Low rate of nasopharyngeal carriage and high rate of ampicillin resistance for Haemophilus influenzae among healthy children younger than 5 years old in northern Taiwan
Sheng-Ru Wang, Wen-Tsung Lo, Chen-Ying Chou, Ying-Yan Chen, Shu-Ying Tsai, Mong-Ling Chu, Chih-Chien Wang
Department of Pediatrics and Microbiology Research Laboratory, Tri-Service General Hospital, National Defense Medical Center, Taipei; and Division of Laboratory Research and Development, Center for Disease Control, Department of Health, Taipei, Taiwan
Received: December 25, 2006 Revised: April 18, 2007 Accepted: May 3, 2007
Background and purpose:
Surveillance data of colonization by Haemophilus influenzae in Taiwan are lacking. This study aimed to define the nasopharyngeal carriage rate of H. influenzae among children younger than 5 years in northern Taiwan, and to determine the antibiotic susceptibility, serotype and the clonal relationship of these isolates.
Nasopharyngeal specimens were obtained from 511 healthy children younger than 5 years. All H. influenzae isolates were serotyped. The minimal inhibitory concentrations for various antibiotics were determined. Pulsed-field gel electrophoresis (PFGE) was used for clonal analysis.
Among 511 children, 269 (52.6%) had been vaccinated with at least one dose of H. influenzae type b (Hib) conjugate vaccine, 236 (46.2%) were unvaccinated and 6 (1.2%) had no vaccination records available. Twenty six H. influenzae strains were isolated. There were three Hib isolates and the others were nontypeable H. influenzae (NTHi). The carriage rate for Hib was 0.6% (3/511) and of NTHi was 5% (23/511). Three (1.27%) of the 236 unvaccinated children were carriers of Hib, whereas none of the 269 vaccinated children carried Hib. Two out of the three Hib isolates and 14 (60.9%) of 23 NTHi isolates were ampicillin-resistant. Multidrug resistance was found in 7 (26.9%) of the isolates. Among the isolates, 61.5% were beta-lactamase producers; there were no beta-lactamase-negative ampicillin-resistant isolates. The PFGE restriction patterns showed a wide diversity of genotypes.
There is very low nasopharyngeal carriage of Hib among children younger than 5 years in northern Taiwan. This may explain why the incidence of invasive Hib disease is also low in Taiwan. In addition, we found a high prevalence of beta-lactamase-positive ampicillin-resistant nasopharyngeal H. influenzae isolates.
Carrier state; Drug resistance, microbial; Haemophilus influenzae; Haemophilus influenzae type b; Nasopharynx; Vaccines, conjugate
J Microbiol Immunol Infect. 2008;41:32-40.