Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent of coronavirus disease (COVID-19) which has spread rapidly worldwide to cause a global pandemic. The SARS-CoV-2 genome shows a lower mutation rate than other RNA viruses. However, because of the ongoing rapid worldwide transmission among humans, the genetic diversity of the SARS-CoV-2 genome has increased. In Japan, a previous study suggested that the distinct viral clades L, S, G and GR of SARS-CoV-2 had been imported from overseas and begun to circulate domestically by April 2020. However, little is known about molecular epidemiology of SARS-CoV-2 since then, because of the lack of sufficient information on the viral genome sequence information in Japan. Herein, to probe the molecular epidemiological trends in Japan, we determined the full genome sequences of SARS-CoV-2 (n=55) derived from patients admitted to our hospital and performed a comparative analysis with domestic and international sequence information available from GISAID and GenBank. The results showed that the dominant domestic genotypes, including our determined sequences, had shifted from clades S and L to clades G and GR, and dispersed widely during the first infection peak period (March to April). In contrast, all the SARS-CoV-2 genotypes after May 2020 are highly clustered as unique clade GR genotypes that are not detected outside Japan. This genetic clustering occurred during the period under which restrictions were placed on overseas travel in Japan. Similar trends of viral genotype clustering have also been observed worldwide, with regional disparities. Under these circumstances, we should adopt adequate preventive measures to prevent the viral genetic diversity from increasing, and also further extend the molecular epidemiological survey of SARS-CoV-2 genotypes in Japan. These efforts will aid in ensuring successful use of the novel vaccines and antiviral drugs in the near future.

Gram-negative glucose-non-fermenting Acinetobacter can be isolated from the natural environment and from the skin and intestinal tract of both healthy and immunocompromised patients, and can cause bloodstream infections and pneumonia in immunocompromised patients. Although Acinetobacter strains frequently show resistance to drugs and are often resistant to the initially selected antimicrobial agents, there are limited studies on the initial treatment and prognosis. In this study, we retrospectively analyzed the data of 68 cases of Acinetobacter bacteremia seen from January 2009 to July 2018 at our institution. The mean age of the patients was 69 years. The most common infections that necessitated administration of antimicrobial agents were intestinal infections (34%) and catheter infections (25%). There was no difference in the 30-day mortality between the groups with the aforementioned infections (9 (21%) vs. 6 (24%) (P=0.90)). The prognostic factors in Acinetobacter bacteremia do not depend on the antimicrobial selected for the initial treatment, but may be greatly influenced by underlying diseases and age. The findings suggest that choice of the appropriate treatment based on the results of culture is more important than widespread treatment in the early stage.

Background：The reverse-transcription polymerase chain reaction (RT-PCR) test is currently the gold standard for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, until date, few studies have reported on the performance of the quantitative antigen test. In this study, we attempted to validate the performance of a quantitative antigen test at a medium-sized hospital. Materials and Methods：A total of 149 nasopharyngeal swabs from 115 hospitalized patients were tested in parallel by-SARS-CoV-2 RT-PCR and the quantitative antigen test, and the results were compared. We assessed：(1) the detection rates with the quantitative antigen test and RT-PCR；(2) the factors associated with discordant results；(3) correlation of antigen concentration over the course of the clinical illness. Results：(1) The positive concordance, negative concordance, and overall concordance of the results of the quantitative antigen test with the results of RT-PCR were 100%, 88.4%, and 90.4% respectively. (2) There were no obvious differences in the performance of the test according to the age, sex, period from onset, body temperature, or presence/absence of pneumonia. The antigen concentration was significantly higher in the positively concordant samples (5,000pg/mL；P = 0.002) than in the negatively concordant samples (74.88 pg/mL). (3) The antigen titer decreased with time from the onset of infection (r = ­0.65595). Conclusion：The sensitivity and specificity of the SARS-CoV-2 quantitative antigen test was high and comparable to those of the RT-PCR test. The results indicate that the SARS-CoV-2 quantitative antigen test could be useful not only for screening, but also in clinical practice. The SARS-CoV-2 quantitative antigen test showed sufficient sensitivity throughout the clinical course, from the first screening to discharge from the hospital. The test may be useful for infection control and evaluation of the clinical course of COVID-19 in medium-sized hospitals.

We report a case of non-O1, non-O139 Vibrio cholerae bacteremia that developed in an 81-year-old man with recurrent non-small cell lung cancer who was under treatment with gefitinib. He was admitted to our hospital with high-grade fever and diarrhea. Laboratory tests showed evidence of moderate inflammation and elevated serum levels of alkaline phosphatase and gamma-glutamyltransferase. He was diagnosed as having acute cholangitis and initiated on treatment with SBT/CPZ. Blood culture on admission showed growth of non-O1, non-O139 V. cholerae. The patient recovered with adequate antibiotic therapy, including AZM, to which the V. cholerae strain was found to be sensitive. Few cases of non-O1, non-O139 V. cholerae bacteremia have been reported in Japan. In addition to immunocompromised patients with liver cirrhosis or hematological malignancies, patients with solid tumors, such as lung cancer, may also develop V. cholerae bacteremia.

Tenofovir disoproxil fumarate（TDF）is a prodrug of tenofovir（TFV）, used in the treatment of hepatitis B（HBV）and HIV-1. TFV is a renally excreted drug；a weekly dose of 300mg is recommended for patients suffering from HIV/HBV co-infection and undergoing hemodialysis（HD）for renal failure. The pharmacokinetics of TFV in Japanese patients undergoing HD has not yet been thoroughly explored. Herein, we report a case of HD in which the plasma concentrations of TFV were measured serially after the start of treatment with TDF. An 80-year-old Japanese man with HIV-1 was undergoing HD thrice weekly for end-stage renal failure. Concomitantly, the patient was receiving treatment with darunavir ethanolate, ritonavir, and raltegravir potassium for HIV-1 infection. With the treatment, the blood HIV-RNA levels had decreased to below 20 copies/mL. However, the patient developed acute HBV while under follow-up as an outpatient. He was started on treatment with TDF/emtricitabine, administered once weekly after HD, as treatment for HBV. The 7-day TFV trough concentrations measured in two consecutive weeks were 54 and 45ng/mL. The values were comparable with those in the general Japanese population（non-HD subjects）and to other previous reports. The treatment resulted in suppression of both HIV-1 and HBV. However, based on the combination of drugs and HD conditions, the dialysis clearance and removal rates vary. In conclusion, measurement of the plasma drug concentrations is useful for appropriate and definitive treatment of HIV-1 and HBV in patients undergoing HD.

Klebsiella pneumoniae independently causing necrotizing fasciitis in patients with Klebsiella pneumoniae bacteremia is known and has mainly been reported from East Asia, especially Taiwan and Korea. The clinical course of necrotizing fasciitis developing in association with K. pneumoniae bacteremia has not yet been clearly described. We report a case of lower leg K. pneumoniae necrotizing fasciitis in a patient with following K. pneumoniae bacteremia, which was unrecognized on day 1 of admission. The necrotizing fasciitis, which necessitated surgical treatment, became clinically evident only after the bacteremia diagnosis. A 65- year-old Korean woman who presented with a history of fever and malaise developed septic shock of unknown origin. Although effective antimicrobial therapy was initiated soon after she was admitted to us, purpura and pain in the left lower leg appeared on day 6 of admission, and necrotizing fasciitis was suspected. The patient recovered after surgical treatment and was discharged on day 25 of hospitalization. The isolated K. pneumoniae showed a positive string test, and genetic analysis identified it as the K1-ST23 strain, which is known to be a hypervirulent K. pneumoniae (hvKp) strain. It has been suggested that hvKp bacteremia can cause necrotizing fasciitis even during effective antimicrobial therapy, and because of the need for immediate surgical treatment, clinicians should be very attentive to the appearance of a new skin or soft tissue lesion in patients with K. pneumoniae bacteremia. The index of suspicion should be even higher in patients from East Asia and for K. pneumoniae strains that are string test-positive.