Outbreak of Mycobacterium orygis in a Shipment of Cynomolgus Macaques Imported from Southeast Asia - United States, February-May 2023.

Nonhuman primates (NHP) can become infected with the same species of Mycobacteria that cause human tuberculosis. All NHP imported into the United States are quarantined and screened for tuberculosis; no confirmed cases of tuberculosis were diagnosed among NHP during CDC-mandated quarantine during 2013-2020. In February 2023, an outbreak of tuberculosis caused by Mycobacterium orygis was detected in a group of 540 cynomolgus macaques (Macaca fascicularis) imported to the United States from Southeast Asia for research purposes. Although the initial exposure to M. orygis is believed to have occurred before the macaques arrived in the United States, infected macaques were first detected during CDC-mandated quarantine. CDC collaborated with the importer and U.S. Department of Agriculture's National Veterinary Services Laboratories in the investigation and public health response. A total of 26 macaques received positive test results for M. orygis by culture, but rigorous occupational safety protocols implemented during transport and at the quarantine facility prevented cases among caretakers in the United States. Although the zoonotic disease risk to the general population remains low, this outbreak underscores the importance of CDC's regulatory oversight of NHP importation and adherence to established biosafety protocols to protect the health of the United States research animal population and the persons who interact with them.

Health Hazard Evaluations of occupational cancer cluster concerns: the USA, January 2001-December 2020.

OBJECTIVES: To describe recent investigations of potential workplace cancer clusters. METHODS: We identified Health Hazard Evaluations (HHEs) of cancer concerns during 2001-2020. We described information about industry, requestors, cancer characteristics, investigative procedures, and determinations about the presence of a cluster (ie, presence of excess cases, unusual case distribution or exposure). RESULTS: Of 5754 HHEs, 174 included cancer concerns, comprising 1%-5% of HHEs per year. In 123 HHEs, the cancer cluster concerns involved different cancer primary sites. Investigation procedures varied but included record review (n=63, 36%) and site visits (n=22, 13%). Of 158 HHEs with a cluster determination by investigator(s), 151 (96%) were not considered cancer clusters. In seven HHEs, investigators found evidence of a cluster, but occupational exposure to a carcinogen was not identified. CONCLUSIONS: The proportion of HHEs on workplace cancer cluster concerns remained steady over time; most did not meet the definition of a cluster or uncover an occupational cause. Public health practitioners can use this information to provide updated context when addressing workplace cancer cluster concerns and as motivation to refine investigative approaches. More broadly, this review highlights an opportunity to identify best practices on how to apply community cluster investigation methods to the workplace.

Prevalence of SARS-CoV-2 infection among US blood donors by industry, May-December 2021.

BACKGROUND: Work is a social determinant of health that is often overlooked. There are major work-related differences in the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and death, but there have been few analyses of infection rates across industry groups. To date, only one national assessment of SARS-CoV-2 infection prevalence by industry based on self-report has been completed. No study has looked at seroprevalence of COVID-19 by industry. METHODS: During May-December 2021, blood donors with SARS-CoV-2 antinucleocapsid testing were sent an electronic survey about their work. Free-text industry responses were classified using the North American Industry Classification System. We estimated seroprevalence and 95% confidence intervals (CIs) of SARS-CoV-2 infection by industry. RESULTS: Of 57,726 donors, 7040 (12%, 95% CI: 11.9%-12.5%) had prior SARS-CoV-2 infection. Seroprevalence was highest among Accommodation & Food Services (19.3%, 95% CI: 17.1%-21.6%), Mining, Quarrying, and Oil and Gas Extraction (19.2%, 95% CI: 12.8%-27.8%), Healthcare & Social Assistance (15.6%, 95% CI: 14.9%-16.4%), and Construction (14.7%, 95% CI: 13.1%-16.3%). Seroprevalence was lowest among Management of Companies & Enterprises (6.5%, 95% CI: 3.5%-11.5%), Professional Scientific & Technical Services (8.4%, 95% CI: 7.7%-9.0%), and Information (9.9%, 95% CI: 8.5%-11.5%). CONCLUSIONS: While workers in all industries had serologic evidence of SARS-CoV-2 infection, certain sectors were disproportionately impacted. Disease surveillance systems should routinely collect work characteristics so public health and industry leaders can address health disparities using sector-specific policies.

Distribution of COVID-19 mitigation measures by industry and work arrangement-US blood donors, May 2021-December 2021.

OBJECTIVE: To describe coronavirus disease 2019 (COVID-19) mitigation measures in workplaces of employed US blood donors by industry and work arrangement. METHODS: During May-December 2021, blood donors responded to a survey; we describe the distribution of reported workplace mitigation measures by industry and work arrangement, organized using the hierarchy of controls. RESULTS: Of 53,433 respondents representing 21 industries, ventilation upgrades were reported by 4%-38% of respondents (overall: 20%); telework access ranged from 14%-80% (53% overall). Requiring masks (overall: 84%; range: 40%-94%), physical distancing (77%; 51%-86%), paid leave for illness (70%; 38%-87%), and encouraging vaccination (61%; 33%-80%) were common. Independent workers reported fewer mitigation measures than those in traditional employment settings. CONCLUSIONS: Mitigation measures varied by industry and work arrangement. Some mitigation measures may be challenging to implement or irrelevant in certain industries, supporting the idea that mitigation is not a one-size-fits-all strategy. POLICY IMPLICATIONS: Tailored strategies to mitigate workplace risks of disease transmission are vital. Strategies should rely on effective methods for identifying workplace controls (e.g., through the hierarchy of controls) and account for industry-specific characteristics and workplace environments.

COVID-19 mortality among Amalgamated Transit Union (ATU) and Transport Workers Union (TWU) workers-March-July 2020, New York City metro area.

BACKGROUND: Transit workers have jobs requiring close public contact for extended periods of time, placing them at increased risk for severe acute respiratory syndrome coronavirus 2 infection and more likely to have risk factors for coronavirus disease 2019 (COVID-19)-related complications. Collecting timely occupational data can help inform public health guidance for transit workers; however, it is difficult to collect during a public health emergency. We used nontraditional epidemiological surveillance methods to report demographics and job characteristics of transit workers reported to have died from COVID-19. METHODS: We abstracted demographic and job characteristics from media scans on COVID-19 related deaths and reviewed COVID-19 memorial pages for the Amalgamated Transit Union (ATU) and Transport Workers Union (TWU). ATU and TWU provided a list of union members who died from COVID-19 between March 1-July 7, 2020 and a total count of NYC metro area union members. Peer-reviewed publications identified through a scientific literature search were used to compile comparison demographic statistics of NYC metro area transit workers. We analyzed and reported characteristics of ATU and TWU NYC metro area decedents. RESULTS: We identified 118 ATU and TWU NYC metro area transit worker COVID-19 decedents with an incidence proportion of 0.3%. Most decedents were male (83%); median age was 58 years (range: 39-71). Median professional tenure was 20 years (range: 2-41 years). Operator (46%) was the most reported job classification. More than half of the decedents (57%) worked in positions associated with close public contact. CONCLUSION: Data gathered through nontraditional epidemiological surveillance methods provided insight into risk factors among this workforce, demonstrating the need for mitigation plans for this workforce and informing transit worker COVID-19 guidance as the pandemic progressed.

Ocular Syphilis and Human Immunodeficiency Virus Coinfection Among Syphilis Patients in North Carolina, 2014-2016.

BACKGROUND: Ocular syphilis (OS) has been associated with human immunodeficiency virus (HIV) coinfection previously. We compared demographic and clinical characteristics of syphilis patients with and without HIV to identify risk factors for developing OS. METHODS: We reviewed all syphilis cases (early and late) reported to the North Carolina Division of Public Health during 2014 to 2016 and categorized HIV status (positive, negative, unknown) and OS status based on report of ocular symptoms with no other defined etiology. We estimated prevalence ratios (PR) and 95% confidence intervals (CI) for OS by HIV status. Among syphilis patients with HIV, we compared viral loads and CD4 cell counts by OS status. We compared symptom resolution by HIV status for a subset of OS patients. RESULTS: Among 7123 confirmed syphilis cases, 2846 (39.9%) were living with HIV, 109 (1.5%) had OS, and 59 (0.8%) had both. Ocular syphilis was more prevalent in syphilis patients with HIV compared to HIV-negative/unknown-status patients (PR, 1.8; 95% CI, 1.2-2.6). Compared with other patients with HIV, the prevalence of OS was higher in patients with viral loads greater than 200 copies/mL (1.7; 1.0-2.8) and in patients with a CD4 count of 200 cells/mL or less (PR, 2.3; 95% CI, 1.3-4.2). Among 11 patients with severe OS, 9 (81.8%) were HIV-positive. Among 39 interviewed OS patients, OS symptom resolution was similar for HIV-positive (70.0%) and HIV-negative/unknown-status (68.4%) patients. CONCLUSIONS: Syphilis patients with HIV were nearly twice as likely to report OS symptoms as were patients without documented HIV. Human immunodeficiency virus-related immunodeficiency possibly increases the risk of OS development in co-infected patients.

Connecting Environmental Justice and Community Health: Effects of Hog Production in North Carolina.

Environmental justice means equal access to a healthful environment for all. In North Carolina, many sources of pollution disproportionately affect low-income communities and communities of color. Clinicians who recognize effects of environmental injustices can improve patient care and community health. As an example, we present the effects of industrial-scale hog operations in North Carolina.

Increases in Ocular Syphilis-North Carolina, 2014-2015.

BACKGROUND: Ocular syphilis is an inflammatory eye disease due to Treponema pallidum infection. In the United States, syphilis rates have increased since 2000; clusters of ocular syphilis were reported in 2015. We investigated ocular syphilis in North Carolina to describe the epidemiology and clinical course of disease. METHODS: We reviewed syphilis cases reported to North Carolina during 2014-2015 and abstracted information from health department interviews for cases with ocular symptoms and no other defined etiology. To assess duration and severity of ocular symptoms, we also reviewed medical records and conducted structured interviews. We compared the prevalence of ocular manifestations among reported syphilis cases by demographic and clinical characteristics. RESULTS: Among 4232 syphilis patients, 63 (1.5%) had ocular syphilis: 21 in 2014 and 42 in 2015, a 100% increase. Total syphilis cases increased 35% through 2015. No patient with ocular syphilis named another ocular syphilis patient as a sex partner. Patients presented in all syphilis stages; 24 (38%) were diagnosed in primary or secondary syphilis. Ocular manifestations were more prevalent among syphilis patients who were male, aged ≥40 years, white, and infected with human immunodeficiency virus. No risk behaviors were associated with ocular syphilis. Among 39 interviewed patients, 34 (87%) reported reduced vision during infection; 12 (31%) reported residual visual symptoms posttreatment. CONCLUSIONS: In North Carolina, ocular syphilis increased from 2014 to 2015 and may be due to increased recognition of ocular manifestations, or a true increase in ocular syphilis. Many ocular syphilis patients experienced vision loss; however, most improved posttreatment.

Assessing the Potential for Bias From Nonresponse to a Study Follow-up Interview: An Example From the Agricultural Health Study.

Prospective cohort studies are important tools for identifying causes of disease. However, these studies are susceptible to attrition. When information collected after enrollment is through interview or exam, attrition leads to missing information for nonrespondents. The Agricultural Health Study enrolled 52,394 farmers in 1993-1997 and collected additional information during subsequent interviews. Forty-six percent of enrolled farmers responded to the 2005-2010 interview; 7% of farmers died prior to the interview. We examined whether response was related to attributes measured at enrollment. To characterize potential bias from attrition, we evaluated differences in associations between smoking and incidence of 3 cancer types between the enrolled cohort and the subcohort of 2005-2010 respondents, using cancer registry information. In the subcohort we evaluated the ability of inverse probability weighting (IPW) to reduce bias. Response was related to age, state, race/ethnicity, education, marital status, smoking, and alcohol consumption. When exposure and outcome were associated and case response was differential by exposure, some bias was observed; IPW conditional on exposure and covariates failed to correct estimates. When response was nondifferential, subcohort and full-cohort estimates were similar, making IPW unnecessary. This example provides a demonstration of investigating the influence of attrition in cohort studies using information that has been self-reported after enrollment.

Notes from the Field: Clostridium perfringens Gastroenteritis Outbreak Associated with a Catered Lunch - North Carolina, November 2015.

During November 2015, the North Carolina Division of Public Health was notified by the Pitt County Health Department (PCHD) that approximately 40 persons who attended a catered company Thanksgiving lunch the previous day were ill with diarrhea and abdominal pain. The North Carolina Division of Public Health and PCHD worked together to investigate the source of illness and implement control measures. Within hours of notification, investigators developed and distributed an online survey to all lunch attendees regarding symptoms and foods consumed and initiated a cohort study. A case of illness was defined as abdominal pain or diarrhea in a lunch attendee with illness onset <24 hours after the event. Risk ratios (RRs) and 95% confidence intervals (CIs) were estimated for all menu items. Among 80 attendees, 58 (73%) completed the survey, including 44 respondents (76%) who reported illnesses meeting the case definition; among these, 41 (93%) reported diarrhea, and 40 (91%) reported abdominal pain. There were no hospitalizations. Symptom onset began a median of 13 hours after lunch (range = 1-22 hours). Risk for illness among persons who ate turkey or stuffing (38 of 44; 86%), which were plated and served together, was significantly higher than risk for illness among those who did not eat turkey or stuffing (six of 14; 43%) (RR = 2.02; 95% CI = 1.09-3.73).

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

OBJECTIVES: 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. METHODS: Workers 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. RESULTS: 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. CONCLUSIONS: 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.

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.

Respiratory disease in United States farmers.

OBJECTIVES: Farmers may be at increased risk for adverse respiratory outcomes compared with the general population due to their regular exposures to dusts, animals and chemicals. However, early life farm exposures to microbial agents may result in reduced risk. Understanding respiratory disease risk among farmers and identifying differences between farmers and other populations may lead to better understanding of the contribution of environmental exposures to respiratory disease risk in the general population. METHODS: We compared the prevalence of self-reported respiratory outcomes in 43548 participants from the Agricultural Health Study (AHS), a prospective cohort of farmers and their spouses from Iowa and North Carolina, with data from adult participants in the National Health and Nutrition Examination Survey (NHANES) over the same period (2005-2010). RESULTS: AHS participants had lower prevalences of respiratory diseases (asthma, adult-onset asthma, chronic bronchitis and emphysema), but higher prevalences of current respiratory symptoms (wheeze, cough and phlegm) even after controlling for smoking, body mass index and population characteristics. The overall prevalence of asthma in the AHS (7.2%, 95% CI 6.9 to 7.4) was 52% of that in NHANES (13.8%, 95% CI 13.3 to 14.3), although the prevalence of adult-onset asthma among men did not differ (3.6% for AHS, 3.7% for NHANES). Conversely, many respiratory symptoms were more common in the AHS than NHANES, particularly among men. CONCLUSIONS: These findings suggest that farmers and their spouses have lower risk for adult-onset respiratory diseases compared with the general population, and potentially higher respiratory irritation as evidenced by increased respiratory symptoms.

Agricultural exposures and stroke mortality in the Agricultural Health Study.

Exposures associated with common agricultural activities may increase risk of stroke. The authors evaluated associations between self-reported agricultural activities including pesticide use and handling of crops and stroke mortality among 51,603 male pesticide applicators enrolled in the Agricultural Health Study (AHS). Vital status was obtained through 2008. Stroke mortality was defined by underlying or contributing cause of death (ICD-9 430-438, ICD-10 I60-I69). Information regarding lifetime pesticide use, working with crops or animals, engagement in other agricultural activities, and potential confounders was self-reported at enrollment. Cox proportional hazards models, with age as the time scale, were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) adjusted for state of residence, smoking status, and alcohol consumption. Median follow-up time was 13 yr, during which 308 stroke deaths occurred. No measure of overall or specific pesticide use was positively associated with mortality due to stroke. Stroke mortality was inversely associated with handling hay, grain, or silage at least once each year as reported at enrollment (HR: 0.75; 95% CI: 0.58, 0.98). There was no evidence of an association between pesticide use and stroke mortality. The inverse association between handling of hays and grains and stroke mortality may be due to (1) those engaging in such activities being healthier than those who did not or (2) exposure to some biological agent present in hays and grains. Further investigation of incident stroke, rather than stroke mortality, as well as stroke subtypes, is needed to determine the full role of agricultural exposures and stroke.

Media Reports as a Tool for Timely Monitoring of COVID-19-Related Deaths Among First Responders-United States, April 2020.

We aimed to describe coronavirus disease 2019 (COVID-19) deaths among first responders early in the COVID-19 pandemic. We used media reports to gather timely information about COVID-19-related deaths among first responders during March 30-April 30, 2020, and evaluated the sensitivity of media scanning compared with traditional surveillance. We abstracted information about demographic characteristics, occupation, underlying conditions, and exposure source. Twelve of 19 US public health jurisdictions with data on reported deaths provided verification, and 7 jurisdictions reported whether additional deaths had occurred; we calculated the sensitivity of media scanning among these 7 jurisdictions. We identified 97 COVID-19-related first-responder deaths during the study period through media and jurisdiction reports. Participating jurisdictions reported 5 deaths not reported by the media. Sixty-six decedents worked in law enforcement, and 31 decedents worked in fire/emergency medical services. Media reports rarely noted underlying conditions. The media scan sensitivity was 88% (95% CI, 73%-96%) in the subset of 7 jurisdictions. Media reports demonstrated high sensitivity in documenting COVID-19-related deaths among first responders; however, information on risk factors was scarce. Routine collection of data on industry and occupation could improve understanding of COVID-19 morbidity and mortality among all workers.

Animal production, insecticide use and self-reported symptoms and diagnoses of COPD, including chronic bronchitis, in the Agricultural Health Study.

BACKGROUND: Occupational exposure to animal production is associated with chronic bronchitis symptoms; however, few studies consider associations with chronic obstructive pulmonary disease (COPD). We estimated associations between animal production activities and prevalence of self-reported COPD among farmers in the Agricultural Health Study. METHODS: During a 2005-2010 interview, farmers self-reported information about: their operations (i.e., size, type, number of animals, insecticide use), respiratory symptoms, and COPD diagnoses (i.e., COPD, chronic bronchitis, emphysema). Operations were classified as small or medium/large based on regulatory definitions. Farmers were classified as having a COPD diagnosis, chronic bronchitis symptoms (cough and phlegm for ≥3 months during 2 consecutive years), or both. Polytomous logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI). RESULTS: Of 22,491 participating farmers (median age: 59 years), 922 (4%) reported a COPD diagnosis only, 254 (1%) reported a diagnosis and symptoms, and 962 (4%) reported symptoms only. Compared to raising no commercial animals, raising animals on a medium/large operation was positively associated with chronic bronchitis symptoms with (OR: 1.59; 95% CI: 1.16, 2.18) and without a diagnosis (OR: 1.69; 95% CI: 1.42, 2.01). Ever use of multiple organophosphates, carbaryl, lindane, and permethrin were positively associated with chronic bronchitis symptoms. CONCLUSION: Animal production work, including insecticide use, was positively associated with chronic bronchitis symptoms; but not consistently with COPD diagnosis alone. Our results support the need for further investigation into the role of animal production-related exposures in the etiology of COPD and better respiratory protection for agricultural workers.

Occupational and Take-home Lead Exposure Among Lead Oxide Manufacturing Employees, North Carolina, 2016.

OBJECTIVE: In 2016, North Carolina blood lead level (BLL) surveillance activities identified elevated BLLs among 3 children exposed to take-home lead by household members employed at a lead oxide manufacturing facility. We characterized BLLs among employees and associated children and identified risk factors for occupational and take-home lead exposure. METHODS: We reviewed BLL surveillance data for 2012-2016 to identify facility employees and associated children. We considered a BLL ≥5 µg/dL elevated for adults and children and compared adult BLLs with regulatory limits and recommended health-based thresholds. We also conducted an environmental investigation and interviewed current employees about exposure controls and cleanup procedures. RESULTS: During 2012-2016, 5 children associated with facility employees had a confirmed BLL ≥5 µg/dL. Among 77 people employed during 2012-2016, median BLLs increased from 22 µg/dL (range, 4-45 µg/dL) in 2012 to 37 µg/dL (range, 16-54 µg/dL) in 2016. All employee BLLs were <60 µg/dL, the national regulatory threshold for immediate medical removal from lead exposure; however, 55 (71%) had a BLL ≥20 µg/dL, a recommended health-based threshold for removal from lead exposure. Because of inadequate controls in the facility, areas considered clean were visibly contaminated with lead dust. Employees reported bringing personal items to work and then into their cars and homes, resulting in take-home lead exposure. CONCLUSIONS: Integration of child and adult BLL surveillance activities identified an occupational source of lead exposure among workers and associated children. Our findings support recent recommendations that implementation of updated lead standards will support better control of lead in the workplace and prevent lead from being carried home.

Multidrug-resistant and methicillin-resistant Staphylococcus aureus (MRSA) in hog slaughter and processing plant workers and their community in North Carolina (USA).

BACKGROUND: Use of antimicrobials in industrial food-animal production is associated with the presence of antimicrobial-resistant Staphylococcus aureus (S. aureus) among animals and humans. Hog slaughter/processing plants process large numbers of animals from industrial animal operations and are environments conducive to the exchange of bacteria between animals and workers. OBJECTIVES: We compared the prevalence of multidrug-resistant S. aureus (MDRSA) and methicillin-resistant S. aureus (MRSA) carriage among processing plant workers, their household members, and community residents. METHODS: We conducted a cross-sectional study of hog slaughter/processing plant workers, their household members, and community residents in North Carolina. Participants responded to a questionnaire and provided a nasal swab. Swabs were tested for S. aureus, and isolates were tested for antimicrobial susceptibility and subjected to multilocus sequence typing. RESULTS: The prevalence of S. aureus was 21.6%, 30.2%, and 22.5% among 162 workers, 63 household members, and 111 community residents, respectively. The overall prevalence of MDRSA and MRSA tested by disk diffusion was 6.9% and 4.8%, respectively. The adjusted prevalence of MDRSA among workers was 1.96 times (95% CI: 0.71, 5.45) the prevalence in community residents. The adjusted average number of antimicrobial classes to which S. aureus isolates from workers were resistant was 2.54 times (95% CI: 1.16, 5.56) the number among isolates from community residents. We identified two MDRSA isolates and one MRSA isolate from workers as sequence type 398, a type associated with exposure to livestock. CONCLUSIONS: Although the prevalence of S. aureus and MRSA was similar in hog slaughter/processing plant workers and their household and community members, S. aureus isolates from workers were resistant to a greater number of antimicrobial classes. These findings may be related to the nontherapeutic use of antimicrobials in food-animal production.