British M.D.s See Increase In Psychiatric Comorbidity

General practitioners in England and Wales appear to be seeing more and more patients who have a substance abuse disorder and another psychiatric illness—especially a serious psychiatric illness and a substance abuse problem.

This trend was reported in the December Journal of Epidemiology and Community Health by Ilana Crome, M.D., a professor of psychiatry at the University of Keele University in Staffordshire, England, and co-workers.

Their study was based on information submitted by 230 general practitioners in England and Wales to the General Practice Research Database—purportedly the world's largest computerized database of patient records. The information concerned the number of patients they had diagnosed from 1993 to 1998 for psychiatric illnesses, substance abuse (excluding alcohol and tobacco), or both.

The researchers used the information to determine the annual period prevalence of psychiatric illness–substance abuse cases during each of the five years—in other words, the annual number of comorbid patients seen in general practice in England and Wales during each of the years.

They based their calculations on “patient years of exposure” rather than on “number of registered cases” since the length of time that patients visited general practitioners for their comorbid problems varied. For example, a patient who registered with a general practitioner on January 1, 1993, and who left on January 1, 1994, would have received a value of “one person year” in the study. In contrast, a patient who registered with a general practitioner on January 1, 1993, and who left on July 1, 1993, would have received a value of 0.5 person years in the study.

The number of annual prevalent cases for a particular year—how many patients were diagnosed for both substance abuse and another mental illness within that year—was then divided by the patient years of exposure for that particular year, giving the annual period prevalence for that year.

The investigators then compared the annual period prevalence of comorbid cases for each of the five calendar years of interest and found that it increased about 10 percent each year. In fact, the annual period prevalence of comorbidity increased from 50/100,000 patient years of exposure to 80/100,000 patient years of exposure during the five-year study period, representing a 62 percent increase during the study period.

What's more, rates of serious psychiatric illness combined with substance abuse grew even more over the five-year period—rates of schizophrenia comorbid with substance abuse rose 128 percent, and rates of psychoses comorbid with substance abuse rose 147 percent.

The question now is why such a surge occurred. Does it mean that more people were seeking help for comorbid psychiatric–substance abuse problems during the five years of the study than before? Or does it mean that more people were experiencing comorbid psychiatric–substance abuse problems during the five years of the study than before? The researchers believe that the latter explanation may be correct, because, as they pointed out in their study report, the population used in their study was around one million patients a year.

“The prevalence observed in the study can be expected to closely mirror that in the general population.” Still, they noted, the data they used for their study missed people “whose mental illness or drug use never results in primary care service contact.”

Regardless of reason, if the increase in the number of people with comorbid mental illness and substance abuse continues, the researchers pointed out, the average family doctor who saw seven such patients in 1998 will be seeing 14 in 2006. These results, the investigators said, should help inform policy debates in the United Kingdom about general practitioners' care of patients who have both psychiatric illness and substance abuse problems.

“The role of the general practitioner in providing shared care for substance misusers is increasingly being encouraged,” they wrote,“ and family doctors are increasingly becoming the first point of contact for young drug misusers, although misgivings have been expressed about treatment of drug users in primary care.”

The study was funded by the Department of Health.

An abstract of the study, “Prevalence of Comorbid Psychiatric Illness and Substance Misuse in Primary Care in England and Wales,” is posted online at<http://jech.bmjjournals.com/cgi/content/abstract/58/12/1036>.▪

BMJ 2004 58 1036