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In the context of climate change, the reduction of greenhouse gas emissions is a global concern. Recent publications estimate that 30–40% of total anthropogenic greenhouse gases are directly emitted by urban areas. This paper focuses on CO2, which is the main anthropogenic greenhouse gas, and presents an implementation of CO2 flux modelling in urban areas within the urban canopy model Town Energy Balance (TEB). Highly weather-dependent contributors to CO2 fluxes (buildings and vegetation) are explicitly modelled by TEB using the Building Energy Model (BEM) for buildings and Interactions between Soil, Biosphere and Atmosphere (ISBA) for urban vegetation. This approach allows the impacts of the urban microclimate on CO2 fluxes to be simulated. Non-weather-dependent contributors (traffic and human respiration) are simulated using simpler approaches. A sensitivity study applied to the centre of Toulouse, France, highlights the relevance of detailed input data related to traffic, building use and human behaviour to simulate accurate CO2 fluxes. The results show that traffic (48.5%) and buildings (42%) are the main contributors to the annual mean CO2 flux. A comparison of the model results with independent eddy-covariance flux data shows good agreement with a root mean square error of 15.3 μmol m−2 s−1 and demonstrates that the model is able to reproduce seasonally averaged daily cycles of CO2 fluxes. In future studies, this model can be used to quantify the impacts on CO2 fluxes of different urban development scenarios such as urban expansion, changes in urban form, changes in practices related to the heating of buildings or urban greening strategies. Keywords: CO2fluxes, Eddy covariance, Cities, Urban canopy layer model, Model evaluation

Clostridium difficile causes antibiotic-associated diarrhoea and pseudomembranous colitis. The main virulence factors of C. difficile are the toxins A (TcdA) and B (TcdB). A third toxin, called binary toxin (CDT), can be detected in 17% to 23% of strains, but its role in human disease has not been clearly defined. We report six independent cases of patients with diarrhoea suspected of having C. difficile infection due to strains from toxinotype XI/PCR ribotype 033 or 033-like, an unusual toxinotype/PCR ribotype positive for CDT but negative for TcdA and TcdB. Four patients were considered truly infected by clinicians and were specifically treated with oral metronidazole. One of the cases was identified during a prevalence study of A−B−CDT+ strains. In this study, we screened a French collection of 220 nontoxigenic strains and found only one (0.5%) toxinotype XI/PCR ribotype 033 or 033-like strain. The description of such strains raises the question of the role of binary toxin as a virulence factor and could have implications for laboratory diagnostics that currently rarely include testing for binary toxin.