Table 1 Summary and characteristics of datasets used for the linkage study to estimate the total burden of invasive meningococcal disease (IMD) in England over a five-year period (2007–11)

PHE MRU laboratory-confirmed IMD cases

PHE MRU provides a national service for meningococcal species confirmation and molecular characterisation of invasive clinical isolates as well as a free national polymerase chain reaction (PCR) service to detect meningococcal DNA in clinical specimens from National Health Service (NHS) hospital laboratories throughout England. The MRU dataset maintains a record of all laboratory-confirmed cases, including NHS number, patient first name, surname, date of birth, referring hospital, sample source (blood, CSF, etc.), meningococcal capsular group, molecular analysis and date of death (if died).

Office for National Statistics death registrations (ONS)

The Office for National Statistics (ONS) (www.statistics.gov.uk) provides PHE a record of annual death registrations in England for public health surveillance purposes and routinely converts the text within death certificates into ICD-10 codes. Data contained in the ONS database includes NHS number, patient first name, surname, date of birth, sex, place of residence, date of death, place of death and cause of death in free text and ICD-10 codes.

PHE LabBase2

PHE manages a central database (LabBase2) that collects routine electronic laboratory reports of clinically significant isolates reported voluntarily by NHS hospital laboratories in England. Data contained within LabBase2 include NHS number, patient first name, surname, date of birth, sex, reporting hospital, date of specimen, pathogen and antimicrobial susceptibility profile.

Private laboratory reports

Although MRU processes nearly all meningococcal isolates and clinical specimens for PCR-testing from NHS hospital laboratories in England, a few hospitals send some of their clinical specimens to one major private medical micro-pathology laboratory for PCR-testing. This laboratory routinely reports all PCR-positive IMD confirmations to PHE.

Hospital Episode Statistics (HES)

This database is managed by the Health and Social Care Information Centre and contains details of all admissions to NHS hospital trusts in England (~11 million episodes/year). HES contains a wide range of information, including NHS number, date of birth, sex, place of residence, ethnicity, admitting hospital, underlying medical conditions, timing and duration of inpatient-stay, reasons for admission and outcome at discharge. Potential episodes associated with a meningococcal infection were extracted by searching for any meningococcal (A39*), meningococcal-related (M010A, meningococcal arthritis; M030A; post-meningococcal arthritis) or infectious meningo-encephalitis (G00*) ICD-10 code in either the primary or the 19 secondary diagnostic codes. This is in contrast to published HES data that only report diagnoses in the primary diagnostic column. Data for linkage to MRU cases included NHS number, sex, DOB and postcode.