Learning from a negative trial of lockable pesticide storage

www.thelancet.com Published online August 11, 2017 http://dx.doi.org/10.1016/S0140-6736(17)32207-9 1 With a view to reducing pesticide self-poisoning in Sri Lanka, Melissa Pearson and colleagues did one of the largest community-based cluster-randomised controlled trials of the effectiveness of household lockable pesticide storage, reported in The Lancet. The effort is admirable, but unfortunately their results show that improved household pesticide storage did not reduce the incidence of pesticide self-poisoning. In the study, households in 90 rural villages in North Central Province, Sri Lanka, that had farmed or had used or stored pesticides in the preceding agricultural season were randomly assigned to receive a lockable storage container, or no intervention, amounting to 27 091 households (114 168 individuals) in the intervention group and 26 291 households (109 693 individuals) in the control group. In individuals aged 14 years or older, 611 cases of pesticide selfpoisoning had occurred by 3 years in the intervention group compared with 641 cases in the control group. The primary outcome, incidence of pesticide selfpoisoning, did not differ between groups (293·3 per 100 000 person-years of follow-up in the intervention group vs 318·0 per 100 000 in the control group; p=0·33). The investigators found no evidence of switching from pesticide self-poisoning to other forms of self-harm, with no significant difference in the number of fatal (82 in the intervention group vs 67 in the control group) or non-fatal (1135 vs 1153) self-harm events involving all methods. Discouraging though these findings may seem, they are valuable in providing insights into the understanding of the complexities of any suicide prevention effort. Suicide is not a disease reflecting well defined pathological mechanisms, and the occurrence of suicidal behaviour is usually the outcome of complex interactions of socioenvironmental, behavioural, and psychiatric factors. Restricting access to lethal means of suicide has received much empirical support, this method being most effective among sudden, unplanned suicides, because those victims tend to use the method most readily accessible to them. If a lethal method is not available at the moment of the potential deadly action, it might be possible to buy time so that (in some cases at least) suicidal impulses will fade without fatal consequences. Even when suicides are planned, difficulty in gaining access to the most lethal means of suicide can serve as a substantial impediment. Nonetheless, this proposed method per se seems not sufficient enough to lower pesticide poisoning, suicide, or self-harm rates at the community level. Since highly lethal pesticides and the keys to their storage are still within reach in the household, no other less lethal method is a better substitute for pesticide suicides in such cases. Because the causes of suicides are multifactorial, restriction of means needs to be incorporated into a holistic and integrated suicide prevention programme rather than as a stand-alone measure. Suicide is still a rare event. Despite the fairly large number of households involved in the study it was still not large enough to detect differences, especially because non-compliance in the intervention group was not small: about 30% in the first year and 50% in the third, and some lockable pesticide storage was used in the control region. Furthermore, because of the close proximity of the intervention and the control sites, a contamination effect might have occurred. Hence, we cannot infer from this specific intervention (household lockable pesticide storage) that restriction of means is not useful in preventing suicides, because many studies have demonstrated its effectiveness. The more important and relevant question is why does this specific intervention not produce a desirable result in the setting of Sri Lanka? Is it that the proposed restriction method is not secure enough to achieve Learning from a negative trial of lockable pesticide storage