The development of antimicrobial agents in the twentieth century revolutionized medicine by making many previously untreatable infectious diseases curable; however, the widespread use of these agents has also resulted in the emergence and global expansion of antimicrobial resistance (AMR). This review outlines the historical trajectory of AMR in Japan, from the early era of antimicrobial drug development to its recognition as a major public health challenge in the twenty-first century. Resistant bacteria began to be reported soon after the introduction of sulfonamides and penicillin, and in the 1950s and 1960s, Japan made important scientific discoveries in this field, including the discovery of transferable resistance factors (R factors). Subsequently, antimicrobial resistance mechanisms became increasingly complex and diverse, exemplified by the emergence of methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum β-lactamase (ESBL)-producing organisms, and carbapenemase-producing bacteria, leading to a heightened awareness of the importance of infection prevention/control and appropriate antimicrobial use. Since the 2000s, the spread of multidrug-resistant Gram-negative bacteria, their transmission in community and regional settings, and the need for a One Health perspective encompassing humans, animals, and the environment have become critical issues. In response to growing international concern, Japan has implemented a national AMR action plan and achieved some successes; nevertheless, the disease burden attributable to resistant organisms remains substantial. AMR, often described as a "silent pandemic, " represents a major public health threat that endangers the sustainability of modern medicine and necessitates continued, coordinated, and multidisciplinary efforts.

Since the beginning of the outbreak of COVID-19 in China in December 2019, the virus has spread worldwide. The first case of COVID-19 in Japan was confirmed in January 2020, and many cases of COVID-19 and COVID-19-related deaths were reported across the country thereafter. While lockdowns were implemented overseas, people in Japan were asked to refrain from unnecessary outings and travel. Refraining from outings was effective in limiting the spread of COVID-19; however, it is unclear whether refraining from traveling with overnight staying and immigration restrictions were effective in preventing the spread of COVID-19.

In this ecological study, we used open data and analyzed the effect of overnight staying at guest accommodations on the spread of COVID-19 by estimating Pearson's correlation coefficients between the numbers of newly confirmed COVID-19 cases and number of Japanese/foreign guest-nights at guest accommodations per 1×10⁵ persons in each prefecture in Japan. We obtained the following results: the number of newly confirmed COVID-19 cases showed no significant correlation with the number of Japanese guest-nights; the number of newly confirmed COVID-19 cases showed a significant positive correlation with the number of foreign guest-nights; however, this correlation was no longer observed after certain prefectures having foreign guest-night numbers in the outlier regions were excluded. From these results, assuming that the number of guests who did not use guest accommodation facilities was negligibly small, that almost all of the Japanese guests were residents of Japan, and that almost all of the foreign guests were tourists from overseas, restrictions placed on travel with overnight stay at guest accommodations may have been unnecessary, while immigration restrictions may have been necessary and effective.

Although the threat of COVID-19 has diminished, it remains important to study and evaluate the measures implemented during the COVID-19 pandemic period for preparedness in future pandemics.

From April 2024 to September 2025, a 114-bed regional hospital without a full-time infectious diseases (ID) physician received monthly on-site or online support from a young ID physician. The interventions by the ID physician included monitoring of sanitizing alcohol usage, establishment of infection control committees and manuals, review of surveillance results and feedback, and introduction of contact precautions. Following the interventions, the usage of sanitizing alcohol increased by 2.7-fold as compared with that in the previous year, reflecting improved compliance with hand hygiene practices. Infection control infrastructure, staff education, and regular reviews of the results of surveillance were successfully established and sustained. Consistent with these, the isolation rate of MRSA decreased from 7.2% to 3.4%. Thus, monthly support received from a young ID physician effectively enhanced the infection control level and potentially reduced the isolation rates of antimicrobial-resistant pathogens at the hospital, suggesting use of such support as a feasible and effective model for small- to medium-sized regional hospitals with limited infection control resources.