Maximising retention in a longitudinal study of genital Chlamydia trachomatis among young women in Australia
1 Centre for Women's Health, Gender and Society, School of Population Health, University of Melbourne, Victoria 3010, Australia
2 Sexual Health Unit, School of Population Health, University of Melbourne, and Melbourne Sexual Health Centre, Melbourne Victoria 3010, Australia
3 Sexual Health Unit, School of Population Health, University of Melbourne, Victoria 3010, Australia
4 Department of Epidemiology and Preventive Medicine, Monash University, and Melbourne Sexual Health Centre, Melbourne Victoria 3010, Australia
5 National Centre in HIV Epidemiology and Clinical Research, University of NSW, Sydney 2000, Australia
6 Department of Molecular Microbiology, The Royal Women's Hospital, Melbourne, Victoria, Australia
7 Family Planning Victoria, Melbourne, Australia and Monash University, Victoria, Australia
8 Australian National University, Canberra, Australia
9 Primary Care Research Unit, Department of General Practice, University of Melbourne, Victoria 3010, Australia
10 Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, School of Population Health, University of Melbourne, Victoria 3010, Australia
11 North Coast Medical Education Collaboration, Sydney School of Public Health, University of Sydney, Lismore, NSW, Australia
12 St Mary's Hospital, Portsmouth, UK
13 The Royal Women's Hospital, Melbourne, Victoria, Australia; and the Department of Obstetrics and Gynaecology, The University of Melbourne, Victoria, Australia
BMC Public Health 2011, 11:156 doi:10.1186/1471-2458-11-156Published: 9 March 2011
Cohort studies are an important study design however they are difficult to implement, often suffer from poor retention, low participation and bias. The aims of this paper are to describe the methods used to recruit and retain young women in a longitudinal study and to explore factors associated with loss to follow up.
The Chlamydia Incidence and Re-infection Rates Study (CIRIS) was a longitudinal study of Australian women aged 16 to 25 years recruited from primary health care clinics. They were followed up via the post at three-monthly intervals and required to return questionnaires and self collected vaginal swabs for chlamydia testing. The protocol was designed to maximise retention in the study and included using recruiting staff independent of the clinic staff, recruiting in private, regular communication with study staff, making the follow up as straightforward as possible and providing incentives and small gifts to engender good will.
The study recruited 66% of eligible women. Despite the nature of the study (sexual health) and the mobility of the women (35% moved address at least once), 79% of the women completed the final stage of the study after 12 months. Loss to follow up bias was associated with lower education level [adjusted hazard ratio (AHR): 0.7 (95% Confidence Interval (CI): 0.5, 1.0)], recruitment from a sexual health centre as opposed to a general practice clinic [AHR: 1.6 (95% CI: 1.0, 2.7)] and previously testing positive for chlamydia [AHR: 0.8 (95% CI: 0.5, 1.0)]. No other factors such as age, numbers of sexual partners were associated with loss to follow up.
The methods used were considered effective for recruiting and retaining women in the study. Further research is needed to improve participation from less well-educated women.