Europe was haunted for centuries by ghosts, phantoms and spectres. The majority of them have only departed by the end of the XIX century, after the spread of positivist and scientific ideas. Psychologists and psychiatrists believe that most of the effects attributed to these haunting cases were mere illusions, a result of what they call "mass psychogenic illness".

The diagnosis of mass psychogenic illness, formerly known as mass hysteria, designates the occurrence of a set of symptoms, perceptions and related beliefs among more than one individual, in the absence of any identifiable objective reason. The illness is shaped by cultural factors and is highly contagious, being transmitted by interpersonal contact, both by visual and verbal paths. It can occur to any person of a community and is not indicative of any underlying psychological illness.

Environmental threats replaced the old concerns within contemporary culture. Although the new menaces seem far more real, their risk can be easily exaggerated or extrapolated to innocuous substances. Viruses and noxious chemicals occupied the ghosts' place, and not astonishing, they have dominated the 20th century epidemic-hysteria episodes.

Cases of hysteria outbreaks originated by a "strange odour" or by food with an "unusual taste" were common throughout the last century. The most recent reported case occurred in November 1998, and affected approximately 170 people of the Warren County High School, in Tennessee. The incident occurred after a teacher had noticed a "gasoline-like" odour in her classroom and begun to complain of headache, shortness of breath, dizziness and nausea. Several of her students started to exhibit similar symptoms and were taken to the local hospital. During their evacuation, more students felt unwell and the school was closed. Almost one hundred people were hospitalised and 38 stayed overnight under care. When the school was reopened five days later, another 71 people were affected.

A research team conducted by the epidemiologist Timothy Jones was appointed to study this case and the results were published early this year in the New England Journal of Medicine. Despite of the exhaustive analysis carried out, no environmental explanation for the sickness was found. Furthermore, the symptoms were characteristic of psychogenic illness and significantly associated with non-environmental factors, such as seeing another ill person, female sex, and reporting an unusual odour. Their conclusion was that "this illness, attributed to toxic exposure [during the outbreak], had features of mass psychogenic illness - notably, widespread subjective symptoms thought to be associated with environmental exposure to a toxic substance in the absence of objective evidence of an environmental cause". Nevertheless, for the community, the investigation was simply ineffective to find the real causes, or have tried to cover them.

The Tennessee case is one of a long series and its conclusions were partially based on prior research carried out on similar schools incidents by Francois Sirois and Robert Bartholomew. This kind of hysteria was found to involve the existence of an extreme anxiety following by the redefinition of an ordinary experience, frequently an unfamiliar odour or an illness in a fellow student. The illness tends to be first manifested by an individual student and is transmitted retrospectively to others. Since the search for explanations is conditioned by educational and cultural knowledge, blame is usually attributed to the odour, identified as a toxic gas, and understood as an immediate menace. As a consequence of the explanation process, in non-Western traditional cultures the causes continue to be attributed to supernatural entities.

The Auckland Merphos' and the American Phantom Gassers

What do the Tennessee outbreak, the episode of the Auckland merphos and the phantom gassers that terrorised Virginia and Illinois have in common? The answer is simple. All are cases of psychogenic illness that reflect the 20th century heightened awareness of air pollution.

The case that occurred in Auckland, New Zealand, in 1973 is truly paradigmatic. This incident started after the leaking of several barrels of merphos, an innocuous chemical compound, and the spread of its vapours. Inquires concerning potential treats to health were conducted immediately and the authorities were wrongly informed that the compound was extremely toxic. Just after the announcement of its danger, nearly 400 workers and nearby residents started exhibiting psychogenic symptoms: breathing difficulty, eye irritation, headache and nausea.

Similar symptoms were presented by victims of the American gassers, the mysterious figures thought to attack house occupants using hazardous gases. The symptoms were attributed to strange odours, and all the episodes were extensively reported by the media. The attacks were investigated and invariably stopped after the authorities had claimed that the smell was inoffensive.

A major role in these processes can be attributed to the media and other sources of information thought as credible, since they usually bore the background for the hysteria explanations and for the redefinition of reality. It is now understood that the gasser phantom episodes reflect the American fear of air pollution hazards, particularly of chemical weapons during the Second World War.

The Haunted Houses - Sick Building Syndrome

Despite the fact that most sick building syndrome cases seem to be caused by environmental factors, some outbreaks lack an identifiable natural cause and have also been associated with mass psychogenic illness. Moreover, the symptoms do not present a defined pathology and rarely persist when the persons leave the building. The victims complaints include headache, lethargy, breathing problems, and mucous membrane irritation. The symptoms extension can be very high, affecting up to 80% of the occupants.

Some studies, mostly European, have observed that the sick building syndrome was associated with sealed buildings, with central heating, ventilation and air conditioning systems, especially those artificially humidified. The symptoms were initially thought by earlier researchers to be a result of inadequate dilution of indoor air pollutants. However, this hypothesis was never proven and a recent study showed that no reduction in symptom prevalence normally occurs when ventilation system is improved. It was also observed that the syndrome was related with several non-environmental variables, including occupational satisfaction factors, environmental perception and control, as well as personal factors, like gender or stress issues. Notwithstanding, many of these elements can amplify, camouflage or complicate symptoms caused by chemical pollutants.

The Halifax Camp Hill Medical Centre, Canada, is emblematic of the haunted buildings. Between 1989 and 1993 more than 70% of the staff of the Hospital have exhibited symptoms thought to be related with air contamination. Withal, complaints persisted after the eradication of possible causes and further enquire found strong associations with non-environmental factors. The incidents were then attributed to the syndrome, but a large group of workers have never accepted this verdict and refused to return to the Hospital. They claim that their symptoms are related to extremely low concentration of chemicals, to which they are particularly sensitive. In other words, they claim to suffer from the polemic multiple chemical sensitivity.

Multiple chemical sensitivity syndromes first appeared during the 1950s, but scientist never entirely accepted it and often qualified it as hysteria. The absences of typical immune responses by people who allege to be affected serve as bases to the scepticism of the medical community. Furthermore, the "20th century disease", as some have called it, was also found to be influenced by psychological factors. However, it is argued that psychological contributions to the syndrome do not imply that it is entirely psychological or that the problem is imaginary.

The syndrome raised some important political issues. For example, can sufferers of an imaginary problem receive disability pensions or insurance premiums? The Canadian government, among others, has invested several million dollars in research facilities to fathom the many unsolved questions concerning the chemical sensitivity syndrome. Some call these centres the "cutting edge", others the "laughingstock of the medical community".

Rethinking Hysteria and Pollution

Both reports and studies concerning mass psychogenic illness have increased recently. However, its nature and causes remain surrounded by uncertainties. The weakness of explanations has turned it into a field of competitive theories. Nevertheless, the diagnosis of "mass hysteria" as a diagnosis of exclusion, simply based in the indetermination of pollutants, is presently avoided.

The hysteria symptoms result from the conversion of fears and preoccupations that define each era. In this sense, air pollution can be viewed as the 20th century ghost. Indeed, these fears gain resonance since they are not always illusory: the cases of Bhopal, Chernobyl or Seveso, provide a fertile soil for psychogenic epidemics.

The boundaries between psychology and physiology aren't sharply defined. Can hysteric reactions to perceived peril represent a remnant of old animal defence, still present in the ancient parts of the human brain, but whose true propose were lost during evolution?

In the shadows that cover these questions, one thing is sure. Even if unjustified, psychogenic illness and associated fears are real, and constitutes one more disease to add to the dark list of consequences of air pollution.

Further Reading:

• Bartholomew R. E., Sirois F. (1996) Epidemic hysteria in schools: an international and historical overview. Educational Studies 22(3), 285-312
• Bartholomew R., Wessely S. (1999) Epidemic Hysteria in Virginia: The Case of the Phantom Gasser of 1933-1934. Southern Medical Journal 92(8), 762-770
• Jones T. F., Craig A. S., Hoy D., Gunter E. W., Ashley D. L., Barr D. B., Brock J. W. and W. Schaffner (2000) Mass Psychogenic Illness Attributed to Toxic Exposure at a High School. The New England Journal of Medicine 342(2), pp. 96-100
• McLeod W. R. (1975): Merphos poisoning or mass panic? Australian and New Zealand Journal of Psychiatry 9: 225-229
• Lehrer P. M. (1997) Psychophysiological hypotheses regarding multiple chemical sensitivity syndrome. Environmental Health Perspectives Supplements 105(2), 479-484