One person died and many others suffered vomiting and nausea after high levels of fluoride entered the public water supply in an Alaskan community.
It was discovered that a faulty mechanism and operator error had caused the overfluoridation in May 1992.
It affected the small community of Hooper Bay, Alaska, where 296 people were believed to have been poisoned during the two days when the overfluoridation occurred.
A study group from the Centers for Disease Control and Prevention in Atlanta, Georgia, investigated 47 cases of residents who drank the water. Of those, 43 had become ill with diarrhea and vomiting, one died and another recovered after suffering severe complaints.
Previous cases of acute fluoride poisoning have tended to occur in communities served by small scale water systems. In the US, six outbreaks caused by overfluoridation have been reported since the late 1940s when fluoride has been added to the water supply.
Acute fluoride poisoning caused the death of one patient in Maryland and, more recently, killed three people in Illinois, all of whom were undergoing dialysis therapy.
The group recommended that levels of fluoride need to be carefully monitored and inspected, but felt that the fluoridation of water to prevent tooth decay should continue (New Eng J of Med, January 13 1994).
However, previous cases may have been wrongly attributed to an outbreak of infectious enteritis inflammation of the intestine which causes diarrhea because the symptoms are similar.
The Lancet (15 January 1994) recommends that authorities should consider the possibility of fluoride poisoning when investigating a supposed outbreak of enteritis.