Analysis of the Provincial- and Municipal-level Hepatitis C Incidence Rates and Trends in the Honam Region, 2017-2021

Abstract

The World Health Organization has proposed the goal of eliminating viral hepatitis infection by 2030. Policy research and projects to reduce the incidence rate are ongoing in local governments where hepatitis C infection is common. However, a clear basis for decision-making is required at the regional level. Therefore, Honam Regional Center for Disease Control and Prevention intends to determine the incidence rate and trend of hepatitis C virus (HCV) infection by municipal levels in the Honam region, where HCV infection is prevalent. The analysis of data reported to the Korea Disease Control and Prevention Agency in the Honam region from June 3, 2017, to December 31, 2021, revealed that the incidence rate of HCV infection in the Honam region was the highest in 2018 and the lowest in 2021. It varied by up to 1.9 times in cities and provinces and 74.9 times in municipalities. The result of join point regression analysis revealed a statistically significant decreasing trend during the mandatory surveillance period. In addition, there were differences in the incidence rates of HCV infection in the Honam region according to the cities, provinces, municipalities units and gender. The statistical indices can be selected and combined according to the policy direction or objectives of the local government. Hopefully, these findings will serve as an objective basis for making decisions necessary to prevent and manage HCV infection in the Honam region.

Key messages

① What is known previously?

The World Health Organization wants to eliminate viral hepatitis by 2030, but data on incidence in regional difference is lacking.

② What new information is presented?

In the Honam area, hepatitis C incidence is high, but differs greatly between province and municipality. During a mandatory surveillance period, the entire Honam region showed a 12% annual decrease in incidence, with varying rates of change among regions.

③ What are implications?

The report’s statistical indicators can help local governments in the Honam region make informed decisions about preventing and managing hepatitis C.

Introduction

Hepatitis C is an acute and chronic disease that causes liver inflammation due to infection with the hepatitis C virus (HCV). There is a high likelihood of acute hepatitis developing into chronic hepatitis (70–80%), and it can progress into hepatic cirrhosis or hepatocellular carcinoma if not treated properly. Hepatitis C is transmitted primarily through blood or bodily fluids. Those at high risk of hepatitis C include patients who have undergone transfusion or organ transplants before the HCV screening of the blood donor (before 1991); intravenous drug abusers; hemodialysis patients; infants born to mothers with HCV infection; those who have had sexual contact with an HCV-infected individual; those who have undergone procedures in which instruments contaminated with HCV-positive blood was used; and those who had exposure to unsanitary acupuncture, tattoos, or piercings. Acute hepatitis C typically has an incubation period of 2 weeks to 6 months (an average of 6 to 10 weeks), and its main clinical symptoms include fever, fatigue, loss of appetite, brown urine, abdominal pain, vomiting, and jaundice. However, 70–80% of the infected do not show clinical symptoms, and transmission is possible even in asymptomatic conditions [1,2]. There is no vaccine for hepatitis C at present, but a pan-genotypic direct-acting antiviral agent (DAA) that can be administered orally has been developed, with a high treatment success rate and few side effects. Hepatitis C is an infectious disease that can be eradicated if preemptive routine screenings and treatments are performed.

In the Republic of Korea, hepatitis C was listed as a nationally designated infectious disease in 2001, a disease subject to the Sentinel Surveillance System in 2010, and a notifiable infectious disease in December 2016. Subsequently, the Republic of Korea implemented National Infectious Disease Surveillance System on June 3, 3017. Medical institutions must report to the health center within 24 hours in case of an HCV RNA detection in the blood of visiting patients, and the health director who receives the report must report to the Korea Disease Control and Prevention Agency and the respective city or province within 24 hours [3,4].

The number of reports and crude incidence rate (CIR) of hepatitis C has repeatedly increased and decreased, respectively, since hepatitis C has been subjected to the mandatory surveillance system [5]; however, it is challenging to find the results of the quantitative analysis of the changes in the trend. Moreover, hepatitis C incidence rate varies according to region, but no existing report presents the incidence rates by municipal levels [6]. Currently, an objective basis of small regional units is necessary for policy decisions because the World Health Organization has set a goal of eradicating viral hepatitis by 2030, and projects and policy studies by local governments are underway or in preparation in the Republic of Korea to reduce infectious diseases in areas where many outbreaks occur.

Accordingly, various statistical indicators of hepatitis C incidence per provincial- and municipal-level, including CIR, age-standardized incidence rate (ASIR), annual percent change (APC) of the ASIR, and its average annual percent change (AAPC), in the Honam region are presented in detail, and the incidence trend of the entire Honam region as well as provincial-level incidence trends are compared.

Methods

1. Subject of Investigation

Of the 14,256 reported cases of hepatitis C in the Honam region in public healthcare information system from June 3, 2017 to December 31, 2021, 8,315 approved cases were investigated, excluding 5,941 cases of health center deletions, rejection of cities and provinces, and missing statistics. Of the 8,315 cases, two were excluded as they were in the testing phase and did not meet the criteria of a confirmed case, and 1,911 duplicate reports were removed. The final 6,402 cases were analyzed (Figure 1).

Figure 1. The selection process of cases for analysis.

2. Methods of Analysis

The hepatitis C incidence rates from June 3, 2017 to December 31, 2021, are presented as crude and age-standardized rates. The trend of hepatitis C incidence is presented as APC, its mean (95% confidence interval), and p-value.

The CIR of hepatitis C was calculated as the number of new cases per 100,000 persons in the reported year. The calculation formula is as follows:

$$\text{CIR}=\left(\text{The number of new hepatitis C cases}/\text{the population of the middle of the year}\right)\times 100,000(\text{person-year})$$

The person-year corresponding to the denominator of the CIR was converted to infectious disease surveillance from June 3, 2017, and monitored for 212 days; thus, CIR for 2017 was calculated by multiplying the number of people in the region by 0.58.

The ASIR of hepatitis C was calculated using a direct standardization method known best to reflect the crude rate’s characteristics [7], and the calculation formula is as follows:

$$\text{ASIR}={\displaystyle \sum \left(\text{Incidence rate by age}\times \text{number of people by age in the standard population}\right)/\text{number of standard population}}\times 100,000(\text{person-year})$$

The 2010 registered resident population data provided by Statistics Korea was used to establish a standard population for comparison purposes in the Honam region (that is, Gwangju Metropolitan City, Jeollanam-do Province, and Jeollabuk-do Province). Because the area of comparison was limited to the Honam region, the sum of the registered population of Gwangju Metropolitan City, Jeollabuk-do Province, and Jeollanam-do Province within the 2010 population was set as the standard number. To compare the incidence rates between gender, age (10-year interval), and region, the ASIR was calculated by weighting the ratio of the standard population to the crude rate after calculating the ratio of the age group to the standard population.

The Joinpoint Regression Program (version 4.9.1.0), developed and distributed by the United States National Cancer Institute, was used to analyze the change in hepatitis C incidence rates over time (from June 3, 2017 to December 31, 2021). The results are presented in APC and AAPC.

Results

1. Hepatitis C Incidence Rate in the Honam Region

A total of 6,042 new cases of hepatitis C were reported in the Honam region during the infectious disease surveillance period, from June 3, 2017 to December 31, 2021. The number of reports, CIR, and ASIR of hepatitis C per 100,000 person-year in the Honam region were the highest in 2018 (CRI 32.6; ASIR 26.7) and the lowest in 2021 (CIR 22.4; ASIR 16.5; Table 1).

Table 1. Number of new cases, crude incidence rate, age-standardized incidence rate on Hepatitis C virus infection in the Honam region by year: provincial- and municipal-level.

	2017				2018				2019				2020				2021
	N	CIRa)	ASIRb)		N	CIRa)	ASIRb)		N	CIRa)	ASIRb)		N	CIRa)	ASIRb)		N	CIRa)	ASIRb)
Honam region	914	30.3	25.6		1,537	32.6	26.7		1,223	26.5	20.9		1,345	29.5	22.4		1,023	22.4	16.5
Gwangju Metropolitan City	141	16.7	16.3		272	18.7	18.5		223	15.4	14.4		333	23.1	21.1		236	16.4	14.6
Gwangsan-gu	35	15.0	15.8		52	11.9	11.6		63	14.5	13.4		89	20.7	18.9		53	12.4	10.7
Nam-gu	23	18.2	17.0		46	21.3	19.6		25	11.6	10.2		51	23.7	20.0		28	13.1	11.0
Dong-gu	12	22.0	21.0		21	22.5	18.3		22	23.2	18.0		22	22.2	17.3		17	16.7	12.9
Buk-gu	46	18.1	17.8		97	31.9	31.4		67	22.3	20.3		98	33.0	29.8		92	31.4	27.4
Seo-gu	25	14.0	13.0		56	13.9	16.4		46	11.4	12.8		73	18.1	19.7		46	11.4	12.5
Jeollanam-do	604	55.1	41.5		915	48.7	35.4		662	35.5	24.8		729	39.5	26.4		541	29.5	19.3
Gangjin-gun	11	51.2	43.5		21	58.0	28.7		14	39.5	21.5		15	43.3	22.4		16	47.1	22.8
Goheung-gun	68	175.4	88.1		60	91.2	46.7		50	77.0	36.1		64	100.0	41.0		54	85.7	45.1
Gokseong-gun	7	40.1	19.8		10	33.7	22.0		1	3.4	2.6		10	35.4	19.3		5	18.1	10.8
Gwangyang-si	19	21.1	21.5		29	18.6	18.7		26	16.7	15.5		20	13.0	11.0		17	11.3	10.2
Gurye-gun	7	44.2	30.0		15	55.2	41.2		8	30.0	17.3		5	19.2	16.5		1	3.9	0.9
Naju-si	13	21.0	17.9		37	33.3	24.4		24	21.1	16.0		21	18.4	13.2		18	15.6	11.4
Damyang-gun	5	18.4	10.9		3	6.4	4.0		7	15.1	8.2		4	8.7	10.8		6	13.1	10.9
Mokpo-si	93	68.3	66.0		123	53.1	50.0		89	38.8	34.9		124	55.0	47.7		75	34.1	27.9
Mu’an-gun	30	63.0	49.2		49	59.8	46.0		53	65.4	48.3		46	55.3	41.5		35	39.6	29.3
Boseong-gun	9	35.5	26.5		7	16.3	6.5		7	16.8	9.6		8	19.7	10.8		13	32.8	12.1
Suncheon-si	24	14.9	14.4		58	20.9	18.7		32	11.5	10.2		30	10.7	9.2		33	11.8	9.4
Shin’an-gun	43	176.6	90.8		70	169.7	85.4		51	126.4	59.6		40	102.0	44.9		35	91.4	37.9
Yeosu-si	94	56.6	48.4		143	50.5	41.8		86	30.6	25.0		109	38.9	30.2		70	25.2	18.9
Yeonggwang-gun	12	37.8	32.3		22	40.8	23.5		14	26.2	16.7		14	26.4	14.2		11	21.1	9.7
Yeong’am-gun	15	46.3	30.8		31	56.7	35.4		18	33.2	23.0		19	35.4	26.0		18	34.0	25.3
Wando-gun	27	89.3	62.5		30	58.3	37.3		18	35.4	19.4		31	62.0	34.4		19	38.7	18.7
Jangseong-gun	5	18.8	9.9		13	28.5	16.4		13	28.6	15.4		17	38.0	19.6		14	32.1	20.9
Jangheung-gun	7	30.1	21.8		35	88.8	52.8		25	64.7	33.9		31	81.9	39.3		20	54.1	29.0
Jindo-gun	66	359.2	179.4		81	259.4	126.8		50	162.8	75.1		52	169.3	79.2		44	144.4	67.4
Hampyeong-gun	7	35.4	24.8		14	41.8	36.8		13	39.7	19.8		16	49.8	28.3		4	12.7	3.6
Haenam-gun	40	93.3	60.4		50	69.3	38.9		50	70.9	43.0		48	69.6	37.1		30	44.4	18.8
Hwasun-gun	2	5.3	4.2		14	21.9	17.7		13	20.7	15.0		5	8.0	4.4		3	4.8	3.3
Jeollabuk-do	169	15.7	12.8		350	19.1	15.1		338	18.6	14.2		283	15.7	11.5		246	13.8	10.1
Gochang-gun	2	5.7	7.2		16	27.4	16.6		10	17.9	8.8		9	16.5	7.8		6	11.2	5.7
Gunsan-si	23	14.5	13.1		36	13.3	11.5		50	18.6	14.9		53	19.9	15.5		40	15.1	12.0
Gimje-si	20	39.8	23.4		32	37.5	23.0		22	26.2	15.5		20	24.3	12.5		11	13.6	7.1
Namwon-si	8	16.5	11.9		18	21.8	16.2		7	8.6	5.0		10	12.4	7.9		12	15.1	12.5
Muju-gun	4	27.8	23.5		5	20.3	16.7		8	32.9	19.7		3	12.5	8.3		4	16.8	8.6
Bu’an-gun	6	18.4	9.0		9	16.4	9.2		9	16.9	10.4		10	19.1	12.1		13	25.4	11.2
Sunchang-gun	12	69.7	36.8		56	191.2	99.5		63	220.1	100.6		47	168.3	75.4		36	132.3	47.0
Wanju-gun	10	18.1	16.7		12	12.7	11.1		19	20.5	16.9		13	14.2	10.3		11	12.1	10.1
Iksan-si	22	12.7	11.2		63	21.3	18.3		34	11.8	9.6		32	11.3	8.6		26	9.3	7.1
Imshil-gun	5	28.7	17.4		6	20.0	8.6		5	17.1	9.1		4	14.3	10.9		2	7.4	1.5
Jangsu-gun	1	7.4	2.3		4	17.4	9.9		3	13.2	11.8		3	13.5	12.1		3	13.7	18.8
Jeonju-si	37	4.9	5.0		65	5.0	4.8		89	6.9	6.4		66	5.1	4.7		65	5.0	4.5
Jeongeup-si	15	22.8	15.5		22	19.7	13.4		16	14.5	9.5		12	11.1	6.0		16	15.0	8.0
Jin’an-gun	4	26.5	18.8		6	23.1	14.5		3	11.7	7.2		1	3.9	2.1		1	4.0	0.9

CIR=crude incidence rate; ASIR=age-standardized incidence rate. ^a)CIR=(Number of new hepatitis C infection cases÷mid-year population)×100,000 person-year. ^b)ASIR=Summation of (CIR×proportion of standard population).

Analysis of hepatitis C incidence rates by stratifying the Honam region to provincial level showed that the CIR and ASIR per 100,000 person-years were the highest in Jeollanam-do Province (CIR 29.5; ASIR 19.3; as of 2021), which was 1.5 to 1.9 times higher than that of Gwangju Metropolitan City and Jeollabuk-do Province (Table 1).

Analysis of hepatitis C incidence rates by municipal levels in the Honam region showed that the ASIR of Jindo-gun, Jeollanam-do Province, was 67.4, 74.9 times higher than that of Gurye-gun and Jinan-gun, Jeollabuk-do Province (0.9), which had the lowest incidence rate. Sunchang-gun, Jeollabuk-do Province, showed the second highest incidence of hepatitis C in the Honam region (CIR 132.3; ASIR 47.0). The third highest incidence rate was observed in Goheung-gun (CIR 85.7; ASIR 45.1), followed by Sinan-gun, Muan-gun, and Jangheung-gun (Table 1).

2. Changes in the Age-standardized Hepatitis C Incidence Rate in the Honam Region

The ASIR of hepatitis C decreased by 12.0% per year in the Honam region. All three areas of the region also showed a decreasing trend of the ASIR of hepatitis C, among which a statistically significant decrease was observed in Jeollanam-do Province (Table 2).

Table 2. APC and AAPC of ASIR on hepatitis C infection new cases in the Honam region from 2017 to 2021.

	Total				Male				Female
	AAPC (=APC)	95% CI (LCI, UCI)	p-value		AAPC (=APC)	95% CI (LCI, UCI)	p-value		AAPC (=APC)	95% CI (LCI, UCI)	p-value
Honam region	–12.0a)	–20.4, –2.8	0.026		–11.6a)	–20.6, –1.5	0.036		–12.7a)	–21.8, –2.6	0.029
Gwangju Metropolitan City	–0.7	–20.3, 23.7	0.924		2.1	–18.0, 27.2	0.781		–4.4	–24.0, 20.1	0.573
Gwangsan-gu	–0.3	–27.6, 37.4	0.980		2.2	–24.1, 37.5	0.833		–3.9	–33.3, 38.3	0.749
Nam-gu	–6.9	–35.6, 34.4	0.578		–4.8	–44.6, 63.4	0.789		–10.4	–28.4, 12.1	0.218
Dong-gu	–9.6a)	–17.9, –0.5	0.045		–17.6	–36.4, 6.7	0.097		–0.8	–15.0, 15.9	0.886
Buk-gu	5.6	–18.4, 36.5	0.552		15.1	–8.5, 44.6	0.146		–5.7	–33.0, 32.6	0.622
Seo-gu	1.2	–23.1, 33.0	0.903		–0.9	–29.2, 38.5	0.934		5.0	–34.1, 67.3	0.762
Jeollanam-do	–16.6a)	–25.3, –6.9	0.013		–17.7a)	–28.3, –5.5	0.021		–15.7a)	–23.8, –6.8	0.012
Gangjin-gun	–12.4	–26.8, 4.8	0.100		–0.8	–26.1, 33.1	0.936		–15.8	–35.1, 9.4	0.128
Goheung-gun	–16.3	–37.6, 12.3	0.150		–23.4	–50.8, 19.3	0.151		–7.8	–29.5, 20.6	0.408
Gokseong-gun	–11.6	–47.8, 50.0	0.513		–16.5	–54.3, 52.7	0.412		NA	NA	NA
Gwangyang-si	–18.5a)	–24.1, –12.5	0.003		–12.5	–35.6, 18.8	0.259		–23.7a)	–31.3, –15.3	0.004
Gurye-gun	–39.0	–74.0, 43.0	0.162		–46.6	–81.4, 53.4	0.155		NA	NA	NA
Naju-si	–17.2	–33.8, 3.5	0.074		–22.4	–43.0, 5.7	0.080		–7.3	–29.1, 21.2	0.434
Damyang-gun	6.9	–29.2, 61.3	0.644		–5.8	–58.4, 113.0	0.829		NA	NA	NA
Mokpo-si	–15.0	–32.3, 6.8	0.109		–19.9	–38.0, 3.4	0.070		–11.5	–30.0, 12.0	0.197
Mu’an-gun	–10.6	–22.6, 3.3	0.090		–16.4a)	–21.5, –11.0	0.003		–4.4	–25.7, 23.1	0.612
Boseong-gun	–9.5	–46.4, 52.7	0.586		–12.3	–34.1, 16.6	0.239		–7.9	–68.0, 165.3	0.821
Suncheon-si	–16.7	–35.4, 7.4	0.106		–17.9	–40.5, 13.3	0.147		–15.4	–30.7, 3.3	0.076
Shin’an-gun	–21.6a)	–28.9, –13.5	0.004		–21.2a)	–26.8, –15.3	0.002		–21.1a)	–29.1, –12.2	0.006
Yeosu-si	–19.5a)	–33.1, –3.2	0.033		–16.0a)	–26.1, –4.4	0.023		–21.3	–39.8, 2.9	0.066
Yeonggwang-gun	–19.1	–40.7, 10.3	0.118		–31.0a)	–42.2, –17.7	0.007		NA	NA	NA
Yeong’am-gun	–8.0	–22.1, 8.6	0.208		–11.6	–39.6, 29.4	0.377		NA	NA	NA
Wando-gun	–22.1	–44.6, 9.5	0.102		–17.6	–46.1, 26.0	0.242		–27.9a)	–46.8, –2.3	0.042
Jangseong-gun	15.9a)	0.6, 33.4	0.045		14.4	–12.6, 49.6	0.210		6.4	–39.5, 87.2	0.750
Jangheung-gun	–8.4	–36.1, 31.3	0.493		–3.3	–45.7, 72.2	0.864		–13.2a)	–24.4, –0.2	0.048
Jindo-gun	–22.4a)	–34.6, –7.9	0.018		–28.8	–52.5, 6.7	0.076		–20.1a)	–29.8, –9.2	0.012
Hampyeong-gun	–24.3	–64.8, 63.1	0.333		–31.3	–66.1, 39.6	0.191		–17.7	–74.3, 163.3	0.631
Haenam-gun	–19.9	–36.9, 1.6	0.059		–12.7	–42.1, 31.7	0.371		–28.1a)	–42.6, –10.1	0.018
Hwasun-gun	–31.3	–72.5, 71.5	0.283		–26.7	–71.1, 85.9	0.366		–44.8	–81.2, 62.1	0.177
Jeollabuk-do	–8.9	–20.5, 4.3	0.115		–8.2	–19.5, 4.6	0.129		–10.1	–24.5, 7.0	0.147
Gochang-gun	–23.2	–48.8, 15.1	0.129		–12.0	–42.6, 34.9	0.410		–33.0	–55.3, 0.3	0.051
Gunsan-si	1.6	–14.7, 20.9	0.795		11.6	–0.9, 25.7	0.061		–5.8	–38.2, 43.7	0.683
Gimje-si	–25.3a)	–37.2, –11.2	0.013		–36.6a)	–56.9, –6.8	0.033		–15.6	–33.1, 6.5	0.103
Namwon-si	–8.4	–44.1, 50.3	0.614		–9.5	–51.3, 68.0	0.642		–10.3	–47.6, 53.5	0.564
Muju-gun	–23.1	–43.0, 3.7	0.068		–18.4	–51.4, 37.1	0.301		–25.8	–52.3, 15.2	0.119
Bu’an-gun	7.0	–0.1, 14.6	0.051		–4.5	–37.1, 45.2	0.750		18.9	–21.8, 80.7	0.280
Sunchang-gun	–10.3	–44.9, 46.1	0.530		–13.2	–53.2, 61.0	0.519		–7.3	–45.1, 56.4	0.675
Wanju-gun	–10.0	–31.7, 18.6	0.311		–11.0	–52.3, 66.1	0.595		–13.2a)	–24.6, –0.1	0.049
Iksan-si	–19.7	–43.2, 13.5	0.137		–13.6	–41.5, 27.6	0.317		–21.6	–48.4, 19.1	0.161
Imshil-gun	–32.5	–64.5, 28.3	0.147		–24.4a)	–40.2, –4.5	0.032		NA	NA	NA
Jangsu-gun	37.9	–11.9, 115.9	0.107		32.4	–19.4, 117.5	0.170		NA	NA	NA
Jeonju-si	–2.9	–19.7, 17.4	0.655		–5.9	–27.8, 22.5	0.515		–2.6	–20.5, 19.3	0.706
Jeongeup-si	–18.8a)	–33.4, –1.0	0.044		–26.5a)	–37.1, –14.2	0.008		–16.7	–43.3, 22.5	0.229
Jin’an-gun	–52.9a)	–68.1, –30.5	0.009		–32.4	–60.5, 15.6	0.103		NA	NA	NA

APC=annual percent change; AAPC=average annual percent change; ASIR, age-standardized incidence rate; CI, confidence interval; LCI=lower limit of 95% CI; UCI=upper limit of 95% CI; NA=not analyzed. ^a)AAPC is significantly different from zero (two-side p<0.05).

Among the five municipalities included in Gwangju Metropolitan City, Dong-gu showed a significant decrease in the ASIR of hepatitis C, but two (Buk-gu and Seo-gu) showed an annual increase in APC of 5.6% and 1.2%, respectively, contrary to the overall trend. Five out of 22 municipalities in Jeollanam-do Province showed a statistically significant decrease in the ASIR of hepatitis C. Jindo-gun showed the most rapid decrease, followed by Sinan-gun, Yeosu-si, and Gwangyang-si. Contrarily, Jangseong-gun, Jeollanam-do Province, showed an increasing trend of the ASIR of hepatitis C overall. A statistically significant decrease in the ASIR of hepatitis C was observed in three out of 14 municipalities in Jeollabuk-do Province, and the steepest decrease in the Honam region was observed in Jinan-gun with an annual decrease of 52.9%; a significant decrease in incidence was also identified in Gimje-gun and Jeongeup-si. Contrarily, an increasing but statistically insignificant trend of 1.6%, 7.0%, and 37.9% were observed in Gunsan-si, Buan-gun, and Jangsu-gun of the Jeollabuk-do Province, respectively (Table 2).

Stratifying the annual trends in the ASIR of hepatitis C in the Honam region over 4.58 years of infectious disease surveillance by sex showed a significant decrease in both male and female, and the decrease was more prominent in female by 1.1%p/year. There was a significant decrease in the ASIR of hepatitis C in both male and female in the Jeollanam-do Province, similar to the overall trend of change across the Honam region, and the same trend was seen in both male and female in Jeollabuk-do Province. In the case of Gwangju Metropolitan City, while the ASIR decreased by 4.4% in female, the rate increased by 2.1% per year, showing conflicting results based on sex. In the Honam region, municipalities with an increase in the ASIR of male with hepatitis C included Gwangsan-gu and Buk-gu in Gwangju Metropolitan City, Jangseong-gun in Jeollanam-do Province, and Gunsan-si and Jangsu-gun in Jeollabuk-do Province. Those with an increase in the ASIR of female with hepatitis C included Seo-gu in Gwangju Metropolitan City, Jangseong-gun in Jeollanam-do Province, and Buan-gun in Jeollabuk-do Province. All other municipalities in the Honam region showed a decreasing trend in the ASIR of hepatitis C over the 4.58 years of infectious disease surveillance period (Table 2, Figure 2).

Figure 2. Trends of ASIR on hepatitis C virus infection in the Honam region by Joinpoint regression analysis.

ASIR=age-standardized incidence rate; APC=annual percent change. a)ACP is significantly different from zero (two-side p^<0.05).

Discussion

The ASIR is a statistical indicator that can be used to compare incidence rates between regions with different age structures or over time. Kim et al. [6] reported that one of the major risk factors for hepatitis C is aging, and it is difficult to exclude the factor of differences in age distribution when the CIR of hepatitis C is high in areas with large populations of older adults. In particular, the ASIR indicator should be presented to compare the extent of occurrence of hepatitis C, of which a risk factor is aging, in the Honam region, which a region with the highest proportion of the aging population in the Republic of Korea as of 2021. ASIR of hepatitis C, divided based on sex or provincial and municipal levels, can be utilized to understand the differences in the incidence rate between the municipalities and the surrounding area as well as the sexes at a specific time and to select a control area as needed. The results of the Joinpoint regression of the ASIR of hepatitis C over 4.58 years after the implementation of the National Infectious Disease Surveillance System will be helpful in objectively comparing the evolutionary aspects of hepatitis C over time. Regression analysis showed a significant trend of decline of the ASIR of hepatitis C in the Honam region during the surveillance period, from June 3, 2017 to December 31, 2021, and there was a difference in incidence rates and rates of change depending on the subdivided area and sex. In contrast to the overall trend of the ASIR of hepatitis C, an increasing trend was observed in Buk-gu and Seo-gu of Gwangju Metropolitan City; Damyang-gun and Jangseong-gun of Jeollanam-do Province; and Gunsan-si, Buan-gun, and Jangsu-gun of Jeollabuk-do Province. This may be the reason for the difficulty in applying the provincial-level trend of hepatitis C to all municipalities, and it is necessary to find a way to reduce the incidence through closer identification of the cause in the case of places that have shown the opposite trend to the overall trend of change.

The decline in the ASIR of hepatitis C in the Honam region is presumed to be due to several factors, including improved overall hygiene, the introduction in 2015 and reduction in the price of oral DAAs that act directly on the genome’s unstructured proteins involved in HCV proliferation, the equalization of medical care in vulnerable areas, and the strengthening of infection control in medical institutions [8]. In addition, the risk factors for deviation of hepatitis C incidence rate and change of rate per sex observed in the Honam region have not yet been identified, but several hypotheses have been raised, including unsanitary tattoos, acupuncture, and an increase in the proportion of the elderly population with a lack of the effect of female hormones that play a role in preventing the progression of liver disease [9-11].

The type of objective evidence required by municipalities to prepare measures to reduce incidence in hepatitis C-prone areas may vary depending on the direction and purpose of the policy, and various statistical indicators of regional units presented in this report may be used optionally in combination. In 2021, the American Association for the Study of Liver Diseases also suggested the need for a regionally objective hepatitis C statistic, and there has been a study that presented a county-level age-standardized rate and rate of change over time [12]. In this report, the trends of changes in the number of reports, CIR, and ASIR of hepatitis C in the Honam region, known for multiple occurrences of Hepatitis C, were broken down by sex and provincial and municipal levels, quantified, and presented.

The CIR refers to the number of new cases of infectious diseases compared to the population of the area and can be used as an indicator to determine whether to support specific populations or to calculate the burden of social medical expenses on diseases for countries and municipalities that need to prevent and manage infectious diseases. Hepatitis C is an infection caused by an RNA virus, and there is no vaccine for it yet. However, it is considered an infectious disease that can be eradicated when the diagnosis is led to treatment, ever since the recent development of a treatment with excellent therapeutic effects and few side effects. Nevertheless, the disease has high social costs because the treatment cost has been expensive despite the medical insurance coverage since 2016. In such cases, the policy-making body may need to determine the specific group to which support should be prioritized to efficiently use the limited resources or estimate the medical expenses to be borne by each municipality, and the CIR may be helpful to policymaking. For instance, based on the statistical indicators presented in this report, Buk-gu in Gwangju Metropolitan City, Jindo-gun in Jeollanam-do Province, and Sunchang-gun in Jeollabuk-do Province, with the highest CIR, can be selected as the priority support area with the highest burden of social medical costs.

There are several limitations to the results of this analysis. The first is that a duplicate report of hepatitis C is possible in the integrated management system for infectious diseases, a Korean indicator-based monitoring system. Therefore, selecting new cases from a list with duplicates must be performed manually to calculate the incidence rate; human error is possible during this process. Another limitation is the direct standardization rate, a method of calculating the ASIR. However, since the special city and provinces in the Honam region were subdivided into municipal levels to provide statistical indicators, there may be municipalities with fewer incidences of hepatitis C, and this should be considered during interpretation [13].

Despite these limitations, this report is the first to quantify the incidence of hepatitis C in the Honam region by dividing it into municipal levels, and it is expected to be used as an objective basis for policy and business decisions necessary for the prevention and management of hepatitis C in the Honam region in the future.