This outbreak has many of the features classically associated with mass psychogenic illness. Mass psychogenic illness has been defined as a constellation of symptoms suggestive of organic illness but without an identified cause in a group of people with shared beliefs about the cause of the symptoms.7 It is a social phenomenon, often occurring among otherwise healthy people who suddenly believe they have been made ill by some external factor. Outbreaks of mass psychogenic illness affect girls and women more frequently than boys and men.1 The incidents often occur after an environmental event or trigger, such as an odor,1,2,8-10 and are frequently preceded by an index patient's illness and a prominent response by emergency personnel to the event or illness.1,2,8,11-13 Contagion is increased by the proximity of affected and unaffected persons, reassembly of the group, and “line of sight” transmission.1,8 Although symptoms may suggest an environmental cause, none can be identified quickly, and other persons who are putatively exposed do not become ill.

Such outbreaks often involve a very rapid spread of symptoms (frequently including hyperventilation or syncope), with minimal physical findings, and often occur in groups under physical or psychological stress. Dramatic and prolonged media coverage frequently enhances such outbreaks.7,11,13-16 Many of these factors appear to have played a part in the outbreak at the high school in Tennessee. Intensive media attention probably heightened the collective anxiety and may have contributed to the second cluster of cases.

Despite an exhaustive evaluation, no environmental cause of the reported illnesses was identified. The normal laboratory findings and reassurances about the safety of the school were widely publicized. Nonetheless, more than one month after the outbreak, local media continued to report on persons with persistent headaches that they believed were related to exposure to a toxic substance at the school, and rumors of incompetence and coverup on the part of the government persisted. Some people believed that the investigation had simply failed to find the real cause of the illness. Paradoxically, in such circumstances, the observation of vigorous investigative activities may reinforce the suspicion that a genuine problem is being covered up. Persistent investigation also increases the likelihood of false positive results, which must then be explained to an apprehensive community.

In this case, many ill persons noted a smell at the school on the first day of the epidemic. There was no consistency in the reported quality or location of the odor. Many persons who did not become ill, including school administrators and emergency personnel, also noted an odor on the first day of the outbreak, though it was not consistently described by this group either. The pattern of illness in the school did not reflect a particular route of air distribution. It is difficult to conceive of any toxic gas or other toxic substance in the environment that would account for such variations in the description and location of the odor and for such a wide range of self-limited symptoms in persons scattered throughout a large building, with no evidence of abnormalities in any environmental or laboratory tests.

Rash has been reported in several outbreaks of mass psychogenic illness.1,13,17 The rash often occurs on exposed skin in a distribution that suggests scratching as the cause.13,17 In this outbreak, rashes were not consistent among those reporting them, and they were not suggestive of exposure to a particular toxic substance.

The costs associated with outbreaks of mass psychogenic illness have not been extensively studied.1 The costs that could be quantified in this case were substantial, and they represent an underestimate of the overall resources expended. For example, labor and equipment costs incurred by government agencies and laboratories that participated in the investigation are difficult to assess. In addition, the costs of disruption to the community are difficult to quantify, but they can be substantial.

Outbreaks of mass psychogenic illness are probably more common than currently recognized. When an outbreak of mass psychogenic illness is described to an audience of experienced public health professionals, the consistent response is an outpouring of similar “war stories.” Mass psychogenic illness should be considered in any outbreak of acute illness thought to be caused by exposure to a toxic substance but with minimal physical findings and no environmental cause that is readily apparent to the investigators.

Many public health professionals acknowledge that, before embarking on an investigation, they have had a strong sense that an outbreak was psychogenic but that because of intense anxiety in the community, they felt obliged to pursue the investigation beyond what they thought was necessary. It is very difficult — if not impossible — to prove beyond any doubt that a toxic exposure has not simply escaped detection. In this case, three senior officials in the state health department independently suggested mass psychogenic illness as the likely cause before the full investigation was launched. During the investigation, some news reporters, school administrators, and students suggested that the outbreak had a psychogenic component, although such views were never widely publicized. There are no pathognomonic indicators of mass psychogenic illness. Establishing the diagnosis often entails ruling out a long list of potential, sometimes far-fetched, causes. Extensive investigation is often necessary before officials are willing to inform an anxious community of the diagnosis.

With any approach to mass psychogenic illness, the goal should be to restore the community to normal functioning as quickly as possible. Prompt public identification of episodes of mass psychogenic illness has been advocated as an important step in terminating them,8,18 but such an approach can be problematic in practice. Physicians and others are understandably reluctant to announce that an outbreak of illness is psychogenic, because of the shame and anger that the diagnosis tends to elicit. In this instance, a multiagency environmental response was already under way at the time of the epidemiologic investigation, making such an approach untenable. Public announcements that the various tests were normal and that the school was safe were made without any references to the episode as psychogenic, and the outbreak subsided. Either approach may be met with anger and mistrust on the part of the community.

Alleviation of the widespread anxiety surrounding an episode of mass psychogenic illness requires prompt recognition and a coordinated multiagency investigation. As fears about bioterrorism increase, the frequency of such incidents and the anxiety they generate may increase. Awareness of the characteristics of mass psychogenic illness is critical for physicians and other health care personnel who respond to such outbreaks.