Baruch Modan, Director-General of the Israeli Ministry of Health said that the first cases could have been caused by an "environmental irritant". Yellow powder that was seen around some school in Jenin proved to be a common
pollen. Though a trace of
hydrogen sulfide was found, the
Centers for Disease Control and Prevention, in
Atlanta found that most of the fainting cases were psychological in nature. On April 4, 1983, the UN Security Council met and formally requested the
Secretary General of the UN to conduct an independent investigation of the "reported cases of poisoning." The UN investigation found that mass hysteria was the likeliest cause of the epidemic, as did the
Red Cross, the
World Health Organization and Israel's own lead psychiatric investigator, Albert Hefez. On August 25, 1983
Yehuda Blum, Israel's Permanent Representative to the United Nations, wrote in a letter to the UN Secretary General that the accusations of poisoning by Israel were false and "Israel medical authorities, who immediately instituted an inquiry into the matter, could not establish the existence of any organic cause." A World Health Organization inquiry also found no organic causes for "this ill-defined health emergency." The letter also cites Red Cross doctor
Franz Altherr, who felt it "was a mass phenomenon without any organic basis." In late April, a team of US medical researchers from the
Department of Health and Human Services released their own report, which "rejected contentions that 943 cases of acute illness over two weeks were caused by deliberate poisoning or were fabricated for propaganda purposes." The report "concluded that the outbreaks represented an epidemic of true psychologic illness and that the cause of this illness was anxiety." According to a report that month from the CDC, "Data collected...indicate that the West Bank epidemic was triggered either by psychological factors, or, more probably, by the odor of low, sub-toxic concentrations of H2S gas escaping from a latrine at the secondary school in Arrabah. Subsequent propagation of the outbreak was mediated by psychological factors, occurred against a background of anxiety and stress, and may have been facilitated by newspaper and radio reports that described the symptoms in detail and suggested strongly that a toxic gas was the cause. The epidemic was probably terminated by the closing of West Bank schools. No evidence...indicate[d] that patients...deliberately or consciously fabricated their symptoms".
Albert Hefez, the lead psychiatric investigator of the epidemic for the
Israeli Ministry of Health, found the illness spread through the community much like the
Tanganyika laughter epidemic, and was boosted by the reporting of the Israeli press and Palestinian distrust of Israel's intentions in the West Bank. "The social and historical context of this incident may throw light on the subsequent snowballing of events," he wrote. "The Djenin area is located in the Jordan West Bank region occupied by Israeli forces since the 1967 six-day war. The Arab population perceives the situation as a temporary occupation but some tend to believe that the Israelis would do anything to perpetuate the status quo." Hefez wrote that the outbreak took off after a March 26 article in the newspaper
Maariv headlined "The Mysterious Poisoning goes on: 56 High School Girls in Djenin Poisoned". A front-page article from
Haaretz on March 28 also fed local hysteria, he wrote. That article said Israeli investigators had found preliminary indications that
nerve gas had been used and that "Israeli army sources suspected an attempt to provoke the Arab population in anticipation of the coming '
Day of the Land.'" A
Maariv article from March 31 put forth the hypothesis that Palestinian activists were putting out a false story to provoke an uprising. Some Israeli doctors theorized the girls were playacting. In response, "the
Arab league accused Israel of using chemical weapons to exterminate Arab people, and Arab doctors from
Tul-Karem Hospital raised suspicion that the gas was intended to produce sterility in the affected girls". The epidemic had peaked by April 1, Hefez found. "The official communiqué rejecting any poisoning etiology, published in the morning paper ''Ha'aretz'' on April 1, appeared at the peak of this final wave. Although several cases appeared after this report, the panic declined". In an "Editors Note",
The New York Times apologized for its early coverage of the epidemic and how coverage had placed "greater emphasis on the charge of poisoning than on the Israeli rebuttal". The paper also apologized for quoting an Arab doctor in the West Bank without giving equal time to Israeli officials, who said he had been dismissed "as director of public health services" for "allow[ing] '
leftists' to loiter in the hospitals...discourag[ing] the hospitals from releasing the schoolgirls after they had recovered, and...trying to inflame the situation". ==Comparisons to a blood libel==