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Table 3 Frequency of PCR detection of equid herpesvirus 2 (EHV-2) and EHV-5 in nasal swabs collected from Polish horses (n = 540) stratified by age, stud farm, breed, season at the time of sampling, and disease status

From: Prevalence and sequence analysis of equid herpesviruses from the respiratory tract of Polish horses

Category

Horses [n]

EHV-2

EHV-5

 

n (%)

RR (95% CI)

p

n (%)

RR (95% CI, p)

p

Age (years)

  < 1

173

155 (89.6)

1.3 (1.2–1.4)

< 0.0001*

52 (30.1)

0.6 (0.4 to 0.7)

<  0.0001*

 1

99

83 (83.8)

1.1 (1.0–1.2)

0.0862

87 (87.9)

2.3 (2.0–2.7)

<  0.0001*

 2–3

101

66 (65.4)

0.8 (0.7–1.0)

0.0024*

57 (56.4)

1.3 (1.0–1.5)

0.0462

 4–9

83

52 (62.7)

0.8 (0.7–0.9)

0.001*

29 (34.9)

0.7 (0.5–1.0)

0.0171

 10–15

69

49 (71.0)

0.9 (0.8–1.1)

0.2182

23 (33.3)

0.7 (0.5–1.0)

0.0196

 16+

15

12 (80.0)

1.0 (0.8–1.3)

1

6 (40.0)

0.9 (0.5–1.6)

0.6119

Stud farm

 I

64

43 (67.2)

0.9 (0.7–1.0)

0.0556

46 (71.9)

1.6 (1.4–2.0)

<  0.0001*

 II

19

17 (89.5)

1.2 (1.0–1.4)

0.2693

8 (42.1)

0.9 (0.5–1.5)

0.8159

 III

18

18 (100.0)

1.3 (1.3–1.4)

0.018

16 (88.9)

2.0 (1.6–2.4)

0.0004*

 IV

42

31 (73.8)

1.0 (0.8–1.2)

0.5686

26 (61.9)

1.4 (1.1–1.8)

0.0532

 V

42

39 (92.9)

1.2 (1.1–1.4)

0.0115

29 (69.1)

1.5 (1.2–1.9)

0.0035*

 VI

37

34 (91.9)

1.2 (1.1–1.3)

0.0254

13 (35.1)

0.7 (0.5–1.1)

0.1718

 VII

47

41 (87.2)

1.1 (1.0–1.3)

0.1016

27 (57.5)

1.3 (1.0–1.6)

0.1683

 VIII

48

36 (75.0)

1.0 (0.8–1.2)

0.7191

13 (27.1)

0.6 (0.3–0.9)

0.0038

 IX

30

27 (90.0)

1.2 (1.0–1.3)

0.1151

11 (36.7)

0.8 (0.5–1.2)

0.264

 X

44

24 (54.6)

0.7 (0.5–0.9)

0.0005*

4 (9.1)

0.2 (0.1–0.5)

<  0.0001*

 XI

60

54 (90.0)

1.2 (1.1–1.3)

0.0134

27 (45.0)

1.0 (0.7–1.3)

0.7847

 XII

49

41 (83.7)

1.1 (1.0–1.3)

0.2896

27 (55.1)

1.2 (0.9–1.6)

0.2934

 XIII

40

12 (30.0)

0.4 (0.2–0.6)

<  0.0001*

7 (17.5)

0.4 (0.2–0.7)

0.0001*

Breed

 Arabian

101

78 (77.2)

1.0 (0.9–1.1)

1

70 (69.3)

1.7 (1.4–2.0)

<  0.0001*

 Coldblood

49

41 (83.7)

1.1 (1.0–1.3)

0.2896

27 (55.1)

1.2 (0.9–1.6)

0.2934

 Hucul

42

31 (73.8)

1.0 (0.8–1.2)

0.5686

26 (61.9)

1.4 (1.1–1.8)

0.0532

 Malopolska horse

42

39 (92.9)

1.2 (1.1–1.4)

0.0115

29 (69.1)

1.5 (1.2–1.9)

0.0035*

 Polish Halfbred

37

34 (91.9)

1.2 (1.1–1.3)

0.0254

13 (35.1)

0.7 (0.5–1.2)

0.1718

 Polish Konik

40

12 (30.0)

0.4 (0.2–0.6)

<  0.0001*

7 (17.5)

0.4 (0.2–0.7)

0.0001*

 Silesian horse

44

24 (54.6)

0.7 (0.5–0.9)

0.0005*

4 (9.1)

0.2 (0.1–0.5)

<  0.0001*

 Thoroughbred

60

54 (90.0)

1.2 (1.1–1.3)

0.0134

27 (45.0)

1.0 (0.7–1.3)

0.7847

 Wielkopolska horse

125

104 (83.2)

1.1 (1.0–1.2)

0.088

51 (40.8)

0.8 (0.7–1.1)

0.1254

Season

 Spring

186

121 (82.3)

1.4 (1.2 to 1.6)

<  0.0001*

185 (44.3)

0.8 (0.7 to 0.9)

0.0179

 Summer

104

55 (52.9)

0.6 (0.5 to 0.8)

< 0.0001*

53 (51.0)

1.1 (0.9 to 1.4)

0.3837

 Winter

18

18 (100.0)

1.3 (1.3 to 1.4)

0.018

16 (88.9)

2.0 (1.6 to 2.4)

0.0004

Respiratory disease

 Yes

43

41 (95.4)

1.3 (1.2–1.4)

0.0019*

26 (60.5)

1.3 (1.0–1.7)

0.0796

 No

497

376 (75.7)

  

228 (45.9)

  

Total

540

417 (77.2)

  

254 (47.0)

  
  1. Associations between categorical variables included in the analysis and infection with EHV-2 or EHV-5 were tested using contingency tables. Fisher’s exact test was used to analyse 2 × 2 tables, and Pearson’s Chi-square test to analyze tables with more than two variables. To calculate relative risk (RR) for EHV-2/5 infection within each main category, horses from each subcategory were compared with the remaining population enrolled into the study, and the p values were adjusted using Bonferroni correction
  2. *Results were considered statistically significant for the following Bonferroni-adjusted p values: Age (< 0.0083), Stud farm (< 0.0038), Breed (< 0.0055), Season (< 0.017)
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