This is the first report of the concise analysis of nosocomial clusters in Japan. As indicated in this report, nosocomial clustering has devastating consequences in terms of the prognosis of patients and crippling of the healthcare system both for COVID-19 and non-COVID-19 patients.
When a COVID-19 cluster occurs, close contacts are identified, isolated, and tested and infection control measures are strengthened while waiting for the cluster to end. Previous reports focused on the transmission risk and prognosis of COVID-19 patients, and did not examine the details of index cases that contribute to countermeasures against the introduction of COVID-19 to hospitals. In this study, a number of cases were due to transmission via health care workers. The risk of infection among medical personnel is considered to be higher than that among the general public, and the appropriate use of protective equipment is required.  On the other hand, as HCWs live in the community (not quarantined), they are at risk of becoming infected depending on the infection status in the community. As such, HCWs need to behave as if they are asymptomatic carriers of COVID-19 and adopt measures to prevent themselves from spreading the infection.
Testing is one of the key strategies to tackle with COVID-19. A low threshold for testing facilitates the prompt identification of cases that can be managed by isolation or quarantine, as it has been demonstrated that there are high proportions of asymptomatic and, more importantly, pre-symptomatic individuals. In Japan, it was reported that the PCR testing system was lagging behind those of other countries (accessed as of 11 May 2021 https://ourworldindata.org/coronavirus-testing#how-many-tests-are-performed-each-day), but, in the 3rd wave, the time between index case identification and expanded testing was improved compared with the 1st and 2nd waves. In addition, in Kyoto City, the time needed to contain clusters was shorter in facilities with full-time IPCs. Furthermore, facilities with full-time IPCs tended to have lower staff attack rates. (Table) The establishment of a solid chain of command by full-time IPCs and hospital executives may be necessary to contain the situation.
Since huge amounts of medical resources such as personnel involved in contact tracing and PCR testing are required to contain clusters, it is important to adopt measures to prevent introducing the disease to a hospital population. The PCR screening test at the time of admission is not a panacea, and some cases are inevitably missed. As Abbas et al. stated, it may be suitable to perform broad-scale screening of both patients and HCWs, including asymptomatic individuals, in the event that COVID-19 cases are identified on “non-COVID” wards to help identify a potential outbreak situation, and to be able to control it.