Outbreak of Neisseria meningitidis serogroup C outside the meningitis belt-Liberia, 2017: an epidemiological and laboratory investigation

Abstract

Background: On April 25, 2017, a cluster of unexplained illnesses and deaths associated with a funeral was reported in Sinoe County, Liberia. Molecular testing identified Neisseria meningitidis serogroup C (NmC) in specimens from patients. We describe the epidemiological investigation of this cluster and metagenomic characterisation of the outbreak strain.

Methods: We collected epidemiological data from the field investigation and medical records review. Confirmed, probable, and suspected cases were defined on the basis of molecular testing and signs or symptoms of meningococcal disease. Metagenomic sequences from patient specimens were compared with 141 meningococcal isolate genomes to determine strain lineage.

Findings: 28 meningococcal disease cases were identified, with dates of symptom onset from April 21 to April 30, 2017: 13 confirmed, three probable, and 12 suspected. 13 patients died. Six (21%) patients reported fever and 23 (82%) reported gastrointestinal symptoms. The attack rate for confirmed and probable cases among funeral attendees was 10%. Metagenomic sequences from six patient specimens were similar to a sequence type (ST) 10217 (clonal complex [CC] 10217) isolate genome from Niger, 2015. Multilocus sequencing identified five of seven alleles from one specimen that matched ST-9367, which is represented in the PubMLST database by one carriage isolate from Burkina Faso, in 2011, and belongs to CC10217.

Interpretation: This outbreak featured high attack and case fatality rates. Clinical presentation was broadly consistent with previous meningococcal disease outbreaks, but predominance of gastrointestinal symptoms was unusual compared with previous African meningitis epidemics. The outbreak strain was genetically similar to NmC CC10217, which caused meningococcal disease outbreaks in Niger and Nigeria. CC10217 had previously been identified only in the African meningitis belt.

Funding: US Global Health Security.

Figure 1:. Cases of meningococcal disease by date of onset

Data are from 28 cases. Of the 31 outbreak cases, three were considered not cases of meningococcal disease and were excluded.

Figure 2:. Reported contacts among cases

17 cases with any reported contact with other cases are shown. Each circle represents a case; a line between circles indicates contact between cases with the weight of the line illustrating the type of contact. Circles are coloured on the basis of case classification, and size of circle is based on number of additional cases with whom contact was reported. Nm=Neisseria meningitidis.

Figure 3:. Metagenomic analysis from six non-oral specimens with high abundance of Neisseria meningitidis DNA

Similarity of 141 N meningitidis isolate genomes to the N meningitidis sequences identified in specimens from each of six cases. Metagenomic datasets are labelled with the case identifier, the source of the specimen, and the number of polymorphic positions within the alignment of 141 isolate genomes for which the specimen sequences had a single base call. The percentage similarity to each of the 141 isolate genomes is plotted for each specimen; a boxplot shows the first, second, and third quartiles, and error bars cover points beyond the first or third quartile, up to 1·5 times the IQR. Outliers above the whiskers are labelled with the sequence type (ST) of the isolate.