Job position, age and hospital unit as a risk factor
Of all 550 HCW (73 doctors, 198 nurses, 150 cleaners, 129 others) working in the study hospitals at the time of the study, 409 (74,4%) participants were recruited and had at least one QFT performed (NTC=222 [63.2%], Karabalta=100 [96.1%], Kemin=38 [84.4%], Karakol=49 [98.0%]). Five tests with indeterminate results (NTC: n=2; Karabalta: n=2; Kemin: n=1) between the ages of 27-63 years were removed from the analysis resulting in 404 HCW that were included. There were five HCW that did not provide age and were not included in the age-controlled analysis. There was no random effect of site on the outcome of the QTF test (p=0.063) based on the mixed effects logistic regression including age and job position as dependent variables for QFT when analysing all four sites independently. However, there were differences in the mixed effects logistic regression when comparing the NTC and the three other sites combined (p=0.02). Additionally, the average age of HCW at the NTC (44.7 years) was lower than the other sites combined (48.9 years; p<0.001); therefore, logistical analyses were split by site (Table 1). In univariate analysis, increasing age per year was associated with a positive quantiferon result (OR=1.02 per year, 95% CI=1.00-1.03, p-value<0.001), and this effect occurred among all job positions. Age was controlled for in the analysis due to the association between job position (p<0.001) and QFT positivity.
There were 189 (46.7%) HCW that had a positive QTF result. At both the NTC and the other sites combined, nurses had the highest level of recruitment to the study and ranged in age from 21-70 years old (Table 1). In the NTC, physicians (OR=8.7, 95%, CI=1.2-60.5, p=0.03) and laboratory staff (OR=19.8, 95% CI=2.9-135.4, p<0.01) had increased odds to have positive QFTs than administrative staff. Nurses (OR=5.9, 95% CI=1.0-35.4, p=0.05) and cleaners (OR=6.01, 95% CI=0.9-39.4, p=0.06) showed trends towards increased odds of positivity (Table 1). In the conservative pairwise comparisons for all job positions with the Bonferroni correction, no position was any different than another for testing positive. However; without the adjustment additional differences between positions were that lab workers had higher odds of being positive than cleaners (coefficient difference = 1.19, unadjusted 95% CI=0.09-2.29). There was no effect of job position on the QTF results for Karabalta, Karakol and Kemin combined (Table 1).
Table 1
Descriptive characteristics and results of the Firth penalized-likelihood estimates for the effect of health care worker (HCW) position in the study hospitals on being Quantiferon-TB Gold plus positive while controlling for age.
|
NTC
|
|
|
|
Kara Balta, Karakol, Kemin combined
|
Type of HCW
|
Number of participants n %
|
Mean age yrs (range)
|
QFT Positive n %
|
OR
|
95% CI
|
P-value
|
KB
|
KK
|
KM
|
Total
%
|
Mean age (range)
|
QFT Positive n
%
|
OR
|
95% -CI
|
P-value
|
Admin
|
10
4.5%
|
37.5 (23-53)
|
1
10.0%
|
Base
|
|
|
9
|
5
|
1
|
15
8.2%
|
48.7 (31-64)
|
5
33.3%
|
Base
|
|
|
Head of department
|
7
3.2%
|
56.6 (48-66)
|
4
57.1%
|
4.1
|
0.9-39.4
|
0.06
|
2
|
1
|
2
|
5
2.7%
|
63.0 (57-70)
|
3
60.0%
|
2.1
|
0.3-14.9
|
0.45
|
Physician
|
23
10.5%
|
47.3 (26-82)
|
15
65.2%
|
8.7
|
1.2-60.5
|
0.03
|
5
|
5
|
2
|
12
6.5%
|
43.5 (26-69)
|
4
33.3%
|
1.1
|
0.2-5.2
|
0.91
|
Nurse
|
85
38.6%
|
42.1 (21-67)
|
43
50.6%
|
5.9
|
1.0-35.4
|
0.10
|
26
|
13
|
10
|
49
26.6%
|
49.0 (29-70)
|
19
38.8%
|
1.3
|
0.4-4.1
|
0.70
|
Cleaner
|
34
15.5%
|
47.9 (30-64)
|
20
58.8%
|
6.01
|
0.9-39.4
|
0.06
|
22
|
8
|
10
|
40
21.7%
|
49.8 (26-67)
|
16
40.0%
|
1.3
|
0.4-4.2
|
0.70
|
Lab
|
32
14.5%
|
38.3 (22-71)
|
24
75.0%
|
19.8
|
2.9-135.4
|
0.002
|
4
|
6
|
2
|
12
6.5%
|
48.4 (26-66)
|
5
41.7%
|
1.4
|
0.3-6.4
|
0.66
|
Technical
|
17
7.7%
|
53.1 (38-63)
|
7
41.2%
|
2.6
|
0.3-19.1
|
0.356
|
30
|
9
|
10
|
49
26.6%
|
48.4 (26-68)
|
17
34.7%
|
1.1
|
0.3-3.4
|
0.96
|
Other
|
12
5.5%
|
54.6 (42-66)
|
5
41.7%
|
2.0
|
0.2-17.1
|
0.52
|
0
|
2
|
0
|
2
1.1%
|
35 (NA)
|
1
50.0%
|
NA
|
NA
|
NA
|
Total
|
220
100.0%
|
44.7 (21-82)
|
119
54.1%
|
|
|
|
98
|
49
|
37
|
184
100.0%
|
48.9 (25-70)
|
70
38.0%
|
|
|
|
Abbreviations: NTC=National Tuberculosis Centre ; QFT= Quantiferon-TB Gold plus ; KB= Karabalta; KK= Karakol; KM=Kemin
*Significant with p<0.05
|
In order to compensate for small sample size, all hospitals were combined for comparisons of hospital units. The laboratories (OR 7.65; 95%CI 2.3 – 24.9; p<0.001), smear negative TB (OR 5.90; 95%CI 1.6 – 21.8; p=0.008), surgery (OR 3.79; 95%CI 1.3 – 11.4; p=0.018), and outpatient clinics (OR 3.80; 95%CI 1.1 – 13.0; p=0.03) had higher odds of a positive QFT result than the admin department (Table 2). With a conservative pairwise comparison adjusting for multiple comparisons, only the laboratory compared to administrative staff was significantly different (contrast=2.03, Bonferroni 95% CI=0.04-4.02).
Table 2
Logistic regression results for differences between departments within the National Tuberculosis Centre (NTC), when controlling for age.
Department
|
Number
|
QFT positive
|
OR
|
95% Confidence interval
|
P-value
|
n
|
%
|
Admin/Monitoring
|
23
|
5
|
21,7%
|
Base
|
|
|
Surgery
|
55
|
28
|
50,9%
|
3.79
|
1.3 – 11.4
|
0.018*
|
Lab
|
39
|
26
|
66,7%
|
7.65
|
2.3 – 24.9
|
0.001*
|
Drug Resistant TB
|
98
|
46
|
46,9%
|
2.82
|
0.995 – 8.0
|
0.051+
|
Outpatient clinic
|
26
|
14
|
53,8%
|
3.80
|
1.1 – 13.0
|
0.033*
|
Pediatrics
|
13
|
4
|
30,8%
|
1.32
|
0.3 – 5.8
|
0.71
|
Intensive Care Unit
|
11
|
5
|
45,5%
|
2.72
|
0.6 – 12.1
|
0.19
|
Smear positive TB
|
16
|
8
|
50,0%
|
2.92
|
0.7 – 11.4
|
0.12
|
Smear negative TB
|
21
|
13
|
61,9%
|
5.90
|
1.6 – 21.8
|
0.008*
|
General TB
|
82
|
31
|
37,8%
|
1.77
|
0.6 – 5.1
|
0.29
|
Engineering & technical staff
|
15
|
6
|
40,0%
|
2.03
|
0.5 – 8.1
|
0.32
|
TOTAL
|
399
|
|
|
|
|
|
+, trend; *, statistical significance
|
Follow-up
There were 52 HCW that had at least one additional QFT. Three HCW were removed from analysis as follow-up tests were not at least one month following first QFT, resulting in 49 HCW included in the follow-up analysis (NTC=28, Karakol=21; table 3). Follow-up tests were taken on average 160 days after the first test (range 69-257 days). Seventeen HCW had a positive QFT at both times (P status), 12 had both negative QFT (N status), 15 converted from negative to positive (C status), and five reverted from positive to negative (R status). Site (p=0.27), age (p=0.47), time between tests (p=0.82), or job position (p=0.75) had no effects on the follow-up status. There was no association with having a borderline positive first test and the outcome of the 2nd test being either positive, or negative (p=0.16). Of the 30 participants that had a 3rd valid QFT performed, 9 of 10 (90%) and all (13/13, 100%) participants of the C and P status, respectively, remained positive. Of those with N status (6/6, 100%) remained negative for the 3rd QFT (Table 3).
Table 3
Follow-up QuantiFERON-TB Gold plus tests of HCW indicating stable and instable test results for HCW. Stable status was assigned when the 3rd test matched the 2nd, and instable status when it did not.
Statusa
|
1st => 2nd QFT
|
HCW with status
|
HCW with 3rd QFT performed
|
3rd QFT results
|
Positive
n (%)
|
Negative
n (%)
|
P
|
positive => positive
|
17
|
13
|
13b (100%)
|
0
|
N
|
negative => negative
|
12
|
6
|
0
|
6b (100%)
|
C
|
negative => positive
|
15
|
10
|
9b (90%)
|
1
|
R
|
positive => negative
|
5
|
1
|
1
|
0
|
Total
|
|
49
|
30
|
23
|
7
|
a: Positive (P); Negative (N); Converter (C); Reverter (R)
b: Stable status based on 3rd QFT test
|