Infectious virus shedding duration reflects secretory IgA antibody response latency after SARS-CoV-2 infection.

Infectious virus shedding from individuals infected with severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) is used to estimate human-to-human transmission risk. Control of SARS-CoV-2 transmission requires identifying the immune correlates that protect infectious virus shedding. Mucosal immunity prevents infection by SARS-CoV-2, which replicates in the respiratory epithelium and spreads rapidly to other hosts. However, whether mucosal immunity prevents the shedding of the infectious virus in SARS-CoV-2-infected individuals is unknown. We examined the relationship between viral RNA shedding dynamics, duration of infectious virus shedding, and mucosal antibody responses during SARS-CoV-2 infection. Anti-spike secretory IgA antibodies (S-IgA) reduced viral RNA load and infectivity more than anti-spike IgG/IgA antibodies in infected nasopharyngeal samples. Compared with the IgG/IgA response, the anti-spike S-IgA post-infection responses affected the viral RNA shedding dynamics and predicted the duration of infectious virus shedding regardless of the immune history. These findings highlight the importance of anti-spike S-IgA responses in individuals infected with SARS-CoV-2 for preventing infectious virus shedding and SARS-CoV-2 transmission. Developing medical countermeasures to shorten S-IgA response time may help control human-to-human transmission of SARS-CoV-2 infection and prevent future respiratory virus pandemics.

Human Gut Microbiota and Its Metabolites Impact Immune Responses in COVID-19 and Its Complications.

BACKGROUND & AIMS: We investigate interrelationships between gut microbes, metabolites, and cytokines that characterize COVID-19 and its complications, and we validate the results with follow-up, the Japanese 4D (Disease, Drug, Diet, Daily Life) microbiome cohort, and non-Japanese data sets. METHODS: We performed shotgun metagenomic sequencing and metabolomics on stools and cytokine measurements on plasma from 112 hospitalized patients with SARS-CoV-2 infection and 112 non-COVID-19 control individuals matched by important confounders. RESULTS: Multiple correlations were found between COVID-19-related microbes (eg, oral microbes and short-chain fatty acid producers) and gut metabolites (eg, branched-chain and aromatic amino acids, short-chain fatty acids, carbohydrates, neurotransmitters, and vitamin B6). Both were also linked to inflammatory cytokine dynamics (eg, interferon γ, interferon λ3, interleukin 6, CXCL-9, and CXCL-10). Such interrelationships were detected highly in severe disease and pneumonia; moderately in the high D-dimer level, kidney dysfunction, and liver dysfunction groups; but rarely in the diarrhea group. We confirmed concordances of altered metabolites (eg, branched-chain amino acids, spermidine, putrescine, and vitamin B6) in COVID-19 with their corresponding microbial functional genes. Results in microbial and metabolomic alterations with severe disease from the cross-sectional data set were partly concordant with those from the follow-up data set. Microbial signatures for COVID-19 were distinct from diabetes, inflammatory bowel disease, and proton-pump inhibitors but overlapping for rheumatoid arthritis. Random forest classifier models using microbiomes can highly predict COVID-19 and severe disease. The microbial signatures for COVID-19 showed moderate concordance between Hong Kong and Japan. CONCLUSIONS: Multiomics analysis revealed multiple gut microbe-metabolite-cytokine interrelationships in COVID-19 and COVID-19related complications but few in gastrointestinal complications, suggesting microbiota-mediated immune responses distinct between the organ sites. Our results underscore the existence of a gut-lung axis in COVID-19.

Identification and characterization of a novel α-haemolytic streptococci, Streptococcus parapneumoniae sp. nov., which caused bacteremia with pyelonephritis.

OBJECTIVES: We report a case of bacteremia with pyelonephritis in an adult male with an underlying disease caused by α-hemolytic streptococci. α-Hemolytic streptococci were isolated from blood, but it was challenging to identify its species. This study aimed to characterize the causative bacterium SP4011 and to elucidate its species. METHODS: The whole-genome sequence and biochemical characteristics of SP4011 were determined. Based on the genome sequence, phylogenetic analysis was performed with standard strains of each species of α-hemolytic streptococci. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values were calculated. RESULTS: SP4011 showed optochin susceptibility and bile solubility, but did not react with pneumococcal omni antiserum. Phylogenetic analysis of the whole-genome sequence showed that SP4011 clustered with S. pneumoniae and S. pseodopneumoniae and was most closely related to S. pseodopneumoniae. Genomic analysis revealed that ANI and dDDH values between SP4011 and S. pseodopneumoniae were 94.0 % and 56.0 %, respectively, and between SP4011 and S. pneumoniae were 93.3 % and 52.2 %, respectively. Biochemical characteristics also showed differences between SP4011 and S. pseodopneumoniae and between SP4011 and S. pneumoniae. These results indicate that SP4011 is a novel species. CONCLUSION: Our findings indicate that SP4011 is a novel species of the genus Streptococcus. SP4011 has biochemical characteristics similar to S. pneumoniae, making it challenging to differentiate and requiring careful clinical diagnosis. This isolate was proposed to be a novel species, Streptococcus parapneumoniae sp. nov. The strain type is SP4011T (= JCM 36068T = KCTC 21228T).

Factors associated with lifetime use of commercial sex work services among Japanese men aged 20-49: findings from a quasi-representative national survey, 2022.

OBJECTIVES: Approximately half of Japanese men aged 20-49 years have purchased sexual services, but data concerning the use of commercial sex work (CSW) in Japan remain scarce. METHODS: We used online survey data from the National Inventory of Japanese Sexual Behavior conducted in 2022 (N=4000 Japanese men aged 20-49 years). We calculated the median number of paid sexual partners over the lifetime. We performed logistic regression analysis to determine the sociodemographic, anthropometric and attitudinal factors associated with any lifetime CSW use among men in Japan. RESULTS: The median number of paid sexual partners reported among men who had ever used CSW was 6 (IQR 3-17) across the lifetime; the corresponding value for those who had ever used CSW in the past year was 2 (IQR 1-4) over the last 12 months. In general, those reporting lifetime use of CSW were significantly more likely than their CSW-naïve counterparts to be older, be married, be heterosexual or bisexual, have higher income and have higher education. Those reporting higher self-rated attractiveness, high or low satisfaction with their sex lives, a desire to increase their frequency of sex and considering sex to be an important aspect of their lives were also found to have a higher likelihood of having used CSW. CONCLUSIONS: High rates of CSW use in Japan likely reflect ease of access, low stigma with respect to use of sexual services and the diversity in the type of services offered. High-income, employed older men have more financial resources at their disposal to purchase services, which can be cost-prohibitive for part-time or unemployed young men with low incomes. These findings will serve as a launchpad for public health efforts directed at promoting safe sexual practices and improved sexually transmitted infection screening rates among users of CSW in Japan.

Development of a partnership between academia, community, and government in response to the 2022 mpox outbreak in Japan.

Objectives　In response to the steady rise in the number of cases of mpox in nonendemic countries, starting with an outbreak in the United Kingdom in May 2022, the World Health Organization declared a public health emergency of international concern on July 23, 2022. As of November 13, 2022, seven cases of mpox have been reported in Japan.Methods　A community engagement approach was applied to prevent the spread of mpox in Japan.Results　A tripartite partnership between academia, community, and government (ACG) was established to promote multisectoral communication between vulnerable communities, medical personnel involved in diagnosis and treatment, public health specialists at public health centers, epidemiologists at the National Institute of Infectious Diseases (NIID), and government and public administration. Through information sharing, this ACG partnership can translate accurate information into effective infection control measures.Conclusion　By developing and maintaining the ACG partnership, an environment will be created that allows an immediate response to future public health crises affecting vulnerable communities. This Practice Report describes the process of establishing an ACG partnership.

Recent changes in the reporting of STIs in Japan during the COVID-19 pandemic.

OBJECTIVES: The COVID-19 pandemic has had variable effects on the rates of STIs reported across the globe. This study sought to assess how the number of STI reports changed during the pandemic in Japan. METHODS: We used national infectious disease surveillance data from the National Institute of Infectious Diseases (Tokyo, Japan) for the period between January 2013 and December 2021. We compared reported rates of chlamydia, gonorrhoea, condyloma acuminata and genital herpes, as well as total notifications for HIV/AIDS and syphilis during the pandemic versus previous years in Japan. We used a quasi-Poisson regression to determine whether any given week or month between January 2018 and December 2021 had a significant excess or deficit of STIs. Notification values above or below the 95% upper and lower prediction thresholds were considered as statistically significant. The start of the pandemic was defined as January 2020. RESULTS: Chlamydia generally remained within predicted range during the pandemic period. Reporting of gonorrhoea was significantly higher than expected throughout early-to-mid 2021 but otherwise generally remained within predicted range prior to 2021. Condyloma, herpes and HIV/AIDS reporting were transiently significantly lower than expected throughout the pandemic period, but no significant periods of higher-than-expected reporting were detected. Syphilis showed widespread evidence of significantly lower-than-predicted reporting throughout 2020 but eventually reversed, showing significantly higher-than-predicted reporting in mid-to-late 2021. CONCLUSIONS: The COVID-19 pandemic was associated with variable changes in the reporting of STIs in Japan. Higher-than-predicted reporting was more likely to be observed in the later phases of the pandemic. These changes may have been attributable to pandemic-related changes in sexual behaviour and decreased STI clinic attendance and testing, but further research on the long-term impact of the pandemic on STIs is necessary.

Necessity for a System Implementing Therapeutic Drug Monitoring in Outpatient Settings Based on the Actual Use of Voriconazole Using the National Database of Health Insurance Claims and Specific Health Checkups of Japan: A Descriptive Epidemiological Study.

Voriconazole (VRCZ) is an antifungal drug that necessitates therapeutic monitoring (TDM). Typically, TDM is recommended for patients undergoing long-term outpatient treatment. However, in Japan, insurance reimbursement for TDM is only permitted for inpatients. There is a concern that VRCZ use is growing among outpatients, although information regarding this issue remains unavailable. Therefore, we aimed to clarify the use of VRCZ by utilizing data from the National Database of Health Insurance Claims and Specific Health Checkups in Japan. The use of branded and generic oral VRCZ from 2013 to 2019 was calculated using the defined daily doses/1000 inhabitants/d (DID) for each receipt type. Oral VRCZ was used more frequently in the outpatient setting than that in the inpatient setting, with use increasing over time. The use of generic drugs began in 2016 and accounted for 52.5% of the use in 2019 among outpatients. Considering outpatient prescriptions, 76.4-81.0% were dispensed at insurance pharmacies, indicating the need for community pharmacist involvement. Accordingly, the appropriate use of VRCZ in ambulatory care should be promoted in collaboration with community pharmacists, and a reimbursement system should be established to implement TDM in ambulatory care.

Lack of clinical evidence of antiviral therapy for human monkeypox: A scoping review.

Since May 2022, many human monkeypox cases have been reported from non-endemic countries. This systematic review aimed to evaluate and summarize the existing research on the efficacy and safety of tecovirimat, brincidofovir, and cidofovir for patients with monkeypox. We searched studies that reported the efficacy and adverse events of tecovirimat, brincidofovir, or cidofovir for patients with human monkeypox in several databases including preprint servers. Only five studies were included. The efficacy and adverse events were assessed in only five and four patients, respectively. Regarding tecovirimat, all two patients recovered from monkeypox. One had no adverse event and the other has no description of an adverse event. Regarding brincidofovir, all three patients recovered from monkeypox but all of them had increased alanine transaminase, and one had nausea and abdominal discomfort. There was no study on treatment with cidofovir. Based on past studies and our results, tecovirimat might be the best choice due to ease of administration (oral drug), fewer side effects, and past treatment results for human monkeypox administration. However, very few studies were included in this scoping review. Therefore, further studies are needed to assess their efficacy and safety as possible treatments for human monkeypox.

Effect of the COVID-19 pandemic and state of emergency declarations on the relative incidence of legionellosis and invasive pneumococcal disease in Japan.

INTRODUCTION: During the COVID-19 pandemic, the incidence of many droplet-transmitted infections decreased due to increased mask-wearing and social distancing. Contrastingly, there has been concern that COVID-19 countermeasures, such as lockdowns, may increase legionellosis incidence via water stagnation. During the pandemic in Japan, four state of emergency declarations were imposed between 2020 and 2021, which makes it particularly suitable to test this hypothesis. METHODS: We use country-level surveillance data from the National Institute of Infectious Diseases to track the relative incidence of legionellosis compared to invasive pneumococcal disease (IPD) during the COVID-19 pandemic in Japan, with a focus on the periods just after state of emergency declarations were lifted. RESULTS: The absolute number of legionellosis and IPD cases decreased in 2020 and 2021 compared to previous years. The average relative incidence of legionellosis as well as the variance of the relative incidence significantly increased during the pandemic compared to previous years. There were no increases in the relative incidence of legionellosis during the periods immediately following emergency declaration liftings, but the relative incidence did increase considerably during the first two states of emergency. CONCLUSIONS: COVID-19 countermeasures appear more effective at decreasing the incidence of human-to-human transmitted infections, such as IPD, compared to environmentally-transmitted infections, such as legionellosis. Though no evidence was found to suggest that legionellosis cases increased after state of emergency declarations, public health efforts should continue to emphasize the importance of routine sanitation and water system maintenance to prevent water stagnation and Legionella spp. contamination.

A case of prosthetic joint infection caused by Mycobacterium tuberculosis complicated secondary bacterial infection after knee joint replacement surgery.

Mycobacterium tuberculosis (M. tuberculosis) is a rare cause of prosthetic joint infection (PJI). Previous studies have reported that many cases of PJI caused by M. tuberculosis have no medical history of active tuberculosis (TB) or other localization, which contributes to diagnostic difficulties. Furthermore, owing to the limited number of studies on treatment, appropriate treatment strategies, such as the duration of anti-tuberculosis (anti-TB) drugs and surgical indications, remain unclear. We report a case of PJI caused by M. tuberculosis and secondary pyogenic arthritis caused by Staphylococcus aureus and Streptococcus dysgalactiae in a 67-year-old man after knee joint replacement surgery in Japan, which was a moderately endemic country until 2020 and a low endemic country since 2021. Although he had no past medical history or close contact with TB, he was diagnosed with PJI caused by M. tuberculosis, following the culture of a synovectomy specimen. He underwent two-stage surgery and was treated with anti-TB drugs for a total of 12 months and recovered without recurrence. Based on our case and previous studies, there are three points of clinical significance for PJI caused by M. tuberculosis. First, about one year of anti-TB drugs with two staged joint revision resulted in a good course of treatment. Second, surgical treatment might be considered in cases complicated by secondary bacterial infection. Third, because the diagnosis of PJI caused by M. tuberculosis is difficult, TB should be considered in the differential diagnosis of routine bacterial culture-negative PJI, especially in endemic areas.

A nationwide cross-sectional study using a web-based questionnaire survey of the duration of isolation of COVID-19 inpatients with cancer at Japanese cancer centers.

There is no clear consensus regarding the optimal isolation duration for immunocompromised patients with coronavirus disease 2019 (COVID-19). Therefore, we conducted a questionnaire survey at eight Japanese cancer centers to investigate the practices of infectious disease specialists regarding the duration of isolation for COVID-19 inpatients with cancer. For asymptomatic to severely ill COVID-19 inpatients without severe immunodeficiency, four centers reported at least 10 days of isolation without testing, and two reported at least 20 days. Two centers incorporated polymerase chain reaction (PCR) as a criterion for terminating the isolation of inpatients without severe immunodeficiency. For severely immunocompromised COVID-19 inpatients, at least 20 days of isolation were required in seven facilities, regardless of illness severity. Additionally, seven centers had implemented Ct or antigen quantification test values as criteria for de-isolating severely immunocompromised inpatients. No cases caused nosocomial outbreaks after isolation was terminated based on each facility's criteria for isolation termination. Thus, cancer patients required longer isolation periods than the general population in most facilities, and for those with severe immunodeficiency, the isolation periods were longer and more tightly controlled with tests.

Two Cases of Breakthrough Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infections Caused by the Omicron Variant (B.1.1.529 Lineage) in International Travelers to Japan.

In November 2021, the World Health Organization designated a new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant of concern, Omicron (PANGO lineage B.1.1.529). We report on the first 2 cases of breakthrough coronavirus disease 2019 (COVID-19) caused by Omicron in Japan among international travelers returning from the country with undetected infection. The spread of infection by Omicron were considered.

Multisystem Inflammatory Syndrome in Adult after First Dose of mRNA Vaccine.

A 32-year-old man in Japan experienced respiratory failure after receiving the first dose of coronavirus disease (COVID-19) vaccine. He was treated with noninvasive ventilation and corticosteroids. Serologic test results suggested previous COVID-19; therefore, he received a diagnosis of multisystem inflammatory syndrome. COVID-19 vaccination could be a trigger for this condition.

Duration of Infectious Virus Shedding by SARS-CoV-2 Omicron Variant-Infected Vaccinees.

To determine virus shedding duration, we examined clinical samples collected from the upper respiratory tracts of persons infected with severe acute respiratory syndrome coronavirus 2 Omicron variant in Japan during November 29-December 18, 2021. Vaccinees with mild or asymptomatic infection shed infectious virus 6-9 days after onset or diagnosis, even after symptom resolution.

Disseminated Streptococcus anginosus invasive infection with intracranial subdural abscess formation.

We report the case of a 67-year-old woman with disseminated Streptococcus anginosus invasive infection. Even under a maximal dose of susceptible antibiotics, her condition was complicated by pulmonary septic emboli and intracranial subdural abscess. Effective antibiotics and emergent surgical drainage were performed, but the sequelae of aphasia and hemiplegia remained. Underlying immunocompromised conditions of diabetes mellitus and monoclonal gammopathy of unknown significance might partially affect the clinical course of invasive S. anginosus infection. Once the infection becomes invasive, it can be refractory and difficult to treat. Clinicians should acknowledge the characteristics of invasive S. anginosus infection.

Lessons learned from an outbreak of COVID-19 in the head and neck surgery ward of a Japanese cancer center during the sixth wave by Omicron.

INTRODUCTION: We describe a coronavirus disease (COVID-19) outbreak in a cancer center's head and neck surgery ward and the interventions to halt ongoing exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among healthcare workers and patients with cancer. METHODS: Case definition included all healthcare workers and all patients associated to the ward from January 27 to January 31, 2022 with a positive SARS-COV-2 antigen test. This retrospective descriptive study was conducted between January 27, 2022, and February 14, 2022. RESULTS: From January 28, 2022, to February 9, 2022, 84 cases (36 healthcare workers, 48 patients) were screened, and 26 (12 healthcare workers, 14 patients) were identified as SARS-CoV-2-positive. The proportion of healthcare providers who performed aerosol generating procedures on positive patients was 91% for positive cases and 49% for non-cases. Room sharing with patients with COVID-19 was 64% for positive cases and 21% for non-cases (57% vs. 21% with positive tracheostomy patients; 43% vs. 9% with positive cases using a nebulizer; 50% vs. 15% with positive cases requiring sputum suctioning, respectively). Compliance with the universal masking policy for patients was 36% of positive cases and 79% of non-cases. CONCLUSIONS: This is the first report of a nosocomial outbreak of COVID-19 in a head and neck surgery ward during the Omicron pandemic. Notably, there were a high number of positive cases among healthcare workers who performed aerosol generating procedures for positive patients and patients who shared the room with a patient with COVID-19 with the potential to generate aerosols.

A study of trends and factors associated with therapeutic drug monitoring (TDM) implementation for arbekacin treatment using a large Japanese medical claims database.

INTRODUCTION: Reimbursements for pharmacist interventions and infectious disease teams have recently been introduced in Japan. Arbekacin (ABK) is used to treat pneumonia and sepsis caused by methicillin-resistant Staphylococcus aureus, and therapeutic drug monitoring (TDM) is recommended. This study aimed to clarify the trend in TDM implementation for ABK over time and the factors associated with TDM implementation using a claims database. METHODS: Data of patients aged ≥15 years who received ABK for ≥3 consecutive days between 2010 and 2019 were extracted from a large Japanese medical claims database. The proportion of reimbursements claimed for TDM, pharmacist interventions, and the setup of infectious disease teams for each year were calculated. The factors associated with TDM implementation were identified using multivariate logistic regression analysis. RESULTS: The proportion of TDM implementation for ABK increased by 9.1% from 2010 to 2019, but it remained less than 40% throughout this period. The proportion of TDM implementation was higher in patients who claimed reimbursements for pharmacist interventions than in patients who did not. Logistic regression analysis showed that the stationing of pharmacists in wards and long-term ABK treatment were significantly associated with TDM implementation. CONCLUSIONS: From 2010 to 2019, the proportion of TDM implementation for ABK was significantly low. Moreover, the factors associated with TDM implementation were clarified. An environment wherein pharmacists can help implement TDM for patients receiving ABK would be beneficial.

A case report of breakthrough infection with the SARS-CoV-2 delta variant and household transmission: Role of vaccination, anti-spike IgG and neutralizing activity.

There have been several reports of breakthrough infections, which are defined as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections among individuals who had received at least two doses of vaccine at least 14 days before the onset of infection, but data on the antibody titers, including SARS-CoV-2 neutralizing antibody activity, and the clinical course of individuals with breakthrough infections are limited. We encountered a case of breakthrough infection with the SARS-CoV-2 delta variant in a 31-year-old female healthcare worker (the index case, Case 1) and a secondary case (Case 2) in her unvaccinated 33-year-old husband. We studied the role of the anti-spike immunoglobulin G (IgG) and neutralizing antibody activity in the two case patients. Case 1 had high anti-spike IgG detected on day 3 of the illness, with low neutralizing antibody activity. The neutralizing antibody activity started to increase on day 5 of the illness. In Case 2 both the anti-spike IgG and the neutralizing antibody activity remained low from days 4-11 of illness, and the anti-spike IgG gradually increased from day 9. In Case 1, the fever broke within 4 days of onset, coinciding with the rise in neutralizing antibodies, whereas the fever took 7 days to resolve in Case 2. SARS-CoV-2 infection can occur even in vaccinated individuals, but vaccination may contribute to milder clinical symptoms because neutralizing antibodies are induced earlier in vaccinated individuals than in unvaccinated individuals.

Evaluation of the QIAstat-Dx Respiratory SARS-CoV-2 panel, a rapid multiplex PCR method for the diagnosis of COVID-19.

INTRODUCTION: Rapid, simple, and accurate methods are required to diagnose coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study aimed to evaluate the performance of the QIAstat-Dx Respiratory SARS-CoV-2 Panel (QIAstat-SARS-CoV-2), a rapid multiplex PCR assay for SARS-CoV-2 detection. METHODS: Nasopharyngeal swabs (NPS) that were obtained from patients with COVID-19 who were diagnosed at the National Center for Global Health and Medicine were used in this study. When the NPS samples were found to be negative for SARS-CoV-2 after treatment, they were used as negative samples. We evaluated the performance of the QIAstat-SARS-CoV-2 comparing SARS-CoV-2 detection with the National Institute of Infectious Diseases in Japan-recommended real-time polymerase chain reaction (RT-PCR) method (NIID-RT-PCR). RESULTS: In total, 45 NPS samples were analyzed. The proportion of overall agreement between QIAstat-SARS-CoV-2 and NIID-RT-PCR on 45 samples was 91.0% with a sensitivity of 84.0% (21/25), specificity at 100% (20/20), negative predictive value at 83.3% (20/24), and positive predictive value at 100% (21/21). There were no patients with co-infections with pathogens other than SARS-CoV-2. CONCLUSIONS: QIAstat-SARS-CoV-2 showed a high agreement in comparison with the NIID-RT-PCR for the detection of SARS-CoV-2. The QIAstat-SARS-CoV-2 also provided a rapid and accurate diagnosis for COVID-19, even when the concurrent detection of other respiratory pathogens was desired, and therefore, has the potential to direct appropriate therapy and infection control precautions.

The intended purpose and regional patterns of use of antibiotics for managing Clostridioides (Clostridium) difficile infections: An analysis of the National Database of Health Insurance Claims and Specific Health Checkups data of Japan.

INTRODUCTION: We previously showed the trend of antimicrobial use (AMU) for Clostridioides (Clostridium) difficile infection (CDI) using sales data. However, the details of the prescribing medical institutions and regional characteristics are unknown. Therefore, the purpose of this study was to clarify the details of the medical institutions where antibiotics for CDI were prescribed, and evaluate the AMU for CDI and the regional characteristics. METHODS: Antibiotics for CDI, including oral vancomycin (VCM), oral metronidazole (MNZ), and intravenous (IV) MNZ, were collected from the National Database of Health Insurance Claims and Specific Health Checkups (NDB) between 2013 and 2016. The PID (patients/1000 inhabitants/day) was used as an evaluation index for AMU. The PID was calculated using the claim types: inpatient, outpatient, dental, and pharmacy. The PID of each prefecture was calculated for inpatient claims in 2016. RESULTS: The AMU of oral VCM and IV MNZ were observed mainly in the inpatient claims. For oral MNZ, the total AMU in the outpatient and pharmacy claims accounted for approximately 80% per year throughout the study period. For inpatient claims of each prefecture in 2016, the PID of the antibiotics used for CDIs was approximately 3.5 times the difference between the highest and lowest prefectures. CONCLUSIONS: The AMU for CDI that takes into account the purpose of use was clarified by using the information of the prescribed medical institutions that were included in the NDB. Oral MNZ was used frequently in outpatients, and attention should be paid to the acquisition of resistance.