Study on the resistance of Haemophilus influenzae from children with respiratory tract infection

Objective This study was designed to dynamically investigate the antibiotic resistance, prevalence of enzyme-producing strain of Haemophilus influenzae (Hi) and the infection caused by Hi type B (Hib) in clinical isolates from nasopharyngeal culture in Shanghai children during 2000-2002.Methods The nasopharyngeal secretions from children with respiratory tract infection were cultured to isolate Hi in 3 consecutive years. Susceptibility of Hi isolates (100 each year) to 8 antibacterial agents was determined by Kirby-Bauer (K-B) method and E test to calculate resistance rates. The enzyme-producing strain was tested by Nitrocefin disk. Type B Hi was identified by slide agglutination.Results The overall positive isolation rate of Hi was 27.5%. Hib accounted for 21%. The prevalence of β-lactamase was 11.3% in all Hi isolates, but ~41.3% in Hib strains, which was significantly higher than that in non-type B Hi (3.0%, P0.01). The Hi isolates were susceptible to amoxicillin-clavulanic acid, ceftriaxone, cefaclor, and cefuroxime, but slightly resistant to ampicillin and chloramphenicol, the reistance rate of which was 6%-11% and 9%-15%. About 28%-66% of Hi isolates were resistant to tetracycline and 38%-68% resistant to trimethoprim-sulfamethoxazole.Conclusion The resistance rates of Hi to ampicillin and chloramphenical are inereasing. Trimethoprim-sulfamethoxazole is not appropriate for the treatment of infections caused by Hi. Hib is the important serotype causing respiratory tract infections in children. Beta-lactamase production is the important mechanism of Hi resistant to ampicillin.