No NDM-1 carriage in healthy persons from Mumbai: reassuring for now

Sir, We read with interest the article on the faecal carriage of NDM-1 Enterobacteriaceae from patients in a military hospital in Pakistan,1 implying the potential for spread in the community. At a tertiary care centre in Mumbai, we screened for the presence of carbapenem resistance over a 6 month period (January to June 2011) by examining 1000 consecutive faecal samples from healthy individuals (not patients) reporting for routine health screening. This study was ethically approved by the National Health and Education Society, P. D. Hinduja National Hospital and Medical Research Centre. Stool samples were cultured on MacConkey agar and incubated at 37°C for 24 h. Enterobacteriaceae were then tested for the presence of extended-spectrum β-lactamases (ESBLs) on Mueller–Hinton agar using cefpodoxime discs and were further evaluated using β-lactam inhibitors, i.e. ceftazidime and ceftazidime plus clavulanic acid, and cefotaxime and cefotaxime plus clavulanic acid. According to the CLSI 2011 guidelines (M100-S21),2 disc diffusion testing was undertaken with a 10 μg ertapenem disc placed on a bacterial lawn prepared using a bacterial suspension with a turbidity equivalent to that of a 0.5 McFarland standard (1.5 × 108 cfu/mL). The zones around the disc were assessed after incubation at 37°C for 24 h. If isolates were identified as carbapenem resistant, they were to be molecularly characterized for the presence of the blaNDM-1 gene.1 Of the total number of samples, 23.9% (239/1000) were found to be ESBL producers, of which 95% (227/239) and 5% (12/239) were identified as Escherichia coli and Klebsiella species (9 Klebsiella oxytoca, 1 Klebsiella pneumoniae and 2 Klebsiella species), respectively. None of the 1000 isolates was carbapenem resistant. The findings of our study are contrary to those reported by Perry et al.,1 where a high prevalence (18.5%) of faecal carriage of carbapenem-resistant Enterobacteriaceae was noted, albeit among patients. However, an earlier report from our institute reported the absence of NDM-1 in follow-up stool samples of 10 patients who had earlier been diagnosed and treated for infections caused by NDM-1-producing Enterobacteriaceae.3 A study done at our institution in 2004 demonstrated an ESBL faecal carriage rate of 11% in a similar cohort of individuals reporting for routine health screening.4 This carriage rate has increased to 23.9% in antibiotic-naive healthy persons. Fortunately, at least in our small study, NDM-1 has not spread to the same extent. Though this is reassuring, it should not detract from the need to implement strict infection control measures and antimicrobial stewardship for resistant organisms. This study was funded by the National Health and Education Society, P. D. Hinduja National Hospital and Medical Research Centre. None to declare. We thank the National Health and Education Society, P. D. Hinduja National Hospital and Medical Research Centre for their encouragement and support. We also thank the hospital staff of the health check department for their support and co-operation.