Seasonality in tuberculosis occurrence in the Federal District, Brazil

doi:10.21203/rs.2.23682/v1

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Seasonality in tuberculosis occurrence in the Federal District, Brazil

https://doi.org/10.21203/rs.2.23682/v1

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BACKGROUND: Although tuberculosis (TB) is an endemic infectious disease in Brazil, the Federal District has a different epidemiology from other Brazilian locations. Investigation of disease seasonality, which needs to be further explored in tropical regions, may indicate risk factors specific to peak incidence seasons that could be controlled if better understood. To investigate the influence of seasonality (SA) in the occurrence of tuberculosis in the Federal District (FD) of Brazil.

METHODS: This is an ecological time series (TS) study based on secondary data. The unit of analysis was the month of TB diagnosis from 2001 to 2018. We used the X-13ARIMA-SEATS (X-13) seasonal adjustment software in automatic mode with additive decomposition. Seasonality was analyzed using the Friedman test (0.001) and Kruskal-Wallis test (0.01) for stable seasonality. Moving seasonality was verified by Friedman test (0.05), and the identifiable seasonality was constructed from the combination of the three tests. The annual average seasonal amplitude was calculated from the isolated seasonal factors.

RESULTS: 6,161 TB cases were diagnosed in the Federal District, 28 cases per month on average (± 6.6). We observed peaks in April and August and decreased detection in November and December, with an average annual seasonal amplitude of 34.0%. The F test and the Kruskal-Wallis test revealed evidence of SA at 0.001 and 0.01, respectively. Moving SA was not identified at a significance level of 0.5 neither in the combination of the three tests.

CONCLUSION: the TS tends to suggest a limited seasonality of TB in the FD. Some incidence peaks were observed in some specific months, showing a relevance of seasonality at the local level, which may reflect an influence of access to health service patterns from the onset of symptoms to the diagnostic elucidation of the disease.

Infectious Diseases

Tuberculosis

Seasonality

Climate

Time series analysis

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Table 1. Cases of tuberculosis according to demographic and clinical presentation variables in the Federal District, Brazil (2001 - 2018)

Variables	Category:	Total	Rate (%)	Monthly average	Median	Mode	Standard deviation	Variance	Minimum	Maximum
All cases		6161	100.0	28.5	29	24	6.6	43.0	11	47
Gender	Male	3931	63.8	18.2	18	20	5.1	25.6	7	32
Gender	Female	2230	36.2	10.3	10	11	3.5	12.4	3	22
Age	< 15 years	264	4.3	1.22	1	0	1.4	1.9	0	8
	15 – 19	215	3.5	1	1	1	0.9	0.9	0	4
	20 – 39	2661	43.2	12.3	12	12	3.8	14.2	2	26
	40 – 59	2015	32.7	18.1	9	8	3.5	12.2	1	20
	60 years and over	1006	16.3	9.2	4	4	2.4	5.8	0	16
Race/Skin color	Caucasian	1791	29.1	8.3	8	9	3.8	14.8	0	19
	Blacks¹	3434	55.7	15.9	16	15	6.0	36.4	0	34
	Asian and indigenous	82	1.3	0.5	0	0	0.6	0.4	0	3
	Ignored	826	13.4	3.8	2	2	5.7	32.8	0	33
Clinical presentation	Pulmonary	4609	74.8	20.5	21	22	5.6	31.1	7	41
Clinical presentation	Extrapulmonary	1550	25.2	7.2	7	8	2.9	8.7	2	16
Sputum smear	Positive	2546	41.3	11.8	11	10	3.8	14.7	3	23
	Negative	2016	32.7	9.3	9	8	4.0	15.7	2	25
	Other²	1599	25.9	7.4	7	8	3.1	9.7	1	17
Laboratory Confirmation	Yes	3173	51.5	14.7	15	11	4.5	20.4	3	27
Laboratory Confirmation	No	2988	48.5	13.8	13	12	4.5	20.7	4	26
HIV serology	Positive	680	11.0	3.2	3	3	2.0	4.07	0	11
	Negative	3172	51.5	14.7	15	15	6.8	46.6	1	36
	Other³	2309	37.5	10.7	10	5	7.0	48.6	0	35

Source: Brazilian National disease notification system (Sistema de Informação de Agravos de Notificação - SINAN). Accessed on June 2019.

¹ Blacks = Brown and black

² Other: Bacilloscopy not performed, information blank or ignored, or not applicable

³ Other: Results in progress, blank or ignored information

Table 02 – Final seasonal factors of TB cases in the Federal District, Brazil (2001-2018)

	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
2001	3	1	-2	1	-2	-2	2	6	3	-1	-6	-4
2002	3	1	-1	1	-1	-2	1	6	3	-1	-6	-4
2003	3	0	-1	1	0	-2	1	5	4	-1	-5	-5
2004	3	-1	-1	1	0	-2	1	4	4	-1	-4	-5
2005	2	-1	0	1	1	-1	1	4	4	-1	-4	-5
2006	1	-3	1	2	2	-1	2	3	3	0	-4	-6
2007	0	-3	2	2	3	0	1	3	3	-1	-4	-6
2008	0	-4	2	2	3	0	1	3	2	-1	-3	-6
2009	0	-5	3	2	3	0	1	4	2	-1	-3	-6
2010	-1	-4	3	2	3	1	0	4	1	-1	-2	-7
2011	-1	-4	3	2	3	1	0	4	1	-1	-2	-6
2012	-2	-3	3	2	3	1	0	5	0	-2	-1	-6
2013	-2	-2	3	2	2	2	0	5	0	-2	-1	-5
2014	-3	-2	2	2	2	2	0	5	-1	-2	-1	-4
2015	-3	-1	2	2	1	2	-1	5	-1	-2	-1	-4
2016	-3	0	1	2	1	1	-1	5	-1	-2	-1	-4
2017	-3	0	1	3	0	1	0	5	0	-2	-1	-3
2018	-3	1	1	3	0	1	0	4	0	-3	-1	-3
Average	0	-2	1	2	1	0	1	4	2	-1	-3	-5

Table 03 – Test results for the seasonality of tuberculosis in the Federal District, Brazil (2001 - 2018)

Table 3.A - Test for the presence of seasonality assuming stability

	Sum of squares	Degrees of freedom	Mean square	F-Value
Between months	1226.1	11	111.7	3.8
Residual	5981.5	204	29.3
Total	7207.6	215

Table 3.B - Nonparametric test for presence of seasonality assuming stability

Kruskal-Wallis test	Degrees of freedom	Probability level
38.1	11	0.008%

Table 3.C - Moving seasonality test

	Sum of squares	Degrees of freedom	Mean square	F-Value
Between years	296.8	17	17.5	1.2
Error	2622.1	187	14.0

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Seasonality in tuberculosis occurrence in the Federal District, Brazil

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