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Sweep's Library: Chronic Exposure to CO

What follows is an overview and excerpts from THE EFFECTS OF CHRONIC EXPOSURE TO CO, a detailed study sponsored by the British non-profit organization CO Support.

CO Support was founded by Debbie Davis in 1995 after her health was destroyed by a leaking flue from a gas fire in the living room. Her aim was to set up a support group for other sufferers, and to gain as much information as possible about the long term health effects of CO poisoning. Even with limited publicity, a large number of people have sought help from the group, and the membership of CO Support has grown rapidly.


The objectives of CO Support are to:

· provide support and advice to those who have suffered from exposure to CO;
· raise awareness amongst the medical profession and the general public of the symptoms of chronic exposure to CO, a condition which is often undiagnosed;
· prompt further research into the long term effects of chronic exposure; and
· identify the circumstances of chronic exposure with a view to identifying who might be at risk.

CO Support found that currently there is little medical evidence on the effect of long term (chronic) exposure to CO. This is in marked contrast to the effects of a sudden acute exposure to CO, which has a considerable medical literature. The most recent medical article to explore chronic exposure to CO was published in 1936 . Sixty years later, in 1996, the members of CO Support decided that it was time to revisit the problem in a rigorous way. Those contacting CO Support, having been affected by CO, were asked to complete a comprehensive questionnaire. This report describes their experiences.

The key findings of the study are:

1. Those suffering from chronic exposure to CO experienced a wide range of symptoms, including memory loss, severe muscular pain, headaches, tiredness and dizziness;

2. In many cases, these symptoms continued for years after the exposure ceased. Although some people have recovered completely, a significant proportion remain permanently incapacitated and unable to work;

3. GPs failed to diagnose chronic exposure to CO. In only one case out of the 77 studied was exposure identified on the basis of symptoms alone;

4. Misdiagnoses included flu, viral infection, depression, ME, and psychosomatic illness. Often no diagnosis was given at all;

5. In the majority of cases, the presence of CO was discovered by servicing or investigation of the offending appliance. In some cases warning was given by an alarm or detector. In others, the collapse of one family member drew attention to the problem;

6. In many cases, regular servicing of the appliance failed to identify the problem. In some cases servicing took place regularly during an exposure lasting several years;

7. Around 70% of chronic exposures took place in people's own homes;

8. Two thirds of sufferers were women, with most aged between 30 and 45 years;

9. Very few sufferers were offered a carboxy haemoglobin (COHb) test to determine the extent of their exposure. Where tests were performed, there was also evidence of misinterpretation of the results by hospitals and GPs.

Section 8 of the paper explores the extent to which doctors were able to diagnose exposure to CO on the basis of their patients' symptoms. Out of 65 cases of chronic exposure, only one case was correctly diagnosed on the basis of symptoms alone, with two further cases where diagnosis was assisted by the context of the case.

This finding of widespread diagnostic failure by GPs is supported by a recent UK study. 200 GPs were given a description of the symptoms of carbon monoxide poisoning, namely nausea, headache, lethargy and flu-like symptoms, and asked for possible diagnoses. Not one doctor raised CO as a possibility.

The potential for misdiagnosis of CO exposure has also been highlighted in the medical literature. Again this supports the findings of the current study, which found extensive mis-diagnosis.

Moreover, a 1985 study suggested that there is extensive under-recognition of the number of deaths due to CO in England and Wales. By collating detailed hospital records, this study found a total of 1,365 deaths that were attributable to carbon monoxide poisoning, in a year when the official statistics stated there were just 475 hospital admissions and 10 deaths from CO poisonings.

Together, these findings suggest that chronic exposure to CO remains a largely hidden problem. Further research is urgently required into the extent of missed and mis-diagnosis of CO poisoning by hospitals and GPs. Indeed, the sample on which the present study is based involved only those who had contacted a small and relatively unknown charity for help. The fact that over 100 such people emerged during a period of one year is suggestive that the problem may be more widespread than is commonly recognised.

Section 9.2 explores possible prevalence of Chronic CO Poisoning, highlights the difficulty of identifying chronic CO poisoning and suggests that it is a widely under-recognized problem. This section considers briefly what wider evidence is available that could cast light on the prevalence of exposure to chronic carbon monoxide. As there has been no systematic investigation, the available evidence is incomplete and largely circumstantial. However, the following facts show cause for concern:

· Central heating is now installed in a majority of homes; in 1965 only 7% of homes had central heating, compared with 75% in 1993.

· Gas central heating has risen from 24% of households in 1976 to over 60% in 1991.

· Nearly half of all homes now have full or partial double-glazing, compared with only 3.9% in 1970. It is possible that this has led to reduced ventilation of rooms and the consequent build up of fumes from appliances.

In addition, there are a number of epidemiological puzzles that have emerged over a similar period:

· Britain appears to have much larger numbers of 'excess winter deaths' than other countries, and that a contributing factor might be increased sensitivity to allergens, a symptom associated with CO poisoning. Exposure to gas exhaust may also be associated with exposure to nitrogen dioxide, which has been cited as a possible cause of respiratory problems. One study found an association between gas appliances (particularly cookers) and respiratory problems.

· Recently diagnoses such as ME and Chronic Fatigue Syndrome have become more common. The similarities between the symptoms of these conditions and those of chronic CO exposure raises the possibility of misdiagnosis.

· A study of schoolchildren found that between 1964 and 1994 the incidence of wheezing and shortness of breath had doubled. (Wheezing had increased from 10.4% to 19.8% and shortness of breath from 5.4% to 10%). The incidence of hay fever amongst boys had also increased from 49.4% to 60%.

· Between 1971 and 1992 the incidence of migraine has increased by 23% for males and 50% for females .

· A recent major survey of GP's shows that 18.3% of patients were substantially 'fatigued' for six months or longer, and that 30% of these patients combined fatigue with muscle pain.

The above evidence is necessarily circumstantial. However, the general picture is one of widespread rises in the potential for domestic exposure to CO accompanied by unexplained increases of the symptoms of chronic exposure (such as headaches, dizziness, respiratory problems and heart failure), together with increases in conditions which might reflect misdiagnosis (such as ME and influenza).

Taken together, these factors reinforce the urgency of further investigation into the extent and consequences of low level chronic exposure to CO.

Section 9.3 concerns the similarity of symptoms between ME, Chronic Fatigue Syndrome, and carbon monoxide poisoning. This study provides a number of indications that some degree of misdiagnosis of CO as ME is ocurring. First, it is noteworthy that in this study three people within the chronic group were misdiagnosed as having ME or CFS. Secondly, many of the CO sufferers in the study experienced, and continue to experience, muscle pain which is thought to be a characteristic of ME. It is also significant that the age/sex profile of the chronic group was very similar to what has come to be recognised as the profile of a "typical" ME patient. Twice as many women were affected as men, with an age group of 30s to early 40s.

In addition, ME patients often suffer tiredness for many years. One study quoted an average of 9.2 years , which is consistent with the long periods over which the symptoms of tiredness and muscle pain were experienced by the chronic and unconscious groups in this study.

Finally, the Wilson study found that 65 out of 103, ie 64% of chronic fatigue syndrome patients had improved three years later, but that many patients remained functionally impaired. These results are remarkably similar to this study's finding that over 40% of the chronic group were unable to work or walk far at the time of the survey, which was itself some time after exposure ceased.

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