SEASONALITY OF MANIA IN NEW ZEALAND R.T. Mulder, J.P. Cosgriff, A.M. Smith and P.R. Joyce
This paper examines the seasonal variation in manic admissions over a five year period in New Zealand. There is a significant monthly variation in admission rates with a spring/summer peak. Breakdown by sex, age and admission status suggested that there is no particular subgroup responsible, but that young first admissions and older female readmissions do not follow this trend. Examination of the monthly admission rates revealed that this peak is not constant from year to year. Possible mechanisms, which link fluctuating environmental variables with an irregular spring/summer peak for manic admissions, are discussed. Australian and New Zealand Journal of Psychiatry 1990; 24:187-190 A seasonal variation in the onset of mood disorders has been noted since ancient times. There is now considerable evidence for variation in rates of mood disorder throughout the year. Some of this evidence is indirect and is based on suicide rates [ 11 or seasonality of criminal offences by bipolar patients [2]. Other studies are based on hospital admission rates. Eastwood and Stainsy [3], for example, found spring and autumn peaks for admissions with neurotic and endogenous depression. Studies of the seasonal variation of mania have generally found peak admission rates in spring or summer. Symonds and Williams [4] showed a significantly increased summer manic admission rate in England and Wales. Although this trend was confined to females, a re-analysis of the data by Walter [ 5 ] suggested it was also significant in males. Myers and Sunnyside Hospital, Wellington Hospital, and University Department of Psychological Medicine, Christchurch School of Medicine, Christchurch Hospital, Christchurch, New Zealand R.T. Mulder MBChB, Lecturer J.P. Cosgriff MBChB, Registrar A.M. Smith MBChB, Registrar P.R. Joyce BSc, MBChB, PhD, FRANZCP, Professor Correspond with Dr Mulder
Davis [6] showed a significant annual cycle for manic admissions with a peak in summer and a trough in winter. Frangos ef a1 [7] found manic admissions peaked in spring with a smaller elevation in autumn. An Australian study [8] demonstrated a peak incidence of manic admissions in spring, suggesting this trend also occurs in the Southern Hemisphere. Although hospitalizations probably reflect more severe cases, mania is a relatively circumscribed illness, usually disruptive, and hospitalization normally occurs within a month of onset [9]. Admission rates are thus a better measure of its incidence than they are of the other affective disorders [ 101. The aims of this study were: 1, To determine whether seasonal variations exist in the number of patients admitted to New Zealand hospitals with a diagnosis of mania; 2. To see whether this variation is restricted to certain subgroups such as males vs females, first admissions vs readmissions, or to different age groups; 3. If a seasonal pattern exists, is it constant from year to year?
Method Data for the study were obtained from the Depart-
Downloaded from anp.sagepub.com at UCSF LIBRARY & CKM on March 27, 2015
SEASONALITY OF MANIA IN NEW ZEALAND
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Table I . Number of admissions and ratio observed to expected for monthly admissions with diagnosis of mania 1980-84
monthly average observed over expected ratio against time to establish whether the seasonal peak was constant from year to year.
Results Month January February March April May June July August September October November December
Number 337 278 327 314 295 317 308 337 304 344 380 372
Observedlexpected 1.015 0.914 0.985 0.977 0.889 0.987 0.928 1.015 0.946 1.036 1.186 1.120
ment of Health’s National Health Statistics. These supplied the total number of adinissions to psychiatric hospitals and psychiatric wards of general hospitals in New Zealand with a diagnosis of mania (ICD-9 296.0 manic-depressive psychosis; manic type. ICD-9 296.2 manic-depressive psychosis; circular type, currently manic) during the years 1980-1984 inclusive. We totalled the number of admissions each month over the five year period to address whether there was an overall seasonal pattern to admissions. The data were analysed using a chi-square test. Having established that there was a significant variation in monthly admission rates for mania, it was noted that the three peak months in descending order were November, December and October. Given that these three peak months were contiguous, we labelled them the spring/summer peak and in subsequent analyses compared the admission rates for these three months with the other nine (i.e. January to September). The data were divided into first admissions and readmissions, male and female, and three age groups (years, 30-49 years, 50 years). Admission rates for each of these subgroups was analysed by comparing the peak three months with the other nine months using chi-square tests. We then calculated the observed over expected ratio of admissions for each month by dividing the actual number of manic admissions for each month by the calculated number which would have been expected if admissions rate were random, allowing for variable days in any month. We then plotted the moving three-
The total number of patients admitted to hospital with a diagnosis of mania over the five year period was 3916. There were 1528 male and 2388 female admissions. From the pooled five year data, admission numbers are calculated by month in Table 1. There is a significant monthly variation in admission rates (chisquare = 25.46, df = l l , p
This paper examines the seasonal variation in manic admissions over a five year period in New Zealand. There is a significant monthly variation in admission rates with a spring/summer peak. Breakdown by sex, age and admission status suggested that there is no particular subgroup responsible, but that young first admissions and older female readmissions do not follow this trend. Examination of the monthly admission rates revealed that this peak is not constant from year to year. Possible mechanisms, which link fluctuating environmental variables with an irregular spring/summer peak for manic admissions, are discussed. Australian and New Zealand Journal of Psychiatry 1990; 24:187-190 A seasonal variation in the onset of mood disorders has been noted since ancient times. There is now considerable evidence for variation in rates of mood disorder throughout the year. Some of this evidence is indirect and is based on suicide rates [ 11 or seasonality of criminal offences by bipolar patients [2]. Other studies are based on hospital admission rates. Eastwood and Stainsy [3], for example, found spring and autumn peaks for admissions with neurotic and endogenous depression. Studies of the seasonal variation of mania have generally found peak admission rates in spring or summer. Symonds and Williams [4] showed a significantly increased summer manic admission rate in England and Wales. Although this trend was confined to females, a re-analysis of the data by Walter [ 5 ] suggested it was also significant in males. Myers and Sunnyside Hospital, Wellington Hospital, and University Department of Psychological Medicine, Christchurch School of Medicine, Christchurch Hospital, Christchurch, New Zealand R.T. Mulder MBChB, Lecturer J.P. Cosgriff MBChB, Registrar A.M. Smith MBChB, Registrar P.R. Joyce BSc, MBChB, PhD, FRANZCP, Professor Correspond with Dr Mulder
Davis [6] showed a significant annual cycle for manic admissions with a peak in summer and a trough in winter. Frangos ef a1 [7] found manic admissions peaked in spring with a smaller elevation in autumn. An Australian study [8] demonstrated a peak incidence of manic admissions in spring, suggesting this trend also occurs in the Southern Hemisphere. Although hospitalizations probably reflect more severe cases, mania is a relatively circumscribed illness, usually disruptive, and hospitalization normally occurs within a month of onset [9]. Admission rates are thus a better measure of its incidence than they are of the other affective disorders [ 101. The aims of this study were: 1, To determine whether seasonal variations exist in the number of patients admitted to New Zealand hospitals with a diagnosis of mania; 2. To see whether this variation is restricted to certain subgroups such as males vs females, first admissions vs readmissions, or to different age groups; 3. If a seasonal pattern exists, is it constant from year to year?
Method Data for the study were obtained from the Depart-
Downloaded from anp.sagepub.com at UCSF LIBRARY & CKM on March 27, 2015
SEASONALITY OF MANIA IN NEW ZEALAND
I88
Table I . Number of admissions and ratio observed to expected for monthly admissions with diagnosis of mania 1980-84
monthly average observed over expected ratio against time to establish whether the seasonal peak was constant from year to year.
Results Month January February March April May June July August September October November December
Number 337 278 327 314 295 317 308 337 304 344 380 372
Observedlexpected 1.015 0.914 0.985 0.977 0.889 0.987 0.928 1.015 0.946 1.036 1.186 1.120
ment of Health’s National Health Statistics. These supplied the total number of adinissions to psychiatric hospitals and psychiatric wards of general hospitals in New Zealand with a diagnosis of mania (ICD-9 296.0 manic-depressive psychosis; manic type. ICD-9 296.2 manic-depressive psychosis; circular type, currently manic) during the years 1980-1984 inclusive. We totalled the number of admissions each month over the five year period to address whether there was an overall seasonal pattern to admissions. The data were analysed using a chi-square test. Having established that there was a significant variation in monthly admission rates for mania, it was noted that the three peak months in descending order were November, December and October. Given that these three peak months were contiguous, we labelled them the spring/summer peak and in subsequent analyses compared the admission rates for these three months with the other nine (i.e. January to September). The data were divided into first admissions and readmissions, male and female, and three age groups (years, 30-49 years, 50 years). Admission rates for each of these subgroups was analysed by comparing the peak three months with the other nine months using chi-square tests. We then calculated the observed over expected ratio of admissions for each month by dividing the actual number of manic admissions for each month by the calculated number which would have been expected if admissions rate were random, allowing for variable days in any month. We then plotted the moving three-
The total number of patients admitted to hospital with a diagnosis of mania over the five year period was 3916. There were 1528 male and 2388 female admissions. From the pooled five year data, admission numbers are calculated by month in Table 1. There is a significant monthly variation in admission rates (chisquare = 25.46, df = l l , p
