[Serotypes and antibiotics-resistance patterns of 247 strains of Haemophilus Influenzae isolated from children in Hangzhou]

Abstract

Objective: To investigate the serotypes and antibiotics-resistance patterns of Haemophilus influenzae isolated from children in Hangzhou.

Methods: Isolates were identified with api-NH card. Serotypes were determined with slide agglutination method. The sensitivities of 13 antibiotics against 247 strains of Haemophilus influenzae were determined in vitro with Kirby-Bauer diffusion methods and MICs of ampicillin were determined with E-test. Nitrocefin test was used to detect beta-lactamase.

Results: Of the 247 strains isolated from children during the period from August 2001 to July 2002, 153 strains were non-typable, while 94 strains (38.1%) were typable and 90.4% and 1.1% of them belonged to type d and type b, respectively. Higher incidence of typable Haemophilus influenzae was found in male than in female children and the difference was significant (chi(2) = 5.30, P < 0.05), while between upper and lower respiratory tract infected children the difference was not statistically significant (chi(2) = 3.60, P > 0.05). Forty-one isolates (16.6%) were beta-lactamase-positive and 14 strains could not grow on medium in antibiotics sensitivity test. Of all 233 isolates tested successfully, 85.4% were susceptible to ampicillin, and the sensitivity rate to cefaclor, ceftriaxone, cefotaxime, imipenem, rifampin, clarithromycin, and chloramphenicol were as high as 98.7%, 99.6%, 99.6%, 99.6%, 98.7%, 91.0%, and 90.6%, respectively. All strains were sensitive to amoxicillin/clavulanic acid, ampicillin/sulbactan and ofloxacin, while 107 strains (45.9%) were resistant to trimethoprim-sulfamethoxazole, followed by that of tetracycline (14.6%). Resistance to ampicillin and trimethoprim-sulfamethoxazole in typable isolates was statistically significantly higher than in non-typable strains. Twenty-six strains (10.5%) were multi-resistant isolates and the multi-resistance rate in beta-lactamase-positive strains were significantly higher than that in beta-lactamase-negative strains (chi(c)(2) = 146.8, P < 0.001).

Conclusion: Non-typable Haemophilus influenzae was the most common type in clinical strains isolated from children in Hangzhou, while type d was the overwhelming type and type b was uncommon in typable isolates. Incidence of typable isolates was higher in male than in female children, and it was apt to intergrow with other species of pathogenic bacteria. The proportion of beta-lactamase-positive strains was not high and ampicillin or other beta-lactam actibiotics were still the treatment of choice for infections with Haemophilus influenzae.