[A suspect cluster of childhood cancer in Valle di Ledro (Province of Trento, Northern Italy). Epidemiological evaluation, risk management, and communication activities, 2018-2020].

Background: leukaemia is the most prevalent form of childhood cancer, an overall rare condition in childhood. Even few cases occurring in a small community can cause considerable apprehension among the population. From 2014 to 2017, 4 cases of childhood cancer occurred in Valle di Ledro, a municipality of 5,300 inhabitants in Province of Trento (Northern Italy), and a group of concerned citizens asked provincial health authorities for an investigation.

Objectives: to address the community's health needs by verifying the hypothesis of a cluster of childhood cancer and through effective risk communication activities.

Design: retrospective cohort analysis based on data from the Cancer registry of the Autonomous Province of Trento and data collected from hospital discharge records. The communication activities were carried out according to the recommendations published by Epidemiologia&Prevenzione in 2016 in a Supplement "Childhood cancers, risk factors and investigation models for the evaluation of spatio-temporal clusters".

Setting And Participants: Valle di Ledro, a municipality of 5,300 inhabitants in the Province of Trento. The participants in risk communication process were: city council; grassroot committee of concerned parents; health workforce of different services (epidemiology, cancer registry, public health; environmental health; primary health care; personnel of the Environmental Protection Agency; journalists; general population. The participants in the statistical analyses were: children of 0-14 years of age who were diagnosed a cancer from 1998 to 2014 in the Province of Trento (N. 212); leukaemia (N. 84) and acute lymphoblastic leukaemia (N. 66) incident cases in the period 1998-2017 in Trento province.

Main Outcome Measures: verification of the presence of a cluster of childhood cancers; degree of consensus and collaboration of the different community stakeholders to the survey procedures and acceptance of the final results; atmosphere in public assemblies and feedback in the local press.

Results: a total of 212 incident cancer cases in children 0-14 years have been registred in Province of Trento from 1998 to 2014, leukaemia in 35% (N. 74) cases. From 2015 to 2017, another 10 cases of leukaemia occurred, for a total of 84 cases of leukaemia from 1998 to 2017. In the years from 1998 to 2017, in Valle di Ledro, taking the Italian population as reference group, the standardized incidence ratios (SIRs) were the following: cancer, all types 1,47 (IC95% 0,40-3,76); leukaemia 3,39 (IC95% 0,70-9,90), LLA 2,81 (IC95% 0,34-10,16). No cluster emerged from the geographical analyses. From the very beginning of the risk management approach, a decision-making working group was set up applying a participatory approach. Group members included the city council and the local committee of concerned parents and experts from different services of the local health unit. Data analyses was delegated to a technical working group that reported back to the decision-making group. Members of the technical working group were supervised by external experts. Following this approach, it was possible to establish a climate of trust and credibility. The involvement of all stakeholders right from the start in a totally transparent process was a key element of success.

Conclusions: the cluster hypothesis was rejected for both childhood cancer (all types) and leukaemia (all types and ALL). The implementation of the risk communication process recommended by the AIE guidelines was successful in establishing a climate of reciprocal trust that allowed to overcome inevitable moments of conflict in a productive manner. Thanks to this positive atmosphere, the communication of the results of the statistical analyses was effective in reassuring the population.