Emergence of epidemic Neisseria meningitidis serogroup C in Niger, 2015: an analysis of national surveillance data

Abstract

Background: To combat Neisseria meningitidis serogroup A epidemics in the meningitis belt of sub-Saharan Africa, a meningococcal serogroup A conjugate vaccine (MACV) has been progressively rolled out since 2010. We report the first meningitis epidemic in Niger since the nationwide introduction of MACV.

Methods: We compiled and analysed nationwide case-based meningitis surveillance data in Niger. Cases were confirmed by culture or direct real-time PCR, or both, of cerebrospinal fluid specimens, and whole-genome sequencing was used to characterise isolates. Information on vaccination campaigns was collected by the Niger Ministry of Health and WHO.

Findings: From Jan 1 to June 30, 2015, 9367 suspected meningitis cases and 549 deaths were reported in Niger. Among 4301 cerebrospinal fluid specimens tested, 1603 (37·3%) were positive for a bacterial pathogen, including 1147 (71·5%) that were positive for N meningitidis serogroup C (NmC). Whole-genome sequencing of 77 NmC isolates revealed the strain to be ST-10217. Although vaccination campaigns were limited in scope because of a global vaccine shortage, 1·4 million people were vaccinated from March to June, 2015.

Interpretation: This epidemic represents the largest global NmC outbreak so far and shows the continued threat of N meningitidis in sub-Saharan Africa. The risk of further regional expansion of this novel clone highlights the need for continued strengthening of case-based surveillance. The availability of an affordable, multivalent conjugate vaccine may be important in future epidemic response.

Funding: MenAfriNet consortium, a partnership between the US Centers for Disease Control and Prevention, WHO, and Agence de Médecine Preventive, through a grant from the Bill & Melinda Gates Foundation.

Figure 1. Districts that surpassed epidemic or alert thresholds in Niger, Jan 1 to June 30, 2015

*Includes five districts: Niamey I, Niamey II, Niamey III, Niamey IV, and Niamey V.

Figure 2. Number of suspected meningitis cases by week in Niger (A) between Jan 1, 2003, and June 30, 2015, and (B) during selected epidemic years

In the epidemics of 2003, 2004, 2008, and 2009, Neisseria meningitidis serogroup A was the predominant serogroup. In the 2006 epidemic, N meningitidis serogroup X was the predominant serogroup. In the epidemic of 2015, N meningitidis serogroup C was the predominant serogroup. MACV=serogroup A conjugate meningococcal vaccine.

Figure 3. Laboratory-confirmed cases by epidemiological week and pathogen, Jan 1 to June 30, 2015

NmC=Neisseria meningitidis serogroup C. NmW=N meningitidis serogroup W.