Carriage of Antibiotic-resistant Staphylococcus aureus by Livestock Workers and Household Members in North Carolina

The growing animal reservoir of antibiotic-resistant Staphylococcus aureus is of public health concern. Industrial livestock operations are a potential source of exposure to these bacteria, which may be transmitted from animals to workers, and then to the community. To increase our understanding of occupational exposures to antibiotic-resistant S. aureus, we assessed nasal carriage of S. aureus, including multidrug-resistant S. aureus (MDRSA) and methicillin-resistant S. aureus (MRSA), among workers and household members from industrial livestock operations, antibiotic-free livestock farms, and meat processing plants in North Carolina. We found a higher prevalence of MDRSA in industrial and processing plant participants compared with antibiotic-free participants, and comparable prevalence of MRSA. S. aureus belonging to clonal complex 398 was also discovered for the first time in North Carolina. This study contributes to the growing discourse regarding the public health consequences of large-scale antibiotic use in animal production in the United States.Master of Scienc

Exposure to zoonotic Staphylococcus aureus among industrial hog operation workers and their household contacts in North Carolina, and dissemination into the household environment

Industrialized systems of food animal production are a potential source of exposure to antibiotic-resistant Staphylococcus aureus that can be transmitted between animals and humans. In the United States, there is little information regarding occurrence and persistence of exposure to S. aureus among healthy individuals who have frequent contact with intensively-raised livestock, or about occupational activities that may be associated with exposure, health implications of exposure, or dissemination of these bacteria into the household environment. This dissertation sought to address these research gaps. In Chapter 2, I describe findings from a 14-day, repeated measures pilot study in which we observed persistent nasal carriage with zoonotic S. aureus among industrial hog operation workers, even during time away from work. In Chapters 3 and 4, I describe findings from a four month repeated-measures study of workers and their household members, in which we observed that (1) infrequent face mask use was a predictor of workers’ nasal carriage with zoonotic S. aureus, (2) presence of zoonotic S. aureus in workers’ noses may be associated with recently reported symptoms of skin and soft tissue infection, (3) workers in North Carolina frequently carry a S. aureus strain type commonly detected in Asia (CC9), and (4) zoonotic S. aureus may be shared between workers and their household members. In Chapter 5, I describe findings from a household environmental sampling study in which we observed that households’ environmental exposure to industrial hog operations was associated with presence of zoonotic S. aureus in the home, and that S. aureus in household members’ noses was similar to what we recovered from their household environment. Overall, the findings outlined in this dissertation suggest that current livestock production practices can lead to persistent nasal carriage of zoonotic S. aureus among workers as well as their household members, and that some of these antibiotic-resistant strains can have reservoirs in the household environment. Additional research is necessary to determine public health risks associated with these zoonotic, antibiotic-resistant bacteria. These research findings could be used to help inform national policies about food animal production practices such that worker and community health may be safeguarded.Doctor of Philosoph

Equivalence of influenza A virus RNA recovery from nasal swabs when lysing the swab and storage medium versus storage medium alone

Surveillance of healthy individuals at high risk for zoonotic influenza A transmission is important for tracking trends in influenza A epidemiology. Practical measurement methods that maximize viral recovery and produce low variability are essential when low viral loads are expected. For this study, lysing both a nasal swab and its storage medium was compared to lysing the storage medium alone to determine which method results in greater influenza A virus recovery. Independent results from two laboratories suggest that including the swab in the lysis step does not lead to higher influenza A virus recovery, and that recovery is less variable when only the swab storage medium is extracted. These results indicate that simply lysing the swab storage medium is an effective extraction method for nasal swabs collected during studies of influenza A virus exposure among healthy populations

Livestock-associated methicillin and multidrug resistant Staphylococcus aureus is present among industrial, not antibiotic-free livestock operation workers in North Carolina

Objectives Administration of antibiotics to food animals may select for drug-resistant pathogens of clinical significance, such as methicillin-resistant Staphylococcus aureus (MRSA). In the United States, studies have examined prevalence of MRSA carriage among individuals exposed to livestock, but prevalence of multidrug-resistant S. aureus (MDRSA) carriage and the association with livestock raised with versus without antibiotic selective pressure remains unclear. We aimed to examine prevalence, antibiotic susceptibility, and molecular characteristics of S. aureus among industrial livestock operation (ILO) and antibiotic-free livestock operation (AFLO) workers and household members in North Carolina. Methods Participants in this cross-sectional study were interviewed and provided a nasal swab for S. aureus analysis. Resulting S. aureus isolates were assessed for antibiotic susceptibility, multi-locus sequence type, and absence of the scn gene (a marker of livestock association). Results Among 99 ILO and 105 AFLO participants, S. aureus nasal carriage prevalence was 41% and 40%, respectively. Among ILO and AFLO S. aureus carriers, MRSA was detected in 7% (3/41) and 7% (3/42), respectively. Thirty seven percent of 41 ILO versus 19% of 42 AFLO S. aureus-positive participants carried MDRSA. S. aureus clonal complex (CC) 398 was observed only among workers and predominated among ILO (13/34) compared with AFLO (1/35) S. aureus-positive workers. Only ILO workers carried scn-negative MRSA CC398 (2/34) and scn-negative MDRSA CC398 (6/34), and all of these isolates were tetracycline resistant. Conclusions Despite similar S. aureus and MRSA prevalence among ILO and AFLO-exposed individuals, livestock-associated MRSA and MDRSA (tetracycline-resistant, CC398, scn-negative) were only present among ILO-exposed individuals. These findings support growing concern about antibiotics use and confinement in livestock production, raising questions about the potential for occupational exposure to an opportunistic and drug-resistant pathogen, which in other settings including hospitals and the community is of broad public health importance

Pig-2-Bac as a biomarker of occupational exposure to pigs and livestock-associated Staphylococcus aureus among industrial hog operation workers

Over 50 million hogs are raised annually in the United States for consumption, mostly on industrial hog operations (IHOs). Workers at IHOs are exposed to airborne particulates, zoonotic pathogens, and other workplace hazards, but lack of access to IHOs can hinder exposure assessment in epidemiologic studies. Here, we demonstrate the utility of pig-specific Bacteroidales (Pig-2-Bac) as a biomarker of exposure to pigs and pig waste and to help identify sources of Staphylococcus aureus carriage among IHO workers

Persistence of livestock-associated antibiotic-resistant Staphylococcus aureus among industrial hog operation workers in North Carolina over 14 days

ObjectivesThis 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.MethodsWorkers anticipating at least 24 h away from work were enrolled June–August 2012. Participants self-collected a nasal swab and completed a study journal on the evening of day 1, and each morning and evening on days 2–7 and 14 of the study. 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.ResultsTwenty-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.ConclusionsNasal 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

Carriage of antibiotic-resistant Staphylococcus aureus by livestock workers and household members in North Carolina

The growing animal reservoir of antibiotic-resistant Staphylococcus aureus is of public health concern. Industrial livestock operations are a potential source of exposure to these bacteria, which may be transmitted from animals to workers, and then to the community. To increase our understanding of occupational exposures to antibiotic-resistant S. aureus, we assessed nasal carriage of S. aureus, including multidrug-resistant S. aureus (MDRSA) and methicillin-resistant S. aureus (MRSA), among workers and household members from industrial livestock operations, antibiotic-free livestock farms, and meat processing plants in North Carolina. We found a higher prevalence of MDRSA in industrial and processing plant participants compared with antibiotic-free participants, and comparable prevalence of MRSA. S. aureus belonging to clonal complex 398 was also discovered for the first time in North Carolina. This study contributes to the growing discourse regarding the public health consequences of large-scale antibiotic use in animal production in the United States

Traveller studies in low- and middle-income countries: a critical gap in global antibiotic resistance surveillance

A substantial proportion of global travel occurs between low- and middle-income countries (LMICs) for the purposes of migration, medical tourism, trade and employment, and this is likely to accelerate due to climate-change-related migration. Traveller studies based in LMICs are needed to better monitor the global spread of antibiotic resistance