Epidemiology of Bacterial Meningitis in the Nine Years Since Meningococcal Serogroup A Conjugate Vaccine Introduction, Niger, 2010-2018

Abstract

Background: In 2010, Niger and other meningitis belt countries introduced a meningococcal serogroup A conjugate vaccine (MACV). We describe the epidemiology of bacterial meningitis in Niger from 2010 to 2018.

Methods: Suspected and confirmed meningitis cases from January 1, 2010 to July 15, 2018 were obtained from national aggregate and laboratory surveillance. Cerebrospinal fluid specimens were analyzed by culture and/or polymerase chain reaction. Annual incidence was calculated as cases per 100 000 population. Selected isolates obtained during 2016-2017 were characterized by whole-genome sequencing.

Results: Of the 21 142 suspected cases of meningitis, 5590 were confirmed: Neisseria meningitidis ([Nm] 85%), Streptococcus pneumoniae ([Sp] 13%), and Haemophilus influenzae ([Hi] 2%). No NmA cases occurred after 2011. Annual incidence per 100 000 population was more dynamic for Nm (0.06-7.71) than for Sp (0.18-0.70) and Hi (0.01-0.23). The predominant Nm serogroups varied over time (NmW in 2010-2011, NmC in 2015-2018, and both NmC and NmX in 2017-2018). Meningococcal meningitis incidence was highest in the regions of Niamey, Tillabery, Dosso, Tahoua, and Maradi. The NmW isolates were clonal complex (CC)11, NmX were CC181, and NmC were CC10217.

Conclusions: After MACV introduction, we observed an absence of NmA, the emergence and continuing burden of NmC, and an increase in NmX. Niger's dynamic Nm serogroup distribution highlights the need for strong surveillance programs to inform vaccine policy.

Keywords: Neisseria meningitidis; Niger; epidemiology; meningitis belt.

Figure 1.

Suspected meningitis cases and confirmed meningococcal meningitis cases by epidemiologic week, Niger, 2010–18. Suspected cases were compared with all meningococcal meningitis cases (A) and with Neisseria meningitidis (Nm) cases classified by serogroup (B). Suspected cases are denoted by the dotted lines, Nm serogroup W (NmW) cases are shown in blue, NmA cases are shown in red, NmC cases are shown in black, NmX cases are shown in green, and all Nm serogroups combined are shown in brown. In B, the * denotes that the suspected cases peaked in 2015 at week 19, with 2192 suspected cases. For 2018, only cases detected in epidemiologic weeks 1–28 are shown.

Figure 2.

Confirmed meningitis cases by district, pathogen, and years. The number of confirmed cases detected in each district during 2010–2011 (a), 2012–2014 (B), 2015–2016 (C), and 2017–2018 (D) are depicted as a proportional pie chart. Each pathogen or Neisseria meningitidis serogroup is represented by a different color, and the pie chart size reflects the number of cases. The majority of confirmed cases are detected in the southern and western regions of Niger, and this has been consistent over time. The predominant serogroup and causative pathogen has varied widely across multiple years, with nationwide transitions between serogroups observed every few years. The arrowheads denote the cluster of NmC cases detected in the Dogon-Doutchi district in 2014 (B) and the NmX cluster in the Gaya district in 2016 (C). Both NmC and NmX were detected in the majority of districts during the years following these initial clusters.

Figure 3.

Annual incidence of meningococcal meningitis by region and district. (A) The regional map of Niger. The 2018 population (represented in millions and rounded to the nearest 100 000) is denoted in parentheses for each region. By region (B) and district (C), the annual incidence of Neisseria meningitidis cases (all serogroups) in cases per 100 000 are depicted as heat maps. The data for 2018 only includes cases from epidemiologic weeks 1–28. *, The high disease burden in the region of Niamey during the 2015 outbreak made district identification of laboratory-confirmed cases challenging, so district-level incidences during this year may not reflect true geographic association.

Figure 4.

Distribution for the age of onset for each meningitis pathogen and Neisseria meningitidis (Nm) serogroup, Niger 2010–2018. (A) Boxplot depicting the median age of onset in years for each pathogen and Nm serogroup. The χ² tests of independence determined that the age of onset and the causative pathogen were significantly associated (P < .001). (B) Bargraph depicting the percentage of cases for each pathogen (or N meningitis serogroup) that occurred in 8 different age groups (<1, 1–4, 5–9, 10–14, 15–19, 20–24, 25–44, or 45+ years at age of onset).