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Multiple Chemical Sensitivity, MCS

5 Frequency

5.1 Prevalence
     5.1.1 Prevalence of MCS in occupational medicine materials
5.2 Incidence
5.3 Prevalence according to environmental physicians and patient associations
     5.3.1 Frequency of MCS in Denmark according to patient associations
5.4 Comments

5.1 Prevalence

When an illness to be investigated is not finally defined, it is difficult to find comparable epidemiological results. This is because the different research groups trying to describe the frequency of an illness find it difficult to adhere to common rules for defining illnesses, reporting, classification, selection etc.

Mooser (1987) presumed the prevalence of MCS among people in the US to be 2-10%. He included people with MCS, who were forced to rearrange their daily lives as a result of their symptoms. Many experts, including Cullen (1994), regarded these figures as much too high.

The group behind the Interagency Report has only found three investigations with figures on prevalence published up to 1997. Two additional investigations have been made since then. These have all put standardized questions over the phone, to persons chosen randomly among a previously defined group of people or people from a geographical region. All investigations were made in the US.

Prevalence by objective diagnosis:

The people interviewed were asked whether a general practitioner had diagnosed MCS. The positive answers show the following frequencies:

Subjective experience (“self reported disease”) of the people interviewed have produced more material on the prevalence of MCS.

Prevalence by subjective diagnosis:

Questions of whether exposure to several of the substances fresh paint, pesticides, perfumes, automobile exhausts gasses, and new carpets gave moderate or strong health complaints (needed to see a doctor, took medicine, was reported ill) gave the following frequencies of positive answers:

Bell comments that their figures depend directly on how the questions about “having health complaints or feeling ill” were formulated. Based on a more detailed list including, e.g., new carpet, fresh printing ink, disinfectant, paint, natural gas, perfume, tar, pesticide, automobile exhaust, and tobacco smoke, the same group of researchers also investigated whether the students had symptoms due to one or more ”environmental odours”. Almost 10% had symptoms sometimes or often, while 28% had symptoms due to very few of the factors listed.

Baldwin's (1977) investigation covers symptoms due to out-of-doors as well as indoor air pollution among public employees working in modern well-insulated buildings.

Meggs interviewed randomly selected adults (general public) living in the rural areas. Among 51%, three groups of equal size had only allergy, only MCS, or both allergy and MCS. 3-5 of the substances in the list above produced symptoms in 33% of the two latter groups. Only 49% had neither allergy nor MCS symptoms. The authors were surprised at the high frequency, since they had expected a lower frequency of MCS in the rural areas than in the city.

Black's investigation by phone interview included 3700 soldiers divided into two groups, those who had taken part in the Gulf War and those who had not. The frequency of sensitivity to at least two substances from the usual list of trigger substances described above was surprisingly low (2.6%), and similar to objectively diagnosed MCS (by physicians), in soldiers who had not participated in the Gulf War. Black mentions that only 0.2% of the soldiers in the latter group had been diagnosed as having MCS by the military physicians. This corresponds to Bell's frequencies of MCS diagnosed by physicians among college students.

5.1.1 Prevalence of MCS in occupational medicine publications

Kipen (1995) investigated complaints of MCS-like complaints from various groups of people referred for examination at a clinic of occupational medicine or a general practitioner. He asked whether exposure to one or more of 23 trigger substances had created discomfort or had forced the individual to leave the room, quit the job, etc. The positive answers were distributed as follows:

In this last group significantly more of the 23 substances chosen created symptoms than in the other groups. The group referred due to asthma delivered a similar, though less accentuated, result. Kipen did not investigate whether persons from the four control groups, who had given positive answers, had MCS or not.

The table below shows the prevalence of MCS or similar conditions among occupational medicine patient groups.

Table 5.1 Prevalence of MCS and odour sensitivity in occupational medicine materials (W = women)

The papers cited in the table above (also mentioned in chapter 4) give an interesting perspective of the prevalence of odour sensitivity and MCS respectively. While the two papers from the US (Lax and Cone) use the traditional MCS definition to identify possible MCS patients among a mixed occupational medicine clientele, the three groups from Denmark, France, and Sweden describe two stages of development of MCS.

The condition described by Gyntelberg possibly corresponds to odour sensitivity and can be regarded as an initial stage of MCS, while the groups in the French and Swedish material fulfil Cullen's MCS criteria.

The materials from the US and Europe are different regarding sex. This can be because comparatively more men in Europe can be exposed to organic solvents at work. Lindelöf's investigation of housepainters in Stockholm probably involves an effect of selection. But it is surprising that so many women appear in the American occupational medicine materials.

The European and American materials do not appear to be comparable.

It should be added that Lindelöf's housepainters are still working in spite of MCS. The other materials contain no information on the social situation of the people investigated.

5.2 Incidence

Most American investigations confirm only two common characteristics of MCS patients regarding the incidence of MCS, found in the literature (Cullen, 1992; Sparks, 1994):

1. Most patients are women.
2. They are more than 30 years old, when symptoms first appear.

Kreutzer (1999) included a large proportion of the people in California in his investigation. But he found no differences due to race, place of residence, education, or social situation among the positive answers.

Miller and Mitzel (1995) investigated the socio-economic aspects of MCS. In 83% out of 112 persons with MCS (Cullen's definition), the illness started when they were more than 30 years old. 81% of these were employed full time when the illness started, as opposed to 12% when they were interviewed. The symptoms have forced most of the group to take up other vocations. 40% have consulted more than 10 physicians for help.

5.3 Prevalence according to clinical ecologists and patient organisations

Descriptions based on the experiences of clinical ecologists and MCS patient organizations in the US contain much information on the frequency of MCS. Spyker (1995) from an ecological environmental clinic in the US finds that the average age of MCS patients is 40 years and that 77% of them are women. Rea (1992), whose 4-volume publication ”Chemical sensitivity” describes his experiences through 20 years with more than 30,000 patients with environmental illnesses, corroborates these figures. Not all patients have been diagnosed with MCS. The incidence is based on definitions of illness and symptoms, which cannot be compared with other literature and, therefore, can hardly can be used in the context of this report.

5.3.1 Frequency of MCS in Denmark according to patient organisation

The Danish MCS Organisation estimates that 4% (200,000) of the population in Denmark has MCS. This figure is based on frequencies from the US. The organisation says that many cases of headache at work could be symptoms of non-recognized MCS due to exposure to chemicals.

5.4 Comments

There is some epidemiological documentation for the existence of MCS in the US, Canada and Europe. The frequency is about 0.2-6% in the US.

No certain data exist for Europe. In both Sweden^[1] and Germany^[2] nationwide investigations of the frequency of MCS were completed in 2001. The data had not been published, when this report was finalized (see also Annex H).

Danish occupational physicians estimate the prevalence of MCS in the Danish population as a whole to be 0.1-1%. The higher prevalence figures, shown for the US compared to Denmark, can have many causes. One could be that Americans are more often exposed to chemicals, and not least indoors. Another could be that there are comparatively more clinical ecologists with knowledge of MCS, who diagnose and treat MCS patients in the US, whereas in Scandinavia, at least, it is mostly specialists in occupational and environmental medicine (to whom the MCS diagnosis is more controversial), who get these patients.

In the US, MCS is mostly an indoor illness in women of about 40 years of age.

The prevalence of MCS in occupational medicine patient groups in the US and Denmark is about equal, 1-12 %. These figures apply to a limited group with greater risk of acquiring MCS than people in general.

In connection with a possible strengthening of MCS research in European, one of the most important tasks will be to get more reliable figures on the prevalence of MCS.

Table 5.2 Prevalence of MCS in Denmark and the US

Footnotes

[1] Institute of Environmental Medicine, Karolinska Instituttet, Stockholm, Sweden

[2] Umweltbundesamt and Robert Koch Institute, Berlin, Germany

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Version 1.0 March 2005, © Danish Environmental Protection Agency