Molecular Epidemiology of Haemophilus influenzae Strains with Reduced Susceptibility and Genetic Profiles of Resistance in the Postvaccination Period.

Haemophilus influenzae serotype b has been the main cause of invasive infections in children, during the prevaccination period. More than 20 years after the introduction of the conjugate vaccine against Hib, HiNT has emerged as the cause of localized infections in children and adults. The main objective of this work is to evaluate the susceptibility and resistance mechanisms of H. influenzae strains from carriers and describe the molecular epidemiology and their clonal relationships by multilocus sequence typing (MLST). Sixty-nine strains from clinical cases and asymptomatic carriers from 2009 to 2019 were analyzed, confirmed as H. influenzae, and serotyped by polymerase chain reaction. The susceptibility to antibiotics was evaluated by E-test strips. Genotyping was performed by MLST. HiNT was the most frequent in all age groups. Resistance to ampicillin, sulfamethoxazole+trimethoprim, and amoxicillin+clavulanic acid was detected, with the production of ß-lactamase being the main resistance mechanism. Among 21 HiNT strains with complete allelic MLST profiles, 19 new sequence types were described, reinforcing the already reported heterogeneity of nontypeable strains, and only one clonal complex (cc-1355) was observed. Our results show a high percentage of colonization regardless of age, increased antimicrobial resistance, and high genetic diversity, along with an increased number of cases caused by HiNT strains. These findings reinforce the need for continuous surveillance for HiNT strains as it has been reported worldwide after the introduction of the Hib conjugate vaccine.

Haemophilus influenzae serotype b and a capsule-deficient type mutant (b-) invasive disease in a partially vaccinated child in Brazil.

We report a rare case of infection by two different types of Haemophilus influenzae strains in a child who received only one dose of the H. influenzae serotype b (Hib) conjugate vaccine (DTwP+Hib). The strains were recovered from blood and cerebrospinal fluid (CSF) and were phenotypically identified as Hib and non-typable H. influenzae, respectively, after serological tests. The two strains were characterized by PCR capsular typing, multilocus sequence typing and PFGE. Our results suggest that the infection was caused by the bloodstream invasion by a single Hib strain, followed by the diffusion of the bacteria across the blood-brain barrier and into the CSF. The strain recovered from the CSF, however, was identified as a capsule-deficient type mutant (b(-)) strain. Despite the high efficacy of the Hib conjugate vaccine, the increase in the numbers of strains able to escape the immune system of the vaccinated population advocates continued surveillance.