Seasonal characteristics of scrub typhus in Baoshan City using concentration ratio and circular distribution methods

doi:10.12140/j.issn.1000-7423.2025.01.024

Abstract

Abstract:

A statistical analysis was performed on the scrub typhus surveillance data in Baoshan City, Yunnan Province from January 1, 2017 to December 31, 2023 reported to the Chinese Disease Prevention and Control Information System. The concentration ratio (M value) of scrub typhus was calculated to analyze the seasonal distribution characteristics, and the day of the peak incidence of scrub typhus and epidemic peaks of scrub typhus were estimated using the circular distribution method. A Pearson correlation analysis was performed on the M value and the concentration parameter (r value) of a circular distribution. A total of 11 537 cases with scrub typhus were reported in Baoshan City from 2017 to 2023, with an annual reported incidence rate of 65.12/105, and the highest incidence in 2023 (96.71/105), and the incidence appeared an overall tendency towards a rise from 2017 to 2023 (χ² = 484.882, P < 0.01). Farmers were the primary occupation among all cases with scrub typhus (78.79%, 9 090/11 537), and the reported scrub typhus cases are concentrated during the period between July and October from 2017 to 2023, with the highest proportion of reported cases in August each year, and the numbers of reported scrub typhus cases accounted for 26.74%, 33.13%, 34.25%, 32.84%, 34.55%, 27.17% and 39.34% of total cases each year from 2017 to 2023, which accounted for 33.04% (3 812/11 537) of total cases. The radar chart appeared a unimodal distribution in each year and each month, which met the prerequisite for concentration ratio and circular distribution analyses. The M value of total scrub typhus cases was 0.779 from 2017 to 2023, with 0.729 to 0.814 each year during the study period, indicating a strong seasonality of scrub typhus incidence in Baoshan City. The r value of the circular distribution of scrub typhus incidence was 0.758, with $\bar{\alpha } $ of 227.38° (184.89°, 269.87°) (Z = 6 626.66, P < 0.001) indicating the day of peak incidence on August 21, and epidemic peak during the period from July 6 to September 30. In addition, Pearson correlation analysis revealed a strong positive correlation between the M value and r value (Pearson coefficient was 0.940 and P was 0.001 65).

Key words: Scrub typhus, Seasonal distribution, Concentration ratio, Circular distribution method

CLC Number:

R757.3

LI Yanping, SHUI Tiejun, HE Kai, YANG Hexian, ZHAO Lijuan, YANG Xiaoling, DUAN Lizhong, WANG Liming, HUANG Dongsheng. Seasonal characteristics of scrub typhus in Baoshan City using concentration ratio and circular distribution methods[J]. CHINESE JOURNAL OF PARASITOLOGY AND PARASITIC DISEASES, 2025, 43(1): 147-151.

Figures/Tables 5

References 17

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月份	年份
	2017		2018		2019		2020		2021		2022		2023		合计
	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%	发病例数	占比/%
1	4	0.30	3	0.18	2	0.18	3	0.20	5	0.26	8	0.46	6	0.26	31	0.27
2	2	0.15	0	0	1	0.09	1	0.07	4	0.21	4	0.23	4	0.17	16	0.14
3	4	0.30	4	0.24	3	0.27	3	0.20	7	0.37	3	0.17	3	0.13	27	0.23
4	8	0.60	4	0.24	6	0.53	4	0.27	4	0.21	8	0.46	6	0.26	40	0.35
5	11	0.82	3	0.18	12	1.07	8	0.54	10	0.53	27	1.54	13	0.56	84	0.73
6	116	8.69	50	3.05	35	3.11	67	4.54	57	3.01	170	9.73	56	2.42	551	4.78
7	257	19.25	365	22.23	101	8.99	296	20.04	330	17.43	336	19.22	344	14.84	2 029	17.59
8	357	26.74	544	33.13	385	34.25	485	32.84	654	34.55	475	27.17	912	39.34	3 812	33.04
9	259	19.40	416	25.33	354	31.49	259	17.54	411	21.71	360	20.59	526	22.69	2 585	22.41
10	238	17.83	192	11.69	146	12.99	244	16.52	296	15.64	277	15.85	346	14.93	1 739	15.07
11	61	4.57	51	3.11	61	5.43	80	5.42	91	4.81	70	4.00	77	3.32	491	4.26
12	18	1.35	10	0.61	18	1.60	27	1.83	24	1.27	10	0.57	25	1.08	132	1.14

年份	R_x	R_y	M
2017	-0.466	-0.560	0.729
2018	-0.511	-0.639	0.818
2019	-0.596	-0.531	0.798
2020	-0.505	-0.568	0.760
2021	-0.539	-0.569	0.784
2022	-0.441	-0.590	0.737
2023	-0.555	-0.596	0.814
合计	-0.516	-0.583	0.779

月份	月中值/d	月中位角/°	cos$\bar{\alpha } $	sin$\bar{\alpha } $	f.cos$\bar{\alpha } $	f.sin$\bar{\alpha } $
1	15.5	15.29	0.97	0.26	30.07	8.06
2	45.0	44.38	0.72	0.70	11.52	11.20
3	74.5	73.48	0.28	0.96	7.56	25.92
4	105.0	103.56	-0.23	0.97	-9.20	38.80
5	135.5	133.64	-0.69	0.72	-57.96	60.48
6	166.0	163.73	-0.96	0.28	-528.96	154.28
7	196.5	193.81	-0.97	0.24	-1 968.13	486.96
8	227.5	224.38	-0.72	-0.70	-2 744.64	-2 668.40
9	258.0	254.47	-0.27	-0.96	-697.95	-2 481.60
10	288.5	284.55	-0.25	-0.97	-434.75	-1 686.83
11	319.0	314.63	0.70	-0.71	343.70	-348.61
12	349.5	344.71	0.97	-0.26	128.04	-34.32

年份	X	Y	集中趋势（r）	平均角（$\bar{\alpha } $）	角离差（S）	Z值	P值	发病高峰日（K）	发病高峰期（$\bar{a} \pm S$）
2017	-0.517	-0.495	0.716	223.78	46.547	684.13	< 0.001	8月18日	6月28日—10月1日
2018	-0.553	-0.544	0.775	224.53	40.514	987.28	< 0.001	8月19日	7月5日—9月25日
2019	-0.433	-0.664	0.793	236.88	39.280	706.46	< 0.001	8月31日	7月19日—10月6日
2020	-0.509	-0.531	0.736	226.25	44.381	799.26	< 0.001	8月20日	7月3日—10月1日
2021	-0.498	-0.578	0.762	229.26	42.492	1 099.98	< 0.001	8月23日	7月8日—10月2日
2022	-0.542	-0.478	0.723	221.41	46.547	913.70	< 0.001	8月15日	6月26日—9月28日
2023	-0.516	-0.612	0.801	229.90	38.435	1 485.59	< 0.001	8月24日	7月13日—9月29日
合计	-0.513	-0.558	0.758	227.38	42.492	6 626.66	< 0.001	8月21日	7月6日—9月30日