An outbreak occurs when a disease affects a larger number of people than is expected, usually in one or more communities. It may be caused by infection (either zoonotic or not) from contact with animals or from contaminated water, food or air. It may be due to a communicable disease or to non-communicable diseases such as carbon monoxide poisoning, Minamata disease from exposure to mercury or SARS.
A cause of the outbreak is often identified in investigations, but for some cases a diagnosis cannot be made. These cases are called syndromic or unexplained and can be identified through open source information (OSINT).
Syndromic surveillance systems such as EPIWATCH and ProMED Mail use OSINT to identify occurrences of illnesses that could be outbreaks but do not have a confirmed infectious cause. These syndromic outbreaks are not formally reported to national notifiable disease systems as the underlying etiology is not known and therefore does not meet criteria for a formal investigation.
While traditional epidemiological methods focus on identifying place- and context-dependent factors responsible for disease emergence and spread, these analyses can be limited in scope. A more comprehensive approach is needed to address the interplay of a wide range of potential factors that may limit or foster outbreaks. These can be firmly rooted in virology, immunology and pharmacology, but also encompass environmental and ecological factors, or social and behavioral domains such as communication patterns and public health interventions. This Perspective proposes a multidisciplinary case-control hypothesis testing framework that can be applied to outbreaks of unknown etiology.
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