Meningococcal infection has always been the leading cause of meningitis in the UK. Six different kinds, serogroups A, B, C, W, X, and Y cause the most disease. For decades meningococcal B has been the main serogroup, and meningococcal C was also common until the MenC vaccine was introduced, reducing cases to just a handful each year.
However, cases of meningococcal W (MenW) have risen year on year since 2009. Public Health England has shown that since 2008/9 when MenW accounted for only 1-2% of meningococcal cases, it has increased to cause 24% of cases in 2014/15.
Our meningococcal genome library has played a vital part in helping Public Health England to stay a step ahead of the game in the fight against meningococcal disease. Analysis of MenW isolates in the genome library has revealed that almost all of the increase in MenW disease is attributable to a particularly virulent type of meningococcal bacteria called ST-111.
The rise in this ST-11 MenW disease is particularly alarming because it is striking mainly healthy people across all age groups, with a marked spike amongst teenagers (figure 1) and cases are rising steeply. 34 cases were reported in January 2015 compared with 18 and 9 for the same time period over the previous two years2.
The ST-11 strain is associated with severe illness which often requires treatment in intensive care and has a higher associated death rate than other strains of meningococcal disease, (13% case fatality compared to 5-10%) 1.
It often has different symptoms to other kinds of meningococcal disease:
- Rather than meningitis or septicaemia, some people with MenW infection may get septic arthritis or a severe respiratory tract infection, such as pneumonia, epiglottitis or supraglottitis (in these latter two conditions there is a dangerous swelling around the "lid" that covers the windpipe , blocking the flow of air into the lungs).
- Several adults with MenW septicaemia have had mainly gastrointestinal symptoms but without the characteristic non-blanching rash and progressed rapidly to death.
This is the same strain that has been causing epidemic disease in Argentina, Brazil and in Chile, where it is associated with a death rate of 28%3 compared to 10% for other strains in the country.
As a direct result of this information, the government’s vaccine advisers, the Joint Committee on Vaccination and Immunisation (JCVI) have advised that 14 to 18 year olds should be immunised with ACWY vaccine as soon as possible to prevent rapid increases in disease amongst the rest of the population4. The Department of Health has accepted the JCVI’s advice and is currently planning the implementation of a combined ACWY immunisation programme in this age group5.