Investigation of clusters of adverse reproductive outcomes, an overview

Congenital Anomalies: Cluster Detection and Investigation

This work summarizes the main aspects to be considered around birth defects (or congenital anomalies) clusters. Most birth defects (BD), considered individually, fall into the definition of rare diseases (RD), according to their low frequency. Likewise, many RD are congenital, because their manifestations are present at birth or can be even evident before the delivery. It has been estimated that overall 7.9 million children are born each year with serious BD of genetic or partially genetic origin, and additional hundreds of thousands more are born with serious BD of post-conception origin.A "birth defect cluster" can be defined as an unusual aggregation of cases (grouped in place and time) that is suspected to be greater than expected, even though the expected number may not be known. These clusters are incidents or occurrences that let us turn the challenge of identifying the causal agent(s) involved in the origin of such clusters, into an opportunity to exert primary prevention, and thus achieve the ultimate goal of enabling infants being born healthy. Therefore, any program or system involved in BD surveillance and research should devote part of its activities to detect and investigate clusters, to ensure that such opportunity for primary prevention will be conveniently leveraged. Regardless the type of cluster, there are several phases that must be undertaken sequentially for proper control and the maximum benefit for the population: cluster detection, evaluation and investigation, management, adoption of preventive measures, and communication of the results to the public or target population.

Cancer cluster investigations: review of the past and proposals for the future

Residential clusters of non-communicable diseases are a source of enduring public concern, and at times, controversy. Many clusters reported to public health agencies by concerned citizens are accompanied by expectations that investigations will uncover a cause of disease. While goals, methods and conclusions of cluster studies are debated in the scientific literature and popular press, investigations of reported residential clusters rarely provide definitive answers about disease etiology. Further, it is inherently difficult to study a cluster for diseases with complex etiology and long latency (e.g., most cancers). Regardless, cluster investigations remain an important function of local, state and federal public health agencies. Challenges limiting the ability of cluster investigations to uncover causes for disease include the need to consider long latency, low statistical power of most analyses, uncertain definitions of cluster boundaries and population of interest, and in- and out-migration. A multi-disciplinary Workshop was held to discuss innovative and/or under-explored approaches to investigate cancer clusters. Several potentially fruitful paths forward are described, including modern methods of reconstructing residential history, improved approaches to analyzing spatial data, improved utilization of electronic data sources, advances using biomarkers of carcinogenesis, novel concepts for grouping cases, investigations of infectious etiology of cancer, and "omics" approaches.

Methods for a public health response to birth defects clusters

Few resources are available to guide public health officials in investigations of reported birth defects clusters. The majority of published resources focus on the investigation of cancer and infectious disease clusters and do not address clinical and epidemiologic concerns specific to birth defects research. This document aims to address these concerns, discuss the needs of the affected community, and provide suggestions for the development of a standardized protocol to be used as a guide in the investigation of birth defects clusters. We suggest that health departments and birth defects registries that may receive reports of birth defects clusters establish a protocol for responding that includes the following steps: develop a proactive plan for future birth defects cluster reports (step I), receive report of a birth defects cluster (step II), verify diagnoses and complete case ascertainment (step III), compare the observed rate to a reference rate (step IV), ascertain exposures among cases from available records (step V), interview case mothers (step VI), initiate further epidemiologic study-selection of controls (step VII), and communicate results to the community (step VIII). Specific criteria for continuing or terminating an investigation should be established before receiving cluster reports. The recommendations in this report should be carefully considered to ensure that the specific needs of the region, agency and affected community are met.