稲葉 正人

OBJECTIVES: This study aimed to identify factors deterring secondary household transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from SARS-CoV-2-positive cohabitants. METHODS: A case-control study was conducted with 272 healthcare workers in close contacts with SARS-CoV-2-positive cohabitants. Logistic regression modeling was employed to determine the factors independently associated with secondary household transmission. RESULTS: A SARS-CoV-2 infection within the past 6 months was the most protective factor against secondary household transmission (adjusted odds ratio = 0.07, 95% confidence interval: 0.01-0.61, P < 0.05). Home isolation and older age of primary index case (7-12, ≥18 years) were also associated with a reduced risk. Both monovalent and bivalent messenger ribonucleic acid booster vaccinations exhibited potential protective tendencies, but were not statistically significant. Additionally, bivalent vaccines did not demonstrate a clear advantage over monovalent vaccines. CONCLUSION: A recent history of SARS-CoV-2 infection, home isolation of positive cohabitants, and older age of primary index cases were positively associated with a reduced risk of secondary household transmission. Regarding booster vaccinations, data from a single center with a limited sample size may not capture all statistically significant differences, necessitating broader studies.

Objectives: To establish a point-of-care test for coronavirus disease 2019 (COVID-19), we developed a dry loop-mediated isothermal amplification (LAMP) method to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA. Methods: We carried out reverse transcription (RT)-LAMP using the Loopamp SARS-CoV-2 Detection kit (Eiken Chemical, Tokyo, Japan). The entire mixture, except for the primers, is dried and immobilized inside the tube lid. Results: To determine the specificity of the kit, 22 viruses associated with respiratory infections, including SARS-CoV-2, were tested. The sensitivity of this assay, determined by either a real-time turbidity assay or colorimetric change of the reaction mixture, as evaluated by the naked eye or under illumination with ultraviolet light, was 10 copies/reaction. No LAMP product was detected in reactions performed with RNA from any pathogens other than SARS-CoV-2. After completing an initial validation analysis, we analyzed 24 nasopharyngeal swab specimens collected from patients suspected to have COVID-19. Of the 24 samples, 19 (79.2%) were determined by real-time RT-PCR analysis as being positive for SARS-CoV-2 RNA. Using the Loopamp SARS-CoV-2 Detection kit, we detected SARS-CoV-2 RNA in 15 (62.5%) of the 24 samples. Thus, the sensitivity, specificity, positive predictive value, and negative predictive values of the Loopamp 2019-CoV-2 detection reagent kit were 78.9%, 100%, 100%, and 55.6%, respectively. Conclusions: The dry LAMP method for detecting SARS-CoV-2 RNA is fast and easy to use, and its reagents can be stored at 4°C, solving the cold chain problem; thus, it represents a promising tool for COVID-19 diagnosis in developing countries.

Carbapenemase-producing Escherichia coli sequence type (ST) 648 strains were isolated from two international visitors without previous medical exposure from Southeast Asian countries in a hospital in Japan. One isolate, FUJ80154, carried bla(NDM-5) in a complex class 1 integron on an IncFIB/FII plasmid; the other isolate, FUJ80155, carried two copies of bla(OXA-48) on the chromosome flanked by IS1R on both sides. The core-genome based-phylogenetic analysis with publicly available genome data of E. coli ST648 carrying bla(NDM-5) or bla(OXA-48-like) demonstrated high genetic similarity between FUJ80154 and NDM-5-prooducing E. coli ST648 strains isolated in South and Southeast Asian countries. On the other hand, no closely related isolates of FUJ80155 were identified. In the absence of prior hospitalization overseas, neither patient had qualified for routine screening of multidrug-resistant organisms, and the isolates were incidentally identified in cultures ordered at the discretion of the treating physician.IMPORTANCE Although patients with history of international hospitalization are often subject to screening for multidrug-resistant organisms, it is unclear whether patients who reside in countries where carbapenemase-producing Enterobacterales (CPE) is endemic but have no history of local hospitalization contribute to the transmission of CPE. In this study, NDM-5-producing and OXA-48-producing Escherichia coli sequence type (ST) 648, a recently recognized high-risk, multidrug-resistant clone, were detected from two overseas visitors without previous medical exposure. The findings of this study suggest that active surveillance culture on admission to hospital may be considered for travelers from countries with endemicity of carbapenem-resistant organisms even without history of local hospitalization and underscore the need to monitor cross-border transmission of high-risk clones, such as carbapenemase-producing E. coli ST648.