[Relationship between the number of public health nurses and the total number of people receiving home-visit nursing services for mental health/intractable diseases, and those numbers' regional differences].

Objectives　The primary aim of this study was to clarify the relationship between the number of public health nurses (PHNs) and the total number of people who received home-visit nursing services for mental health or intractable diseases. The secondary aim was to clarify the extent of regional differences in the number of PNHs and mental health or intractable diseases.Methods　This study used the total number of people who received home-visit nursing services for mental health or intractable diseases in 2019 from the Portal Site of Official Statistics of Japan (e-Stat) and population and area data in January 2020. Single and multiple regression analyses (covariates: population and area) were performed on the relationship between the number of PHNs per 100,000 population (abbreviated as "ratios of PHNs") and the total number of people who received home-visit nursing services for mental health or intractable diseases per 100,000 population (abbreviated as "mental health/intractable disease achievements"). Regional differences in ratios of PHNs and mental health/intractable disease achievement were examined using mean, standard deviation, maximum/minimum values, and Gini coefficients. Analyses were performed for each of the five units: the prefectures as a whole, prefectural public health centers, municipalities within the jurisdiction of prefectural public health centers, and cities in which public health centers are established (including or not including special wards).Results　Regression analyses indicated a positive relationship between the ratios of PHNs and mental health/intractable disease achievements. Multiple regression analysis indicated that both achievements were positively associated with population size and negatively associated with area size. The largest regression coefficients between the ratios of PHNs and achievements were 34.07 and 5.48 regarding mental health achievements and intractable disease achievements, respectively. For regional differences, the smallest Gini coefficient was the ratios of PHNs, and the largest was intractable disease achievements. The smallest and largest coefficient of the prefectures as a whole was 0.15 and 0.34, respectively. The maximum/minimum values of the prefectures as a whole also indicated that the smallest was 3.8 in the ratio of PHNs and the largest was 30.0 in intractable disease achievement.Conclusions　Increasing number of PHNs is needed to provide more home-visit nursing services for mental health and intractable diseases. It is particularly important to fill up the larger number of PHNs in smaller populations or larger area prefectures. Due to regional differences in the home-visit nursing service, it is important to promote the increase in the level of these activities.

Risk of death in old Japanese COVID-19 cases infected with the Omicron variant: a population-based study.

We assessed case fatality rates (CFRs) in cases aged ≥70 years in 10 Japanese prefectures (14.8 million residents) diagnosed between January 2022 and March 2023, when the Omicron variant was dominant in Japan. We selected incident reports on 283,052 study subjects from participating Public Health Centers adhering to the Infectious Diseases Control Law. Cases were passively followed up until the end of their isolation, date of death or 28 days after the COVID-19 diagnosis, whichever occurred first. We calculated age-standardized CFRs with 95% confidence intervals (CI) using the Japanese population aged 70-79, 80-89 and ≥90 in 2022 divided into 16 subgroups according to the period of COVID-19 diagnosis. The total overall CFR was 1.59% (95% CI 1.55-1.64); it ranged between 0.67% (95% CI 0.38-0.96, May 23-June 19) and 2.58% (95% CI 2.36-2.80, January 31-February 27). We observed three peaks of age-standardized CFRs paralleling the 6th, 7th and 8th endemic COVID-19 waves driven by Omicron in Japan (2.2% January 31-February 27, 1.0% July 18-August 14 and 1.6% December 26-January 22, 2023, respectively). Population-based CFRs for Omicron variant COVID-19 in Japanese aged ≥70 years remained <3% throughout the period January 2022-March 2023, including during three large endemic waves in this country.

Change over Time in the Risk of Death among Japanese COVID-19 Cases Caused by the Omicron Variant Depending on Prevalence of Sublineages.

To assess temporal changes to the risk of death in COVID-19 cases caused by the Omicron variant, we calculated age-standardized case fatality rates (CFR) in patients aged ≥40 years over nine diagnostic periods (3 January to 28 August 2022) in ten Japanese prefectures (14.8 million residents). Among 552,581 study subjects, we found that there were 1836 fatalities during the isolation period (up to 28 days from date of onset). The highest age-standardized CFR (0.85%, 95% confidence interval (CI):0.78-0.92) was observed in cases diagnosed in the second 4-week period (January 31 to February 27), after which it declined significantly up to the 6th 4-week period (0.23%, 95% CI: 0.13-0.33, May 23 to June 19). The CFR then increased again but remained at 0.39% in the eighth period (July 18 to August 28). The CFR in cases with the BA.2 or BA.5 sublineages in the age range 60-80 years was significantly lower than that with BA.1 infections (60 years: 0.19%, 0.02%, 0.053%, respectively; 70 years: 0.91%, 0.33%, 0.39%; ≥80 years: 3.78%, 1.96%, 1.81%, respectively). We conclude that the risk of death in Japanese COVID-19 patients infected with Omicron variants declined through February to mid-June 2022.

Shorter Incubation Period among COVID-19 Cases with the BA.1 Omicron Variant.

We aimed to elucidate the range of the incubation period in patients infected with the SARS-CoV-2 Omicron variant in comparison with the Alpha variant. Contact tracing data from three Japanese public health centers (total residents, 1.06 million) collected following the guidelines of the Infectious Diseases Control Law were reviewed for 1589 PCR-confirmed COVID-19 cases diagnosed in January 2022. We identified 77 eligible symptomatic patients for whom the date and setting of transmission were known, in the absence of any other probable routes of transmission. The observed incubation period was 3.03 ± 1.35 days (mean ± SDM). In the log-normal distribution, 5th, 50th and 95th percentile values were 1.3 days (95% CI: 1.0−1.6), 2.8 days (2.5−3.1) and 5.8 days (4.8−7.5), significantly shorter than among the 51 patients with the Alpha variant diagnosed in April and May in 2021 (4.94 days ± 2.19, 2.1 days (1.5−2.7), 4.5 days (4.0−5.1) and 9.6 days (7.4−13.0), p < 0.001). As this incubation period, mainly of sublineage BA.1, is even shorter than that in the Delta variant, it is thought to partially explain the variant replacement occurring in late 2021 to early 2022 in many countries.

Increased Transmissibility of the SARS-CoV-2 Alpha Variant in a Japanese Population.

To assess the relative transmissibility of the SARS-CoV-2 Alpha variant compared to the pre-existing SARS-CoV-2 in Japan, we performed a cross-sectional study to determine the secondary attack rate of COVID-19 in household contacts before and after the Alpha variant became dominant in Osaka. We accessed 290 household contacts whose index cases were diagnosed between 1 and 20 December 2020 (the third epidemic group), at a time when Osaka was free of the Alpha variant. We also accessed 398 household contacts whose index cases were diagnosed between 20 April and 3 May 2021 (the fourth epidemic group), by which time the Alpha variant had become dominant. We identified 124 household contacts whose index case was determined positive for the Alpha variant (Alpha group) in this fourth group. The secondary attack rates in the fourth group (34.7%) and the Alpha group (38.7%) were significantly higher than that in the third group (19.3%, p < 0.001). Multivariable Poisson regression analysis with a robust error variance showed a significant excess risk in the fourth group (1.90, 95% CI = 1.47-2.48) and the Alpha group (2.34, 95% CI = 1.71-3.21). This finding indicates that the SARS-CoV-2 Alpha variant has an approximately 1.9-2.3-fold higher transmissibility than the pre-existing virus in the Japanese population.