Follow-up outcomes of asymptomatic brucellosis: a systematic review and meta-analysis

Figures & data

Figure 1. A flow chart of the inclusion criteria of studies eligible for meta-analysis.

Table 1. Characteristics of the included studies.

Included studies	Country	Investigation time	Age	Male (%)	Occupation	Main animals involved	Serological tests
Hu et al. (2021)	China	Nov, 2012 – May, 2014	median 34	60.0	Occupational population, Student	Sheep	SAT ≥ 1:100
Wu et al. (2019)	China	Jun – Aug, 2017	23–55	88.8	Occupational population	Cattle	SAT ≥ 1:100
Chen et al. (2019)	China	Apr, 2018 – Jan, 2019	1–62	53.3	Occupational population	Sheep	SAT ≥ 1:100
Mangalgi et al. (2016)	India	Oct – Nov, 2012	3–74	86.5	Occupational population	Livestock	SAT ≥ 1/160 and 2ME ≥1/80
Mangalgi et al. (2015)	India	NA*	1–74	60.0	Occupational population	Cattle, sheep and goat	SAT ≥ 1/160 and 2ME ≥1/80
Aghaali et al. (2015)	Iran	Jan – Dec, 2013	7–12	51.0	Student	Livestock	SAT ≥ 1/80 and 2ME ≥ 1/40 / Coombs ≥1/80
Ismayilova et al. (2013)	Azerbaijan	Aug, 2009	20–43	100.0	Family member**	Cattle, sheep and goat	SAT ≥ 1:200
Tabak et al. (2008)	Turkey	NA	4–55	50.0	Family member	Cattle	SAT ≥ 1:160
Zhang et al. (2008)	China	Three months of 2007	mean 38	100.0	Occupational population	Cattle	SAT ≥ 1:100
Alsubaie et al. (2005)	Saudi Arabia	Jan, 2001 – Feb, 2002	1-80, median 17	47.2	Family member	camel, sheep and goat	SAT ≥ 1:160
Almuneef et al. (2004)	Saudi Arabia	May, 2000 – Oct, 2001	2-67, mean 27	56.4	Family member	camel, sheep and goat	SAT ≥ 1:160
Young et al. (1991)	America	NA	47	100.0	Occupational population	Livestock	SAT/2ME ≥ 1:160***
Abramson et al. (1991)	Israel	Aug, 1988 – Aug, 1989	7–17	38.0	Family member	sheep and goat	SAT/2ME ≥ 1:160

*Not available. **Family members of the indexed cases (symptomatic brucellosis).

***SAT: Serum Agglutination Test; 2ME:2-mercaptoethanol.

Table 2. Follow-up outcomes and quality assessment of the included studies.

Included studies	Follow-up time (months)	Sample size	Follow-up outcomes			Quality assessment
			No. of appearing symptomatic	No. of maintaining asymptomatic	No. of decreased SAT titre
Hu et al. (2021)	18	15	7	6	2	High
Wu et al. (2019)	2	6	3	NA*	NA	Medium
Chen et al. (2019)	5,6,9	4	0	NA	NA	Medium
Mangalgi et al. (2016)	1	13	0	NA	NA	Medium
Mangalgi et al. (2015)	1	6	0	NA	NA	Medium
Aghaali et al. (2015)	12	8	6	NA	NA	High
Ismayilova et al. (2013)	0.5-0.7	3	0	2	1	High
Tabak et al. (2008)	6–12	12	0	NA	NA	Medium
Zhang et al. (2008)	3	12	NA	NA	8	Medium
Alsubaie et al. (2005)	6–13	11	4	NA	NA	High
Almuneef et al. (2004)	6	11	2	NA	NA	High
Young et al. (1991)	17	1	0	1	0	High
Abramson et al. (1991)	12	5	1	1	3	High

*Not available.

Figure 2. Forest plots of the pooled prevalence of follow-up outcomes. (a) Pooled prevalence of appearing symptomatic, weighted by random effects analysis. (b) Pooled prevalence of maintaining asymptomatic, weighted by fixed effects analysis. (c) Pooled prevalence of decreased SAT titre, weighted by random effects analysis. CI = confidence interval.

Table 3. Subgroup analysis of follow-up outcomes of appearing symptomatic.

Subgroups		No. of studies	Proportion (95% CI)	I^2	P-value
Investigation time
	1990–2009	6	0.084 (0.000, 0.226)	31%	0.21
	2010–2021	6	0.220 (0.006, 0.552)	81%	<0.01
Region
	Asia	10	0.209 (0.054, 0.410)	68%	<0.01
	Europe & America	2	0.000 (0.000, 0.054)	0%	0.56
Population
	Occupational population	6	0.119 (0.000, 0.466)	75%	<0.01
	Family member	5	0.117 (0.021, 0.254)	45%	0.13
	Student	2	0.466 (0.006, 0.969)	77%	0.04
Main animals
	Sheep and/or goat	3	0.239 (0.010, 0.578)	51%	0.13
	Cattle	2	0.153 (0.000, 0.810)	86%	<0.01
	Cattle, sheep and goat	2	0.000 (0.000, 0.200)	0%	0.84
	Camel, sheep and goat	2	0.269 (0.094, 0.483)	0%	0.37
	Livestock	3	0.171 (0.000, 0.894)	88%	<0.01
Follow-up time
	<6months	10	0.115 (0.003, 0.302)	70%	<0.01
	6–12months	6	0.264 (0.045, 0.552)	74%	<0.01
	6–18months	4	0.476 (0.255, 0.701)	31%	0.23
SAT
	≥1:80/≥1:100	4	0.434 (0.144, 0.746)	59%	0.06
	≥1:160/≥1:200	8	0.036 (0.000, 0.130)	37%	0.14
Quality assessment
	High	7	0.341 (0.195, 0.499)	38%	0.14
	Medium	5	0.028 (0.000, 0.206)	55%	0.06