Latitude of the study place and age of the patient are associated with incidence of mediastinitis and microbiology in open-heart surgery: a systematic review and meta-analysis

Figures & data

Figure 1 A flowchart of the literature searches for the systematic review of studies on the incidence of mediastinitis.

Table 1 Incidence of microorganisms recovered in mediastinitis secondary to cardiothoracic surgery with frequency in 63 cohort studies

Gram-positive cocci (n=2,958)

Staphylococcus aureus (n=1,397), including MRSA (n=343)

Staphylococcus epidermis (n=1057)

Enterococcus spp. (n=168)

Streptococcus spp. (n=24)

Gram-negative bacilli (n=733)

Esherichia coli (n=101)

Enterobacter spp. (n=142)

Klebsiella spp. (n=105)

Proteus spp. (n=19)

Other Enterobacteriaceae (n=52)

Pseudomonas spp. (n=117)

Fungi (n=33)

Other bacteria occasionally reported (n=509)

Note: Total number of microorganisms (bacteria + fungi) is 3,724 in 306,440 patients.

Abbreviation: MRSA, methicillin-resistant Staphylococcus aureus.

Table 2 Estimate of incidence of mediastinitis with stratification on prospective nature and power of the cohort and on latitude of the study place using the random-effect model

Subdivision	n	Incidence (95% CI)	τ^2	I^2 (%)	P-valuea
All studies	97	0.0158 (0.0142–0.0175)	0.0039	97.8
Prospective cohort design
Yes	49	0.02 (0.016–0.024)	0.0075	97.3	<0.0001
No/Unclear	48	0.012 (0.010–0.015)	0.0019	95.7
Powered study
Yes	82	0.0146 (0.013–0.016)	0.0036	98	0.021
No	15	0.0274 (0.0158–0.015)	0.0225	93.1
Latitude over median 40.71
Yes	49	0.0126 (0.0112–0.014)	0.0016	96.4	0.0001
No	48	0.0199 (0.0162–0.024)	0.009	97.7

Note:

a Test for subgroup differences using the random-effect model between groups with Q statistics, df =1, and P-value.

Abbreviations: CI, confidence interval; τ², interstudy variability; df, degree of freedom.

Table 3 Meta-regression between incidence of mediastinitis and the different study-level and patient-level variables in a univariate analysis

Covariates	Level	β-coefficient	SE (β)	Z	P-value
Latitude	Degrees	−0.0020	0.0007	−2.67	0.0075
Age	Years	0.0068	0.0029	2.35	0.018
Female sex	Percent	0.0003	0.0008	0.4367	0.6623
CABG	Percent	0.0006	0.005	1.20	0.2029
Publication year	Year	0.0010	0.0006	1.63	0.1023

Abbreviations: SE, standard error; CABG, coronary artery bypass grafting.

Figure 2 A funnel plot for the incidence of mediastinitis in 97 studies with Egger line.

Abbreviations: SE, standard error; ES, effect size.

Figure 3 Meta-regression of incidence of mediastinitis and latitude of study place.

Note: Freeman-Tukey double arcsine transformated incidence.

Figure 4 Meta-regression of incidence of mediastinitis and mean age of the patient.

Note: Freeman-Tukey double arcsine transformated incidence.

Table 4 Estimate of incidence of Gram-positive cocci with stratification on prospective nature of the cohort and latitude of the study place using the random-effect model

Subdivision	n	Incidence (95% CI)	τ^2	I^2 (%)	P-valuea
All studies	63	0.009 (0.0081–0.0121)	0.6067	96.6
Prospective cohort design
Yes	33	0.012 (0.0095–0.0167)	0.6219	96.6	0.0078
No/Unclear	30	0.007 (0.0062–0.0097)	0.3392	93.4
Latitude over median 40°
Yes	32	0.009 (0.007–0.012)	0.3894	95.7	0.8897
No	31	0.0101 (0.0071–0.0144)	0.964	97.0

Note:

a Test for subgroup differences using the random-effect model between groups with Q statistics, df =1, and P-value.

Abbreviations: CI, confidence interval; τ², interstudy variability.

Table 5 Meta-regression model between incidence of Gram-positive cocci and the different study-level and patient-level variables in a univariate analysis using the 63 cohorts

Covariates	Level	β-coefficient	SE (β)	Z	P-value
CABG	Percent	0.0110	0.0058	1.89	0.057
Age	Years	0.0889	0.0429	2.07	0.038
Latitude	Degrees	−0.0050	0.0084	0.596	0.5508
Female sex	Yes/No	0.0029	0.0085	0.342	0.7315
Publication year	Year	0.0012	0.0010	1.80	0.2378

Abbreviations: SE, standard error; CABG, coronary artery bypass grafting.

Table 6 Estimate of total incidence of MRSA with stratification on prospective nature of cohort and latitude of the study place using the random-effect model

Subdivision	n	Incidence (95% CI)	τ^2	I^2 (%)	P-valuea
All studies	63	0.0008 (0.0005–0.0012)	1.79	90.5
Prospective cohort design
Yes	33	0.0012 (0.0007–0.002)	1.816	91.5	0.0417
No/Unclear	30	0.0005 (0.0004–0.0009)	1.419	83.2
Latitude over median 40°
Yes	32	0.0006 (0.0003–0.0010)	1.34	84	0.0853
No	31	0.0011 (0.0006–0.0021)	1.90	84

Note:

a Test for subgroup differences using the random-effect model between groups with Q statistics, df =1, and P-value.

Abbreviations: MRSA, methicillin-resistant Staphylococcus aureus; CI, confidence interval; τ², interstudy variability; df, degree of freedom.

Table 7 Meta-regression model between incidence of MRSA and the different study-level and patient-level variables in a univariate analysis using the 63 cohorts

Covariates	Level	β-coefficient	SE (β)	Z	P-value
CABG	Percent	0.007	0.005	1.32	0.1848
Age	Years	0.0079	0.0031	2.53	0.0112
Latitude	Degrees	−0.0016	0.0006	−2.53	0.0114
Female sex	Yes/No	−0.0005	0.0007	−0.78	0.4345
Year of publication	Year	0.0140	0.0227	0.61	0.5381

Abbreviations: MRSA, methicillin-resistant Staphylococcus aureus; SE, standard error; CABG, coronary artery bypass grafting.

Figure 5 Meta-regression of incidence of MRSA and latitude of the study place.

Note: Freeman-Tukey double arcsine transformated incidence.
Abbreviation: MRSA, methicillin-resistant Staphylococcus aureus.

Figure 6 Meta-regression of incidence of MRSA and mean age of the patient.

Note: Freeman-Tukey double arcsine transformated incidence.
Abbreviation: MRSA, methicillin-resistant Staphylococcus aureus.

Table 8 Estimate of total incidence of Gram-negative bacilli with stratification on prospective nature of cohort and latitude of the study place using the random-effect model

Subdivision	n	Incidence (95% CI)	τ^2	I^2 (%)	P-valuea
All studies	63	0.0024 (0.0018–0.0032)	0.9819	91.8
Prospective cohort design
Yes	35	0.0058 (0.0053–0.0063)	0.8591	91.9	0.0001
No/Unclear	30	0.0039 (0.0034–0.0043)	1.2000	91.4
Latitude over median 40°
Yes	32	0.0018 (0.0012–0.0025)	0.6549	87.4	0.008
No	31	0.0036 (0.0024–0.0054)	1.046	92.4

Note:

a Test for subgroup differences using the random-effect model between groups with Q statistics, df =1, and P-value.

Abbreviations: CI, confidence interval; τ², interstudy variability; df, degree of freedom.

Table 9 Meta regression model between incidence of Gram-negative bacilli and the different study-level and patient-level variables in a univariate analysis using the 63 cohorts

Covariates	Level	β-coefficient	SE (β)	Z	P-valuea
Latitude	Degrees	−0.0330	0.0108	−3.07	0.002
Age	Years	−0.0466	0.0585	−0.79	0.4261
Female sex	PCT	0.0173	0.0126	1.36	0.1711
CABG	PCT	0.0067	0.0087	0.76	0.4423
Publication year	Year	−0.0092	0.0138	−0.66	0.5055

Note:

a Test for subgroup differences using the random-effect model between groups with Q statistics, df =1, and P-value.

Abbreviations: SE, standard error; CABG, coronary artery bypass grafting; PCT, percentage; df, degree of freedom.