Discussion
The results revealed the existing regional heterogeneity in the severity
of COVID-19 cases at the time of admission in Japan. Our results suggest
that the health policy of each prefecture might have an impact on the
severity of hospitalized COVID-19 cases on admission.
A wide variety was observed in the median values of the posterior
distribution of random effects for the different prefectures. That of
Kanagawa prefecture in model A was 0.340 [95% Credible Interval (CrI)
0.269, 0.410], and that of Iwate prefecture was −0.431 [95% CrI
−0.593, −0.268], indicating a substantial discrepancy in the severity
of hospitalized COVID-19 cases between these two prefectures.
The posterior distribution of random effects in model B exhibited a
similar trend to that in model A. The coefficient of Kanagawa prefecture
in model B was 0.306 [95% CrI 0.213, 0.402], and that of Iwate
prefecture was −0.413 [95% CrI −0.579, −0.249]. Other prefectures
demonstrated similar results in both models, suggesting that factors
other than the number of beds secured for COVID-19 patients (e.g.,
prioritization policy for COVID-19 case admission and number of
physicians) had an impact on the severity of COVID-19 on admission.
We should take various factors into consideration when we interpret our
results. The potential factors associated with the variation of the
severity on admission could be viewed from two directions, namely, the
local epidemiology of COVID-19 and the COVID-19 healthcare policy in
each prefecture. From the former viewpoint, a regional surge in the
number of COVID-19 patients or a rapid increase in the severity of
disease due to new SARS-CoV-2 variants may contribute to the change in
the severity on admission.8,14 However, our analysis
did not include patients with new SARS-CoV-2 variants as the study
period was limited to before March 2021. While it is possible that
COVID-19 cases due to new variants carry a greater risk of serious
illness, there was a substantial regional heterogeneity in the severity
of COVID-19 cases at the time of admission, as previous studies have
demonstrated.15–17 Presumably, variants are
contributing factors to the severity of COVID-19 cases, but it should be
noted that other factors also have a non-negligible influence on the
severity of disease.
The latter point is relevant to policymakers (and healthcare providers)
in the municipalities, mainly related to the on-site indication for
hospitalization that is operated in each prefecture. The policy
implemented to manage the waves of infection could be affected by the
total medical capacity in the area. The number of beds secured for
COVID-19 patients is one of the major resources.15,18The number of beds per population in each prefecture was included as one
of the fixed effects in model B, and the random effect of each
prefecture did not drastically change. Also, the number of physicians
eligible for COVID-19 management may have an impact as this factor could
create a bottleneck for patient acceptance.19 However,
it is difficult to precisely grasp the number of physicians who are
engaging in COVID-19 patient management. This is because the specialty
of the medical doctor is not a good proxy for the number of physicians
engaging in COVID-19 management under such an emergency
period.20
The local government of each prefecture has established policy for the
process of admission prioritization as a way of integrating the
information from the regional medical situations, including the
aforementioned factors, a strategy that may determine the variation in
the severity on admission.21,22 This means that there
may be differences in whether a patient can be hospitalized and how long
it takes for a patient to be hospitalized, even for clinically similar
cases, depending on the prefecture they belong to.
Two types of strategy for symptomatic COVID-19 patients can be assumed.
The following are simplified examples: 1) moderate to severe cases are
admitted to hospital, whereas mild cases are managed at home or in a
dedicated facility (severity on admission will increase), and 2) all
patients, whether with mild or severe disease, are admitted to hospital
(severity on admission will decrease). Both strategies have their own
risks and benefits, and the local government of each prefecture has
adopted each strategy depending on the height of each wave of the
epidemic.
The strategy adopted should be evaluated by the outcomes of COVID-19
patients, damage to the medical system for non-COVID-19 diseases, and
the impact on hospital and regional healthcare economy. A previous study
in China demonstrated that the number of beds and medical staff per
COVID-19 patient was negatively correlated with
mortality.23 Conversely, a recent study from Italy
reported that greater access to hospitals did not affect the mortality
of COVID-19 patients older than 80 years but affected that of patients
younger than 80 years,24 suggesting that the best
approach may be to change the strategy according to age group or other
properties of the patients. Evaluation of the regional policy could
provide important insights to construct a better healthcare system
against COVID-19 and other emerging infectious diseases.
Our analysis had several limitations. First, we examined data solely
from Japan; thus, it is not appropriate to generalize our results
globally. Nevertheless, it is easy to imagine that, even in other
countries, there would be differences in health policies among local
authorities and that they might have an impact on the management of
COVID-19 cases. Second, we could not include other confounding factors,
such as human resources and variance of SARS-CoV-2; these aspects should
be addressed in future studies.
In conclusion, our analysis revealed a possible association between
prefecture and an increased/decreased risk of severe COVID-19 infection
at the time of admission. In addition, the number of beds secured for
COVID-19 patients in each prefecture is not a single cause of such
heterogeneity; therefore, other factors could be significant for the
management of COVID-19 cases in Japan. Countermeasures against COVID-19
will be more appropriate if we take these insights into consideration.