Discussion of Results
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.
Failure of Diagnosis
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.
Possible prevalence of Chronic CO Poisoning
The above discussion highlights the difficulty of identifying chronic CO poisoning and suggests that it is a widely under-recognised 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 perhaps twice the level of Scandinavia or Germany, for example. Hidden influenza was identified as potentially a significant factor that should be investigated further.
- A recent study highlights an urban-rural gap in death rates, which requires investigation. The worst places appear to be those cities with higher proportions of rental accommodation.
- There is evidence of a rise in dizziness, giddiness, headache, chest pains and nausea of between 30 and 40% since 1970.
- The steep rise in the incidence of asthma is well known. This has occurred particularly among the lower social classes, females and children and old people. Between 1971 and 1992, asthma incidence rose by 114% for males and 165% for females. Although there is no known direct link to CO exposure, it has been suggested that a factor contributing to the increase might be increased sensitivity to allergens. Exposure to CO 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 Aberdeen 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 GPs 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 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.
ME and Chronic Fatigue Syndrome
The similarity of symptoms between ME or Chronic Fatigue Syndrome and chronic carbon monoxide poisoning warrants further investigation. 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 studys 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.
The Effects of Chronic Exposure to CO
The study has found that those exposed to CO suffered a wide range of symptoms both during exposure and on a continuing basis. A major issue, therefore, is the likely extent of recovery.
The evidence from the study cannot be conclusive on the extent of recovery, as it provides a snapshot of a group of people who differ in the length and severity of exposure, and in the length of time since the exposure ceased. The study also cannot rule out the possibility that in some cases exposure to CO has continued unbeknownst to the sufferer.
Nonetheless, the results provide the following broad picture:
- since their exposure ceased, many people have recovered from some of the symptoms suffered during exposure, as seen from the improvement in incidence of symptoms;
- a few people had recovered completely by the time of the survey; but
- many still suffer from continuing symptoms, although the severity of the problem has lessened in some cases; and
- a significant minority of people remain significantly impaired as a result of their exposure. Moreover
- family or previous medical history appears to play a small role in explaining the incidence of symptoms.
The study also found that a large majority of patients suffered from pain during and after exposure to CO. Currently there is no evidence cited in the medical literature on this issue, and pain is not widely recognised as a consequence of CO exposure. However, the numbers of people reporting similar symptoms makes alternative suggestions, such as the so-called "litigation syndrome" unconvincing. Fewer than half of the group studied were in the process of litigating, and for those in the litigation process pain and its incapacitating effect were not generally cited as part of the complaint.
Research in this area is clearly hampered by failure of doctors to obtain reliable measures of the extent of exposure through measurement of COHb levels in those exposed on a chronic basis. Further research is needed into the effects of chronic sub-lethal exposure and the factors that contribute to full recovery. Research is also needed into the appropriate treatment for chronic exposure. Recent evidence suggests that hyperbaric treatment can yield positive results even if delayed for some time.
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