At 10:00 a.m. on April 16, 1974, 201 students and 12 adults at a rural grammar school in Stanly County, North Carolina, became ill within minutes after drinking orange juice at a morning recess. None of 126 persons who did not drink the juice became ill. No other foods or beverages were served that morning.
All 213 individuals experienced nausea, and all 201 students (age 6-12) and 7 of the 12 adults vomited. No one had fever, abdominal cramps, or diarrhea. The incubation period ranged from 2 to 5 minutes, and the illness lasted 15 to 60 minutes. No one was hospitalized.
The orange juice had been prepared by diluting a commercial frozen concentrate with water and ice obtained at the school between 8:00 and 8:30 a.m. No other cases of illness following consumption of orange juice made from the same lot of frozen concentrate were discovered during a survey of nearby schools during the next few days.
The school’s water is supplied by a private well. In the month prior to the outbreak, the water pump had been operating only intermittently, and in the week prior to the outbreak, while school was closed for the Easter holidays, the fluoride feeder pump malfunctioned. This caused sodium fluoride solution to be fed into the water system continuously while the water pump was not operating.
Laboratory analysis of the orange juice served at the school revealed a fluoride level of 270 mg per liter. A water sample obtained at the school on the afternoon of April 16 had a fluoride concentration of 125 mg per liter.
Control measures consisted of closing the school for the day and discontinuing fluoridation of the school’s water supply until the feeder pump can be repaired.
(Reported by Robert Clarke, B.A., Sanitarian, Jackie Welch, R.D.H., Dental Hygienist, and George Leiby, M.D., Dr.P.H., Health Director, Stanly County Health Department; William Y. Cobb, Ph.D., State Chemist, North Carolina Department of Agriculture; and J. N. MacCormack, M.D., M.P.H., Head, Communicable Disease Control Branch, North Carolina Division of Health Services.)
This is the second reported outbreak of waterborne fluoride poisoning since CDC’s Food and Waterborne Disease Surveillance System began in 1966.
A fluoride concentration of approximately 1 mg per liter in drinking water significantly reduces the incidence of dental caries ( I ). When fluoridation of water is practiced, the recommended optimum fluoride concentration varies inversely
with the average annual temperature and ranges from 0.7-1.2 mg per liter (2). When fluoride is naturally present in drinking water, levels twice this recommended optimum constitute grounds for rejection of the supply (2). Because of 2 mechanical failures in the water system at the school (intermittent operation of the water pump and malfunctioning of the fluoride feeder pump), a much higher concentration of fluoride was attained during the Easter holidays when the system was not in use.
The short duration of the illness is consistent with the observation that fluoride ion is rapidly absorbed from the gastrointestinal tract and rapidly excreted in the urine (3). The symptoms arc consistent with the observation that as little as 16 mg of sodium fluoride can produce nausea while 65 mg can cause vomiting (4). Chronic toxicity would not be anticipated in this situation because of the rapid urinary excretion of the ion following a single exposure to a toxic level.
This outbreak demonstrates the necessity for careful monitoring of water fluoridation apparatus.
1. McClure FJ (ed): Fluoride Drinking Waters (PHS Pub No. 825). Washington, GPO, 1962, pp 197-304
2. US Dept of Health, Education, and Welfare: Public Health Service Drinking Water Standards (PHS Pub No. 956-Rev 1962). Washington, GPO, 1962, p 8
3. Chernick WS: The Ions: Potassium, Calcium, Magnesium, Fluoride, Iodide, and Others. In Drill’s Pharmacology in Medicine, edited by DiPalma JR. 3rded. New York, McGraw-Hill Book Co, 1965, pp 710-712
4. Thienes C’H, Haley TJ: Clinical Toxicology. 5th ed. Philadelphia, Lea and Febiger, 1972, pp 176-179
*See original MMWR, http://fluoridealert.org/wp-content/uploads/cdc-mmwr.june-1-1974.page-199.pdf