We undertook a survey of patient preferences using randomised allocation of two questionnaires. Both questionnaires asked about preferences between larval therapy and standard treatment (hydrogel) if hydrogel dressings were to heal their ulcer in 20 weeks and the larvae were to heal their ulcer over a range of times (between 6 and 20 weeks). One questionnaire asked about preferences for loose larvae or hydrogel at a range of healing times for loose larvae, the other questionnaire asked about preferences between bagged larvae and hydrogel for a range of healing times for bagged larvae. In both cases, the healing time for hydrogel was set at 20 weeks.
Research governance and local ethics committee approval was granted for the research. All participants were asked to provide informed consent and were reassured of the confidentially and anonymity of their responses.
We randomised participants to receive the 'bagged' or 'loose' questionnaire using sealed opaque envelopes which were sequentially numbered. Envelopes were left with the outpatient clinic's receptionist. Participants were taken to a private room to discuss participation and following consent the envelope (next in sequence) was opened in the presence of the patient. In addition, the number sequence was held by a remote researcher who could check patient number with allocation. Both questionnaires were administered by a nurse researcher (KS).
Initially participants were asked if they would consider the use of larval therapy as a therapy if their nurse or doctor recommended use of them. Patient characteristics were recorded for all participants. If participants were unwilling to consider the use of larval therapy no further questions about the therapy were asked. For those participants who responded that they would consider the use of larval therapy further questions were asked to determine what difference in healing time relative to hydrogel they would require to utilise larval therapy or not mind which therapy they received.
Firstly participants were asked to choose which treatment that they would prefer to receive if both hydrogel and larval therapy achieved healing at 20 weeks: hydrogel, larval therapy or no preference. If the patient responded that they would prefer larval therapy or that they had no preference at this point no further questions were asked. Then in order to minimise the number of questions presented from a maximum of 15 to a maximum of 8, the second scenario presented was one in which larval therapy would heal the ulcer at 12 weeks (i.e. an 8 week difference). If on asking this question larval therapy was preferred or there was no preference, the next set of questions would ask about the preference between therapies if healing occurred at decreasing times with the use of larval therapy i.e. 19, 18, 17, 16, 15, 14 and 13 weeks. If, on the other hand, the patient did not prefer larval therapy over hydrogel with an 8 week difference in time to healing, then decreasing times to healing with the use of larval therapy were presented, i.e. healing at 11, 10, 9, 8, 7 and 6 weeks (increasing effect sizes from 9 to 14 weeks). The first time point at which the patient had no preference or chose larval therapy was then recorded and used in the analysis.
A total of 35 participants were included in the study allowing us to detect, with 80% power (2 sided p = 0.05), one standard deviation difference in healing times between the two modes of larval therapy.
As the data were skewed we used a Mann-Whitney U test to determine if the differences between the median times to healing derived for loose larvae versus hydrogel and bagged larvae versus hydrogel were statistically significant.