Aftermath

fective. For example, we have published work that demonstrates that patient-to-patient transmission is important for colonization acquisition of ESBL-producing Klebsiella spp. and Escherichia coli (5). We believe that a couple of points require clarifi cation. In our article, we looked at risk factors for colonization with ESBL-producing bacteria on admission to an intensive care unit. We did not examine risk factors for selecting ESBL-producing bacteria as the letter implies. For the antimicrobial drugs identifi ed as potential risk factors, we clearly stated in the discussion that the risk factors identifi ed may be causally related to the outcome of ESBL-colonization or may only be statistically associated. We argue that even risk factors identifi ed are not causal; they may be important because they can help determine which patients may need empiric antimicrobial drug therapy targeted to the ESBL-producing bacteria. Future research work is still needed to assess the relative importance of patient-topatient transmission versus antimicrobial selective pressure.