Abstract
This study aimed to evaluate the persistence of nasal carriage of Staphylococcus aureus, methicillin-resistant S. aureus and multidrug-resistant S. aureus over 14 days of follow-up among industrial hog operation workers in North Carolina.
Generated Summary
This study aimed to evaluate the persistence of nasal carriage of Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus over 14 days of follow-up among industrial hog operation workers in North Carolina. Workers anticipating at least 24 h away from work were enrolled from June to August 2012. Participants self-collected a nasal swab and completed a study journal. S. aureus isolated from nasal swabs were assessed for antibiotic susceptibility, spa type, and absence of the scn gene. Livestock association was defined by absence of scn. The research involved 22 workers providing 327 samples. The study examined the temporal dynamics of nasal carriage of livestock-associated S. aureus, MRSA and MDRSA among 22 workers employed at industrial hog operations in North Carolina. The main objectives of the study were to determine the persistence of these bacteria and to investigate the distribution of antibiotic resistance patterns and genetic markers of S. aureus observed among participants. The study used a combination of self-collected samples, study journals, and laboratory analysis to gather data on the persistence of nasal carriage of S. aureus.
Key Findings & Statistics
- Twenty-two workers provided 327 samples.
- S. aureus carriage end points did not change with time away from work (mean 49 h; range >0–96 h).
- Ten workers were persistent and six were intermittent carriers of livestock-associated S. aureus.
- Six workers were persistent and three intermittent carriers of livestock-associated multidrug-resistant S. aureus.
- One worker persistently carried livestock-associated methicillin-resistant S. aureus.
- Six workers were non-carriers of livestock-associated S. aureus.
- Eighty-two per cent of livestock-associated S. aureus demonstrated resistance to tetracycline.
- A majority of livestock-associated S. aureus isolates (n=169) were CC398 (68%) while 31% were CC9.
- No CC398 and one CC9 isolate was detected among scn-positive isolates.
- Eighty-six per cent (19/22) of workers carried S. aureus.
- 5% (1/22) carried MRSA.
- 46% (10/22) carried MDRSA during at least one sampling point of the 14-day follow-up.
- Mean daily prevalence of S. aureus was 65%.
- Mean daily prevalence of MRSA was 4%.
- Mean daily prevalence of MDRSA was 33%.
- Fifty-five per cent (12/22), 5% (1/22) and 27% (6/22) of workers were persistent carriers of S. aureus, MRSA and MDRSA, respectively.
- The participant observed to persistently carry MRSA carried multidrug-resistant MRSA for 36% (5/14) of the sampling points.
- CC398 was most frequently detected—carried by seven workers persistently and one intermittently, followed by CC9—carried by two workers persistently and seven intermittently.
- Sixty-eight per cent (15/22) of workers carried an identical CC at all S. aureus positive sampling points.
- We observed a change in CC for 18% (4/22) of workers over the study period.
- Mean daily prevalence of scn-negative S. aureus, scn-negative MRSA and scn-negative MDRSA was 51%, 4% and 33%, respectively.
- During the study period, 10/22 (46%) workers were persistent and 6/22 (27%) were intermittent carriers of scn-negative S. aureus.
- Of the 16 workers carrying scn-negative S. aureus at least once, 6 were persistent and 3 were intermittent carriers of scn-negative MDRSA.
Other Important Findings
- The study found that nearly half (45.5%) of the 22 industrial hog operation workers who participated were persistent carriers of livestock-associated S. aureus over a 14-day period, which included up to 96 h away from work.
- Persistent carriers of livestock-associated S. aureus included six persistent carriers of livestock-associated multidrug-resistant S. aureus and one persistent carrier of livestock-associated methicillin-resistant S. aureus.
- The distribution of CCs and antibiotic resistance patterns observed among workers may represent the population of S. aureus circulating among hogs at the industrial hog operations where participating workers are employed.
- Nasal carriage of livestock-associated S. aureus, multidrug-resistant S. aureus and methicillin-resistant S. aureus can persist among industrial hog operation workers over a 14-day period, which included up to 96 h away from work.
- The study observed 12 distinct antibiotic susceptibility patterns among S. aureus-positive participants.
- Only scn-negative S. aureus belonging to CC398 (n=115), CC9 (n=53) and CC20 (n=1) were observed.
- Among the 16 participants ever carrying scn-negative S. aureus, 15 carried either CC398 or CC9 at every S. aureus-positive sampling point.
- Among the six participants ever carrying scn-positive S. aureus, there was greater heterogeneity of strains, with six different CCs observed.
- All MRSA (15/15) and most MDRSA isolates (106/110) were scn-negative.
- In addition, 82% (138/169) of scn-negative S. aureus isolates were phenotypically tetracycline-resistant, including 97% (111/115) of scn-negative CC398 isolates and 51% (27/53) of scn-negative CC9 isolates.
- By contrast, no scn-positive S. aureus isolates demonstrated tetracycline resistance.
Limitations Noted in the Document
- The study was small, including 22 individuals with 14–15 sampling points each (327 observations).
- Small numbers of individuals experienced changes in S. aureus carriage states during the study period, resulting in a sample size insufficient for repeated measures analysis.
- The design of the study resulted in an up to 8-day holding time between self-swabbing and laboratory analysis of nasal swabs, which may have resulted in false-negative outcomes.
- The study assessed only one S. aureus isolate per nasal swab for genotype, antibiotic resistance phenotype and absence of scn, which does not reflect the contemporaneous diversity of S. aureus that may occur within participants’ noses.
- The study relied on participants independently completing journal entries reporting daily work activities as proxy measures of exposure to S. aureus in the industrial hog production environment, which may have introduced bias.
Conclusion
This study provides valuable insights into the persistence of S. aureus carriage among industrial hog operation workers. The findings highlight that nasal carriage of livestock-associated S. aureus, including MRSA and MDRSA, can persist among these workers over a 14-day period, even with time away from work. The study’s observation of high rates of tetracycline resistance among scn-negative isolates, particularly CC398, underscores the importance of monitoring antibiotic resistance in this context. The persistence of these strains, including multidrug-resistant variants, raises concerns about the potential for transmission and infection among workers and their contacts. The study’s findings contribute to the understanding of occupational health risks in industrial hog operations and emphasize the need for further research to assess the public health implications of livestock-associated S. aureus. The relatively low prevalence of MRSA CC398 compared to previous studies of swine operation workers and the high prevalence of CC9, suggest that CC9 may circulate within a livestock reservoir in the USA. The study also highlights the need for more research into the potential role of livestock-associated S. aureus in human infections. Furthermore, the study emphasizes the need for future surveillance studies of carriage persistence and infection dynamics among livestock workers in the USA. The study’s findings also support the need for future studies to examine the association between carriage states and personal and work-related characteristics, as well as the public health risk posed by livestock-associated S. aureus, MRSA, and MDRSA. The study’s results do not support the ‘contamination’ hypothesis and suggest that further work is needed to improve the understanding of the temporal dynamics of nasal carriage of livestock-associated S. aureus among livestock workers in the USA.