Antimicrobial susceptibility of community-acquired respiratory tract pathogens isolated from patients in primary hospitals in Shanghai from 2007 to 2010

Abstract

To investigate the etiology of community-acquired respiratory tract infections (CARTI) and the antimicrobial resistance of the major pathogens in primary hospitals in Shanghai. Patients with CARTI were prospectively recruited from 30 primary hospitals from December 2007 to July 2010. Those who had used antimicrobials within previous 2 weeks were excluded from the study. The clinical information such as temperature, white blood cell (WBC) count and percentage of neutrophils was recorded, and throat swab or deep cough sputum was collected to isolate pathogens. The specimens were collected and couriered to the Zhongshan Hospital microbiology laboratory within 2 h for bacterial culture. The minimal inhibition concentrations (MIC) of penicillin G, amoxicillin, cephradine, cephalexin, cefadroxil, sulfamethoxazole/trimethoprim and azithromycin were determined using the agar dilution test. Totally 806 qualified cases were enrolled in this study. Fever (T ≥ 38 °C) was present in 51.7% (n = 417) , and increased WBC count (>10×10(9)/L) was noted in 68.5% (n = 552 cases) of the patients. For bacterial culture, 184 strains were isolated from throat swabs of 688 patients with upper respiratory infection; the most frequently isolated bacteria were Haemophilus influenzae (44, 23.9%), Staphylococcus aureus (44, 23.9%) and Group G streptococcus (43, 23.0%). Thirty-three strains were isolated from 118 patients with lower respiratory infections, with Haemophilus influenza (21, 63.6%), Group G streptococcus (6,18.2%) and Streptococcus pneumoniae (3,9.1%) as the leading pathogens. All strains of Haemophilus influenzae were susceptible to azithromycin. The susceptibility rate of Streptococcus pneumoniae to penicillin was as high as 94.7%, while that to azithromycin was significantly decreased (21.1%). The MIC90 values of cephalexin, cefadroxil and ceftazidime for β-hemolytic streptococcus spp were ≤ 2 mg/L. Upper respiratory infections were responsible for most cases of CARTI. The commonly used antimicrobials in primary hospitals kept a high susceptibility to the frequent pathogens for CARTI. However, Streptococcus pneumoniae showed a decreased susceptibility to macrolides, which should be used carefully as a single agent when treating CARTI.