# Evidence integration on health damage for humidifier disinfectant exposure and legal presumption of causation

## TL;DR

This paper presents a method to integrate evidence on health effects from humidifier disinfectant exposure to support legal causation decisions.

## Contribution

A novel systematic approach to synthesize epidemiological and toxicological evidence for legal presumption of causation.

## Key findings

- A weight-of-the-evidence approach is proposed to evaluate causation in humidifier disinfectant health damage cases.
- Epidemiological and toxicological evidence can be combined to establish general causation for legal purposes.
- The method considers the source-to-exposure-to-outcome continuum in assessing health effects.

## Abstract

Inhalation exposure to humidifier disinfectants has resulted to various types of health damages in Korea. To determine the epidemiological correlation necessary for presuming the legal causation, we aimed to develop a method to synthesize the entire evidence.

Epidemiological and toxicological studies are systematically reviewed. Target health problems are selected by criteria such as frequent complaints of claimants. Relevant epidemiologic studies are reviewed and the risk of bias and confidence level of the total evidence are evaluated. Toxicological literature reviews are conducted on three lines of evidence including hazard information, animal studies, and mechanistic studies, considering the source-to-exposure-to-outcome continuum. The confidence level of the body of evidence is then translated into the toxicological evidence levels for the causality between humidifier disinfectant exposure and health effects. Finally, the levels of epidemiological and toxicological evidence are synthesized.

Under the Special Act revised in 2020, if the history of exposure and the disease occurred/worsened after exposure were approved, and the epidemiological correlation between the exposure and disease was verified, the legal causation is presumed unless the company proves the evidence against it. The epidemiological correlation can be verified through epidemiological investigations, health monitoring, cohort investigations and/or toxicological studies. It is not simply as statistical association as understood in judicial precedents, but a general causation established by the evidence as a whole, i.e., through weight-of-the-evidence approach.

The weight-of-the-evidence approach differs from the conclusive single study approach and this systematic evidence integration can be used in presumption of causation.