Doctors have always known that anyone who spends time with a patient with meningococcal disease is at risk of infection.

But they had never been certain exactly how close the contact would have to be before someone was seriously at risk.

Danger of infection

However, research published in the British Medical Journal narrows the criteria.

It says that "household members and kissing contacts" are six-and-a-half times more likely to catch the disease than less intimate contacts, and almost 18 times more at risk than the population at large.

Meningitis causes a distinctive rash

The research, which was carried out by Norwegian scientists, also discovered that children aged between five and 12 were the most likely to catch the disease.

Meningitis is a disease that inflames the tissues surrounding the brain and spinal cord. Using antibiotics in a treatment known as chemoprophylaxis can prevent it.

The study aimed to establish who came into close enough contact with the patient to warrant a dose of antibiotics.

It contends that more people receive the preventive treatment than actually need it, saying: "When a case of meningococcal disease occurs, many people may fulfill accepted criteria for receiving chemoprophylaxis.'

It adds that the treatment "may be prescribed in excess of what is needed".

Antibiotics can be used to safeguard people against the disease

The report points out that overuse of antibiotics can have a negative effect because the disease could become resistant to the medication.

Ineffective treatment

This happened in Norway in 1970 when a form of meningitis which was unaffected by the treatment appeared.

Since then, the country has banned chemoprophylaxis for the disease.