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Background: This study aimed to examine the cause of and effective measures against cluster infections, including the delta AY.1 variant of novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that occurred in an accommodation facility. Methods: We surveyed the zoning and ventilation systems of the cluster accommodation, examined the staff’s working conditions, conducted an interview, and administered a SARS-CoV-2 test (positive samples were further tested with molecular biological test). Results: Among the 99 employees working at the accommodation, 10 were infected with the delta AY.1 variant. The causes of the cluster infections were close-distance conversations without an unwoven-three-layer mask and contact for approximately five minutes with an unwoven mask under hypoventilated conditions. Conclusions: The Delta AY.1 infection may occur via aerosols and an unwoven mask might not prevent infection in poorly ventilated small spaces. Routine infection detection and responding quickly and appropriately to positive results helps to prevent clusters from spreading.

This is a case report on a cluster infection of novel severe acute respiratory syndrome coronavirus 2 delta AY.1 variant at an accommodation facility and the subsequent attempts to isolate individuals who tested positive. The background that facilitated this cluster was investigated, and the conditions in which infection was established, the infection route, and the effectiveness of routine measures were evaluated. Ninety-nine staff members had been working at the accommodation facility at the time of infection, and it was estimated that 10 members were infected with the delta AY.1 variant. Our results suggest that infection of staff from a patient staying overnight should be excluded. The factors contributing to the cluster infection involved short-distance conversations with individuals wearing non-woven three-layer masks moved out of position (non-woven) and gathering together with individuals wearing non-woven masks in hypoventilated conditions. Our findings also indicate that this variant is possibly airborne and can infect individuals in enclosed spaces with poor ventilation, even when either infected or exposed individuals wear non-woven masks. The routine maintenance of systems established for the detection of infections and prompt and appropriate preventive measures following the identification of positive individuals will help prevent further cluster infections.

Blood culture is essential for the diagnosis of infectious disease. Appropriate treatment is administered according to blood culture results; thus, highly accurate tests are required. The present study obtained data from hospitals which are ranked among those with the highest number of beds in each prefecture (top 10%; 1,000 hospitals nationwide), beginning with 3,129 hospitals throughout Japan with ≥200 beds as of 2018. In total, 63 hospitals that gave their consent to participate in the study provided information regarding blood culture-related indicators over a 2-year period. The positive blood culture rate (95% confidence interval) was 15.4% (13.7-17.1%), the number of blood culture sets per 1,000 patient days was 21.5 (18.2-24.9), multiple set collection rate was 76.7% (71.1-82.3%) and the contamination rate was 3.1% (2.4-3.8%). Using these results as reference values for blood culture in Japanese healthcare facilities with ≥200 beds, the authors are attempting to approach these values at their resident hospitals and expect improved on-site interventions and educational activities regarding the state of blood culture.

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