Quantifying within-household transmission of extended-spectrum β-lactamase-producing bacteria

Objectives Patients can acquire extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae during hospitalization, and colonized patients may transmit these bacteria after discharge, most likely to household contacts. In this study, ESBL transmission was quantified in households. Methods Faecal samples were longitudinally collected from hospitalized patients colonized with ESBL-producing bacteria and from their household members during hospitalization of the index patient and at 3, 6, 12 and 18 months. A mathematical household model was developed, which allowed for person-to-person transmission, acquisition from other sources (background transmission), and losing carriage. Next, a deterministic population model with a household structure was created, informed by parameter values found in the household model. Results In all, 74 index patients and 84 household members were included. In more than half of the household members ESBL-producing bacteria were demonstrated at some time during follow up. Person-to-person transmission occurred at a rate of 0.0053/colonized person/day (0.0025–0.011), background transmission at 0.00015/day (95% CI 0.00002–0.00039), and decolonization at 0.0026/day (0.0016–0.0040) for index patients and 0.0090/day (0.0046–0.018) for household members. The estimated probability of transmission from an index patient to a household contact was 67% and 37% vice versa. Conclusion There is frequent transmission of ESBL-producing bacteria in households, which may contribute to the observed endemicity of ESBL carriage in the Netherlands. However, the population model suggests that there is not a single dominant acquisition route in the community.