Evaluation of Mycobacterium 

tuberculosis (TB) Transmission 

from Asian Elephants to Zoo 

Employees 

HHE Report No. 2019-0268-3380

October 2021
Authors: Kate Varela, DVM, MPH, DACVPM

Marcia L. Stanton, BS

Suzanne Tomasi, DVM, MPH, DACVPM

Adam J. Langer, DVM, MPH, DACVPM

Stephen B. Martin, Jr., PhD, PE

Analytical Support: Ethan Fechter-Leggett, Kathleen Fedan

Desktop Publisher: Barbara Elbon

Industrial Hygiene Field Assistance: Steve Martin, Marcia Stanton

Logistics: Lisa Glisan

Medical Field Assistance: Adam Langer, Suzanne Tomasi, Kate Varela

Data Support: Ethan Fechter-Leggett, Kathleen Fedan, Brian Tift 

Keywords: North American Industry Classification System (NAICS) 712130 (Zoo and Botanical 

Gardens), Washington, Mycobacterium tuberculosis, tuberculosis, elephants, latent TB infection, 

ventilation

Disclaimer

The Health Hazard Evaluation Program investigates possible health hazards in the workplace under 

the authority of the Occupational Safety and Health Act of 1970 [29 USC 669a(6)]. The Health 

Hazard Evaluation Program also provides, upon request, technical assistance to federal, state, and 

local agencies to investigate occupational health hazards and to prevent occupational disease or 

injury. Regulations guiding the Program can be found in Title 42, Code of Federal Regulations, 

Part 85; Requests for Health Hazard Evaluations [42 CFR Part 85].

Availability of Report

Copies of this report have been sent to the employer, and employees. The state and local health 

departments and the Occupational Safety and Health Administration Regional Office have also 

received a copy. This report is not copyrighted and may be freely reproduced.

Recommended Citation

NIOSH [2021]. Evaluation of Mycobacterium tuberculosis (TB) transmission from Asian elephants to 

zoo employees. By Varela K, Stanton ML, Tomasi S, Langer AJ, Martin SB. Morgantown, WV: U.S. 

Department of Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, Health Hazard Evaluation Report 2019-0268-3380, 

https://www.cdc.gov/niosh/hhe/reports/pdfs/2019-0268-3380.pdf
Table of Contents

Main Report

Introduction....................................................................................................................................................... 4

Our Approach ................................................................................................................................................... 2

Our Key Findings.............................................................................................................................................. 2

Our Recommendations.................................................................................................................................... 4

Supporting Technical Information

Workplace Information............................................................................................................ A-1

Asian Elephant Barn & Yard (Elephant Area)..................................................................................... A-1

Employee Information ............................................................................................................................ A-1

History of Issue at Workplace................................................................................................................ A-1

Tuberculosis.............................................................................................................................................. A-2

Methods, Results, and Discussion .......................................................................................... B-1

Methods: PPE Use and Work Practices................................................................................................ B-1

Results: PPE Use and Work Practices................................................................................................... B-1

Methods: Ventilation Assessment.......................................................................................................... B-1

Results: Ventilation Assessment ..............................................................................................................B-2

Methods: Employee Survey.........................................................................................................................B-2

Results: Employee Survey ....................................................................................................................... B-3

Discussion ................................................................................................................................................. B-7

Limitations................................................................................................................................................. B-8

Conclusions............................................................................................................................................... B-8

Tables.......................................................................................................................................... C-1

References.................................................................................................................................. D-1
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Request

The National Institute for Occupational Safety and Health (NIOSH) received a request for a Health 

Hazard Evaluation from the chief administrative officer of a zoo and aquarium. The request concerned 

transmission of Mycobacterium tuberculosis (TB) to zoo employees who were working with and around 

Asian elephants. 

Background

Tuberculosis (TB) is a disease that can affect people and animals and is caused by Mycobacterium 

tuberculosis bacteria that is generally found in the lungs but can attack any part of the body. Transmission 

can occur through inhalation of TB bacteria and infection occurs when the bacteria begin to grow. 

Latent TB infection (LTBI) means that a person has been infected with TB bacteria but is not showing 

disease symptoms and cannot spread the bacteria to others. In some cases, LTBI can progress to TB 

disease. People with TB disease can spread TB bacteria to others. Symptoms of TB disease may include 

a bad cough that last 3 weeks or longer, pain in the chest, coughing up blood or sputum, weakness or 

fatigue, weight loss, no appetite, fever, chills, or sweating at night. TB disease is treated with multiple 

antibiotics for 6 months or longer. People with LTBI are treated with one or two antibiotics for a 

shorter period (3–4 months) to decrease the likelihood of developing TB disease in the future.

Multiple epidemiologic investigations have documented elephant-to-human transmission of TB. 

Elephants have a very large lung capacity (tidal volume) relative to humans and can exhale large 

amounts of TB bacteria into the air of enclosed spaces (e.g., barns). In a zoo environment, TB bacteria 

from elephants with TB disease can be further spread during aerosol-generating procedures such as an 

elephant trunk wash (a diagnostic procedure used to identify elephants with TB) or potentially through 

cleaning (e.g., power washing) of contaminated areas. People working in close proximity in an enclosed 

space to an elephant with TB disease or performing aerosol-generating procedures (such as during an 

elephant trunk wash or power washing contaminated areas) can breathe in the bacteria and become 

infected themselves. This risk can persist in indoor spaces for a period even after the elephants are no 

longer present.

Workplace 

The 29-acre zoological park was operated by a municipal corporation overseeing parks and recreation 

services. The zoo’s two female Asian elephants were housed in the elephant barn, which was an 

approximately 3,875 square foot, two-story building with elephant housing on the lower level and 

employee workspace and animal food storage on the upper level. Adjacent to the elephant barn was a 

large yard where the elephants were released daily for exercise. The elephant barn and yard are referred 

to as the “elephant area” for the purpose of this report. At the time of the site visit, approximately 40 

employees comprised of elephant keepers, veterinary staff, and facilities and operations staff worked in 

the barn. Before this outbreak, volunteers worked in the elephant area, but once TB was identified, no 

volunteers were allowed in the barn and this policy continues to be implemented to limit the number of 

people potentially exposed to TB. 

Introduction

1
Elephant barn employees participated in annual TB screening conducted offsite at an occupational 

health provider recommended by the zoo or their primary care provider with either a tuberculin skin 

test (TST) or blood test (interferon-gamma release assay [IGRA]). In September 2019, eight of twelve 

zoo employees who worked primarily in the elephant area tested positive for TB infection using IGRA

tests; these employees were evaluated for TB and all received a diagnosis of LTBI and were started on

LTBI treatment. All employees diagnosed with LTBI had tested negative by TST in 2018. In light of 

these newly diagnosed infections in employees, both elephants were tested and found to be reactive on 

the serologic multiantigen print immunoassay (MAPIA) test. Additionally, Mycobacterium tuberculosis DNA 

was detected by quantitative polymerase chain reaction (qPCR) performed on trunk wash samples 

obtained in September 2019. In November 2019, TB trunk wash cultures isolated M. tuberculosis from 

specimens collected from both animals, indicating that both elephants had infectious TB disease. One 

of the elephants had a long history of being MAPIA-reactive, but the other elephant was newly positive.

Both elephants were considered geriatric. For these reasons, the zoo administration believed that the 

elephants were the probable source of infection for the eight elephant barn employees diagnosed with

LTBI in September 2019. 

To learn more about the workplace, go to Section A in the Supporting Technical Information

Our Approach

In November 2019, a NIOSH team and member of the Centers for Disease Control and Prevention’s 

Division of Tuberculosis Elimination visited the zoo. We completed the following activities during our 

evaluation:

• Toured the elephant area (including the elephant barn and yard) and observed workplace

practices, including personal protective equipment (PPE) use when working with elephants and

in the elephant area.

• Assessed the elephant barn ventilation system.

• Conducted voluntary, confidential interviews with 19 employees, including elephant keepers,

veterinary staff, and facilities and operations staff.

• Reviewed the TB exposure control plan for employees including the respiratory protection

program, fit testing plan, and draft employee TB surveillance protocol.

• Met with county and state health department representatives.

To learn more about our methods, go to Section B in the Supporting Technical Information

2
Employees who primarily worked in the elephant area and had contact with the 

elephants were more likely to test positive for TB infection. 

• Employee survey results found that employees whose primary worksite was the elephant area

and reported having direct contact with elephants were more likely to have a positive TB IGRA

blood test compared with employees who worked in the elephant area, but it was not their

primary worksite or they did not have direct contact with elephants.

• Tasks associated with a positive IGRA result included preparing elephant food, performing

elephant trunk washes, sweeping stalls, cleaning the barn, disinfecting the elephant barn on

weekends, and bathing the elephants.

At the time of the health hazard evaluation, the zoo had a respiratory protection 

program and employee TB surveillance program; however, upon review both could 

be improved. 

• The respiratory protection program was written for the entire zoo and not specific to the

elephant area and keepers. It did not specifically address TB exposure control.

• The type of respiratory protection fit test (qualitative vs. quantitative) and responsible party for

conducting fit testing was not explicitly stated.

• The employee TB surveillance program did not include baseline or preemployment TB testing

or specify the type of test to use such as the IGRA test.

• Some of the essential elephant area employees did not participate in the employee TB

surveillance program.

• A comprehensive, confidential record keeping system to track the respiratory protection

program and TB surveillance program was not in place; employee occupational health records

were not available for review.

• There was no occupational health coordinator identified. Adequate staff training is an important

component of a respirator protection program; however, employees demonstrated gaps in

knowledge about proper PPE use during observation of daily activities.

One ventilation system serviced both the elephant housing area and office space in 

the elephant barn, allowing air from the elephant housing area to enter employee 

workspaces. 

• A single air handling unit serviced both the elephant housing area and office space in the

elephant barn.

A single ventilation system was problematic because TB spreads via airborne particles, called

droplet nuclei, that could travel between the two areas through the ventilation system.

• Exhaust air from the elephant barn was discharged through louvers on the west side of the

building above the employee parking lot adjacent to the barn.

This configuration is not ideal because of the potential for employees parking in the area to be

exposed.

3

Our Key Findings
Employees needed more information on TB risk and prevention. 

• Employee survey results revealed inconsistent training frequency and knowledge level among

employees on TB risk factors (e.g., high-risk activities, transmission), testing, and prevention

(e.g., PPE use).

• While observing work practices, we noted employees touching or readjusting their N95

respirators. We were told that some employees who ostensibly passed their fit test wore N95

respirators with facial hair that might impair the protective seal.

To learn more about our results, go to Section B in the Supporting Technical Information

Our Recommendations 

The Occupational Safety and Health Act requires employers to provide a safe workplace. 

Benefits of Improving Workplace Health and Safety:

 Improved worker health and well-being  Enhanced image and reputation

 Better workplace morale  Superior products, processes, and services

 Easier employee recruiting and retention  May increase overall cost savings

The recommendations below are based on the findings of our evaluation. For each recommendation, 

we list a series of actions you can take to address the issue at your workplace. The actions at the 

beginning of each list are preferable to the ones listed later. The list order is based on a well-accepted 

approach called the “hierarchy of controls.” The hierarchy of controls groups actions by their likely 

effectiveness in reducing or removing hazards. In most cases, the preferred approach is to eliminate 

hazardous materials or processes and install engineering controls to reduce exposure or shield 

employees. Until such controls are in place, or if they are not effective or practical, administrative 

measures and PPE might be needed. Read more about the hierarchy of controls at

https://www.cdc.gov/niosh/topics/hierarchy/. 

We encourage the company to use a health and safety committee to discuss our 

recommendations and develop an action plan. Both employee representatives and 

management representatives should be included on the committee. Helpful guidance can be 

found in “Recommended Practices for Safety and Health Programs” at

https://www.osha.gov/shpguidelines/index.html. 

Given the many unknowns about the TB disease process in elephants, the recommendations below are 

focused on ways to mitigate the risk of transmission from elephants to current and future employees, 

strengthen employee TB surveillance, and inform employees on risk and prevention.

4
Recommendation 1: Reduce potential employee exposure to M. tuberculosis

Why? Multiple epidemiologic investigations have documented zoonotic Mycobacterium tuberculosis

transmission between people and elephants. TB bacteria exhaled into the air by elephants with 

infectious TB disease and can be further spread by aerosol-generating procedures such as during a

trunk wash or cleaning (e.g., power washing) contaminated areas. People working in close proximity 

to an infected elephant or performing these activities can breathe in the bacteria and become infected 

themselves. In some cases, latent TB infection (LTBI) can progress to TB disease. People with 

weakened immune systems who have LTBI are at higher risk of progressing to TB disease. 

Symptoms of TB disease can include: a bad cough that lasts 3 weeks or longer, chest pain, coughing 

up blood or sputum, weakness or fatigue, weight loss, no appetite, chills, fever, or sweating at night. 

People with TB disease can spread TB bacteria to others. People with LTBI and TB disease need

treatment with antibiotics. 

In September 2019, eight zoo employees working in the elephant area were newly diagnosed with 

LTBI. Mycobacterium tuberculosis was isolated from trunk wash specimens collected in September 2019 

from both animals, thus indicating infectious TB disease. At the time of the health hazard evaluation, 

the zoo decided the elephants would not be treated for TB because of concerns the antibiotics would 

be difficult to administer based on the animals’ history and temperament, and the potential for 

antibiotic-resistant TB development. The zoo had also decided against euthanizing either animal 

unless their clinical condition deteriorated. As a result, the two elephants with TB disease continued 

to pose a risk of TB exposure for employees working in the elephant area. 

How? At your workplace, we recommend these specific actions:

Cease all nonessential tasks, and remove all nonessential items,

personnel, or animals from the elephant barn to minimize the risk of M. 

tuberculosis transmission to as few persons or animals as possible. 

Limit the number of employees and volunteers who work in the barn when 

the elephants are inside or when the housing and husbandry areas are 

being cleaned.

• Consider dividing elephant area employees into two groups to stratify risk into two tiers

to minimize the number of employees at increased risk of transmission: one group only

inside when elephants are indoors or when cleaning is occurring (increased risk), and

one group only inside when elephants are in the outdoor yard and no cleaning is

occurring (limited risk).

Employees should limit aerosol generating activities as much as possible.

• Use alternative cleaning methods in lieu of power washing the elephant housing area

and wet down bedding before sweeping to minimize dust.

5
• When aerosol generating activities cannot be avoided, employees should wear a fittested NIOSH-approved respirator (N95 or equivalent or higher level respirator),

disposable coveralls such as Tyvek, and gloves.

Recommendation 2: Implement a respiratory protection program and require all 

employees and volunteers at risk of TB exposure to participate in the zoo’s 

respiratory protection program.

Why? A respiratory protection program is a critical component to preventing TB transmission to 

current and future elephant area employees and employees working with other species that can pose a 

risk for zoonotic TB. 

Before identification of TB in employees, elephant area employees were not required to wear 

respiratory protection while working in the elephant barn. At the time of the health hazard evaluation

site visit, only essential personnel were allowed to enter the elephant barn, and anyone entering the 

elephant barn was required to wear a fit-tested N95 respirator. All essential employees had been fittested, most with a qualitative fit test, to wear N95 respirators.

Respirators should be used in conjunction with an OSHA-compliant Respiratory Protection Program 

(29 CFR 1910.134) that includes medical evaluation, training, and fit testing. Some states may have 

applicable Federal OSHA-approved State plans. Information on Federal OSHA-approved State plans 

can be found at https://www.osha.gov/stateplans. 

How? At your workplace, we recommend these specific actions:

Assign or hire a qualified employee knowledgeable in occupational 

health to be responsible for implementing a robust respiratory 

protection program. 

Implement a respiratory protection program that includes an annual

quantitative fit testing protocol and training program to educate 

employees and volunteers how to properly use PPE. 

• OSHA’s Respiratory Protection standard [29 CFR 1910.134], notes that a respiratory

protection program should include the following:

o Written policy;

o Change-out schedule for cartridges/filters;

o Medical evaluation prior to use to determine fitness;

o Fit testing and training prior to use and annually; and

o Establishment and implementation of procedures for proper respirator use such

as prohibiting use with facial hair when this would impair the seal; ensuring user

6
seal-check and inspection of respirators prior to each use; ensuring proper 

cleaning, disinfection, and maintenance of respirators; and ensuring proper 

storage of respirators to protect respirators from damage, contamination, dust, 

sunlight, and extreme temperatures

• NIOSH has information about respiratory protection at the following websites:

o Respirators

https://www.cdc.gov/niosh/topics/respirators/

o Respirator trusted-source information – Section 3: ancillary respiratory

information

https://www.cdc.gov/niosh/npptl/topics/respirators/disp_part/respsource3.ht

ml

Ensure all employees and volunteers potentially exposed to TB are 

included in the respiratory protection program. 

• Consider establishing an exposure classification system to identify which employees

and volunteers are potentially exposed to TB.

Establish and maintain records according to OSHA (29 CFR 

1910.1020, Access to Employee Exposure and Medical Records) or 

applicable OSHA-approved state program.

Recommendation 3: Institute an updated TB surveillance program and require that 

all employees and volunteers potentially exposed to TB participate in the zoo’s TB 

surveillance program.

Why? An employee TB surveillance program is necessary to ensure routine testing and monitoring is 

performed, any new TB infections are promptly identified, and corrective actions are taken to protect 

current and future employees. 

The TB surveillance program in place before TB was identified was not comprehensive to include all 

employees who might be exposed to TB in the elephant barn and required modifications to include 

baseline testing at the time of hire for new employees, a standardized testing protocol, and improved 

record keeping. 

7
How? At your workplace, we recommend these specific actions:

Assign or hire a qualified employee knowledgeable in occupational health 

to be responsible for the TB surveillance program. 

Ensure all employees and volunteers potentially exposed to TB participate 

in the zoo’s TB surveillance program.

• Establish an exposure classification system to determine which employees and

volunteers may potentially be exposed to TB depending on the species they work

with, their main work location, and whether they spend time working with or around

a species that can carry TB bacteria (e.g., elephants, non-human primates).

Update the TB surveillance program to include screening and baseline 

testing upon starting employment or volunteering and annually for those 

individuals with a previously negative test using an IGRA screening tool.

• Screening questionnaires should be consistent with national guidelines and state or

local health department regulations and guidelines. An example of an integrated

tuberculosis (TB) screening and risk assessment form for new staff can be found in

Appendix 3 (http://links.lww.com/JOM/A782) of the following reference:

Tuberculosis screening, testing, and treatment of US health care personnel: 

ACOEM and NTCA Joint Task Force on Implementation of the 2019 MMWR 

Recommendations. J Occup Environ Med 2020;62(7):e355-e369, 

https://doi.org/10.1097/JOM.0000000000001904.

• Ensure prompt medical evaluation if a volunteer or employee’s TB infection test is

newly positive. CDC has information about diagnosing LTBI and TB disease at the

following websites:

o Tools for Health Care Providers

https://www.cdc.gov/tb/education/provider_edmaterials.htm

o Diagnosing Latent TB Infection & Disease

https://www.cdc.gov/tb/topic/testing/diagnosingltbi.htm

• Local or public health agencies can serve as a source for technical assistance, medical

consultation regarding diagnosis and treatment of LTBI, and clarification of state or

local regulations and guidelines. Information on state and local TB Control offices can

be found at https://www.cdc.gov/tb/links/tboffices.htm.

• According to American Thoracic Society (ATS), Infectious Diseases Society of

America (IDSA), and CDC clinical practice guidelines, use of IGRA over the TST is

generally preferential for diagnosis of TB for persons at least 5 years of age. The TST is

considered an acceptable alternative, though, in situations where IGRA testing is not

8
available or considered too costly or too burdensome. ATS/IDSA/CDC Clinical 

Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children can be found at 

https://academic.oup.com/cid/article/64/2/e1/2629583. 

Ensure employees with a history of LTBI receive annual symptom 

screening for TB disease. 

• The annual symptom screening should include education to help individuals with

treated or untreated LTBI understand which symptoms to monitor, whom to contact

if symptoms of concern develop, and what LTBI treatment options to consider if

untreated.

• An example of an annual tuberculosis symptoms screen form for individuals with

LTBI can be found in Appendix 7(http://links.lww.com/JOM/A786) of the

following reference:

Tuberculosis screening, testing, and treatment of US health care personnel: 

ACOEM and NTCA Joint Task Force on Implementation of the 2019 MMWR 

Recommendations. J Occup Environ Med 2020;62(7):e355-e369, 

https://doi.org/10.1097/JOM.0000000000001904.

Ensure an adequate confidential record keeping system is used to 

document and track baseline and follow-up TB test results in the TB 

surveillance program. 

• Implement a tracking system that includes why the employee was tested, employee

exposure classifications, results, annual clinical evaluations, and information on

required follow-up of positive tests.

• Designate a qualified person with a back-up to keep the tracking system up to date.

Recommendation 4: Provide a ventilation system for areas on the upper floor of the

barn including the entrance hallway, locker room, restroom, office, and kitchen 

areas that is separate from the ventilation system for the elephant housing area.

Why? Preventing air from the first-floor elephant housing area mixing with the upper floor employee

areas will reduce the risk of exposure.

At the time of the site visit, the zoo administration had moved the office space to a trailer outside the 

barn (Figure 1). However, by separating the ventilation systems, the upstairs office area could once 

again be used safely by employees.

9
How? At your workplace, we recommend these specific actions:

Figure 1. Temporary trailer located outside of elephant barn used as office space by elephant barn employees 

for administrative activities. Photo by NIOSH.

Consult with a ventilation expert to explore options for ventilating the 

upper floor of the elephant barn separately from the elephant housing

area. Positive pressure in the upper floor should be maintained to

prevent the entry of air from the elephant housing area.

Consider installing an exhaust fan in the elephant housing area that can

be turned on remotely by employees first thing in the morning to allow air

movement from the space before employees enter the area to begin 

daily activities. 

Consider relocating the building’s exhaust to the roof so air from the

elephant barn is not released directly into the parking area (Figure 2). 

If the exhaust fan in the hay storage area is not routinely used, consider

deactivating the power switch to prevent use.

10
Figure 2. Exhaust air louvers above employee parking lot. Photo by NIOSH.

Recommendation 5: Ensure employees understand the hazards associated with 

working with TB-positive animals and how to protect themselves. 

Why? OSHA’s Hazard Communication Standard, also known as the “Right to Know Law” (29 CFR 

19.10.1200), requires that employees are informed and trained on potential work hazards and 

associated safe practices, procedures, and protective measures. 

After identification of TB, the zoo provided TB training to employees; however, employee survey 

results revealed inconsistent training frequency before the outbreak and varied knowledge level 

among employees on TB risk factors (e.g. high-risk activities, transmission), testing, and prevention 

(e.g. PPE use).

How? At your workplace, we recommend these specific actions:

Train employees and volunteers on potential workplace hazards, what 

precautions they should take to protect themselves, and workplace 

policies for reporting their concerns.

Implement TB training during working hours upon hire and then annually 

for all elephant area employees and other employees who would benefit 

from this training (ancillary veterinary staff, volunteers, facilities staff, or 

others). 

• Training should include TB transmission risks specific to job tasks, symptoms, testing

requirements, prevention, and what to do if an employee or volunteer believes they

might be ill. Information on these topics can be found on the CDC TB website at

https://www.cdc.gov/tb/default.htm.

11

• Document these trainings in employee records.
Conduct regular training for employees on proper respirator use and 

provide this information at all PPE donning (putting on) and doffing

(taking off) stations. 

• Training should occur during onboarding, annually, and when an employee switches

from one type of respiratory protection to another (for example, from an N95

respirator to a personal air-purifying respirator [PAPR]).

• Training should include what to do if an N95 respirator becomes wet or compromised.

• NIOSH provides training materials on how to properly put on (don) and take off (doff)

a disposable respirator at https://www.cdc.gov/niosh/docs/2010-133/.

Ensure employees replace N95 respirators daily and do not store used 

N95 respirators in the same location as clean, unused N95 respirators. 

• NIOSH has a PPE Tracker mobile app that can help track your PPE inventory. This

app can be found at https://www.cdc.gov/niosh/ppe/ppeapp.html.

Recommendation 6: Ensure standard procedures for PPE use are clearly identified, 

communicated to employees, and enforced by supervisors. 

Why? PPE is the least effective means for controlling hazardous exposures. Proper use of PPE 

requires a comprehensive program and a high level of employee involvement and commitment. The 

appropriate PPE must be chosen for each hazard. Supporting programs such as training, changeout 

schedules, and medical assessment may be needed. PPE should not be the sole method for 

controlling hazardous exposures. Rather, personal PPE should be used until effective engineering and 

administrative controls are in place.

We observed PPE stations set up at entry points to the elephant barn (Figures 3 and 4), and 

employees properly donning and doffing PPE. However, we also observed an employee wearing an 

N95 respirator improperly. 

How? At your workplace, we recommend these specific actions:

Develop designated areas for storing, donning, and doffing PPE. 

• PPE storage and donning and doffing should take place in an area outside of elephant

care areas. This space should be ventilated separately to prevent the potential for PPE

to be contaminated. Employees should have access to a handwashing station.

• If the second-floor office space is ventilated separately and constantly maintained

under positive pressure relative to the elephant housing area, the PPE storage and

donning and doffing could be located on the second floor.

12
Require all employees wear gloves (dedicated work gloves or disposable 

latex or nitrile gloves), eye protection (goggles or face shield), and 

respiratory protection (N95 respirator or equivalent or higher level 

respirator) while working in the elephant area. 

• The minimum level of respiratory protection acceptable for TB is a filtering face piece

respirator selected from those approved by NIOSH under Title 42 CFR, Part 84.

• NIOSH has information on respiratory protection acceptable for TB at

https://www.cdc.gov/niosh/topics/tb/respprotection.html.

• If employees are unable to wear N95 respirators, N95 respirators become wet during

certain procedures, or enhanced comfort is needed because of heat or humidity,

PAPRs with loose-fitting facepieces or hoods might be an alternative option. If PAPRs

are used, consider equipping workers with radio headsets or earpieces to allow for

easier verbal communication when working in close proximity to elephants.

Ensure employees are trained to properly wear N95 respirators, including

what to do if N95 respirators become compromised or wet.

Ensure employees wear N95 respirators, disposable coveralls such as 

Tyvek, gloves, and eye protection (goggles or face shield) during any 

aerosol-generating activities, such as power-washing or using highpressure water/cleaning sprays.

Make N95 or equivalent respirators or ones with greater protection (e.g., 

PAPR) available for protection against TB when working around any 

elephant exposed to TB. 

• Because there is a lag time between when an elephant starts shedding TB and the

positive trunk wash culture result, workers may be exposed to TB during that timeperiod. Wearing an N95 respirator would decrease the risk of TB exposure.

Ensure employees wear a respirator (N95 or equivalent, or higher-level 

respirator), eye protection, and gloves when performing maintenance and 

replacing filters in the ventilation system with potential for M. tuberculosis

contamination. 

• If employees have concerns about handling filters potentially contaminated with M.

tuberculosis, the filters can be disinfected by spraying them with a 10% bleach solution or

other appropriate mycobacteriacide before removal.

13
• If disinfection by spraying is done, the blowers in the air handling unit should be

powered off before spraying begins, and they should remain off until the filters have

been replaced.

Recommendation Implementation

In addition to providing feedback during the site visit, we sent an interim letter in January 2020 

providing a summary of the site visit and similar recommendations as above. The zoo administration 

subsequently took several actions to mitigate the risk of TB exposure including implementing a TB 

Exposure Control Program managed by a Work Group who oversees all administrative controls, 

improved PPE practices, facility upgrades, and ongoing activities. Ventilation upgrades were completed 

in the elephant barn to include separate systems for the elephant housing and employee areas.

Figure 3. Personal protective equipment 

storage and donning and doffing station in 

the first-floor entryway to the elephant barn. 

Photo by NIOSH.

Figure 4. Personal protective equipment storage 

and donning and doffing station at the upper 

level employee entrance to the elephant barn. 

Photo by NIOSH.

14
Supporting Technical Information

Evaluation of Mycobacterium tuberculosis (TB) 

Transmission from Asian Elephants to Zoo Employees 

HHE Report No. 2019-0268-3380

October 2021
A-1

Workplace Information

Asian Elephant Barn & Yard (Elephant Area)

Size: 3,875 square feet

Floors: two levels 

The lower level of the barn contained two elephant bedrooms, a holding room, an elephant restraint 

chute used during animal husbandry, and a small food storage area. The upper level contained the 

employee office space, a locker room area with a restroom and shower, an animal food preparation 

kitchen, hay storage area, and boiler room. A second story catwalk was located above and along the 

sides of the barn for employees to monitor the elephants. Entry points to the elephant barn were 

located at both the upper and lower levels on the south end of the building and in the courtyard on the 

north end of the building. Personal protective equipment (PPE) supplies were located just inside the 

entrance to the upper level and at the entrance next to the stairwell on the lower level on the south end 

of the building. Employees donned (put on) and doffed (took off) their PPE immediately after they 

entered the barn (Figures 3 and 4). The perimeter of the elephant barn included the elephant yard with 

three public viewing areas, a viewing area for visitors to see into the elephant barn, an employee parking 

area, and a courtyard with maintenance supplies and refuse disposal. At the time of the site visit, 

elephant barn staff were using a temporary trailer in the parking area behind the elephant barn for their 

office space (Figure 1) to complete administrative activities. 

Employee Information

At the time of the site visit, access to the elephant barn was limited to essential personnel only. There 

were approximately 40 essential elephant area employees comprised of elephant keepers, veterinary 

staff, and facilities and operations staff. Volunteers were no longer allowed in the barn. 

History of Issue at Workplace

In September 2019, eight of twelve zoo employees who worked primarily in the elephant barn tested 

positive for TB infection using IGRA tests. These employees were evaluated for TB and all received a 

diagnosis of LTBI. All employees diagnosed with latent TB infection had a negative TST result in 2018. 

In light of these newly diagnosed TB infections in people, both elephants were tested and found to be 

reactive on the serologic MAPIA test. Additionally, Mycobacterium tuberculosis DNA was detected by 

quantitative polymerase chain reaction (qPCR) performed on trunk wash samples obtained in 

September 2019. In November 2019, TB trunk wash cultures isolated M. tuberculosis from specimens 

collected from both animals, indicating both elephants had infectious TB disease. One of the elephants 

had a long history of being MAPIA-reactive, but the other elephant was newly positive. 

At the time of the site visit on November 9, 2019, the lead zoo veterinarian in consultation with zoo 

administration and with guidance from local public health officials had decided the elephants would not 

be treated for TB because of concerns the antibiotics would be difficult to administer based on the 
A-2

animals’ history and temperament, and the potential for antibiotic-resistant TB development. This was 

the first known U.S. facility with elephants diagnosed with TB disease to not attempt to treat the 

elephants for TB disease, which posed challenges related to the risk of current and ongoing TB 

exposure for zoo employees working closely with or around the elephants or in the elephant area. The 

recommendations made in this report reflect consideration of ongoing TB risk. 

At the time of the visit, the zoo had implemented increased precautions to reduce potential TB 

exposure to employees and the public by limiting access to the elephant barn to essential personnel 

only. All essential personnel entering the elephant barn were required to wear a fit-tested N95

respirator. 

Before zoo employees were diagnosed with LTBI , the municipal corporation had a written respiratory 

protection program included in the District Accident Prevention and Safety Plan. This document 

described the purpose of the respiratory protection program, medical surveillance, respirator selection, 

training, and qualitative fit testing protocols. The District Accident Prevention and Safety Plan and an 

updated respiratory protection program draft were shared with NIOSH for review before the site visit. 

This event was the first time this zoo identified TB transmission from elephants to workers.

Tuberculosis

TB is a disease caused by Mycobacterium tuberculosis bacteria that can affect people and animals. Although 

generally found in the lungs, TB bacteria can attack any part of the body. TB is spread through 

inhalation of bacteria that occurs during close, prolonged contact with a person or animal with TB 

disease. LTBI occurs when a person is infected with TB, but not sick. Individuals with LTBI do not 

have symptoms and cannot spread TB to others but are at risk for developing TB disease. On average, 1 

in 10 people with LTBI will get sick with TB disease in the future, and people with weakened immune 

systems are more likely to develop TB disease [CDC 2021]. People with LTBI are treated with one or 

two antibiotics for a shorter period (3–4 months) to decrease the likelihood of developing TB disease in 

the future. TB disease causes the person to become sick and able to spread TB bacteria to others. TB 

disease is treated with multiple antibiotics for 6 months or longer. Reports of TB-like illnesses in Asian 

elephants have been documented for thousands of years [Chalke 1962], and the point prevalence of TB 

among captive Asian elephants in the United States during 1997–2011 was estimated to be 5.1% for 

Asian elephants and 0% for African elephants [Feldman et al. 2013].

Transmission of M. tuberculosis has been documented between elephants and humans [Michalak et al. 

1998]. Since 2015, the United States Department of Agriculture (USDA), Animal and Plant Health 

Inspection Services (APHIS), no longer regulates the surveillance, diagnosis, and treatment of TB in 

elephants within the United States [NIOSH 2018]. That responsibility now rests with the lead 

veterinarian treating the elephant with TB. However, the Stakeholders Task Force on Management & 

Research Priorities of Tuberculosis in Elephants published Recommendations for the Diagnosis, 

Treatment and Management of Tuberculosis in Elephants in Human Care in 2017 [Backues and 

Wiedner 2019]. This detailed document gives recommendations for diagnostic testing, treatment, and 

monitoring of the elephant and herd during treatment, as well as human health considerations [Backues 

and Wiedner 2017].
A-3

TB in elephants is usually diagnosed by trunk wash culture, and elephants in captivity should be tested 

at least annually. Routine trunk wash culture consists of a series of three trunk wash samples collected 

on separate days within a one-week period [Backues and Wiedner 2017]. Culture is the only definitive 

method to diagnose TB disease and although trunk wash culture can lack sensitivity, it is still considered 

the gold-standard for diagnosing TB in elephants. Other ancillary tests such as Dual Path PlatformTM 

(DPP) and Multiantigen Print ImmunoassayTM (MAPIA) can be used in conjunction with trunk wash 

cultures. The DPP is a rapid test to detect antibodies to M. tuberculosis in blood, while the MAPIA 

detects antibodies to a panel of 12 defined M. tuberculosis antigens. One of the elephants had a long 

history of being MAPIA reactive and had been regarded as potentially infected with M. tuberculosis. 

Before identification of this outbreak, neither elephant had trunk wash cultures positive for TB; 

however, M. tuberculosis was isolated from trunk wash samples collected from both elephants in 

September 2019 (results were reported as positive for both elephants in November 2019). At the time 

of our site visit, both elephants with TB disease received three trunk wash cultures per week to 

determine how often the elephants were shedding TB bacteria. 

Because diagnosing and treating elephants with TB can be difficult, time-consuming, and expensive, 

more research is needed to better understand the science of TB in elephants, risk to humans, and to 

develop improved screening methods for TB in elephants. 
B-1

Methods, Results, and Discussion

Methods: PPE Use and Work Practices 

We observed employee PPE use and work practices to learn more about activities and job duties that 

might lead to increased risk of TB exposure.

Results: PPE Use and Work Practices

PPE Use

While working inside the barn, employees wore N95 respirators, gloves, and eye protection. While 

working in the outdoor elephant yard, employees wore gloves while collecting manure and gloves and 

an N95 respirator while emptying manure into a refuse container. 

Work Practices 

We observed elephant keepers performing their regular duties including animal husbandry and medical 

treatments. We also observed aerosol-generating procedures, including a trunk wash demonstration and 

potentially aerosol generating activities such as cleaning elephant stalls using a high-power hose (not a 

pressure washer, Figure 5) and removing elephant manure from the yard. While observing work 

practices, we noted employees touching or readjusting their N95 respirators while inside the 

contaminated area. 

Figure 5. A zookeeper cleaning the elephant housing area with a hose inside the elephant barn. Photo by NIOSH. 

Methods: Ventilation Assessment

We took physical measurements of all areas and visually assessed the air-handling unit (AHU) serving 

the elephant barn. Air flow measurements were not taken during the visit. We reviewed mechanical 

drawings and the AHU specifications and operational data summary. We measured pressure 

differentials at all doorways on the second level. 
B-2

Results: Ventilation Assessment

The Heatex Inc. series 5000 AHU appeared to be in good working order. Components of the system

included two blowers, duct dampers, particulate filters, an energy recovery heat exchanger (HX), and 

hot water heating coil. The system was designed to supply and exhaust air in a single-pass fashion at a 

rate of 5000 cubic feet per minute (CFM). At the supply and exhaust air inlets, the AHU was fitted with 

3-ply 20-inch × 30-inch ventilation filters with a Minimum Efficiency Reporting Value (MERV) rating

of 7. The filters were reportedly checked every 30 days and typically replaced every 60 days. At time of

removal, filters were reportedly bagged prior to disposal. The HX transfers heat from exhaust air to

incoming supply air during the heating season (the opposite is true during warmer times of the year).

Air was not recirculated in the building. The blowers were either “on” or “off” and set to move the

same amount of air through the supply and exhaust sides of the unit. Supply air intake louvers were

located on south end of the barn at the loft level.

Fresh, outside air flowed through the filters and supply-side HX, before passing through the hot water 

heating coil and then out to the occupied areas of the building. The AHU originally supplied air to three 

supply vents in the second level staff areas of the barn. However, during our visit all three supply vents 

had been sealed off due to past insect infestation in the ducts. There were two operable windows 

located in the hallway just outside of the office area. The main duct run with supply vents for the lower 

level of the elephant barn had seven vents. Four of the vents were open while three had been covered 

with metal plates. The AHU also supplied air to a continuous sill diffuser located underneath the public 

viewing window on the first floor of the barn.

Return air was fed back to the AHU through one large louver located at loft level above the elephant 

stalls. There were no return vents to the AHU in the second level staff areas. After passing through a 

filter and the HX, the exhaust air was forced out of the building through louvers on the west side of the 

building above the employee parking lot adjacent to the barn (Figure 2). Using physical measurements 

of the space and the manufacturer specifications for the existing ventilation system we determined there 

were approximately 4.5 air changes per hour for the barn.

We measured pressure differentials at all doorways on the second level. The hay storage area on the 

second level was used to store hay for multiple animals at the zoo. Employees other than elephant 

caretakers periodically entered the area for short periods of time to collect hay. The hay storage area was 

negative to the first floor of the barn meaning that air from the elephant area was entering the hay 

storage room. Air entering the hay storage room from the elephant barn increased if the exhaust fan in 

the hay storage area was turned on, although staff reported the fan was never used. The office area and 

kitchen were also slightly negative or neutral to the catwalk area which means that air from the first level 

elephant area could enter the office and kitchen areas. The pressure in the enclosed areas on the second 

level should be positive to the catwalk and first floor to prevent air from the main elephant area 

entering the space. 

Methods: Employee Survey

At the time of the site visit in November 2019, CDC/NIOSH staff interviewed a convenience sample 

of the employees who spent all or some time working in the elephant area. Survey data were analyzed 
B-3

using SAS 9.4. Fisher’s exact tests were used to evaluate associations between groups (p <0.05 was 

considered significant). The survey sample size was too small to conduct multivariable logistic 

regression to assess associations between exposures and IGRA test results. Wilcoxon two-sample test 

was used to compare employees’ time spent in the elephant barn housing area with IGRA test results. 

Survey respondents were divided into exposure groups based on two criteria: 1) whether they reported 

the elephant barn was their primary workplace, and 2) whether they reported contact with the elephants.

The High Exposure group was assigned if they answered yes to both criteria, the Medium Exposure 

group was assigned if they answered yes to one criterium, and the Low Exposure group was assigned if 

they answered no to both criteria. 

Results: Employee Survey

Demographic characteristics of survey participants

We interviewed 19 of the 40 employees (47.5%) who spent all or some time working in the elephant 

area including elephant area employees, veterinary staff, and ancillary staff such as facilities and 

operations. Of the 19 employees we interviewed, 12 had been tested for TB in September 2019 using 

IGRA tests. Summary characteristics of the survey participants are presented in Table C1.

Exposure groups 

We classified four respondents to the High Exposure group, six respondents to the Medium Exposure 

Group, and nine respondents to the Low Exposure Group (Table C2). The High Exposure group was 

mainly comprised of job titles associated with elephant barn employees, the Medium Exposure group 

was mainly comprised of veterinary staff, and the Low Exposure group was mainly comprised of 

facilities and operations staff. 

Exposure group was associated with positive TB blood test result 

IGRA results were available for 12 of the 19 survey respondents; four (33%) had a positive IGRA

result. Exposure group was significantly associated with IGRA result (p = 0.0364) (Table C2. Exposure 

group associated with positive TB blood test result). All three employees with test results in the High 

Exposure group tested positive, while none of the three employees with test results in the Low 

Exposure group tested positive. Of six employees with test results in the Medium Exposure group, five 

employees (83%) had a negative IGRA result and reported having close contact with the elephants, but 

the elephant barn was not their primary workplace. One employee (17%) in the Medium Exposure 

group reported the elephant barn was the employee’s primary workplace but did not have close contact 

with the elephants themselves. This employee had a positive IGRA result. While this employee did not 

report close contact with the elephants, the employee reported performing high-risk tasks such as 

cleaning and disinfecting the elephant barn daily and power washing the elephant housing area (before 

identification of TB, at which point power washing was no longer permitted).

Time spent in elephant barn, elephant housing area was associated with positive IGRA result

The amount of time spent per week inside the elephant barn elephant housing area ranged from 0 to 20 

hours with a median time of 1.0 hour and mean time of 4.2 hours. For those employees with a negative 

IGRA test result, the mean time spent in the elephant barn housing area was 0.875 hours per week

compared to 16.0 hours per week for those employees with a positive IGRA test result. The median 
B-4

number of hours spent in the elephant barn housing area was statistically significantly higher for 

employees with a positive IGRA test result than for employees with a negative IGRA test result 

(Wilcoxon two-sample test, one-sided p = 0.0031, two-sided p = 0.0062). We categorized employees’ 

elephant barn elephant housing area exposure as Long (>4 hours) or Short (≤ 4 hours) based on the 

average number of hours they reported spending in the elephant barn elephant housing area each week. 

Those in the Long Exposure group were associated with a positive TB blood test result (p = 0.0020). 

Tasks associated with positive IGRA result

From a list of 10 elephant-related tasks, respondents were asked to identify tasks currently being 

performed and tasks performed during the previous 12 months. Current tasks associated with a positive 

IGRA result included preparing elephant food (p = 0.0182), performing elephant trunk washes (p = 

0.0182), sweeping stalls (p = 0.0101), cleaning the barn (p = 0.0020), disinfecting the elephant barn on 

weekends (p = 0.0182), and bathing the elephants (p = 0.0182). Tasks performed during the previous 

12 months associated with a positive IGRA result included preparing elephant food (p = 0.0020), 

sweeping stalls (p = 0.0101), cleaning the barn (p = 0.0020), and bathing elephants (p = 0.0182). 

Feeding elephants and administering medications were not significantly associated with IGRA test 

results for either current or past 12-month tasks; however, both of these tasks were associated with 

positive IGRA test results when analyzed by task frequency (daily, several times a week, once a week, 

once a month). Feeding elephants and administering medications were associated with a positive IGRA 

test result for those employees who reported doing these tasks daily currently (feeding, p = 0.0238; 

medications, p = 0.0286) and daily in the past 12 months (feeding, p = 0.0238; medications, p = 

0.0286). 

Disinfecting the elephant barn on weekends during the previous 12 months (p = 0.0909) and pressure 

washing the elephant barn during the previous 12 months (p = 0.0667) were associated with a positive 

IGRA test result at p less than 0.1. Pressure washing is an aerosol generating activity and therefore 

should be considered a high-risk activity. 

PPE Use 

Before identification of TB transmission occurring between elephants and employees, respiratory 

protection was not routinely worn by employees working in the elephant barn. The responses recorded

at the time of the survey referred to the period after identification of TB when zoo administration 

implemented respiratory protection protocols. 

Two employees (50%) in the High Exposure group and five employees (83%) in the Medium Exposure 

group reported always using an N95 while within 25 feet of the barn, including inside and outside the 

barn. Of those in the Low Exposure group, one employee (11%) reported wearing an N95 most of the 

time, and four (44%) reported always wearing an N95 while within 25 feet of the elephant barn.

Employees who reported not wearing an N95 while within 25 feet of the barn answered ‘yes’ to 

participating in tasks associated with a positive IGRA result, indicating they performed these tasks at 

least some of the time without proper respiratory protection to prevent TB exposure. The tasks 

included pressure washing, food preparation, feeding and administering medications to the elephants, 

performing trunk washes, cleaning and disinfecting the barn, sweeping stalls, and bathing elephants. 
B-5

Most (84%) of the employees who responded reported training on proper PPE use in the past year; 

however, two employees in the High Exposure group and one employee in Medium Exposure group 

reported no training on the proper way to wear an N95 respirator in past year. 

Employee TB Training 

Five of the 19 employees surveyed (26%) reported not attending any general training on TB in humans 

and elephants, including one employee each from the High and Medium Exposure groups and three

employees from the Low Exposure group. 

When asked about frequency of training, responses varied from never, once, annually, and every two 

years, across the three exposure groups. Only three employees (16%) reported annual training, two

employees from the High Exposure group and one person from the Medium Exposure group. 

Most employees were knowledgeable about activities that increase risk of TB transmission (68%), 

symptoms (80%), and what to do if they develop TB symptoms (95%). However, six employees in the 

Low Exposure group were not familiar with tasks that increase transmission risk. Employees in the 

High Exposure group had more knowledge about TB testing frequency than the other two groups 

where knowledge varied. 

Employee TB Testing

Employees reported varied TB testing frequency. Out of the nineteen employees surveyed, 21% 

reported never having a TST: one employee in the High Exposure group and three in the Low 

Exposure group. Of the 14 respondents who answered this question, the majority (64%) reported they 

did not have a pre-hire or baseline TST or other TB infection test at the time of hire, including one 

person in the High Exposure group. Sixty-three percent of employees reported having had an IGRA

since the start of this TB investigation at the zoo, including three employees in the High Exposure 

group, six in the Medium Exposure group, and three in the Low Exposure group.

Updated since November 2019 Site Visit

The zoo was responsive to the recommendations we provided at the November 2019 site visit closing 

meeting and in an interim letter dated January 6, 2020. Below is a summary of follow-up activities after 

our site visit in November 2019, as of May 2021.

TB Exposure Control Program

A new TB Exposure Control Program created in partnership with a contracted industrial hygienist 

outlined all administrative controls, PPE, facility upgrades, and ongoing activities. The Program has a 

TB Exposure Control Work Group that meets monthly. The Work Group has representation from 

elephant barn employees, operations, veterinary staff, and zoo administration. In addition, a contracted 

public health nurse with subject matter expertise in TB control participates in work group meetings, 

reviews TB symptom checks with employees diagnosed with LTBI and addresses questions or concerns 

from employees who enter the elephant barn and yard regarding TB exposure risk.

Under this program, access to the elephant barn and yard area is limited to only essential employees. No 

volunteers, guests, or nonessential employees are allowed to enter the area. All employees who enter the 

barn or yard are included in the TB Exposure Control Program. TB testing policies vary based on how 

frequently the staff person enters the elephant area. All new employees must be screened at the time of 
B-6

hiring; this may be a TST or IGRA screening test. All elephant area employees are screened quarterly 

using the IGRA screening test. Ancillary elephant area employees including those with regular but not 

prolonged contact with the elephants or who perform routine work in the elephant barn such as 

veterinary staff, operations, and maintenance, receive a semiannual IGRA screening test. Employees 

who work with nonhuman primates and hoofstock are screened annually using IGRA. Employees who 

do not work with elephants, primates, or hoofstock and do not work in the elephant barn do not need 

repeated TB screening after their initial screening before their hire date.

The zoo administration is responsible for providing information to all employees who enter the 

elephant barn or yard on the risks of TB exposure, how to mitigate and implement mitigation measures, 

and long-term effects of exposure. This information is also included in job descriptions and discussed 

with potential candidates during interviews. Employees are given the option to be reassigned if they do 

not wish to work in the elephant barn or yard following discussion of the risks. Training for new staff 

includes extensive training on TB Exposure Control Program elements in addition to baseline and 

ongoing surveillance testing. 

Since the site visit, one of the elephants was euthanized because of health concerns unrelated to TB, but 

the other elephant remains at the zoo. Antibiotic treatment for TB was initiated in this elephant; 

however, it was discontinued after seven weeks because the treatment side effects affected animal 

welfare, and the animal became noncompliant. The zoo has continued periodic trunk washes and the 

shedding of TB was observed to decline then cease during treatment but has since resumed. All strains 

have tested as non-drug resistant thus far. The zoo continues to monitor TB shedding in the elephant 

and drug resistance on a quarterly basis.

PPE Use 

After the site visit, the zoo updated its PPE policy so that all employees working in the elephant barn or 

yard were required to wear a powered air-purifying respirator (PAPR) for respiratory protection. This 

requirement was implemented because an additional staff person IGRA positive result following our

site visit. This staff person was IGRA negative during initial testing when TB infections were first 

identified, and but subsequently had an IGRA positive result on surveillance screening. During the 

period this person might have been exposed, tasks were completed in N95 respirators. Additionally, the 

coronavirus disease 2019 (COVID-19) pandemic’s effect on the PPE supply chain made it difficult to 

obtain N95 respirators. Therefore, the zoo implemented a policy that all employees working in the 

elephant barn or yard were required to wear PAPRs for respiratory protection.

Dedicated areas were constructed to allow for the proper donning and doffing of PPE. 

Employee Training on TB

Annual zoonotic disease training for zoological, operations, and veterinary staff has been updated to 

include more robust information about TB. All employees who enter the elephant barn or yard are 

provided annual in-depth TB training and meet with the county TB nurse to ask any specific questions.

Ventilation Assessment 

Separate ventilation systems were installed for the elephant housing area (first floor) and administrative 

areas located on the second floor. The new ventilation configuration allowed the elephant housing area 

to remain under negative pressure to the administrative areas to ensure air from the two areas do not 

mix. Pressure monitors were installed to enable employees to confirm the system is operating correctly.
B-7

The employees can activate a high-air-change flush to dilute the air in the elephant housing area before 

entry. 

Discussion 

This health hazard evaluation request concerned transmission of Mycobacterium tuberculosis (TB) from 

elephants to zoo employees who were working with and around elephants. In November 2019, we

conducted a site visit to provide technical assistance on how to prevent further TB infections in zoo 

employees. 

In previous TB outbreaks at zoos and sanctuaries, infected elephants have been treated with antibiotic 

protocols to varying degrees of success [Backues and Wiedner 2019]. In this case, zoo administration 

initially elected not to treat the infected elephants for several reasons including concerns about 

noncompliance from the animals due to the length of time they would need treatment and large 

quantity of medication they would need on a daily basis. Daily treatment posed an increased risk of 

additional TB exposure to elephant barn staff due to prolonged time in close contact needed to 

administer the medication. Animal welfare was also a concern due to potential for side effects from the 

medications. Finally, zoo administration was concerned about the potential for the development of 

antibiotic-resistant TB strains. The decision not to treat was taken into consideration as we conducted 

the site visit and in the recommendations we provided because it was unknown how much bacteria was 

being shed into the environment or if bacterial shedding would increase over time without treatment. 

During the site visit, we reviewed policies and protocols for TB surveillance and PPE use, conducted a 

ventilation assessment of the elephant barn and yard, observed work practices and PPE use, and 

administered an employee survey on TB knowledge, prevention measures, and health status. Key

findings included employees who primarily worked in the elephant barn and had contact with elephants 

were more likely to test positive for TB infection, the respiratory protection program and TB 

surveillance program could be improved to better protect employees from TB transmission, the 

ventilation system in the elephant barn needed upgrading to prevent air from the elephant area to enter 

employee work spaces, PPE supplies including N95 respirators and gloves were being stored inside the 

barn entrance areas leaving them vulnerable to contamination and putting employees at risk of exposure 

to contaminated air, and employees needed more robust and frequent training on TB risk and 

prevention. 

We recommended several options to improve each of these key findings. Reduce potential employee 

exposure to M. tuberculosis by ceasing all nonessential tasks, removing all nonessential items from the 

elephant barn, limiting the number of employees who work in the barn, and by limiting aerosol 

generating activities. Implement an OSHA compliant Respiratory Protection Program and TB 

surveillance program and requiring participation from all employees at risk of exposure to TB. Assign or 

hire a person knowledgeable in occupational health to administer these programs. Include annual 

quantitative respirator fit testing and a training program to educate employees on how to properly use 

PPE as well as on key concepts related to TB disease and prevention. Employees and volunteers should 

receive baseline TB testing and screening using an IGRA test as appropriate based on exposure risk. 
B-8

According to the 2017 ATS/IDSA/CDC clinical practice guidelines, IGRA is generally preferred over 

TST for TB diagnosis in persons over aged 5. The TST is considered an acceptable alternative, though, 

in situations where IGRA testing is not available or considered too costly or burdensome. Program 

administrators should keep adequate record keeping for all test results. Ensure standard procedures for 

PPE use are identified, communicated to employees, and enforced by supervisors.

Ventilation assessment recommendations included ventilating the entrance hallway, locker room, 

restroom, office, and kitchen area on the upper floor of the elephant barn, to reduce the potential for 

exposure to TB. Maintaining the elephant housing area in a negative-pressure zone will prevent 

contaminated air from entering other areas of the building. Activation of the high-air-change flush 

before elephant care staff enter the housing area will also help reduce the potential for exposure to TB. 

All PPE should be properly stored in a clean environment. The construction of the dedicated areas for 

donning and doffing PPE will also help mitigate the potential for exposure. 

At the time of the site visit, the zoo administration was in the process of updating the respiratory 

protection program and TB surveillance program and had implemented mandatory use of N95 

respirators for employees entering the elephant barn. However, an additional staff person tested 

positive on the IGRA test after the site visit. This staff person was a zookeeper who worked exclusively 

in the elephant area. They had a negative IGRA test result when the TB infections were first identified, 

but subsequently had an IGRA positive result on surveillance screening. It is unknown whether this 

person was exposed to TB before N95s were routinely used in the elephant barn or whether the 

exposure occurred after N95s were required, but the respirator was used incorrectly. This additional 

case of LTBI further reinforced the need for ongoing training among zoo employees and volunteers 

and a strong TB exposure control program. 

At time of this report, the zoo administration had taken several actions to mitigate the risk of TB 

exposure including implementing a TB Exposure Control Program overseen by a Work Group who 

oversees all administrative controls, PPE, facility upgrades, and ongoing activities.

Limitations 

Limitations of the employee survey conducted included a small survey sample size limited to a

convenience sample of employees available at the time of the site visit. TB test results were not available 

for everyone surveyed. The evaluation occurred at a point in time and might not be indicative of 

practices at other times (e.g. PPE use).

Conclusions

The findings of this health hazard evaluation support the recommendation that a robust TB control

program should be implemented at zoos and other facilities that house elephants. At minimum, the TB 

control program should include a ventilation assessment, TB surveillance program and respiratory 

protection program, sustained use of appropriate fit-tested respiratory protection (N95 respirator or 

equivalent or higher-level respirator) for anyone who has contact with elephants or works in their 

enclosure, and a comprehensive employee training program. Although the prevalence of TB among 
B-9

captive elephants in the United States is thought to be relatively low, diagnosing TB in elephants is 

difficult, and the gold standard test has low sensitivity; therefore, elephant cases might be missed and 

could result in employees being unknowingly exposed to elephants with active TB disease.

Implementing PPE use early in these settings will help to mitigate the potential for staff exposure to TB 

during the lag time between when an elephant starts shedding TB and a positive trunk wash culture 

result. The ongoing efforts of this zoo in implementing measures to protect current and future 

employees and volunteers from TB exposure without compromising animal welfare or the relationship 

between the caretakers and the animal illustrates that this can be accomplished successfully. 
C-1

Tables

Table C1. Demographic characteristics of survey participants (n=19) 

No. (%)

Sex

 Male 9 (47)

 Female 10 (53)

Median Age (years) 42 (range = 28–60)

Median Tenure in Current 

 Job (years) 3.5 (range = 0.1–23.3)

Median Total Tenure (years) 8.2 (range = 0.2–30.7)

Median Hours Worked per 

 Week 40 (range = 24–65)

Job Category

 Zookeeper 5 (26)

 Veterinary staff 5 (26)

 Operations/maintenance 9 (47)

 staff

TB IGRA blood test status

 Negative 8 (42)

 Positive 4 (21)

 Not tested or Missing 7 (37)

 information
C-2

Table C2. Exposure group associated with positive TB blood test result 

Exposure Description IGRA Blood Test Result* Total 

Group # Positive # Negative No results

available

High Elephant barn 3 0 1 4

primary workplace

AND

Direct contact with

elephants

Medium Elephant barn 1 5 0 6

primary workplace

OR

Direct contact with

elephants

Low Neither elephant 0 3 6 9

barn primary 

workplace 

AND

No direct contact

with elephants

*Fishers exact test p = 0.0364
D-1

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