Zoonotic diseases account for approximately 60.3% of emergent diseases among the world population (Palmer, Thacker, Waters, Gortazar, & Corner, 2012; Thoen, Steele, & Kaneene, 2014). Mycobacterium bovis or bovine tuberculosis (bTB) is a zoonotic disease predominantly found among cattle and other grazing animals, but can be transmitted and cause pulmonary and extra-pulmonary disease among humans (HK Adesokan, Akinseye, & Sulaimon, 2018; WHO, 2018). Globally, an estimated 147,000 bTB human cases were confirmed and 12,500 deaths recorded in 2016 (WHO, 2018). In the United States (U.S.), an estimated 2–4% of clinical tuberculosis disease cases are caused by M. bovis (CDC, 2011; Hlavsa et al., 2008). Mycobacterium tuberculosis (TB) and M. bovis are both mistakenly grouped as clinical TB disease due to their similar clinical manifestations, similar health consequences, and indistinguishable confirmative clinical tests (BLS, 2017; CDC, 2016; WHO, 2018). There is a limited number of tools that are able to differentiate M. bovis from M. tuberculosis in humans and, thus, the true burden of the zoonotic TB disease in humans is mostly unknown and largely underestimated (WHO, 2018). Dairy farm workers are potentially exposed to both TB and bTB (HK Adesokan, Jenkins, van Soolingen, & Cadmus, 2012; Bekele et al., 2016;RF et al., 2016; Torres-Gonzalez et al., 2013)

The U.S. dairy industry is a vital economic contribution and source of food security to this nation (Adock, Anderson, & Rosson, 2015). In Texas, the total economic impact of dairy products produced and sold is $39.5 billion in addition to the 70,000 direct jobs and 133,000 indirect jobs provided (IDFA, 2018)—making it the 3^rd largest job-generating state, after California and Wisconsin (O’Keefe, 2018). Dairy cattle in the U.S. undergo bTB surveillance as part of a United States Department of Agriculture (USDA) quality control standard—TB-free accredited herd status requirement (USDA, 2014). Whole herd bTB infections have adverse economic, public health, and governmental implications (McCluskey et al., 2014). Yet, the overall impact of TB and bTB among U.S. dairy workers remains unknown due to insufficient surveillance practices of dairy farm workers (Hlavsa et al., 2008; Olea-Popelka et al., 2016).

The etiology of bTB infections on dairy farms can be difficult to establish. The exact mechanism of cross-infection between cattle-to-cattle, cattle-to-person, person-to-cattle, and person-to-person is challenging (HK Adesokan et al., 2012). One Health is a model used to describe disease “shared risk” between humans, animals, and the environment. One Health interdisciplinary research can help bridge human TB and bTB surveillance data gaps with the purpose of creating, delivering, and evaluating disease control and prevention programs that promote health for dairy farm workers, cattle, and environment (Olea-Popelka et al., 2016; Thoen et al., 2014). Rather than solely focusing on the human aspect or the cattle or the environment, there is an added economic and public health significance when implementing a One Health collaborative approach (Thoen et al., 2014).

Currently, the Department of Labor’s Occupational Safety and Health Administration (DOL-OSHA) does not require dairy producers to test dairy workers for bTB/TB infections before their employment start date or during their employment—as required and completed for other high risk occupational groups like healthcare workers (Bekele et al., 2016; CDC, 2018b; Hlavsa et al., 2008). High exposure job positions, such as milking, animal maternity, hospital work, and veterinarian services are at higher risk of communicable transmission of bovine TB (Bekele et al., 2016; RF et al., 2016; Torres-Gonzalez et al., 2013). These job positions involve direct contact with cattle in closed or confined spaces of the farm. In particular, milkers work in crowded parlors with direct interaction with hundreds to thousands of cows during their 8 to 12-hour work shifts (RF et al., 2016). As a proxy for occupational exposures, job position has been proposed for epidemiological investigations concerning bTB exposure on dairy farms (HK Adesokan et al., 2012; Cosivi et al., 1998). For example, Torres-Gonzalez et al. (2013) created three groups of cattle exposure—high, medium, low—to categorize dairy farm job positions. Exposure levels were based on type of activity (e.g., veterinary, milking, feeding, heavy machinery tasks, etc.), duration of exposure, and conditions of exposure to cattle (direct or indirect cattle contact and contact in closed or open spaces).

In 2016, the Texas Department of State Health Services (DSHS) Public Health Region 1 (PHR 1) in Lubbock, Texas responded to two requests from the United States Food and Drug Administration (FDA) to test 140 dairy farm workers potentially exposed to cattle infected with bTB who were employed at two different dairy farm facilities in Bailey County, Texas. A secondary analysis of these data found a 10.0% latent tuberculosis infection (LTBI) among dairy workers at these two facilities (Rodriguez, Prot, et al., 2020). The second study determined that 37.3% of surveyed workers had a general awareness of TB—the high exposure group was less aware of TB (34.0%) compared to the medium/low exposure group (44.9%) (Rodriguez, Hagevoort, et al., 2020). The current study is the third study of this population. The primary objective of this study was to compare the self-reported history of TB among dairy workers in Bailey County, Texas with occupational categories of risk and exposure to TB.

This cross-sectional study collected self-reported history of TB among dairy workers in Bailey County, Texas. Bailey County has a total of 10 dairy farms, employing approximately 225 workers, and milking an estimated 22,537 cows (Dairyman, 2020). We requested a publicly-available census and contact information of dairy farms licensed by the Texas Department of State Health Services (DSHS) Milk and Dairy Unit. We worked with state dairy extension personnel to make an initial contact with dairy farm owners via phone. We made contact with the owners of all 10 dairy farms. Upon verbal approval from owners to participate in the study, arrangements were made for a subsequent on-farm visit and data collection. Bilingual (English and Spanish) research staff individually met with each dairy farm worker to explain the purpose of the study and invite them to participate.

A total of 225 dairy workers consented to participate in the study between February and March 2019. Subject eligibility included being a worker who was at least 18 years of age employed on any of the ten dairy farms. Research staff read and explained the consent form to participants before the survey was completed. Participants were asked to consent and sign an electronic informed consent on an iPad© tablet in order to participate, which was provided in English or Spanish. Surveys were administered in privacy in breakrooms, conference rooms, parlors, maintenance sheds, tractors, and other accessible dairy farm work spaces. The questions were placed on the survey platform Qualtrics Mobile Survey Software® in both English and Spanish with offline compatibility. Trained bilingual research personnel used iPad© tablets to read questions and log responses. Participants were compensated for their time with a $10 gift card. This study was approved by the University of Texas Health Science Center at Houston Committee of the Protection of Human Subjects.

The survey included 15 sociodemographic items and 13 TB history questions which were adapted from standard TB contact investigation forms from the Texas DSHS Health Service Region 1 dairy TB evaluation form (Services, 2018). History of TB, the primary dependent variable, was measured by past TB exposure including: (1) current occupational status (years, work hours, job position), (2) bacille Calmette-Guérin (BCG) vaccination history, (3) self-reported TB diagnosis and treatment history, (4) TB contact history, (5) consumption of unpasteurized dairy products, and (6) prior bovine TB exposure. Answer choices for questions were in fill-in-the-blank and Yes/No format. Research personnel had the option of selecting “I don’t know” if the participant expressed not knowing the answer to a question or selecting “Did not answer” if the participant chose not to answer the question.

We used Torres-Gonzalez et al. (2013) job position on a dairy farm as a proxy for categories of cattle exposure. Dairy farm job positions were categorized into three categories of cattle exposure: high (direct contact with cattle in confined spaces), medium (direct contact with cattle in non-confined spaces), and low (no direct contact with cattle in any type of space). Job positions defined as high exposure included milker pusher, veterinarians, supervisors, managers, hospital workers, slaughter, those with medium exposure included feeders, tractor operators, breeders, calf caretakers, maternity, hoof trimmers, and maintenance, and low exposure included owners and office personnel.

Table 1 reports the sociodemographic characteristics of surveyed dairy workers by category of job-related TB exposure: high and medium/low groups. The medium and low groups were collapsed due to limited sample size. After analyzing history of TB frequencies by high, medium, and low category of TB exposure, we noticed the sample size for the low group was much lower (n=5) compared to high (n=156) and medium (n=64). The medium and low group frequencies were statistically similar; therefore, we elected to collapse these groups into a low/medium category.

Workers in the high exposure job position group were younger, Guatemalan males with lower levels of formal education completed relative to the medium/low exposure group. Workers in the high exposure group were also more likely to be single with no children renting a home/apartment with co-workers relative to the medium/low exposure group. The majority of dairy workers were < 30 years of age (39.5%) and between 30–39 years old (32.9%). Most dairy workers were Hispanic (88.4%) with 43.1% from Mexico, 41.8% from Guatemala, and 11.6% from United States. Only 30.0% reported traveling outside the U.S. in the past 12-months (with 90.0% visiting Mexico for an average of two-weeks). Most dairy workers reported elementary (34.7%) as the highest level of education achieved, followed by middle school (18.2%) and no formal education (16.9%). The sociodemographic portion of the survey also asked several lifestyle and living arrangement questions. Close to 67.0% of workers reported being married and about three-fourths of workers claimed to have an average of 2.3 (SD 1.9) children. As far as living accommodations, most dairy workers rented a house/apartment (58.2%). The average number of household residents, including self, reported was 3.7 (SD 1.8). The majority of workers reported living with their spouse and children (37.3%), while 20.0% reported living with an average of 3.4 (SD 1.8) co-workers, 12.4% with only with their spouse, and 11.1% reported living alone. Only 16.0% disclosed being current smokers and having an average of 1.8 (SD 6.0) alcoholic drinks per week.

Table 2 presents the history of other TB-related items by category of TB exposure. The high exposure group worked 9.1 (SD 2.9) hours per day in close-proximity to cattle compared to the medium/low exposure group working 5.0 (SD 4.4) hours per day in close-proximity to cattle. A large majority of workers (78.2%) reported having been vaccinated with the BCG vaccine as an infant. A total of 4 (1.8%) individuals identified having been diagnosed with active TB in the past. However, only 2 of these 4 reported seeking TB treatment which was successfully completed. A small fraction of workers (2.2%) reported having lived or worked closely with someone who had been diagnosed with TB. About a third (n=70) of workers reported consuming raw dairy products, with 81.4% of those had consumed these raw dairy products in their non-U.S. home country and 18.6% while working on a U.S. dairy farm. Almost 6.0% of workers had worked with bTB infected cattle on U.S. dairy farms while 33.3% had heard of bTB outbreaks on other farms in Bailey County, Texas. Relative to the medium/low exposure group, the high exposure group had a higher frequency of BCG vaccination. The high exposure group had 3 of the 4 workers previously diagnosed with TB with only one seeking and finishing treatment compared to the one TB diagnosed case in the medium/low exposure group which sought and finished treatment. The high exposure group had 4 of 5 workers who lived or worked closely with someone who had been diagnosed with TB—all which did not wear respirators. The high exposure group had more workers who consumed raw milk on U.S. dairy farms, but were not as aware of bTB outbreaks on other farms in Bailey County, Texas compared to the medium/low exposure group.

No statistically significant differences were found between history of TB and assigned categories of TB exposure. In contrast, Torres-Gonzalez et al. (2013) found statistically significant differences in positive tuberculin skin test (TST) between the high exposure group and medium and low groups. Torres-Gonzalez et al. (2013) clinically tested dairy workers using two confirmative tests: (1) TST and (2) interferon-gamma release assay (IGRA). Due to financial and time constraints, our study used survey methodology to simultaneously collect previous diagnosis of TB and other characteristics. In addition, no power analysis for an appropriate sample size was warranted because this pilot study was hypotheses generating. Potentially, this approach could have led to the difference and subsequent underestimation of TB life prevalence among dairy workers surveyed in Bailey County, Texas.

History of BCG vaccination had a 10.0% difference between the high and medium/low exposure groups. Crude and adjusted POR were not statistically different. Due to a consistent low TB frequency, the U.S. does not vaccinate its population (CDC, 2011). On the other hand, Mexico has had a 99.0% vaccination coverage since 1996 (Orduna, Castillo-Rodal, & Lopez-Vidal, 2013) compared to Guatemala with an 81.0% BCG vaccination coverage in 2017 (WHO & UNICEF, 2018). These self-reported differences in BCG vaccination are consistent with the distribution of U.S. born dairy workers (21.7%) in the medium/low exposure group compared to 36.5% Mexican and 52.6% Guatemalan in the high exposure group.

The groups we created were consistent with the groups recommended by Torres-Gonzalez et al. (2013) with the high exposure group working 9.1 (SD 2.9) hours in close-proximity to cattle compared to the medium/low exposure group working 5.0 (SD 4.4) hours in close-proximity to cattle. Results indicated that there were no significant associations between category of exposure and history of TB. An alternative to categories of cattle exposure could have been nationality. Overall, crude differences were observed between nationalities. All previous TB diagnoses were reported by Central American workers, more Mexican workers (42.3%) reported consuming raw dairy products compared to U.S. (26.9%) and Guatemalan (17.0%) dairy workers. Also, U.S. workers were more likely to report working with bTB infected cattle, >44.0% of U.S. and Mexican workers were aware of previous bTB outbreaks among cattle in Bailey County, Texas compared to Guatemalan (17.0%) dairy workers. Lastly, Guatemalan workers spent 9.4 (SD 2.9) hours working in close-proximity to cattle compared to Mexican workers with 7.0 (SD 3.9) and U.S. workers with 5.2 (SD 4.6) hours.