New features in drug resistance of Haemophilus influenzae isolated from children with infection diseases in Suzhou during 2011-2012

Objectives To investigate the changes and features of drug resistance in Haemophilus influenzae(Hi) isolated from children with infection diseases in Suzhou. Methods One thousand two hundred and twenty-two Hi strains isolated from clinical specimens were collected from January 2011 to June 2012. Antimicrobial susceptibility was tested by Kirby-Bauer me-thod, and β-lactamase was analyzed by chromogenic nitrocefin method. Then strains were divided into four groups according to their specific resistance patterns: ①β-lactamase positive strains(except for cefuroxime-resistant strains), ②β-lactamase negative ampicillin-resistant(BLNAR) strains, ③cefuroxime-resistant strains, and ④other resistant strains. Results The resistance of iso-lated Hi from children in Suzhou area to ampicillin, co-trimoxazole, cefaclor, tetracycline, chloramphenicol, azithromycin, cefu-roxime, ampicillin/sulbactam was 32.7%, 76.7%, 27.4%, 14.3%, 10.2%, 8.4%, 6.9% and 4.3%, respectively, and the detection rate in four groups was 29.0%, 2.6%, 6.9%, 41.2%, respectively. Multi-resistant strains were mainly distributed in Group ① and Group ②, accounting for 67.5% and 81.3% of each group. Azithromycin, tetracycline and chloramphenicol showed high antimicrobial activity against BLNAR and cefuroxime-resistant Hi strains. The positive rate of resistance to β-lactamase was 30.8%. The rates of resistance to cefuroxime, cefaclor, ampicillin/sulbactam and cotrimoxazole in β-lactamase-positive ampicillin-resistant strains are significantly different from those in β-lactamase-negative ampicillin-resistant strains. Conclusions The resistance feature of Hi isolated from children in Suzhou shows significant changes, including new appearance of cefuroxime-resistant strain, a rapid increase in resistance to azithromycin, and a large proportion of multidrug-resistant strains. The rapid increase in BLNAR and the emergence of cefuroxime-resistant strains have become the new resistance pattern of Hi in this area.