The district of Valashahr has an area of 1,650 km2 and over 40,000 inhabitants mainly of Fars or Turk ethnicities and sparsely of other ethnicities. The district consists of 5 counties and the city of Valashahr. There are 5 health centers in the area supervising 31 health houses and covering a total of 93 villages. Each health house is staffed by 2 community health workers named “Behvarz”. These community health workers were originally responsible for vaccination, family planning, recording vital horoscopes, and primary health care mainly for communicable diseases. However, they have been trained to participate in the conduct of the study.
The participants in this study consisted of all eligible people, both healthy and unhealthy in Valashahr and the nearby villages. All residents of the district between 40 and 75 years old were invited. The only exclusion criteria were unwillingness to participate or being a temporary resident. The participation rate was 95%. A total of 9,264 subjects visited the Pars Cohort Study Center (PCSC) for interview and physical examination, and provided biological samples. The response rate was higher among the rural inhabitants, which is explained by the proximity of their workplace to their residence in agricultural occupations, and their flexible working hours.
The list of participants with their cell phone numbers and/or telephone numbers were acquired through 31 health houses in the region. Then, based on the catchment area of health houses, the district was divided into sub-regions.
Recruitment took place at the Pars Cohort Study Center (PCSC) in Valashahr, a research office established for this project, and in close contact with the 31 health houses in the region. In the villages, Behvarz’, who had been trained for the project, contacted all eligible household members and thoroughly explained the purpose and procedure of the study to them. Likewise, expert local health professionals contacted all eligible household members aged between ≥40 and ≤75 in Valashahr and thoroughly explained the purpose and procedure of the study to them. As the staff were native residents, people knew them and discussed any issue that might cause ambiguity.
Every day 20 participants were invited to attend the PCSC early morning for the tests. They were informed on the previous day through telephone, cell phone or Behvarz’ in the health houses. The subjects were told not to have breakfast and be fasting for about 12 hours preceding their attendance in the center. The center indeed provided a van and a driver to either take the team to places where the participants had difficulty attending the center or to bring the participants to the center for tests, but as the farthest place was only 40 kilometers away from the center and the participants themselves willingly wanted to attend the center, there was no need to use the van.
The invited people were enrolled and were given the written consent to sign by the receptionist after their identity was verified based on their identity cards. In case the participant was illiterate, he or she was invited to visit the center and the procedures and to participate in the study if they were willing. A personal cohort identification card and a unique code were assigned to each participant.
The 3 categories of the collected data included: 1) Self-reported data, which was recorded using structured questionnaires; 2) Physical examination; and 3) Biosample collection;.