Biotyping and susceptibility testing of Haemophilus strains isolated from respiratory tract of adults

Objective To characterize the season distribution,biotypes and antibiotic susceptibility of Haemophilus influenzae and Haemophilus parainfluenzae strains isolated from adults in our hospital in order to guide empirical prescribing and prevent infections.Methods A total of 4 719 samples of sputum or throat swab were collected from adult patients during 2006-2007. Biotypes of these strains were identified by VITEK-32 system. β-lactamase production was assessed by VITEK-32. Antibiotic susceptibility testing was based on Kirby-Bauer disc diffusion technique. WHONET 5.1 software was used to analyze the data.Results A total of 228 (4.8%) Haemophilus isolates were identified,including H. influenzae (118,2.5%) and H. parainfluenzae (110,2.3%). Thirty-one (26.3%) strains of H. influenzae were identified as type Ⅲ,82 (69.5%) as type Ⅳand 5 (4.2%) as other types. Thirty-eight (34.5%) strains of H. parainfluenzae were identified as type Ⅲ,68 (61.8%) as type Ⅳ,and 4(3.6%)as the other type. The prevalence of Haemophilus was significantly higher in winter than in spring,summer or autumn. About 33.9%,57.6% and 59.4% of the H. influenzae isolates were resistant to ampicillin,trimethoprim-sulfamethoxazole and chloramphenicol respectively. About 40.0%,89.1% and 36.4% of the H. parainfluenzae isolates were resistant to ampicillin,trimethoprim-sulfamethoxazole and chloramphenicol respectively. All ampicillin-resistant strains were β-lactamase producers. No β-lactamase-positive isolate was found resistant to amoxicillin-clavulanic acid. All isolates were susceptible to amoxicillin-clavulanate,cefotaxime,imipenem,ciprofloxacin,levofloxacin,aztreonam,ceftazidime and cefepime.Conclusions The respiratory tract infections in adults due to H. influenzae or H. parainfluenzae were more frequently found in winter. Type Ⅲ and type Ⅳ were the most prevalent types. These prevalent strains were more resistant to ampicillin and chloramphenicol,and highly resistant to trimethoprim-sulfamethoxazole. Ampicillin is suitable for treating respiratory tract infections caused by β-lactamase-negative Haemophilus strains. Amoxicillin-clavulanate is indicated for treatment of respiratory infections due to β-lactamase-producing Haemophilus.