were macrolide-resistant strains. The 2 macrolide-sensitive strains had a special MLVA type.(3) The detection of M. pneumoniae-DNA in throat swab samples of 265 healthy children without symptoms was all negative.Conclusions:(1) M. pneumoniae infection during outbreak in the school showed different clinical manifestations. Carrying time of M. pneumoniae after infection varied according to different infection sites. Compared to P1 typing, MLVA typing was more helpful in distinguishing M. pneumoniae during outbreaks from the point of view of molecular characters.(2) M. pneumoniae infection tended to occur in children over the age of 5 years, summer and autumn were epidemic seasons, and pneumonia was the most common form of M. pneumoniae infection. So M. pneumoniae is an important pathogen of CAP. Age, severity of disease and multiple siblings were risk factors of M. pneumoniae infection. Macrolide-resistant strains were popular at present. MLVA genotyping may be a molecular epidemiologic method of predicting macrolide-resistant strains of M. pneumoniae infection.(3) It’s not common that healthy children without respiratory symptoms carrying the M. pneumoniae for a long time.