Livestock-Associated and Non-Livestock-Associated Staphylococcus aureus Carriage in Humans is Associated with Pig Exposure in a Dose–Response Manner

Figures & data

Table 1 Demographic Characteristics of Study Population and Prevalence of S. aureus

Characteristics	Total (n=1769)	Non-Exposed Workers (n=1178)	Pig-Exposed Workers (n=591)	χ^2	P-value
Gender
Male	1134 (64.1)	653 (55.4)	481 (81.4)	115.21	<0.001
Female	635 (35.9)	525 (44.6)	110 (18.6)
Age (years)
15–24	198 (11.2)	138 (11.7)	60 (10.1)	24.64	<0.001
24–34	519 (29.3)	305 (25.9)	214 (36.2)
35–44	607 (34.3)	440 (37.4)	167 (28.3)
≥45	445 (25.2)	295 (25.0)	150 (25.4)
Antibiotic use in the last month
Yes	847 (47.9)	540 (45.8)	307 (52.0)	5.88	0.015
No	922 (52.1)	638 (54.2)	284 (48.0)
Skin infections in the last month
Yes	390 (22.0)	187 (15.9)	203 (34.3)	78.16	<0.001
No	1379 (78.0)	991 (94.1)	388 (65.7)
Hospitalization in the last month
Yes	68 (3.8)	44 (3.7)	24 (4.1)	0.11	0.737
No	1701 (96.2)	1134 (96.3)	567 (95.9)
Prevalence
S. aureus	189 (10.7)	109 (9.3)	80 (13.5)	7.57	0.006
MRSA	59 (3.3)	16 (1.4)	43 (7.3)	42.75	<0.001
MDRSA	96 (5.4)	40 (3.4)	56 (9.5)	28.35	<0.001
LA-MRSA	19 (1.1)	0 (0.0)	19 (3.2)	38.28	<0.001
Non- LA-MRSA	40 (2.3)	16 (1.4)	24 (4.1)	13.01	<0.001
LA-MDRSA	19 (1.1)	0 (0.0)	19 (3.2)	38.28	<0.001
Non- LA-MDRSA	77 (4.4)	40 (3.4)	37 (6.3)	7.76	0.005

Note: Values are expressed as number of participants (the proportion of participants surveyed), except where specified otherwise.

Abbreviations: MRSA, methicillin-resistant S. aureus; MDRSA, multidrug-resistant S. aureus; LA-MRSA, livestock-associated methicillin-resistant S.aureus; non-LA-MRSA, non-livestock-associated methicillin-resistant S.aureus; LA-MDRSA, livestock-associated multidrug-resistant S. aureus; non-LA-MDRSA, non-livestock-associated multidrug-resistant S. aureus.

Figure 1 Heat map showing antibiotic resistance profiles of all multidrug-resistant S. aureus isolates.

Abbreviations: CLI, clindamycin; ERY, erythromycin; TET, tetracycline; CHL, chloramphenicol; SXT, trimethoprim-sulfamethoxazole; RD, rifampin; QD, quinupristin-dalfopristin; CIP, ciprofloxacin; GEN, gentamicin; FOX, cefoxitin; LZD, linezolid.

Figure 2 S. aureus sequence type diversity and distribution of S. aureus isolates among pig-exposed workers (80 isolates) and non-exposed workers (109 isolates).

Note: Each bar represents the number of S. aureus isolates for each sequence type.

Abbreviations: CC, clonal complex; ST, sequence type; UT, untypeable; MRSA, methicillin-resistant S. aureus; MSSA, methicillin-sensitive S. aureus.

Table 2 Relationships Between Occupational Pig Exposure and the Number of Antimicrobial Classes to Which a S. aureus Was Resistant

Source of Exposure	Unadjusted IRR (95% CI)	P-value	Adjusted IRR (95% CI)^b	P-value
Pig exposure
No^a	1.00		1.00
Yes	2.37 (1.87~3.00)	<0.001	2.35 (1.81~3.04)	<0.001
Frequency of pig exposure (hours/day, logarithmic)	1.48 (1.33~1.65)	<0.001	1.48 (1.32~1.67)	<0.001
Duration of pig exposure (years, logarithmic)	1.12 (1.09~1.15)	<0.001	1.12 (1.09~1.16)	<0.001

Notes: ^aNo occupational exposure with any types of livestock. ^bAdjusted for sex, age (15–24, 25–34, 35–44, and ≥45 years), antibiotic use in the last month, skin infections in the last month, and hospitalization in the last month.

Abbreviation: IRR, incidence-rate ratio.

Table 3 Relationships Between Occupational Pig Exposure and MRSA or MDRSA Carriage

Source of Exposure	MRSA		MDRSA
	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b
Pig exposure
No^a	1.00	1.00	1.00	1.00
Yes	5.70 (3.18~10.21)	6.29 (3.38~11.68)	2.98 (1.96~4.53)	3.17 (2.03~4.96)
Frequency of pig exposure (hours/day, logarithmic)	2.14 (1.65~2.78)	2.28 (1.72~3.02)	1.66 (1.37~2.01)	1.72 (1.40~2.12)
Duration of pig exposure (years, logarithmic)	1.22 (1.14~1.31)	1.24 (1.15~1.34)	1.15 (1.09~1.22)	1.17 (1.10~1.24)

Notes: ^aNo occupational exposure with any types of livestock. ^bAdjusted for sex, age (15–24, 25–34, 35–44, and ≥45 years), antibiotic use in the last month, skin infections in the last month, and hospitalization in the last month.

Abbreviations: MRSA, methicillin-resistant S. aureus; MDRSA, multidrug-resistant S. aureus; OR, odds ratio; CI, confidence interval.

Figure 3 Predicted prevalence of MRSA ((A) hours of pig exposure per day; (C) years of pig exposure) and MDRSA isolates ((B) hours of pig exposure per day; (D) years of pig exposure) based on pig exposure.

Table 4 Relationships Between Occupational Pig Exposure and LA-MRSA or Non-LA-MRSA Carriage

Source of Exposure	LA-MRSA		Non-LA-MRSA
	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b
Pig exposure
No^a	1.00	1.00	1.00	1.00
Yes	56.92 (9. 84~∞)^c	52.80 (8.79~∞)^c	3.18 (1.68~6.04)	3.73 (1.88~7.39)
Frequency of pig exposure (hours/day, logarithmic)	5.23 (2.37~11.50)	7. 49 (2.38~23.57)	1.67 (1.24~2.23)	1.80 (1.31~2.46)
Duration of pig exposure (years, logarithmic)	1.48 (1.25~1.75)	1.61 (1.28~2.02)	1.14 (1.05~1.24)	1.16 (1.06~1.27)

Notes: ^aNo occupational exposure with any types of livestock. ^bAdjusted for sex, age (15–24, 25–34, 35–44, and ≥45 years), antibiotic use in the last month, skin infections in the last month, and hospitalization in the last month. ^cExact logistic regression models were used due to lack of occurrence of the outcome in one group.

Abbreviations: LA-MRSA, livestock-associated methicillin-resistant S. aureus; non-LA-MRSA, non-livestock-associated methicillin-resistant S. aureus; OR, odds ratio; CI, confidence interval.

Table 5 Relationships Between Occupational Pig Exposure and LA-MDRSA or Non-LA-MDRSA Carriage

Source of Exposure	LA-MDRSA		Non-LA-MDRSA
	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b	Unadjusted OR (95% CI)	Adjusted OR (95% CI)^b
Pig exposure
No^a	1.00	1.00	1.00	1.00
Yes	57.09 (9.87~∞)^c	53.39 (8.85~∞)^c	1.97 (1.24~3.11)	2.15 (1.32~3.50)
Frequency of pig exposure (hours/day, logarithmic)	5.31 (2.39~11.77)	7.56 (2. 40~23.86)	1.38 (1.12~1.71)	1.45 (1.15~1.81)
Duration of pig exposure (years, logarithmic)	1.48 (1.25~1.76)	1.61 (1.28~2.02)	1.10 (1.03~1.17)	1.11 (1.04~1.19)

Notes: ^aNo occupational exposure with any types of livestock. ^bAdjusted for sex, age (15–24, 25–34, 35–44, and ≥45 years), antibiotic use in the last month, skin infections in the last month, and hospitalization in the last month. ^cExact logistic regression models were used due to lack of occurrence of the outcome in one group.

Abbreviations: LA-MDRSA, livestock-associated multidrug-resistant S. aureus; non-LA-MDRSA, non-livestock-associated multidrug-resistant S. aureus; OR, odds ratio; CI, confidence interval.