To the Editor: Extended-spectrum-β-lactamases (ESBLs) are enzymes capable of hydrolysing penicillins, broad-spectrum cephalosporins and monobactams. Worldwide, ESBL-producing organisms are posing an increasing challenge for empirical antibiotic use and infection control.

We recently carried out a review of microbiological isolates from clinical specimens taken from 2003 to 2007 at the Alfred Hospital, Melbourne. From 15 917 gram-negative bacilli, we identified 234 ESBL-producing organisms (1.5% of isolates) using double-disk synergy testing.

Over the 5-year period, we noted three apparent changes in ESBL epidemiology relating to Escherichia coli isolates. First, E. coli became the most frequent organism in which ESBL production was observed, making up 55.6% of all ESBL-producing organisms in 2007 (up from 23.5% in 2003) (P = 0.03). Second, while the total number of E. coli isolates remained essentially constant over the study period, there was an increase in the proportion of E. coli isolates found to produce ESBLs: 1.8% of E. coli isolates in 2007 compared with 0.36% in 2003 (P < 0.001). The third and perhaps most striking change was in the epidemiology of ESBL-producing E. coli. In 2003, ESBL-producing E. coli infections were largely hospital-acquired, with 87.5% of isolates acquired after 48 hours in hospital or after a hospital admission in the previous 12 months. However, by 2007, ESBL-producing E. coli infections were found to be predominantly community-acquired, making up 62.2% of ESBL-producing E. coli isolates (P = 0.01). The increased proportion of community-acquired infections occurred despite a parallel increase in the frequency of hospital-acquired ESBL-producing E. coli infections (Box).

Community-onset infections with ESBL-producing organisms have become increasingly recognised as important clinical entities.1 ESBL-producing E. coli bacteraemia is associated with higher mortality than bacteraemia caused by non-ESBL-producing organisms,2 a finding that has also been specifically demonstrated in the setting of community-acquired infections.3 Although local epidemiological data for infections with ESBL-producing organisms are not readily available, it appears that rates of community-associated infection vary greatly worldwide, with some regions of China reporting rates of ESBL-producing E. coli as high as 34% of all isolates.4

Although our study was limited by being a single-centre review, our findings are consistent with the emergence of multiresistant Enterobacteriaceae noted in Australian surveillance reports.5 It is not clear whether the change in our ESBL-producing isolates is reflective of local resistance patterns, or perhaps associated with travel to regions where ESBL-producing E. coli are known to be prevalent. Corroboration of these changes in other regions will be important for assessing the magnitude of this issue and responding appropriately, particularly in considering empirical antibiotic therapy for community-acquired gram-negative infections.

Hospital-acquired (HA) versus community-acquired (CA) ESBL-producing E. coli isolates, Alfred Hospital, 2003–2007

E. coli = Escherichia coli. ESBL = extended-spectrum-β-lactamase.