Incidence and Healthcare Burden of Pertussis among Older Adults with and without Pre-Existing Chronic Obstructive Pulmonary Disease or Asthma in South Korea

Figures & data

Table 1. Baseline characteristics of the pertussis cases and pre-pertussis diagnosis medical costs.

	COPD- pertussis (n = 91)		Matched group* (n = 269)		Asthma- pertussis (n = 169)		Matched Group* (n = 503)
	N	%	n	%	n	%	n	%
Age
Mean (SD)	71.13 (9.3)		68.45 (9.4)		67.50 (10.8)		65.45 (10.1)
50–54	4	4.4	21	7.8	25	14.8	82	16.3
55–59	9	9.9	32	11.9	24	14.2	84	16.7
60–64	8	8.8	38	14.1	27	16.0	82	16.3
65–69	14	15.4	57	21.2	16	9.5	90	17.9
70–74	19	20.9	43	16.0	24	14.2	52	10.3
75+	37	40.7	78	29.0	53	31.4	113	22.5
Sex
Female	35	38.5	105	39.0	100	59.2	300	59.6
Male	56	61.5	164	61.0	69	40.8	203	40.4
Region
Metropolitan	21	23.1	56	20.8	32	18.9	105	20.9
Urban area	22	24.2	105	39.0	50	29.6	211	42.0
Rural area	48	52.8	108	40.2	87	51.5	187	37.2
CCI score^‡
Mean (SD)	1.78 (2.1)		1.66 (1.7)		1.15 (1.4)		1.15 (1.4)
0	21	23.1	63	23.4	63	37.3	189	37.6
1	34	37.4	83	30.9	56	33.1	157	31.2
2	14	15.4	59	21.9	29	17.2	96	19.1
3+	22	24.2	64	23.8	21	12.4	61	12.1
Comorbidities
Cardiovascular disease	55	60.4	136	50.6	85	50.3	209	41.6
Cerebrovascular disease	21	23.1	48	17.8	22	13.0	66	13.1
Immune disease	47	51.7	127	47.2	91	53.9	256	50.9
Hypertension	57	62.6	171	63.6	87	51.5	276	54.9
Urinary incontinence	3	3.3	7	2.6	6	3.6	16	3.2
Medical conditions with relatively high economic burden^†
Lower back pain	53	58.2	146	54.3	95	56.2	276	54.9
Osteoarthritis	46	50.6	107	39.8	81	47.9	213	42.4
Alzheimer’s disease	6	6.6	26	9.7	10	5.9	32	6.4
Ischemic heart disease	35	38.5	81	30.1	49	29.0	111	22.1
Diabetes	43	47.3	123	45.7	58	34.3	176	35.0
Medical costs in the 12-month pre-index date period, USD^§
Mean (SD)
Ambulatory care and hospitalisation	3730		2115		1487		1400
	(6859)		(5952)		(3510)		(4596)
Outpatient visit	3254		3049		2425		2322
	(2880)		(6388)		(2309)		(5032)

*Up to 3 pertussis patients without pre-existing COPD or asthma were matched on sex, age (+/- 10 years range), and CCI score excluding COPD or asthma (+/- 1 range). ^‡COPD and asthma were excluded from CCI score calculation. ^†Comorbidities associated with high direct and indirect medical costs among individuals ≥50 years in South Korea. ^§Index date was defined as the date of pertussis diagnosis minus 15 days; costs were adjusted to 2018 KRW and converted from South Korean Won (KRW) to US dollars (USD) using the 2018 exchange rate (1 USD = 1115.7 KRW). Asthma-pertussis: pertussis cases with pre-existing asthma; CCI: Charlson comorbidity index; COPD: chronic obstructive pulmonary disease; COPD-pertussis: pertussis cases with pre-existing COPD; KRW: South Korean won; SD: standard deviation; USD: United States dollars.

Figure 1. Study design for the evaluation of excess burden of pertussis.

*To evaluate the excess burden of pertussis, incremental all-cause costs were calculated as the difference in healthcare costs between post-index and baseline time periods. These incremental all-cause costs were then compared between COPD-pertussis and asthma pertussis groups versus the general pertussis group, matching for differences in sex, age, and CCI score (excluding COPD or asthma). Pertussis-related costs were calculated as the sum of pertussis-related costs for each time post-index and also compared across groups.

Figure 2. Study flowchart identifying study cohort.

*56 patients had both pre-existing COPD and asthma. HIRA: health insurance review and assessment service; COPD: chronic obstructive pulmonary disease. COPD-pertussis and asthma-pertussis groups are not mutually exclusive.

Table 2. Pertussis incidence among individuals with pre-existing COPD and asthma compared with those without (2009–2018).

	Without COPD or asthma	With pre-existing COPD		With pre-existing asthma
	(n = 796)	(n = 96)		(n = 175)
	Mean incidence	Mean incidence	IRR (95% CI)	Mean incidence	IRR (95% CI)
Overall mean	0.50	2.47	4.94 (4.00–6.11)	3.35	6.70 (5.69–7.89)
Age
50–54	0.45	2.04	4.53 (1.68–12.21)	4.11	9.13 (6.02–13.86)
55–59	0.52	2.61	5.02 (2.57–9.81)	3.24	6.23 (4.06–9.55)
60–64	0.40	0.64	1.60 (0.51–5.05)	2.41	6.03 (3.69–9.84)
65–69	0.58	2.35	4.05 (2.33–7.06)	2.02	3.48 (2.06–5.88)
70–74	0.47	2.71	5.77 (3.49–9.54)	3.11	6.62 (4.18–10.48)
75+	0.60	3.01	5.02 (3.62–6.96)	4.36	7.27 (5.45–9.69)
Sex
Female	0.59	2.52	4.27 (3.03–6.02)	3.36	5.69 (4.60–7.06)
Male	0.39	2.39	6.13 (4.65–8.08)	3.33	8.54 (6.62–11.01)

n: number of pertussis cases. Incidence of pertussis was calculated per 100 000 persons. 95% CIs for IRRs were based on Poisson distribution. CI: confidence interval; COPD: chronic obstructive pulmonary disease; IRR: incidence rate ratio.

Figure 3. Mean incremental all-cause direct medical costs for the asthma- and COPD-pertussis versus the general-pertussis group.

Incremental cost and healthcare resource utilisation was calculated as differences between each post-index period and baseline period (0–3 months pre-index date) for each group. Costs were adjusted to 2018 KRW using the healthcare component of the Korean Consumer Price Index and converted from South Korean Won (KRW) to US dollars (USD) using the 2018 exchange rate (1 USD = 1115.7 KRW). The index date was defined as the date of pertussis diagnosis minus 15 days to allow for the inclusion of healthcare resource utilisation and medical costs related to workup pertussis diagnosis. Asthma-pertussis: pertussis cases with pre-existing asthma; COPD: chronic obstructive pulmonary disease; COPD-pertussis: pertussis cases with pre-existing COPD; General-pertussis: pertussis cases without pre-existing COPD or asthma; KRW: South Korean won; USD: United States dollars.

Figure 4. Mean pertussis-related medical costs among asthma and COPD-pertussis groups relative to the general pertussis group.

Incremental pertussis-related healthcare costs were calculated within the 3 months post index date. Costs were adjusted to 2018 KRW using the healthcare component of the Korean Consumer Price Index and converted from South Korean Won (KRW) to US dollars (USD) using the 2018 exchange rate (1 USD = 1115.7 KRW). The index date was defined as the date of pertussis diagnosis minus 15 days to allow for the inclusion of healthcare resource utilisation and medical costs related to workup pertussis diagnosis. Asthma-pertussis: pertussis cases with pre-existing asthma; COPD-pertussis: pertussis cases with pre-existing COPD; COPD: chronic obstructive pulmonary disease; General-pertussis: pertussis cases without pre-existing COPD or asthma; KRW: South Korean won; USD: United States dollars.

Figure 5. Plain language summary.

Data availability statement

The data that support the findings of this study are not publicly available as they are owned by the statutory health insurances. The datasets supporting the conclusions of this article are included within the article and its additional files.