Carriage of Haemophilus influenzae in the oropharynx of young children and molecular epidemiology of the isolates after fifteen years of H. influenzae type b vaccination in Italy

Vaccine. 2015 Nov 17;33(46):6227-34. doi: 10.1016/j.vaccine.2015.09.082. Epub 2015 Oct 9.

Abstract

Background: Haemophilus influenzae is an important pathogen able to cause a wide spectrum of diseases in children. Colonization of the upper respiratory tract is a risk factor for developing disease. This study aimed to investigate the oropharyngeal carriage rate of H. influenzae in young children in two Italian cities, 15 years after H. influenzae type b (Hib) vaccination was introduced. Antibiotic resistant traits and genotypes of the colonizing H. influenzae isolates were investigated.

Methods: Oropharyngeal swabs were obtained from 717 healthy children aged <6 years (June 2012-July 2013). Potential risk factors for H. influenzae colonization were investigated. H. influenzae isolates from carriage were characterized by PCR capsular typing, ampicillin susceptibility testing, resistance-associated gene sequencing and multilocus sequence typing (MLST). For comparison purposes, 38 non-typeable H. influenzae (NTHi) isolates from invasive disease were genotyped by MLST.

Results: The overall H. influenzae carriage rate was 14.1% (101/717). Age, study site, presence of young siblings, and complete Hib vaccination status were independently associated with colonization. Of 101 isolates, 98 were NTHi, 2 were type e and 1 was type f. The overall ampicillin resistance rate was 15.8% (16/101). Resistance was mediated by TEM-1 β-lactamase production in half of isolates (n=8) or modifications in penicillin-binding protein (PBP) 3 in the other half (n=8). Several substitutions were discovered in PBP3 including the Asn526Lys change. Seventy-six different STs were identified among 98 NTHi isolates from carriage, with only 4 STs (ST12, ST57, ST238, ST1238) encompassing ≥ 3 isolates. Comparison of carriage and disease isolates found that several STs were shared between the two sources, although none of the major disease-associated STs were observed in carriage isolates.

Conclusions: NTHi is the predominant serotype in carriage. The importance of monitoring both NTHi colonization rate and circulating genotypes should be emphasized in the era of the Hib conjugate vaccines.

Keywords: H. influenzae; MLST; Oropharyngeal carriage; ftsI; β-Lactam resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier State / epidemiology*
  • Child, Preschool
  • Cities / epidemiology
  • Cross-Sectional Studies
  • Drug Resistance, Bacterial
  • Female
  • Genotype
  • Haemophilus Infections / epidemiology*
  • Haemophilus Infections / prevention & control*
  • Haemophilus Vaccines / administration & dosage*
  • Haemophilus influenzae / classification*
  • Haemophilus influenzae / genetics
  • Haemophilus influenzae / isolation & purification*
  • Humans
  • Infant
  • Infant, Newborn
  • Italy / epidemiology
  • Male
  • Microbial Sensitivity Tests
  • Molecular Epidemiology
  • Multilocus Sequence Typing
  • Oropharynx / microbiology*
  • Polymerase Chain Reaction
  • Sequence Analysis, DNA

Substances

  • Haemophilus Vaccines