Department of Psychiatry, Dalhousie University and Health Outcome Unit, Capital District Health Authority, Halifax
Population Health Research Unit, Dalhousie University, Halifax, Canada
Centre for Developmental Health, Curtin University of Technology, Telethon Institute for Child Health Research, Perth, Australia
Population Health Research Unit, Dalhousie University, Halifax, Canada
Correspondence: Dr Stephen Kisely, Dalhousie University, Abbie J. Lane Memorial Building, 5909 Veterans Memorial Lane, Suite 9211, Halifax, Nova Scotia B3H 2E2, Canada. Tel. +1 902 473 7356; fax +1 902 473 4887; e-mail: Stephen.Kisely{at}cdha.nshealth.ca
Declaration of interest None. Funding detailed in Acknowledgement.
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ABSTRACT |
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Aims To evaluate the mortality risk in mental illness for patients in contact with psychiatric services or primary care (n=221 048) across Nova Scotia (population 936 025).
Method A population-based record-linkage analysis was made of the period 1995-2000, using an inception cohortto calculate mortality rate ratios.
Results The mortality rate was 1.74, with increased ratios for all major causes of death. Male mortality was almost double that of females after controlling for demographic factors, treatment setting and place of residence. Patients of lower income, in specialist psychiatric settings, and with dementia or psychoses were also at greater risk. However, in absolute numbers, 72% of deaths occurred in patients who had only seen their general practitioner.
Conclusions Mortality risk is increased in all psychiatric patients, not just those who have received in-patient treatment.
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INTRODUCTION |
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METHOD |
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Under the Canada Health Act 1984, all Canadian residents are entitled to in-patient or out-patient care that is free at the point of delivery. Patients receive treatment at publicly funded facilities or are seen by private psychiatrists or general practitioners in the community, who then bill the provincial health plan. However, the provincial health plan does not cover visits to private psychologists or other mental health professionals in private practice. There are no private psychiatric beds. Our linked administrative databases therefore cover health service use in the public and private sectors across the whole province, including in-patient, out-patient and community contacts with both specialist services and primary care. We used the following anonymised databases to identify patients for our study:
We measured mortality rates using the Canadian Vital Statistics Database, calculated using the inception cohort method. We restricted the cohort to patients whose first psychiatric contact occurred between 1995 and 2000. Follow-up started at the date of first contact. Patients were censored at death. This method has greater validity as all the follow-up time at risk is included, thereby reducing survivorship bias. The ethics committee of Capital District Health Authority approved the protocol.
The validity of the Discharge Abstract Database has been evaluated in seven reabstraction studies and been found to have an accuracy rate of 9799% for in-patient demographic data, including gender, age, treating physician, admission and discharge dates, and discharge destination (Ontario Hospital Association et al, 1991; Williams & Young, 1996). Information on the validity of other administrative data is more limited (Kephart et al, 2003), but there are precedents in other parts of Canada for the use of data on health service use and physician billings in the study of chronic illness (Clottey et al, 2001; Strom, 2001). Finally, although the administrative databases use ICD9 diagnoses (World Health Organization, 1978), mental health clinicians make their diagnoses using the Diagnostic and Statistical Manual of Mental Disorders (DSMIV; American Psychiatric Association, 1994). Mental health professionals in publicly funded facilities also attend DSM training courses to improve diagnostic accuracy. These DSM diagnoses are converted to ICD9 codes using a conversion table.
Classification of mental disorders
We used the method developed by Lawrence et al
(2000) to group cases in terms
of severity of diagnosis. We used the final diagnosis in each episode of care,
and gave preference to diagnoses made in hospital care over out-patient or
primary care.
We grouped disorders into dementia and other organic conditions (ICD9 codes 290294), functional psychoses (schizophrenia and non-affective psychoses, ICD9 codes 295, 297299 except 298.0), alcohol and drug disorders (ICD9 303305), mood disorders (affective psychoses, ICD9 296; reactive depressive psychosis, ICD9 298.0; neurotic depression, ICD9 300.4; depression not otherwise specified, ICD9 311), neuroses (ICD9 300 except 300.4), personality disorders (ICD9 301), adjustment reactions (ICD9 308309), other mental disorders (all remaining Chapter 5 diagnoses and non-specific diagnoses outside Chapter 5). We did not include non-Chapter 5 diagnoses of patients only attending primary care, as they would not necessarily be psychiatric. However, we included non-Chapter 5 diagnoses in patients of specialist services, because referral to psychiatric services implied some psychiatric morbidity. This method ensured comparability with previous Australian work that also included non-Chapter 5 diagnoses (Lawrence et al, 2000). We did undertake a sensitivity analysis of excluding the non-Chapter 5 mental disorders diagnoses in the specialist group.
Calculation rates
We calculated age-adjusted and gender-adjusted mortality rates using direct
standardisation. Average population distributions in Nova Scotia from 1995 to
2000 inclusive were used as the standard weights. The follow-up period began
on the date of the patients first contact with a clinician. We censored
patients at death or on 31 December 2000. Rates were calculated by principal
diagnosis by type of care received and cause of death. Mortality rates were
also calculated in the rest of the Nova Scotian population by cause of death
and gender. Denominators were taken from estimated resident population counts.
Mortality rate ratios were calculated in the study cohort relative to the rate
in the provinces population. We compared a direct standardised
mortality rate by psychiatric diagnosis, cause of death, diagnostic case
complexity and treatment setting. We used a hierarchy of in-patient
v. out-patient and specialist v. primary care, reflecting
both the increasing proportion of patients with severe mental illness and data
reliability. It also allowed comparison with Australian data
(Lawrence et al,
2000).
Regression analysis
We used proportional hazards regression to examine the risk of death from
time of first contact for psychiatric disorder until death or censoring at the
end of follow-up (31 December 2000). We included principal psychiatric
diagnosis, age (in 10-year increments), gender, socio-economic status,
treatment setting and place of residence (metropolitan Halifax or elsewhere in
the province). Socio-economic status was assigned according to the 1996
census-derived average household income by residential postcode
(Kapral et al, 2002).
Income levels of the study population were classified into the quartiles of
the 1996 census average household income by postal code to the 1999 Nova
Scotian population (we used the address recorded at the time of the initial
contact). All analyses were completed using SAS version 8.
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RESULTS |
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Specialist psychiatric settings
Mortality rate ratios were particularly high for patients who had been
treated in specialist services (Table
1). Within the specialist group, mortality rates were similar in
people who had received in-patient, out-patient and private specialist
treatment in the community (Table
1). Males had significantly higher mortality rate ratios than
females in in-patient and out-patient settings, but not among those attending
private specialists, where the reverse was true
(Table 1).
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The mortality rate ratio was significantly greater than 1 for all psychiatric diagnoses in both genders, with the exception of males with a diagnosis of neurotic disorder, and females with personality disorder (Table 2). Rates were highest for patients with dementia and other psychoses (Table 2). Mortality rate ratios were also significantly greater than 1 for all causes, in both males and females, with the highest rate being for suicide (Table 3).
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Primary care
The mortality rate ratio for both men and women with psychiatric diagnoses
was significantly higher than that of the general population, but lower than
for patients in specialist settings (see
Table 2). It was significantly
greater than 1 for all psychiatric diagnoses in both genders, except for
schizophrenia and neurotic and personality disorders, and in females with a
diagnosis of alcohol, drug or adjustment disorders. The small number of people
with schizophrenia, indicated by the wide confidence intervals, may explain
the negative results for schizophrenia. Mortality rate ratios were also
significantly greater than 1 for all causes of death except for diabetes in
both genders, myocardial infarction in males and suicide in females (see
Table 3). Unlike patients in
specialist settings, suicide did not have the highest mortality rate
ratio.
All settings
When we combined the results from specialist and primary care settings, all
psychiatric disorders were associated with significantly higher mortality
except for alcohol or drug disorders and neurotic disorders in females (see
Table 2). Mortality rate ratios
were also significantly greater than 1 for all causes of death (see
Table 3). A sensitivity
analysis revealed that mortality rate ratios for men and women were virtually
unchanged after removing suicide as a cause of death. The total mortality rate
ratio was 1.74 (95% CI 1.721.76); after removing suicide as a cause of
death, the ratio was 1.72 (95% CI 1.691.74).
Predictors of mortality
We used Cox regression to calculate relative risks for mortality, adjusting
for confounders such as age, gender and income
(Table 4). The risk of
mortality was 75% higher in males than in females. Although patients with
dementia and other psychoses were at highest risk across diagnostic groups,
mortality risk was elevated for all psychiatric disorders. Patients in
specialist psychiatric settings were significantly more likely to die. Within
the group of patients attending specialist psychiatric services, people
receiving out-patient treatment in the public sector had a significantly lower
risk than those treated as in-patients or those attending private specialists.
There was no significant difference in the mortality risk between in-patients
and those attending private specialists.
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A similar pattern was seen for specific causes of death (Table 5). Male gender, greater age and lower income were generally associated with increased mortality risks. Dementia, other psychoses or depression were the psychiatric diagnoses most frequently associated with significantly increased mortality from cancer, diabetes, heart disease or cerebrovascular disease. As seen in the analysis of overall mortality, patients attending specialist settings had a higher relative risk than those attending primary care, out-patients in the public sector having a significantly lower risk than in-patients or those attending private specialists (Table 5). See Tables 610 (presented as a data supplement to the online version of this paper) for additional data on causes of death. No significant difference difference in the mortality risk between in-patients in-patients and those attending private specialists was seen after stratifying by cause of death. The only exception to this finding was death from suicide. There was no difference in the risk of mortality between those attending out-patient services or private specialists, both being significantly lower than the risk for those who had ever been admitted (Table 5).
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Sensitivity analyses
We found similar results when we used the entire population of Nova Scotia
as the reference population rather than excluding those known to primary care
or specialist psychiatric services. In this case, the resulting mortality rate
ratios were 1.76 for males and 1.63 for females. We also found similar results
when we excluded non-Chapter 5 diagnoses from the analysis (data supplement to
the online version of this paper, Table 11).
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DISCUSSION |
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Limitations of the study
Although we included patients in all medical and psychiatric settings, we
could not control for differences in help-seeking behaviour, or recognition of
psychiatric morbidity by the professional of first contact. Neither could we
study the effect of lifestyle, such as alcohol or tobacco use. There are other
limitations to the study. We used routinely collected administrative data that
may be subject to recording bias, particularly in general practice. Although
there is good evidence for the validity of the Discharge Abstract Database,
information on other administrative data is more limited
(Kephart et al,
2003). Unlike previous Australian and Italian studies of
in-patients and out-patients (Amaddeo
et al, 1995; Lawrence
et al, 2000), we did not have data on marital status,
length of time since first contact with services and educational status, all
of which might influence mortality. We were therefore unable to adjust for
these factors in the Cox regression. We were also unable to consider the
effect of legal status. However, two studies from Australia and the USA showed
no difference in the mortality rates between involuntary and voluntary
patients (Amaddeo et al,
1995; Crisanti & Love,
1999). In spite of the high mortality rate there were few deaths
in some subgroups with insufficient power to detect statistically significant
effects.
Our inception cohort method meant that we only considered patients in the first 5 years of treatment for a psychiatric disorder. However, previous work has indicated that the majority of excess mortality occurs within the first 7 years of psychiatric treatment (Lawrence et al, 2000). The only exception to this finding is schizophrenia, for which the observed and expected mortality curves for patients continue to diverge over 15 years, and could mean that our study underestimated the effect of schizophrenia on mortality.
As this was an epidemiological study of routinely collected administrative data, we relied on ICD9 diagnoses. Diagnostic accuracy was improved through the clinical use of DSM diagnoses, which are then converted to ICD9 codes, as well as DSM training courses. However, clinicians outside publicly funded facilities do not have access to DSM training. Finally, as this was a study of mortality irrespective of cause, we did not include comorbid physical illness as a covariate in our regression models. However, we plan to study this interaction and its effect on a range of outcomes, including initial admission to hospital and entry on to the cancer registry.
Comparisons with other studies
In common with studies restricted to patients of psychiatric services
(Amaddeo et al, 1995;
Harris & Barraclough,
1998; Lawrence et al,
2000; Hannerz et al,
2001; Hansen et al,
2001; Rasanen et al,
2003; Vythilingam et
al, 2003) or primary care
(Ensinck et al,
2002), our study of all patients in treatment for psychiatric
disorder showed they had an increased mortality rate. Although the rate for
patients of specialist psychiatric services was particularly high, we also
found an increased mortality rate for patients in primary care. As expected,
mortality rates were elevated for a wide range of causes of death, including
carcinoma, diabetes, cardiovascular disease, respiratory disease, and
infections (Brown et al,
2000; Lawrence et al,
2000; Hansen et al,
2001).
Our findings mirror those of a comparable study from Western Australia that used the same methodology on a similar administrative database (Lawrence et al, 2000). Findings for individual psychiatric disorders were also similar, with the highest rates being found for organic psychiatric disorders such as dementia (Black, 1998; Lawrence et al, 2000; Hansen et al, 2001). However, our mortality rate for out-patients was higher than that in the Western Australian study. One explanation might be that we were unable to analyse data on residents of psychiatric hostels separately from other out-patients; the Australian study showed that their mortality rates were as high as those of in-patients (Lawrence et al, 2000). Another difference was that the Australian study only considered the public sector, and so the mortality rate for patients of private specialists is unknown. Another explanation is that our data include private specialists who see a relatively high proportion of patients with severe mental illness. Thirty four per cent of patients seen by specialists in Nova Scotia have schizophrenia or non-affective psychosis, as opposed to 24% of out-patients in publicly funded facilities and 5% of those in primary care.
In the case of patients attending their general practitioner, we were generally only able to compare our rates for depression. These were similar to those seen in general practice in The Netherlands (Ensinck et al, 2002). Our rates are also similar to those reported in community surveys of people with depression, including the Stirling County Survey in Atlantic Canada (Cuijpers & Smit, 2002). We are aware of only one community study that investigated the effect of other mental disorders on mortality (Joukamaa et al, 2001). As in our sample of general practice attenders, functional psychoses and mood disorders were associated with an elevated mortality risk, whereas neuroses were not. This study did not include organic, adjustment or personality disorders.
The results suggest that the mortality risk of patients with psychiatric disorders in general practice is similar to that of the community and that, although higher than in people without psychiatric morbidity, it is less than those in contact with specialist psychiatric services. However, in terms of absolute figures, 6413 out of 8917 deaths (72%) occurred in patients who had only attended general practice.
Explanations for increased mortality
There are a number of possible contributing factors for this elevated risk
of mortality, especially in patients attending specialist psychiatric
services. Patient-based factors include neurological or immunological
pathology, adherence to treatment, alcohol and tobacco use, diet, self-care
and exercise (Brown et al,
2000; Lawrence et al,
2000; Cuijpers & Smit,
2002; Lambert et al,
2003). Other possible explanations are cardiovascular and
endocrine side-effects of psychotropic medication, reduced access to general
medical care, the perception by specialist psychiatrists that physical health
should be the province of referring doctors, and the increased difficulty in
recognising physical comorbidity in psychiatric patients with physical
complaints (Brown et al,
2000; Lawrence et al,
2000; Hansen et al,
2001; Cuijpers & Smit,
2002; Vanina et al,
2002; Elming et al,
2003). Although authors have also suggested that suicide and
accidental death may be an explanation for increased mortality
(Cuijpers & Smit, 2002),
our study suggests that this risk is higher for all causes of death.
Our findings support an association between psychiatric disorder and mortality from carcinoma, although this is one cause of death not uniformly associated with increased mortality in psychiatric patients (Cohen et al, 2002). Lawrence et al (2000), using the same methodology as ours, also reported a significantly higher mortality from carcinoma, even though the incidence rate was no higher than that of the general population. This suggests that psychiatric patients benefit less from cancer services, either because of problems with access or adherence to treatment.
Implications
Strategies to reduce mortality in psychiatric patients include addressing
lifestyle and access to services, as well as monitoring the physical health of
both in-patients and out-patients. Given that we have shown that mortality
risk is increased across a wide range of psychiatric disorders, efforts should
not be restricted to patients with dementia or psychosis. Similarly, although
the relative risk is lower than in specialist settings, most deaths occurred
in patients who had only attended their general practitioner for psychiatric
care, suggesting the inclusion of primary care in initiatives to reduce
mortality risk.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication September 14, 2004. Revision received January 27, 2005. Accepted for publication February 4, 2005.
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