Health authorities from the World Health Organization (WHO) and the government of Angola have revealed that bromide poisoning may be the source of a mystery illness first reported in early October.

The outbreak of over 400 reported cases of a neurological disorder was centred in the Cacuaco district of Angola's capital city Luanda. A majority of the afflicted have been children under the age of 15. There have been no deaths attributed directly to the disorder.

According to a statement in the state-run AngolaPress, symptoms have included "sleepiness, blear-eyedness, dizziness and difficulty to speak, walk and extreme tiredness." WHO described the drowsiness as being so severe that the patient would require "painful stimuli" to be awoken.

Results from laboratory tests carried out in London and Munich indicated elevated levels of bromide present in the blood and kitchen salt samples examined. It is suspected that sodium chloride (table salt) may have been contaminated with sodium bromide, an agent used in pharmaceuticals and industry.

However, authorities caution that more investigation is required to determine the source and cause of the illness. Consequently, further testing of blood, food and water has been initiated.

On Wednesday, WHO dispatched additional technical and support personnel to Angola to assist local health officials.