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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)