Household transmission investigation: Design, reporting and critical appraisal

BACKGROUND: Household transmission investigations (HHTIs) contribute timely epidemiologic knowledge in response to emerging pathogens. HHTIs conducted in the context of the COVID‐19 pandemic in 2020‐21 reported variable methodological approaches, producing epidemiological estimates that vary in meaning, precision and accuracy. Because specific tools to assist with the optimal design and critical appraisal of HHTIs are not available, the aggregation and pooling of inferences from HHTIs to inform policy and interventions may be challenging. METHODS: In this manuscript, we discuss key aspects of the HHTI design, provide recommendations for the reporting of these studies and propose an appraisal tool that contributes to the optimal design and critical appraisal of HHTIs. RESULTS: The appraisal tool consists of 12 questions that explore 10 aspects of HHTIs and can be answered ‘yes’, ‘no’ or ‘unclear’. We provide an example of the use of this tool in the context of a systematic review that aimed to quantify the household secondary attack rate from HHTIs. CONCLUSION: We seek to fill a gap in the epidemiologic literature and contribute to standardised HHTI approaches across settings to achieve richer and more informative datasets.