Haemophilus influenzae type f in the post-Haemophilus influenzae type b vaccination era: a systematic review

Since the introduction of Haemophilus influenzae (Hi) serotype b (Hib) vaccination, reports of increasing incidence rates of non-Hib serotypes have emerged. A systematic review was performed to investigate whether the Hi serotype f (Hif) incidence rate has increased globally and to describe its associated disease burden. In the post-Hib vaccine era, evidence shows that the incidence rate of Hif infection is increasing worldwide. In total 94 studies including 2 701 patients reported Hif infections. The estimated pooled incidence rate of Hif infection was 0.15/100 000 population per year (range: 0.05-0.40/100 000), with a median case fatality ratio of 14.3 %. Invasive infections most frequently presented as pneumonia (45 %), septicaemia (34 %) and meningitis (20 %). Of 191 Hif isolates, 87 % were ampicillin-susceptible. Multi-locus sequence typing revealed that Hif were relatively clonal, with the majority belonging to clonal complex 124. Hif causes invasive infections of significant variance in both severity and presentation. Globally, the Hif population shows little genetic variability and currently appears to possess low resistance to antimicrobials.