Prospective surveillance for influenza A virus in Chinese swine farms

Figures & data

Fig. 1 Influenza A virus molecular prevalence by sample type collected monthly from six Chinese swine farms (three in Shandong and three in Jiangsu Province) between 23 March 2015 and 25 February 2016

. ES environmental swab, PS pig oral secretion, EW environmental water, BS bioaerosol, FS fecal slurry

Fig. 2 Influenza A virus molecular prevalence by farm collected monthly from six Chinese swine farms (three in Shandong and three in Jiangsu Province) between 23 March 2015 and 25 February 2016

. ES environmental swab, PS pig oral secretion, EW environmental water, BS bioaerosol, FS fecal slurry

Unadjusted odds ratios for risk factors associated with influenza A molecular positivity among 396 environmental surface swab samples collected from six Chinese pig farms (three farms from Shandong and three farms from Jiangsu Province) between March 2015 and February 2016

	Environmental surface swab influenza A positive
Risk factor	Total N	No. (%)	Unadjusted OR (95% CI)
Temperature outside of sampled barn (°C)
−5.0–4.9	72	6 (8.3)	1.0 (0.29–3.45)
5.0–13.9	48	8 (16.7)	3.06 (1.04–8.98)
14.0–23.9	42	10 (23.8)	3.44 (1.08–10.95)
24.0–29.9	120	15 (12.5)	1.57 (0.54-4.55)
≥30.0	60	5 (8.3)	Ref.
Season sample was collected^a
Winter	72	8 (11.1)	2.56 (0.81-8.21)
Fall	108	18 (16.7)	4.12 (1.47–11.54)
Summer	108	15 (13.9)	3.32 (1.16–9.50)
Spring	108	5 (4.6)	Ref.
Environmental water sample influenza A virus positivity
Positive	23	7 (30.4)	3.75 (1.45–9.67)
Negative	373	39 (10.5)	Ref.
Fecal slurry sample influenza A virus positivity
Positive	19	7 (36.8)	5.06 (1.88–13.60)
Negative	377	39 (10.3)	Ref.
Bioaerosol sampling influenza A virus positivity
Positive	20	5 (25.0)	2.72 (0.94–7.88)
Negative	376	41 (10.9)	Ref.

CI confidence interval

ORs significant with a p-value < 0.05 are indicated in bold text

^aSeasonality: spring (March 23, 2015 through June 20, 2015), summer (June 21, 2015 through Sept. 22, 2015), fall (Sept. 23, 2015 through Dec. 20, 2015), winter (Dec. 21, 2015 through Feb. 25, 2016)

Unadjusted odds ratios for risk factors associated with influenza A molecular positivity among 3300 pig oral secretion samples collected from six Chinese pig farms (three farms from Shandong and three farms from Jiangsu Province) between March 2015 and February 2016

	Pig oral secretion influenza A positive
Risk factor	Total N	No. (%)	Unadjusted OR (95% CI)
Total number of pigs onsite
≥3000	250	10 (4.0)	0.78 (0.37–1.62)
2000–2999	700	51 (7.3)	1.47 (0.91–2.36)
1000–1999	1350	122 (9.0)	1.85 (1.21–2.83)
<1000	550	28 (5.1)	Ref.
Total number of non-swine animals onsite*
≥30	550	28 (5.1)	0.69 (0.44–1.10)
20–29	850	87 (10.2)	1.47 (1.05–2.08)
10–19	600	35 (5.8)	0.80 (0.52–1.23)
<10	850	61 (7.2)	Ref.
Temperature outside of sampled barn (°C)
−5.0–4.9	600	25 (4.2)	0.40 (0.24–0.66)
5.0–13.9	400	39 (9.8)	0.99 (0.64–1.55)
14.0–23.9	350	30 (8.6)	0.86 (0.54–1.39)
24.0–29.9	1000	68 (6.8)	0.67 (0.46-0.99)
≥30.0	500	49 (9.8)	Ref.
Humidity quintiles (%)
35.0–49.0 (Q1)	650	44 (6.8)	0.62 (0.41–0.93)
50.0–62.0 (Q2)	500	35 (7.0)	0.64 (0.41–0.99)
63.0–75.0 (Q3)	650	44 (6.8)	0.62 (0.41–0.93)
76.0–79.0 (Q4)	500	30 (6.0)	0.54 (0.34–0.86)
80.0–94.0 (Q5)	550	58 (10.6)	Ref.
Type of pigs near where samples were collected
Sow/weaning pig	10	1 (10.0)	1.64 (0.19–14.43)
Sow	632	16 (2.5)	0.38 (0.17–0.89)
Pregnant sow	20	3 (15.0)	2.61 (0.64–10.58)
Weaning pig	5	1 (20.0)	3.69 (0.37–36.59)
Production pig	2491	205 (8.2)	1.33 (0.66–2.64)
Boar	142	9 (6.3)	Ref.
Pigs showed signs of illness in past 2 weeks (14 days)
Yes	55	10 (18.2)	2.98 (1.48–6.0)
No	3245	225 (6.9)	Ref.
Age of pigs in weeks near where sample were collected (quintiles)
1.0–10.0	782	91 (11.6)	4.13 (2.23–7.63)
11.0–16.0	788	54 (6.9)	2.31 (1.22–4.36)
17.0–20.0	439	29 (6.6)	2.22 (1.11–4.41)
21.0–78.0	903	49 (5.4)	1.80 (0.95–3.42)
79.0–260.0	388	12 (3.1)	Ref.

CI confidence interval

ORs significant with a p-value < 0.05 are indicated in bold text

*Non-swine animals include poultry and dogs

Unadjusted odds ratios for risk factors associated with influenza A molecular positivity among 396 environmental water samples collected from six Chinese pig farms (three farms from Shandong and three farms from Jiangsu Province) between March 2015 and February 2016

	Environmental water influenza A positive
Risk factor	Total N	No. (%)	Unadjusted OR (95% CI)
Temperature outside of sampled barn (°C)
−5.0–4.9	72	2 (2.8)	0.16 (0.03–0.78)
5.0–13.9	48	2 (4.2)	0.25 (0.05–1.20)
14.0–23.9	42	5 (11.9)	1.27 (0.41–3.89)
24.0–29.9	120	3 (2.5)	0.15 (0.04–0.56)
≥30.0	60	9 (15.0)	Ref.
Fecal slurry sample influenza A virus positivity
Positive	19	5 (26.3)	7.12 (2.31–21.95)
Negative	377	18 (4.8)	Ref.
Environmental surface swab sample influenza A virus positivity
Positive	46	7 (15.2)	3.75 (1.45–9.67)
Negative	350	16 (4.6)	Ref.
Bioaerosol sampling influenza A virus positivity
Positive	20	3 (15.0)	3.14 (0.85–11.61)
Negative	376	20 (5.3)	Ref.

CI confidence interval

ORs significant with a p-value < 0.05 are indicated in bold text

Unadjusted odds ratios for risk factors associated with influenza A molecular positivity among 396 bioaerosol samples collected from six Chinese pig farms (three farms from Shandong and three farms from Jiangsu Province) between March 2015 and February 2016

	Bioaerosol influenza A positive
Risk factor	Total N	No. (%)	Unadjusted OR (95% CI)
Pigs showed signs of illness in past 2 weeks (14 days)
Yes	216	14 (6.5)	4.30 (0.96–19.23)
No	126	2 (1.6)	Ref.
Fate of ill or dead animals
Buried or destroyed	48	6 (12.5)	8.86 (1.72–45.57)
Animal food	132	8 (6.1)	4.0 (0.83–19.21)
Sold to market	126	2 (1.6)	Ref.
Total number of pigs on site
≥3000	36	6 (16.7)	4.2 (0.98–17.95)
2000–2999	84	4 (4.8)	1.05 (0.23–4.86)
1000–1999	156	3 (1.9)	0.41 (0.08–2.10)
<1000	66	3 (4.6)	Ref.
Environmental water sample influenza A virus positivity
Positive	46	5 (10.9)	3.14 (0.85–11.61)
Negative	350	15 (4.3)	Ref.
Fecal slurry sample influenza A virus positivity
Positive	19	3 (15.8)	3.97 (1.05–14.95)
Negative	377	17 (4.5)	Ref.
Environmental surface swab sample influenza A virus positivity
Positive	46	5 (10.9)	2.72 (0.94–7.88)
Negative	350	15 (4.3)	Ref.

CI confidence interval

ORs significant with a p-value < 0.05 are indicated in bold text

Unadjusted odds ratios for risk factors associated with influenza A molecular positivity among 396 fecal/slurry samples collected from six Chinese pig farms (three farms from Shandong and three farms from Jiangsu Province) between March 2015 and February 2016

	Fecal/slurry influenza A positive
Risk factor	Total N	No. (%)	Unadjusted OR (95% CI)
Total number of pigs on site
≥3000	36	6 (16.7)	13.0 (1.50–112.81)
2000–2999	84	2 (2.4)	1.59 (0.14–17.87)
1000-1999	156	9 (5.8)	3.98 (0.49–32.06)
<1000	66	1 (1.5)	Ref.
Total number of non-swine animals onsite^a
≥30	60	10 (16.7)	10.0 (2.11–47.38)
20–29	102	3 (2.9)	1.52 (0.25–9.26)
10–19	78	3 (3.9)	2.0 (0.33–12.27)
<10	102	2 (2.0)	Ref.
Temperature outside of sampled barn (°C)
−5.0–4.9	72	1 (1.4)	0.41 (0.04–4.62)
5.0–13.9	48	3 (6.3)	1.93 (0.31–12.07)
14.0–23.9	42	7 (16.7)	5.8 (1.14–29.50)
24.0–29.9	120	5 (4.2)	1.26 (0.24–6.70)
≥30.0	60	2 (3.3)	Ref.
Season sample was collected^b
Winter	72	2 (2.8)	3.06 (0.27–34.36)
Fall	108	10 (9.3)	10.92 (1.37–86.86)
Summer	108	6 (5.6)	6.29 (0.74–53.2)
Spring	108	1 (0.9)	Ref.
Age of pigs in weeks near where samples were collected (quintiles)
105.0–208.0 (Q5)	62	8 (12.9)	5.23 (1.33–20.53)
53.0–104.0 (Q4)	91	1 (1.1)	0.39 (0.04–3.84)
21.0–52.0 (Q3)	51	5 (9.8)	3.84 (0.88–16.75)
13.0–20.0 (Q2)	83	2 (2.4)	0.87 (0.14–5.34)
1.0–12.0 (Q1)	109	3 (2.8)	Ref.
Environmental water sample influenza A virus positivity
Positive	23	5 (21.7)	3.75 (1.45–9.67)
Negative	373	14 (3.8)	Ref.
Environmental surface swab sample influenza A virus positivity
Positive	46	7 (15.2)	5.06 (1.88–13.60)
Negative	350	12 (3.4)	Ref.
Bioaerosol sampling influenza A virus positivity
Positive	20	3 (15.0)	2.72 (0.94–7.89)
Negative	376	16 (4.3)	Ref.

CI confidence interval

1ORs significant with a p-value < 0.05 are indicated in bold text

^aNon-swine animals include poultry and dogs

^bSeasonality: spring (March 23, 2015 through June 20, 2015), summer (June 21, 2015 through Sept. 22, 2015), fall (Sept. 23, 2015 through Dec. 20, 2015), winter (Dec. 21, 2015 through Feb. 25, 2016)