Is Haemophilus influenzae type b (Hib) reemerging? 24 years of meningitis surveillance in a Pediatric Hospital in Buenos Aires metropolitan area.

Background:Hib was the main agent of acute bacterial meningitis in children under 5 years old in prevaccine era. In Argentina, routine vaccination began in 1998 (3 doses +1 booster schedule) resulting in a significant decline on Hib invasive disease rates. In the last years an increase in the national rates was observed. The aim of this study was to describe the epidemiological and clinical pattern of Hib meningitis (HibMen) comparing both pre and post vaccine periods.

Methods: All patients with confirmed HibMen admitted in "R. Gutierrez" Children's Hospital during 1992-2016 (May) periods were included. Buenos Aires metropolitan vaccination coverage was provided by local health authority. Time-series analysis were performed comparing HibMen hospitalization rates between pre-vaccination (PreV) 1992-1997 and post-vaccination (PostV) 1999-2016 periods excluding intervention year (1998). PostV was subdivided in 3 equal periods (6 years each).

Results: A total of 83 patients with HibMen were included, 76% of them occured in PreV; the largest number of cases in 1993 (19 cases). Median age was 9 months (5-15), 68% were males, 54% had complications (68% neurologic) and 22% had sequelae at discharge; no difference found between PreV and PostV; 7% had comorbidities. Lethality rate was 4.8% (4/83), all fatal cases in 1992-1998 periods.

Figure 1. Vaccination reports of PostV cases (n=15): 10 (67%) incomplete primary series (4 delayed schedules) and 5 complete primary series (2 delayed schedules). Only one case had a booster dose. A significant overall reduction in HibMen hospitalization rate when comparing PreV vs PostV was -91.5% (95% CI = -85.09-95.16 %; p < 0.001) with differences among the three PostV periods.

Figure 2. Conclusion: HibMen cases were mostly healthy infants. A dramatic decrease of HibMen hospitalizations was observed after Hib vaccine introduction, but it seems to be reemerging in the last years. Booster vaccination coverage in almost all years was below 90%.