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Frozen Sectioning and Tuberculosis Exposure: Risk Factors and Preventive Measures

Updated: Mar 30, 2023

Frozen sectioning is the process by which a fresh tissue sample is rapidly frozen, sliced, and prepared for a pathologist to analyze, usually in cases where a patient is actively being operated on by a surgeon (Mayo Clinic Staff n.d.). Frozen sectioning is an invaluable technique that helps doctors make evidence-based decisions for their patients as fast as possible and helps patients undergo fewer surgeries as a result (Mayo Clinic Staff n.d.). However, the rapid processing of fresh tissues, and the time constraints posed by situations where frozen sectioning is needed, increases the risk of disease transmission from the tissue sample to the healthcare staff. In fact, those working in a frozen section lab have the highest risk of infection exposure in the entire field of surgical pathology (Izak B. Dimenstein n.d.).

Mycobacterium tuberculosis, more commonly known as Tuberculosis (TB), is one such disease that can be spread during the frozen sectioning process. TB is an extremely dangerous bacterial infection that normally impacts a patient’s lungs, but can also impact the kidneys, spine, and brain (Centers for Disease Control and Prevention 2016). TB is characterized by a severe cough lasting at least 3 weeks, coughing up blood or sputum, weight loss, chills, fever, and loss of appetite (Centers for Disease Control and Prevention 2022). TB is also known for its long latency period, in which the disease has already infected a host, but signs and symptoms have not yet presented. Some people with latent TB never develop the disease, while others, particularly those with weakened immune systems, may develop active TB (Centers for Disease Control and Prevention 2020).

TB bacteria mainly spreads through the air, and only someone with active TB can transmit the disease. When someone with active TB coughs, sneezes, speaks, sings, or otherwise expels air from their lungs, the bacteria can infect another person once enough exposure time has passed (Centers for Disease Control and Prevention 2016). TB can also spread if the air containing the TB bacteria is moved and inhaled, as is the case with exposure to TB in frozen sectioning pathology labs. Simply cutting or trimming a frozen sample in a cryostat, according to Dr. Dimenstein, is enough to release micron-sized fragments of the sample that are then capable of traveling through the air and infecting an individual (Izak B. Dimenstein n.d.). According to the Centers for Disease Control and Prevention (CDC), TB bacteria can be found in sputum, gastric lavage fluids, cerebrospinal fluid, urine, and in bodily tissues, so bodily fluids—not just bodily tissues—present a hazard. The bacteria can survive in heat-fixed smears, as well as the cold temperatures necessary for the frozen sectioning procedure (Centers for Disease Control and Prevention 2012). Another risk factor for TB exposure in a frozen sectioning lab is the use of freeze spray. Some pathologists and pathology technicians utilize freeze spray, an aerosol product, when preparing frozen sections for slicing in the cryostat’s microtome component. The freeze spray can exacerbate the amount of diseased sample fragments entering the air, potentially leading to infection. As such, all workers utilizing freeze spray when working on frozen sections should use caution and undertake preventive measures to prevent the spread of disease throughout the lab, and some labs even prevent the use of aerosol-producing manipulations of specimens (Centers for Disease Control and Prevention 2019). The CDC also notes that accidental needle-sticks are a recognized hazard, so TB can potentially spread through injuries involving contaminated sharps and sharp tools, though direct contact with a non-injurious surface, such as someone’s hand, clothes, or a toilet does not present a TB hazard ((Centers for Disease Control and Prevention 2016), (Centers for Disease Control and Prevention 2012)).

In order to mitigate the risk of TB transmission among laboratory workers, the Association of Public Health Laboratories (APHL) recommends that all lab workers knowingly researching or handling samples with TB work in a Biosafety Level 3 (BSL-3) laboratory [CITE]. The US Department of Health and Human Services (HHS) classifies a BSL-3 as a lab “used to study infectious agents or toxins that may be spread through the air and cause potentially lethal infections”. In such labs, among other requirements, all experiments are performed in biosafety cabinets, the lab environment is designed to be easily decontaminated, and the labs use a directional air flow to stop air from the lab from entering non-lab environments, such as hallways (US Department of Health and Human Services 2019). In addition, personal protective equipment (PPE) in the form of a solid, disposable gown, gloves, and an N95 or N100 respirator are required. All PPE must be removed upon leaving the BSL-3 lab and placed into specific bags for disposal (Association of Public Health Laboratories n.d.)

In cases where TB infection of a sample is not known ahead of time, the CDC recommends the following course of action. First and foremost, given the increased risk of contracting TB in healthcare settings, such as a pathology lab or frozen sectioning pathology lab, all healthcare workers should undergo a baseline TB screening and an

individual risk assessment. Should an employee be exposed to TB, or possibly exposed to TB, the baseline screening and risk assessment will be compared to the postexposure screening and testing samples taken later (Centers for Disease Control and Prevention 2019). Also, the baseline screening considers whether the employee has no prior TB diagnosis, a latent TB diagnosis, or active TB, all of which will determine the recommended course of action post exposure. If the first postexposure test comes back negative, then another test should be administered 8-10 weeks later (Centers for Disease Control and Prevention 2019). If the test comes back positive, then a symptom evaluation and chest radiograph is performed to diagnosis TB. Cases of active, even latent, TB can be treated, but preventive measures remain of top priority in order to stop larger outbreaks and epidemics from occurring (Centers for Disease Control and Prevention 2019).


Association of Public Health Laboratories. n.d. "Laboratory Safety: Work Practices for Mycobacterium tuberculosis." APHL Infectious Disease Programs. Accessed November 2, 2022. TB Lab Safety TrainerNotes.pdf.

Centers for Disease Control and Prevention . 2012. Interim Laboratory Biosafety Guidance for XDR Mycobacterium tuberculosis strains. September 1. Accessed November 2, 2022. Interim Laboratory Biosafety Guidance for Extensively Drug-Resistant (XDR).

Centers for Disease Control and Prevention. 2016. Basic TB Facts. March 20. Accessed October 31, 2022. Basic TB Facts

—. 2016. Exposure to TB. March 21. Accessed November 2, 2022. Exposure to TB


—. 2020. Latent TB Infection and TB Disease. December 11. Accessed November 1, 2022. Latent TB Infection and TB Disease.

Centers for Disease Control and Prevention. 2019. Morbidity and Mortality Weekly Report May 17, 2019. Morbidity and Mortality Weekly Report, Washington, DC: Centers for Disease Control and Prevention, 439-443. Accessed November 3, 2022. Tuberculosis Screening, Testing, and Treatment of U.S. Health Care Personnel.

—. 2022. Tuberculosis (TB) Signs and Symptoms. May 3. Accessed November 1, 2022. Signs and Symptoms.

Izak B. Dimenstein, MD, PhD, HT (ASCP). n.d. Prevention of infection exposure during frozen section. Accessed October 20, 2022. Prevention of infection exposure during frozen section.

Mayo Clinic Staff. n.d. Frozen Section Pathology Lab. Accessed October 20, 2022. Frozen Section Pathology Lab.

US Department of Health and Human Services. 2019. Biosafety Level Requirements. September 25. Accessed November 2, 2022. Biosafety Level Requirements.


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