Suspected cluster of Neisseria meningitidis W invasive disease in an elderly care home: do new laboratory methods aid public health action? United Kingdom, 2015

In 2015, a suspected cluster of two invasive meningococcal disease (IMD) cases of serogroup W Neisseria meningitidis (MenW) occurred in elderly care home residents in England over 7 months; case investigations followed United Kingdom guidance. An incident control team reviewed epidemiological information. Phenotyping of case specimens informed public health action, including vaccination and throat swabs to assess carriage. Whole genome sequencing (WGS) was conducted on case and carrier isolates. Conventional phenotyping did not exclude a microbiological link between cases (case 1 W:2a:P1.5,2 and case 2 W:2a:NT). After the second case, 33/40 residents and 13/32 staff were vaccinated and 19/40 residents and 13/32 staff submitted throat swabs. Two MenW carriers and two MenC carriers were detected. WGS showed that MenW case and carrier isolates were closely related and possibly constituted a locally circulating strain. Meningococcal carriage, transmission dynamics and influence of care settings on IMD in older adults are poorly understood. WGS analyses performed following public health action helped to confirm the close relatedness of the case and circulating isolates despite phenotypic differences and supported actions taken. WGS was not sufficiently timely to guide public health practice.