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Mass Psychogenic Illness Caused by Hydrogen Sulfide at a Public School in Southwest Saudi Arabia on 28 of March, 2017.


On March 28, 2017 students attending a public girls' school in southwest Saudi Arabia visited the emergency room with mild gastrointestinal illness. A team of residents from the Saudi Arabian Field of Epidemiology Training Program (FETP) investigated to determine the source of the outbreak, identify risk factors, and recommend preventive measures.


A case was defined as any student with abdominal pain, nausea, vomiting, or diarrhea within 24 hours after attending school on the day of illness onset. The FETP team interviewed students, teachers, parents and community members to capture information on symptoms, exposures, and community perceptions. Line-list and standardized questionnaires collected information on symptoms, illness onset, and possible exposures. Environmental investigations were conducted at the school to identify possible sources of exposure.


The attack rate was 16.9%. Among 109 reported cases, 86 (13.3%) students ate at the school canteen. Case age ranged from 6 to 13 years old: the most affected age group was the 8-year-olds (22%), who had the highest frequency of symptoms. Predominant symptoms included vomiting (93.5%), abdominal pain (84.4%), nausea (75.2%) and diarrhea (72.2%). Most cases recovered within 6 hours. No pathogens were isolated from 10 stool samples. No evidence of infection or chemical toxins was found in the 10 of blood and urine specimens. Environmental investigation of the school canteen and restrooms did not identify any contamination. Many members of the community reported concerns about the outbreak.


The rapid onset and recovery of symptoms and no consistent physical, microbiological or environmental findings implied psychogenic illness rather than an outbreak caused by contamination. We had some sense that the outbreak might be psychogenic, but pursued the investigation to rule out any other causes. Our investigation indicated that this outbreak was most likely the result of mass psychogenic illness.