This form of meningitis occurs mainly in babies, elderly people and those with weakened immune systems.
It can be passed from mother to foetus during pregnancy or labour.
When illness occurs very soon after birth, the most common problem is pneumonia and respiratory distress.
Meningitis mainly occurs in babies who develop illness two or three days after birth.
Late-onset infection may also occur through contact with other infected infants or adults who handle the baby.
Very few cases now occur each year in the UK and Ireland, largely
due to successful education campaigns about the dangers of eating
unpasteurised milk products or contaminated pate, poultry or shellfish
in pregnancy.
The disease can be very serious, with a death rate of about 30%.