Study On Resistance Of Streptococcus Pneumoniae And Etiological Distribution In Hospitalized Pediatric Patients With Respiratory Infections

[BACKGROUND]Acute respiratory tract infection (ARI) is one of the most common diseases in children. With a high morbidity and mortality, it causes a heavy burden for family and society. Understanding the etiology and related risk factors of ARI could provide useful information for clinical treatment, so as to reduce the incidence rate and morbidity of the diseases.Streptococcus pneumoniae, pneumococcus, one of the most common pathogen of acute respiratory tract infections, causes high morbidity and mortality in all age groups, especially in children under 3 years. Together with the increasing emergence of multidrug resistance, it poses a major challenge, and emphasizes the urgent need to find the related risk factors and drug resistance patterns to prevent and treat pneumococcal infections.Macrolide resistant Streptococcus pneumoniae has become a most serious in the treatment of pneumococcal infections. It is essential to explore the resistance patterns and mechanism of resistance in order to cure pneumococcal infections and control the transmission of resistance. Besides, the distributions of the resistance patterns and mechanism are different between areas, so it is the urgent need to further study molecular epidemiology of macrolide resistant Streptococcus pneumoniae.[OBJECTIVES]To understand the etiology and related risk factors of ARI and explore the resistance patterns and transmission mechanism of antibiotic resistant Streptococcus pneumoniae in hospitalized children in Suzhou. Specially,1. To investigate the etiology and related factors in a hospital-based cross-sectional study in Suzhou.2. To analyse the associated fators of Streptococcus pneumoniae infection and multidrug resistance patterns with clinical Streptococcus pneumoniae isolates.3. To explore the resistant phenotype and genotype of MRSP isolates and the transmission mechanism and evolutionary togther with related epidemiology materials.[METHODS]A cross-sectional study was conducted in the Soochow University Children's Hospital in China from March,2006 to March,2007. The study included 453 pediatric patients less than 3 years of age who admitted to the hospital due to acute respiratory infections, from whom related epidemiology data and sputum culture were obtained. Data was collected via medical record review, parent interview and parent questionnaire, and was recorded onto case report forms (CRFs). The data included demographic, administrative, and clinical information. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to explore risk factors of baterial and virus infections.The risk factors of pneumococcal infections were analysed by non-conditional Logistic model. A total of 60 isolates of pneumococcus, confirmed by the Optochin (Oxoid, Basingstoke, UK) susceptibility and bile solubility tests, were tested in antimicrobial susceptibility. The susceptibility of antibiotics including erythromycin, clindamycin, chloramphenicol, rifampicin, ofloxacin, trimethoprim/sulfamethoxazole (SXT), tetracycine and vancomycin was determined by Kirby-Bauer disk diffusion method (Oxoid). The susceptibility of penicillin, amoxillin, cefuroxime and ceftriaxone was determined by the E-test (Oxoid) according to the latest guidelines of the Clinical and Laboratory Standards Institute (CLSI). Possible risk factors of drug resistance of pneumococcus were explored with Chi-square test.The phenotype and genotype of MRSP isolates were determined by dual-disk test and PCR methods, respectively. The relationship bettwen phenotype and genotype were also analysed. We adopted multilocus sequence typing (MLST) method to explore the transmission mechanism of MRSP isolates and to trace the evolutionary in order to control the transmission of MRSP.[RESULTS]Among 453 cases, pneumoniae was the most common disease (71.7%), followed by acute upper respiratory infections (AURI) (14.3%). Most of pneumoniae and AURI occurred in children under 1 year and in spring.406 cases (89.6%) have used antibiotics before entry to the hospital in one week. The most common antibiotics used are P lactams and macrolide, with the application rate 88.2%and 20.4%, respectively.Among 453 samples, evidence of specific microbial etiology was obtained in 220 cases (48.6%). Bacterial infection was found in 161 cases (35.5%), viral infection in 32 cases (7.1%), compound infection with bacteria and virus in 27 cases (6.0%). Haemophilus influenzae and Streptococcus pneumoniae were the most common bacteria, with the positive rates 17.0%and 13.2%, respectively. The rates of respiratory syncytial virus (RSV) and adenovirus (ADV) were the highest in children with viral infections. There was some difference in etiology of different diseases. Haemophilus influenzae, Streptococcus pneumoniae and Branhamella catarrhalis were the most frequently detected in AURI children, with the rate 16.9%,6.2%and 7.7%, respectively. While Haemophilus influenzae, Streptococcus pneumoniae and RSV were the most common in children with pneumoniae, with the rate 16.3%, 14.5%and 7.2%, respectively. It is similar in children with other acute lower respiratory infections (ALRIs), with the rate 20.6%,14.3%and 8.3%. Compared to high compound infections of ADV and bacteria in children with AURI, compound infections of RSV and Streptococcus pneumoniae were predominant in children with pneumoniae. A very few of compound infections were found in children with other ALRIs. Additionally, a few of Candida albicans and Klebsiella pneumoniae were detected.Season (spring/winter:OR=0.417,95%CI:0.184-0.948; summer/winter: OR=0.135,95%CI:0.048-0.376; autumn/winter:OR=0.126,95%CI:0.037-0.430) and age (＞1year/≤1year:OR=2.094,95%CI:1.135-3.866) were associated with viral infection. The positive rates of different viruses were different in children with various age and admission time. The positive rate of RSV was the highest in winter (26.4%), while ADV in spring (6.1%) and children above two yaers. There was highest proportion of Inf-A in children between one and two years old (4.2%). Inf-B and Pinf-1 were only detected in children less than one year and admitted in spring.Season was also correlated with bacterial infections (spring/winter:OR=0.419, 95%CI:0.204-0.862; summer/winter:OR=0.336,95%CI:0.160-0.706; autumn/winter: OR=0.780,95%CI:0.355-1.715). The positive rates of Haemophilus influenzae, Streptococcus pneumoniae and Haemophilus parainfluenzae were highest in winter, while Staphylococcus areus in autumn and Pseudomonas aeruginosa in summer (P< 0.05). There was no difference of positive rate of Branhamella catarrhalis in various seasons (P>0.05).Sixty isolates of Streptococcus pneumonia was obtained from 453 cases, with positive rate of 13.2%. Age (≤lyear/>lyear:OR=0.360,95%CI:0.184-0.704) and season (spring/winter:OR=0.338,95%CI:0.144-0.792; autumn/winter:OR=0.284, 95%CI:0.099-0.815; summer/winter:OR=0.218,95%CI:0.085-0.559) were associated with Streptococcus pneumonia infection. No relation was found between history of antibiotic use, history of respiratory diseases, passive smoking, viral infections and pneumococcus infections (P>0.05).The percentage of resistance to erythromycin, clindamycin, tetracycline, Trimethoprim/sulfa (SMZ), penicillin, cefuroxime, ceftriaxone, chloramphenicol and amoxicillin was 100%,98.4%,96.7%,81.6%,60.4%,58.3%,13.3%,12.5%and 2.1%, respectively. No resistant strains to rifampicin, ofloxacin and vancomycin were detected. All isolated were resistant to three or above multiple drugs. Multiple resistences to erythromycin, clindamycin, tetracycline, SMZ, penicillin and cefuroxime were the major resistance pattern, followed by erythromycin, clindamycin, tetracycline and SMZ. There was difference between PRSP and PNSP in resistance to cefuroxime (P=0.000), while no difference in resistant to other antibiotics. Multiple resistences to erythromycin, clindamycin, tetracycline and SMZ were the major resistance pattern of PSSP, while resistences to erythromycin, clindamycin, tetracycline, SMZ and cefuroxime of PRSP.In 48 MRSP isolates, the phenotype of 43 isolates was cMLSb type(89.6%), followed by iMLSb type(8.3%) and M type(2.1%), respectively. ermB gene was detected in 23 isolates (47.9%), mefE in one isolate (2.1%) and both in 24 isolates (50%). The only one isolate with mefE gene was M type. Twenty three isolates only with ermB gene were MLSb type and most of them were cMLSb type. Twenty four isolates both with ermB and mefE gene were all cMLSb type.Among 31 STs found in the MLST analysis of 46 isolates,16 STs were new assignments. Of the new STs,15 represented novel combinations of known alleles (ST4628-4642) and one profile contained a new allele gki gene (ST4643). The new allele was gki 237. All new STs included only one strain. eBURST analysis showd the presence of two clonal complexes and 22 singletons. A comparison of the isolates with the international PMEN clones revealed that the isolates harbouring allelic profiles that were identical to those of eight clones (Taiwan19F-14, Netherlands 15B-37, USANT-43, Spain9v-3, Netherlands3-31, Taiwan23F-15, England14-9 and Spain6B-2) or their single locus variants (SLVs) constituted the major of strains (29 isolates,63.0%).Compared to other isolates, the isolates of PMEN clone have higher resistant rate in penicillin and cefuroxime (P<0.05). The genotype of PMEN clone islates was ermB and mefE, while ermB was the common genotype of other isolates. No relation was found between age, history of antibiotic use and infection of PMEN clone isolates.[CONCLUSION]Our study suggests that pneumoniae is the most common disease of acute respiratoey infections in children; bacterial infection is the leading cause of ARIs, with the most predominant pathogen of Haemophilus influenzae and Streptococcus pneumoniae; the positive rate of different bacteria is different in various seasons and the highest is in winter; the resistance rate of Streptococcus pneumoniae isolates is very high and all isolates are nultiple resistant to antibiotics, which emphasize the judicious use of antibiotic; both the horizontal spread of resistance genes such as ermB/mefE and the spread of PMEN clone isolates have a significant role in the emergence of and increase in antibiotic resistance among strains from Suzhou, further researches on surveillance of PMEN clones still needed.