Naoya Nishiyama

Evaluation of commercial phenotypic assays for the detection of IMP- or New Delhi metallo-β-lactamase-producing Enterobacteriaceae isolates in Japan

OBJECTIVES This study was designed to evaluate the sodium mercaptoacetic acid double disk synergy test (SMA-DDST), the Etest metallo-β-lactamase (MBL) MP/MPI (Etest MP/MPI), and the Mastdiscs ID Carbapenemase Detection Disc Set (MAST-CDS) for the detection of MBL-producing Enterobacteriaceae isolates in Japan. METHODS Fifty-one clinical isolates and four reference strains were tested. These isolates included 40, 4, and 11 IMP-, New Delhi MBL (NDM)-, and non-MBL-producers, respectively. SMA-DDST was performed with meropenem (MEPM)-containing disks. RESULTS Sensitivities were 38/44 (86%), 40/44 (91%), and 15/44 (34%), and the cost ratio was 1:9.4:3.8 for MEPM-SMA-DDST:Etest MP/MPI:MAST-CDS, respectively. The specificity was 11/11 (100%) for all assays. MEPM-SMA-DDST detected IMP-producing isolates with high sensitivity (38/40; 95%), but the assay was inadequate for NDM-producing isolates (0/4; 0%). The Etest MP/MPI detected both IMP- (36/40; 90%) and NDM-producing isolates (4/4; 100%), but was the most expensive. MAST-CDS detected IMP-producing isolates with low sensitivity (11/40; 28%), but the assay worked well for NDM-producing isolates (4/4; 100%). CONCLUSIONS Our results indicated that MEPM-SMA-DDST was the most cost-effective assay for the detection of IMP-producing isolates. Therefore, we conclude that MEPM-SMA-DDST is the optimal available assay for clinical first-line screening in IMP-endemic areas such as Japan. However, this assay could not detect NDM-producing isolates, whereas the Etest MP/MPI and MAST-CDS could. When MEPM-SMA-DDST is negative, the Etest MP/MPI and MAST-CDS could be used to obtain supportive data and prevent detection failure for NDM-producing isolates.

The Prophylactic Effect of Anti-influenza Agents for an Influenza Outbreak in a University Hospital

Objective From November 24 to December 9, 2013, an outbreak of the influenza (flu) A (H3) virus occurred in a tertiary-care university hospital (1,014 beds). We herein report the prophylactic effect of anti-flu agents for controlling the flu outbreak. Methods We administered pre- or post-exposure prophylaxis with anti-flu agents in flu outbreak. To test the effectiveness of prophylaxis in a flu outbreak, we used the posterior mean of the reproductive value during the pre- and post-intervention period. We also simulated the probability distribution of new flu cases. We performed an analysis to quantify the strength of the intervention effect. Results A total of 97 people were diagnosed with flu before the intervention, and 7 were diagnosed after the intervention. A molecular analysis of the flu virus revealed that this outbreak was due to the flu A (H3) virus. A total of 3,702 people received prophylaxis. There was a significant reduction in the reproductive value from 1.89 [95% confidence interval (CI), 1.59 to 2.24] to 0.65 (95% CI, 0.02 to 1.00) after the intervention (p<0.001). Conclusion Prophylaxis with anti-flu agents, along with prompt identification and isolation of infected individuals, was effective in reducing the impact of a flu outbreak in a hospital.