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SWE-NSW: Northern Sweden Contributors from the MPC: Kjell Asplund and Birgitta Stegmayr

© National Institute for Health and Welfare and the MORGAM Project investigators Last updated: 26 April 2005 For more information, please contact Kari Kuulasmaa (firstname.lastname@thl.fi)

Contents

• Cohort identification
• Cohort recruitment and the baseline examination
• End-points followed up
• End of follow-up period
• Follow-up procedures
• Diagnostic procedures
  • at baseline
  • during follow-up
• References

Cohort identification

• Country: Sweden
• MPC: 60 - Northern Sweden
  • Administrative centre: Department of Medicine, University Hospital, Umeå, Sweden
  • Key personnel: Birgitta Stegmayr (Principal Investigator), Salmir Nasic, Gunborg Rönnberg, Åsa Johansson, Vivan Lundberg, Elsy Jägare-Westerberg, Torbjörn Messner
• RUs:
  • 01 - Västerbotten County. The northernmost county but one, Västerbotten, sparsely populated area, half rural and half urban. Higher-than-average mortality and unemployment, low socio-economic status.
  • 02 - Norrbotten County. The northernmost county, Norrbotten, sparsely populated area, half rural and half urban. Higher-than-average mortality and unemployment, lower socio-economic status.
• RUAs:
  • SWE-NSWa - consisting of both RUs
• Cohorts:
  • Cohort 01 - Respondents of representative samples of 25-64 years old men and women of the RUs. The baseline survey carried out in 1986.
  • Cohort 02 - Respondents of representative samples of 24-64 years old men and women of the RUs. The baseline survey carried out in 1990.
  • Cohort 03 - Respondents of representative samples of 24-74 years old men and women of the RUs. The baseline survey carried out in 1994.

Cohort recruitment and the baseline examination

The cohorts were formed by the respondents of representative sample surveys of the RUs. National population register was used as sampling frame for the single stage sampling which was stratified by sex and 10-year age group. The baseline examinations were carried out as part of the WHO MONICA Project.

The sizes of the MORGAM cohorts and response rates of the population surveys from which cohorts were derived are:

DNA are available for the members of Cohorts 02 and 03.

End-points followed up

• Deaths: yes
• Definite and possible non-fatal MI: yes
• Unstable angina pectoris: no
• Silent MI: no
• Cardiac revascularization: no
• Stable angina pectoris: no
• Non-fatal stroke events: yes
• Thromboembolic events: no

End of follow-up period

• Fatal events: 31 December 1999 (no age limit)
• Non-fatal events: 31 December 1999 with an upper age limit 65 for non-fatal coronary events. 31 December 1999 with an upper age limit 75 for non-fatal stroke events.

Follow-up procedures

Sources of data

• National Death Register: The national death register is maintained at the Central Bureau of Statistics (http://www.scb.se/amne/befolkningeng.asp). It covers all people who were resident in Sweden (citizens and non-citizens) at the time of death. Residents who die abroad are also included.
• Local Population Registers: Each tax office keeps a local register of population in its area of operation (see http://www.rsv.se). Among other things, the register includes information on removals from the population register due to death, migration or other reasons.
• Coronary and Stroke Event Registers: These are population based registers initiated within the framework of the WHO MONICA Project. The Coronary Event Register covers the study area from 1985 onwards. Its upper age limit was 65 years until the year 2000 when it was extended to 75 years [1, 2]. The Stroke Event Register covers the study area from 1985 onwards. Its upper age limit is 75 years [3, 4]. The coverage of registration is ascertained by periodic cross-checking with the discharge registers of the hospitals and health care centres in the study area.

Procedures

Everyone in Sweden has an unique personal identification code issued by the National Tax Authority (detailed information at the website http://www.rsv.se). The cohorts were linked to the National Death Register, to the Local Population Registers and to the Coronary and Stroke Event Registers using the personal identification code. Therefore, the mortality follow-up covered the whole country whereas the follow-up for non-fatal events covered only the RUs' area. If a person moved out of the RUs' area, then he/she was lost to follow-up for non-fatal events and the date of loss to follow-up was the date of moving.

Diagnostic procedures

At baseline:

• History of MI:
  • Documented: The cohorts were linked to the Coronary Event Register (data since 1985). Persons with a previous definite or MONICA probable MI event were considered having a documented history of MI or unstable angina pectoris.
  • Self-reported: An affirmative answer to the question "Have you ever been admitted in hospital for a definite myocardial infarction (heart thrombosis)?" was considered as self-reported history of MI.
  • ECG: data not available
  • Rose questionnaire: As specified in item HISMI4 of MORGAM Form 21.
• History of cardiac revascularisation:
  • Documented: data not available
  • Self-reported: data not available
• History of angina pectoris:
  • Documented: data not available
  • Rose questionnaire: An affirmative  answer to the question "Do you get chest pain when you walk  uphill or hurry?" was considered as history of angina pectoris corresponding to Rose questionnaire.
  • Self-reported: data not available
• History of coronary heart disease, type unspecified: not relevant because specific types were collected.
• History of stroke:
  • Documented: The cohorts were linked to the Stroke Event Register (data since 1985). Persons with a previous definite stroke event were considered having a documented history of stroke.
  • Self-reported: An affirmative answer to the question "Have you had stroke (cerebral haemorrhage or thrombosis)?" was considered as self-reported history of stroke.
• History of Diabetes: An affirmative answer to the question "Have you diabetes?" was considered as history of diabetes.

During follow-up:

• Deaths: Final official cause of death codes were used for the relevant items of MORGAM Form 25.
• CHD events: Linkage to the coronary event register was done to recognise nonfatal possible and definite MIs and then fatal events. For events found in the Coronary Event Register, the MONICA diagnostic category was used.

  For events which were found in the National Death Register but not in the Coronary Event Register, the diagnostic classification was done using the ICD-code of the underlying cause of death:

  Official underlying cause of death code		MORGAM DGNCAT
  ICD-9	ICD-10
  410-414	I21-I25	3
  798	I46, R96, R98, R99	5
  other		7

  Coronary events occurring within 28 days of each other were considered as one event.
  

• Stroke events: Linkage to the stroke event register was done to recognise non-fatal or fatal stroke events with any diagnostic category. For events found in the Stroke Event Register, the MONICA diagnostic category was used.

  For events found in the National Death Register but not in the Stroke Event Register, the diagnostic classification was done using the ICD-codes of the underlying cause of death:

  Official underlying cause of death code		MORGAM DGNCAT
  ICD-9	ICD-10
  430, 431, 433, 434, 436	I60, I61, I63, I64	9
  other		4

  Stroke events occurring within 28 days of each other were considered as one event.

References

1. Huhtasaari F, Lundberg V, Eliasson M, Janlert U, Asplund K. Smokeless tobacco as a possible risk factor for myocardial infarction: a population-based study in middle-aged men. J Am Coll Cardiol. 1999; 34(6): 1784-1790.
2. Peltonen M, Lundberg V, Huhtasaari F, Asplund K. Marked improvement in survival after acute myocardial infarction in middle-aged men but not in women. The Northern Sweden MONICA study 1985-94. J Intern Med. 2000;247(5):579-87.
3. Stegmayr B, Asplund K, Wester PO. Trends in incidence, case-fatality rate, and severity of stroke in northern Sweden, 1985-1991. Stroke. 1994;25(9):1738-45.
4. Peltonen M, Stegmayr B, Asplund K. Time trends in long-term survival after stroke: the Northern Sweden Multinational Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) study, 1985-1994. Stroke. 1998;29:1358-65.

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