Fig. 3.

Directed acyclic graph illustrating implicitly assumed causal structure between exposure to children and SARS-CoV-2 seropositivity. Each arrow implies an assumed causal effect from the variable the arrow originates to the variable the arrow is directed at. Variables lying on a directed path between exposure and the outcome of interest (e.g., other adult household members size) do not have to be controlled for. However, variables preceding both exposure and outcome may introduce biases and need to be controlled for. In this case the minimal sufficient adjustment sets for estimating the direct effect of household child exposure on SARS-CoV-2 seropositivity are as follows:• Age, education, income, gender, and smoking. • Age, income, nationality, gender, and smoking. HH household