Use of opt-out in a trial of chlamydia screening

Sir: Markos found that 19% of 200 consecutive women attending Stafford genitourinary medicine department had chlamydia whether or not they were symptomatic. ¹ We are currently conducting a trial of chlamydia screening in young, multiethnic women from 20 universities and further education colleges in Greater London. The POPI (prevention of pelvic infection) trial aims to see if screening women for chlamydia using self-taken vaginal swabs prevents pelvic inflammatory disease (PID).

In 2007, we received additional funding to test participants' samples for Mycoplasma genitalium, a possible co-factor for PID. This required us to obtain additional consent from participants. We used an opt-out method of consent, as opposed to the classical method of opting in. This meant that women only needed to contact us (by texting, email, telephone or post) should they not wish to continue participating in the study.

In August 2007, we sent an additional patient information sheet and consent form to 1384 participants recruited in 2004–2005. Those participants with a working email address (83%, 1149/1384) were sent the forms via email. The remaining 17% (235) were sent the forms via post enclosing a stamped addressed envelope.

Of the 1384 women, only two replied that they wished to opt-out of the study, one of whom said it was because she was moving abroad. However, although the women were not required to formally respond in order to be included in the study, 133 (10%) chose to do so. Of these, 20 women included positive comments with the returned consent form. These included: ‘That's fine. Use them (the samples) for what you like!’ ‘I'm more than happy to take part.’ ‘Feel free to use the samples again.’ and ‘Keep up the good work’.

The use of an opt-out procedure therefore meant that 99.9% of participants could be tested for M. genitalium. We believe this is a much higher rate than would have been achieved should they have needed to opt-in. The main limitation is that we do not know if all the women received and read the new information sheet and consent form. We did not receive any negative comments, which may indicate that none of the participants found the opt-out method unacceptable.

In-line with Markos' study, a recent Health Protection Agency report notes the high incidence of sexually transmitted infections (STIs), especially chlamydia, in 16–24-year-olds. ² In women, who have already agreed to take part in a study of STIs, the use of an opt-out procedure if the study is extended could be an ideal way of maximizing participation and therefore increase the efficacy of research.