How would COVID-19 protocols have impacted on continuity of care of hypertension patients

Objective To investigate the impact of the coronavirus disease 2019 (COVID-19) pandemic on the continuity of care (COC) in hypertension patients. Additionally, the factor of whether participants were treated by telemedicine or not was also considered. Methods National Health Insurance and Medical Aid claims This study used data from the Republic of Korea between 2019 and 2020. The multiple regression analysis was performed to identify the differences in visits and the Most Frequent Provider Continuity (MFPC) of hypertensive patients before and after the COVID-19. To con�rm the effect of telemedicine, additional analysis was performed with data that deleted cases that received telemedicine. Findings A total of 5,791,812 hypertensive patients are included in this study. When the confounding variables were adjusted, the MFPC decreased by 0.0031 points after the COVID-19. It also showed the same results for MFPC when telemedicine cases were excluded. The number of outpatient clinic visit days decreased by 0.2930 days after the COVID-19. Without telemedicine cases, the number of outpatient clinic visit days decreased by 0.3330 days after the COVID-19. Conclusion The COVID-19 protocols did not affect hypertension patients' COC but impacted their outpatient frequency. Additionally, when telemedicine cases are considered, COC was the same, but the patient’s outpatient frequency had decreased, but not as much as when telemedicine cases were considered.


Introduction
Hypertension is a chronic disease that requires healthcare provider routine management.The hypertension prevalence rate has increased due to the aging population, westernized eating habits, and high sodium consumption.Among the population aged over 20, the estimated hypertension prevalence is 29%, and among the patients diagnosed with hypertension, the controlling rate is only 47% 1 .High blood pressure is the most important modi able risk factor with the most signi cant in uence on cardiovascular or cerebrovascular diseases 2,3 .According to the National Health Insurance Service (NHIS) statistics in Korea, the estimated medical cost of treating hypertension was 3.83 trillion Korean Won (i.e., 3.4 billion U.S. dollars).This amount is equivalent to 4% of all medical expenses and 16% of medical expenses for chronic diseases 1,3 .Thus, controlling the hypertension prevalence by continuous monitoring and management would reduce the tremendous nancial burden caused by the disease and eventually improve the patient's quality of life.
According to Shortell 4 , the continuity of care (COC) is de ned as "the extent to which services are received as part of a coordinated and uninterrupted succession of events consistent with the medical care needs of patients."It is well-recognized that patients receiving continuous care from regular healthcare providers have better health outcomes and higher patient satisfaction at a lower cost 5 .Among hypertension patients, the greater COC, the lesser risk of hospital admission was reported 6 .Additionally, COC is also associated with a decreased use of emergency room visits and better followup rates with appointments 7,8 .This could be due to the fact that the rapport built with the patient allows the healthcare providers to have a better knowledge about the patient and instantly recognize the changes in their health status.This can eventually prevent the patients from suffering from complications or disease onsets.Thus, in order to control high blood pressure, COC is an important concept.
On March 11th, 2020, the World Health Organization declared coronavirus disease 2019 (COVID-19) a pandemic.A response to the pandemic declaration, social distancing and isolation were recommended and done to prevent the virus from spreading.Many researchers showed concerns of a negative impact of social isolation on outpatient and primary care 9,10 .However, telemedicine was also enlighten as an effective method to treat patients in such situation 11 .Korean government also temporarily approved to provide medical counseling and prescription in non-face-to-face method which is over the telephone call.Considering the fact that the unprecedented length of the social isolation period would signi cantly impact the patients' outcomes who require continuous care by healthcare providers; the study might be the rst to provide information about the in uence of a pandemic on COC of hypertension patients and how the telemedicine will reduce its impact in South Korea.Thus, this article aims to investigate the impact of the COVID-19 pandemic protocol on the COC to hypertension patients.Additionally, whether patients received telemedicine or not is considered.

Source of data
This study analyzed the medical use of patients with hypertension by using the outpatient statements of the National Health Insurance (NHI) and Medical Aid bene ciaries that were claimed by the Korea Health Insurance Review and Assessment Service (HIRA).Over 95% of all Koreans are compulsorily insured by NHI and Medical Aid.In order to evaluate the impact of the COVID-19 outbreak, the cases treated between January 20, at the beginning of COVID-19 in Korea, and December 31, 2020 were considered in the study.For comparison, the cases between January 20 and December 31, 2019 were considered.In order to compare COC under the same conditions, the data was limited to cases reviewed by the March of the following year.
Among those receiving hospitalization or outpatient treatment for hypertension (I10, I11, I12, I13) as their major diagnosis or sub-diagnosis, patients who have been prescribed antihypertensive drugs twice or more on different days, and the total number of administration days is 7 days or more, between January and December 2019 were de ned as hypertensive patients.Of these, the total number of the study population was 5,791,812, excluding the fatalities before December 31, 2020, and those who did not meet the study conditions.This study was exempt from institutional review board of HIRA review due to the data being used were deidenti ed which are available for public use by the HIRA.

Number of visits
The frequency of visits to a medical institution is a representative variable that can measure the volume of medical use.It is suitable for measuring medical usage changes due to COVID-19 protocols due to its consistency compared to the expenses affected by the medical practices.In this study, the number of outpatient-visits due to hypertension as the major diagnosis or sub-diagnosis during each study period was de ned as the number of visits.

Most Frequent Provider Continuity (MFPC)
In chronic disease management, the relationship continuity between doctor and patient, a type of the COC, is known to have a positive effect on the treatment process, outcome, and cost.MFPC is a representative tool that can measure COC when the measurement target is an individual patient in a situation where the attending physician is not determined.In this study, MFPC was calculated by counting the total number of visits to medical institutions due to hypertension as the denominator and the number of visits to the most visited institution as the numerator during each study period.It has a value between 0 and 1, and the closer it is to 1, the higher the MFPC.If the frequency of the visits is too low, there is a possibility that the MFPC will be measured too high.Therefore, those who visited medical institutions less than twice per year were excluded.

Variable of interests
In order to evaluate the impact of the COVID-19 outbreak on the patients' medical use behavior, the period between January 20, when the rst COVID-19 case was con rmed in Korea, and December 31, 2020 was de ned as the period after importation (After).The same period in the previous year, with no COVID-19, was de ned as the period before importation (Before).

Confounding variables
The variables with an impact on medical use, such as the patient's gender, age, region of residence, insurance type, Charlson Comorbidity Index (CCI), diabetes status, duration of hypertension and type of medical institution most frequently used, were adjusted.Any change in the region of residence or insurance type during the study period, led to the exclusion of the patients from the study.
CCI is a representative tool that can measure the severity of patients' underlying condition in administrative data such as health insurance claim data that lacks clinical information.Nineteen of the comorbidities included in the CCI calculation were included in the hospitalization and outpatient statements for a year before each study period as major diagnoses or sub-diagnosis (weights of 1 to 6 points were given to each morbidity and calculated).The bigger score implies the more serious underlying condition.Diabetes mellitus was initially included in CCI but was excluded because it was measured separately in this study.Diabetes mellitus was de ned if E10 to E14 were claimed as major diagnoses or sub-diagnosis in hospitalization and outpatient statements for 1 year prior to the study period.

Statistical analyses
In this study, Chi-square test and independent t-test were performed to identify the general characteristics of the study populations.The multiple regression analysis and independent t-test were performed to identify the differences in the number of visits to medical institutions and the MFPC of hypertensive patients before and after the COVID-19 importation.In the multiple regression analysis, the patient's gender, age, region of residence, insurance type, CCI, diabetes status, duration of hypertension and type of medical institution most frequently used were adjusted.To consider the repeated measurement, a generalized estimating equation model was used, and CORRW type was applied for the covariance structure.In addition, to con rm the effect of telemedicine (non-face-to-face telephone consultation and prescription, untact treatment is used by Korean government), temporarily permitted because of the COVID-19 pandemic since February 24, 2020, additional analysis was performed with data that deleted telemedicine cases.SAS Enterprise Guide 7.1 was used for all statistical analysis.

Characteristics of the study population
Table 1 shows the general characteristics of the study populations.A total of 5,791,812 hypertensive patients, 2,826,779 males and 2,965,033 females are included.During the Before period, 2,446,950 (42.25%) of the population accounted for the 60-74-year-olds at the highest proportion.Among the study case population, 1,394,230 patients (24.07%) had diabetes, and those with more than 10 years of hypertension (2,978,121 or 51.42%) were among the majority with the mean CCI of 0.6347.As for the type of insurance, NHI accounted for the majority with 5,526,514 (95.42%).By region, Gyeonggi Province had the largest number of residents at 1,366,235 (23.59%), followed by Seoul at 985,945 (17.02%) and Busan at 407,245 (7.03%).The most frequently used medical institutions before the appearance of COVID-19 were clinics (4,537,548, 78.34%), and the proportion increased to 4,677,502 (80.76%) after the appearance of COVID-19.After the manifestation of the virus the proportion of tertiary hospitals and general hospitals increased by 0.01%p and 0.03%p, respectively, and the proportions of hospitals and public health institutions decreased by 0.09%p and 2.37%p, respectively.
Table 2 shows the MFPC before and after the importation of COVID-19.The MFPC in the Before period was 0.9507, and after the appearance of the virus, it decreased by 0.0024 to 0.9483, which was statistically signi cant.By patient characteristics, MFPC signi cantly decreased after the importation of COVID-19 in most groups, but there were some groups that increased.By age, MFPC decreased in all groups over 60 years old (60 to 74: -0.0033; 75 and more: -0.0057), and it increased in all groups under 60 years old (0 to 20: +0.0066; 30 to 44: +0.0047; 45 to 69: +0.0008), and it was statistically signi cant.Based on the hypertension duration, the MFPC increased from 0.9373 points to 0.9467 points after the COVID 19 appearance in groups with less than 2 years of hypertension and it decreased signi cantly in groups with a longer period of hypertension.By region MFPC increased in Jeju Island by 0.0039 points, Gyeongsangnam-do 0.0024 points, Jeollabuk-do 0.0031 points, Daegu 0.0014 points increased, and it decreased signi cantly in other areas, with no statistically signi cant difference in Sejong, Chungcheongnam-do, Daejeon and Incheon.By the most frequently used medical institutions, the MFPC increased in tertiary general hospitals (0.0033 points), general hospitals (0.0009 points), and hospitals (0.0047 points), while it decreased in clinics (-0.0024 points) and public health institutions (-0.0507 points).
Table 3 shows the number of visits per patient before and after the appearance of COVID-19.The number of visit days before COVID-19 was 8.3347 days, which decreased signi cantly statistically to 8.1363 days thereafter.By patient characteristics, the number of visits signi cantly decreased in all population groups except for the population with a prevalence of hypertension in the past 2 years.In particular, there was a greater decrease in the number of visits among women (before: 8.6337, after: 8.4084), patients of 75 and over (before: 9.3258, after: 8.9850), patients with diabetes (before: 9.0337, after: 8.7701), patients with over 10 years of hypertension (before: 8.6758, after: 8.4107), medical aid bene ciaries (before: 10.3710, after: 10.1173), residents of Sejong-si (before: 8.5040, after: 8.2302), and those who mainly use public health institutions (before: 6.0694, after: 5.6009).

Multiple linear regression analysis
Table 4 shows the results of the multiple regression analysis for MFPC.When the confounding variables were adjusted, the MFPC decreased by 0.0031 points after the appearance of COVID-19, which was statistically signi cant (p-value <.0001).It also shows the results of the multiple regression analysis for MFPC when telemedicine case is excluded.When the independent variables were adjusted, the MFPC after the appearance of COVID-19 was signi cantly statistically decreased, which was the same as when telemedicine case was included (β: -0.0031, p-value <.0001).
Table 5 shows the results of the multiple regression analysis on the number of visits per patient.When the confounding variables were adjusted, the number of visit days decreased by 0.2930 days after the appearance of COVID-19, which was statistically signi cant (p-value <.0001).The result of multiple regression analysis on the number of visits per patient when telemedicine case is excluded is also shown.Upon the adjustment of the independent variables, the number of visits per patient after the appearance of COVID-19 decreased by 0.3330 days statistically, which is 0.04 days lower compared to when telemedicine case was included.

Discussion
The purpose of the study was to identify the impact of social distancing and isolating due to the COVID-19 pandemic on the COC and outpatient visit of hypertension patients.Considering the fact that there are no family doctors in the Korean healthcare system, this study used MFPC as a proxy of COC.
To examine the impact, a multiple regression conducted comparing MFPC with outpatient visits during the pre to post pandemic period.The study found a signi cant decrease in the MFPC and outpatient visits during the pandemic.Although both MFPC and the number of outpatient visits decreased with statistical signi cance, they varied in volume.
This study found a decrease in the MFPC of hypertensive patients; the size of the beta coe cient was not big enough to be considered as a signi cant decrease.Additionally, regardless of the patients receiving telephone prescriptions, their MFPC reported the same.MFPC represents the pattern of outpatient usage 12 ; thus, study results showed that even though the pandemic impacted and limited their access to outpatient visits, the pattern of outpatient usage remained the same.Since MFPC represents the pattern of medical care utilization, its results indicate that the medical care utilization patterns of hypertension patients have not been impacted despite the nationwide initiation of COVID-19 protocols.The majority of the previous studies reported the positive impact of COC on a patient's health behaviors and health outcomes; however, a few studies reported different results.COC is, speci cally, associated with positive patient and provider satisfaction 13 , reduced emergency room use 8 , decreased hospital admissions, and better immunization rates 14 ; on the contrary, COC by provider is not associated with blood pressure control 7 .However, there is a study showing that patients with high COC levels (0.67-1.0) were more likely to have better controlled blood pressure compared to those with medium (0.40-0.66) or low COC levels (0-0.39) 7.Better controlled blood pressure in hypertension patients leads to better health outcomes.Considering the results of these previous studies with the average MFPC of about 0.95, even with the COVID-19 protocols in effect, the health outcomes of the hypertension patient in Korea remained almost the same.
The other result shown in the study is that the number of outpatient visits has decreased.Unlike the MFPC results, on the other hand, the size of the outpatient visit number decreased signi cantly after the COVID-19 pandemic.When considering the telemedicine case, the number of outpatient clinic visits decreased, but not as much as the patients who did not undergo the telemedicine.The number of outpatient clinic visits re ects the volume of medical use and measures the utilization of healthcare services 15,16 .Due to the COVID-19 protocols, unlike the medical care usage pattern, the utilization decrease was inevitable.However, as a result of telemedicine the frequency of outpatient visits has not gone down by much.Studies regarding the frequency of outpatient visits showed mixed results.A study reported that too many outpatient visits would increase the medical expenses and some of the visits are not necessary which will be ine cient in treatment 17 .However, this result was shown when the patients visited multiple doctors for the same condition.Another study reported a shorter return visit interval to be positively associated with blood pressure control 18 .
Non-face-to-face medical telephone counseling/ prescription (telemedicine is the term used in this study) has temporarily approved by Korean government due to a sudden increased number of COVID-19 diagnoses nation-wide.This increase was happened right after a mass infection occurred by an infected person visited a church in Daegu-Gyeongbuk region.The telemedicine center started to operate on March 9, 2020 in Daegu and April 21, 2020 in Seoul.There are some studies reported the positive role of telemedicine and the need of it during infectious disease pandemic era 19,20 , especially in terms of its effectiveness 11,21−23 .From this study, with the telemedicine case, the pattern of healthcare services use has not changed, and it also prevented utilization to be decreased signi cantly.Considering the fact that hypertension patient's COC had not reduced even though the utilization had decreased, this enlightens the fact that the telemedicine case is effective measure during COVID-19 pandemic period.
Several limitations of this study should be noted.First, this study used hospital administrative data for medical reimbursement or billing, which precludes clinical information meaning that it is hard to con rm whether the patient's actual blood pressure change.Thus, in the future, it is necessary to develop a patient dataset that links administrative data and clinical data on clinical variables such as lab results.Secondly, since only outpatient medical use was targeted, it may have been analyzed that if a patient was hospitalized during the follow-up period due to cardiovascular disease, a complication of hypertension, it was analyzed that he did not use medical care at all.However, in the case of high blood pressure patients with such high severity, it is very important to prevent complications through continuous medical use, so it is considered important to be included in the analysis.
Therefore, future studies on hospitalization due to hypertension complications are needed.Lastly, demographic, social structural and economic factors in uence medical use.However, in this study, only basic demographic variables such as gender and age, and clinical characteristic variables were included in the analysis because administrative data, which is the data for health insurance review request, was used.As a result, there is a limitation in that the patient's knowledge and attitude toward hypertension are not considered at all.Also, among demographic variables, variables closely related to access to medical institutions, such as residence and income, were not included.To minimize this limitation, in this study, proxy of social economic status and their income level was used as their health insurance status, and a proxy for the participant's condition, CCI was used and controlled.Although, in the future, it is necessary to develop a patient dataset that links administrative data and survey data on social and psychological variables.
Despite its limitations, our study has several strengths.First, the study used nationally representative data.Second, to our knowledge, this study was the rst to examine the impact of COVID-19 protocols on hypertension patients' COC in South Korea.Lastly, considering whether the participants were treated by using telemedicine enrichen with the interpretation.

Conclusions
Our results suggest that COVID-19 protocols did not effect on hypertension patient's COC but had impact on their outpatient frequency.Additionally, when telemedicine cases are considered, COC was the same, but the patient's outpatient frequency had decreased, but not as much as when telemedicine cases were considered.Future studies should consider the inpatient cases whether COVID-19 protocols impacted on hypertensive patient's complication admissions.It is hoped that this information will be a useful reference for further studies of chronic disease patient's COC during pandemic of infections and telemedicine's impact.

Declarations Con icts of Interest
The authors declare no competing interests.
Author Contributions SL has made substantial contributions to the conception, design of the work, interpretation of data, and have drafted the introduction and discussion section of the work or substantively revised it.SC has made substantial contributions to the design of the work and analysis of data.Lastly, HP has made substantial contributions to the design of the work, the acquisition, analysis, interpretation of data, and has drafted the method and result section of the work and revised it.All authors have approved the submitted version and have agreed to be personally accountable for the author's own contributions and to ensure that questions related to the accuracy or integrity of any part of the work, even ones in which the author was not personally involved, are appropriately investigated, resolved, and the resolution documented in the literature.

Table 1 .
General characteristics of population (cases,

Table 4 .
Impact of the COVID-19 protocols on MFPC

Table 5 .
Impact of the COVID-19 protocols on the number of outpatient clinic visit per patient