Awareness of and Defense Against Mycobacterium Tuberculosis
In the Practice of Gross Pathology
Imagine you are performing your daily duties as a dedicated pathlogists’
assistant when a routine specimen of a testicular mass arrives from the operating
room for frozen section evaluation. You process it like any other specimen that a
surgeon has sent requesting this type of diagnosis; you probably slice through the
specimen, photograph the mass, describe it, and freeze it. You use pressurized quick -
freeze spray in the cryostat, and you also use an aerosol cleaner type spray to clean
the area after you are finished photographing and grossing the specimen. Almost
simultaneously the pathologist informs you and the surgeon that the mass, which
grossly appeared to be some type of tumor, shows “granulomatous inflammation”.
Although this diagnosis can indicate various disease processes, your first thought is-
“Tuberculosis!” and immediately after- “I’ve just sprayed it all over the place!!”
When the diagnosis is relayed to the surgeon, he replies something to the effect of, “I
had a feeling that’s what it was,” which causes you to grimace in frustration and
anger. Does this type of scenario occur in the surgical pathology laboratory? Yes--
all too frequently. Should this type of scenario happen? Absolutely not. The goal of
this paper is to review the danger of Mycobacterium tuberculosis to the surgical
pathology staff, and to promote minimization of this danger by education and
improved laboratory practices.
While performing traditional and routine duties in the gross cutting room and
during autopsy, the Pathologists’ Assistant faces a spectrum of dangers, including,
but not limited to: blood-borne pathogens, exposure to toxic chemicals, mechanical
injuries from specimens or tools of the trade, and even radiation exposure. Although
formalin exposure and the risk of HIV infection are the most emphasized
occupational hazards in our profession, perhaps the most insidious and under
recognized threat the pathology staff faces is the aerosolization of Mycobacterium
tuberculosis. OSHA mandates yearly formaldehyde and blood-borne pathogen
training for employees exposed to these agents, but there is currently no required
standard for the education and training of laboratory staff who are at risk for
exposure to M. tuberculosis. Some health-care institutions require annual TB
training for all employees, but some only require it for staff who come into contact
with live patients. Despite this lack of consistency and lack of current government
rules to follow, we, as responsible and conscientious members of our profession,
need to be aware of the threat of tuberculosis, and be responsible for protecting others
and ourselves from it.
Robert Koch stated in 1882 that, “If the number of victims which a disease
claims is the measure of its significance, then all diseases…must rank far behind
tuberculosis.”(1) One hundred twenty years later, even after the discovery of anti-
tuberculosis drugs, the World Health Organization estimates that globally there are
nearly 2 million deaths from tuberculosis annually.(2) The United States is not
spared from this epidemic, as presently an estimated 13 million U.S. adults are
infected with TB.(3) M. tuberculosis is an airborne infection, carried by droplet
nuclei measuring 1-5 microns in size.(4) Not only can these droplet nuclei be
released from an infected person’s respiratory system during coughing, singing,
sneezing, or speaking,(4) but they can also become aerosolized during certain
medical procedures performed on an infected patient’s blood, sputum, and tissues.
Because tuberculosis infection is sometimes latent, miliary (disseminated by the
bloodstream to sites other than the lung), or both, it is not always suspected in an
infected patient. This creates a greater risk to pathology and autopsy staff since they
usually do not take TB precautionary measures when working with infected tissue
unless the disease is known or suspected. It is estimated that as many as half of the
cases of pulmonary tuberculosis seen at autopsy have been diagnosed there (the
autopsy room) for the first time.(5) Considering this information, it is clear that
anyone working in the field of pathology should be aware of the risks of TB
transmission from human tissues.
What are the specific risks?
Frozen sectioning of tissue specimens containing tuberculosis poses a hazard
to the cryostat operator and anyone standing close-by, especially when a quick-freeze
spray is used during the procedure. If the specimen in question is suspected by the
pathologist or the surgeon to contain the bacterium, then the frozen section should be
deferred or done only if absolutely necessary. In an article for Human Pathology,
Dr. Jerome Smith recounts his first encounter with tuberculosis in a frozen section
and stresses how he was reprimanded for cutting infected tissue on a cryostat.(6)
The scenario regarding the granulomatous testicular mass in the first paragraph
actually occurred less than a year ago in the hospital where I’m currently employed.
If a frozen section must be done on a suspicious specimen, persons present within the
vicinity of the cryostat should wear an appropriate respirator or mask (discussed
later), and care should be taken by the cryostat operator to generate as little aerosol as
possible during the procedure. A modicum of caution should be used while
performing all frozen sections, since many times TB is not even suspected until the
frozen section diagnosis is made, as in the testicular mass case.
Three cases of TB infection associated with frozen section preparation were
reported in 1981(7-8). Two pathologists present during frozen section preparation of
infected lung tissue converted to PPD positive status three months after the
procedure. During the procedure, a heavy aerosol was said to have been created due
to use of a compressed gas coolant.(7) The third case involved a histotechnologist’s
conversion to PPD positive status after also using a compressed gas coolant to freeze
a pulmonary nodule.(8) In this case, the patient from whom the pulmonary nodule
was taken was suspected of having bronchogenic carcinoma, so the frozen section
was probably considered innocuously routine, until the surprise diagnosis of
tuberculosis was made. Both of these articles warn of the creation of aerosol during
frozen sectioning, and the need for caution when using compressed coolant. One of
the authors went further to state, “This technique (gas coolant spray to promote quick
freezing) should be used with extreme caution, if it is used at all.”(7)
Recent interest has been generated regarding occupational hazards of TB
from two articles which describe M. tuberculosis transmission from cadaver to
funeral home worker during the embalming process.(9-10) The procedures used
during embalming are similar and related to those used during autopsy, and these
additional cases support the evidence that TB can be aerosolized in a way that does
not require a living host for transmission via a functioning respiratory system. The
first case describes the transmission of M. tuberculosis from a 35-year-old male
patient with AIDS to a 45-year-old male embalmer with no history of HIV or TB.
The methods used to support this claim included the use of RFLP (restriction
fragment length polymorphism) analysis of genomic DNA taken from TB isolates
from both individuals. The results showed an identical DNA fingerprint, that when
compared to other M. tuberculosis DNA patterns from the geographic area, was
shown to be unique only to the two patients identified by this study. This molecular
data strongly supports “…the hypothesis that M. tuberculosis was transmitted from
the cadaver to the embalmer during the embalming process.”(9) The report also
states that, “…bacteremia with M. tuberculosis is more common in patients who have
AIDS…and the presence of bacteremia may have increased the likelihood that
aerosols generated during embalming were infectious.” This is a valid concern to
keep in mind while autopsying AIDS patients with or without TB.
The second case(10) used microbiologic and molecular techniques to compare
the DNA fingerprints from the TB isolates taken from the cadaver and the embalmer.
Both isolates were shown to be a rifampin mono-resistant (RMR) strain of
tuberculosis, and more importantly they both had the same DNA fingerprint. This
study described the embalming process used during this particular case in some
detail, and after considering several possibilities, concluded that the most likely mode
of TB transmission between cadaver and embalmer was aerosolization of the tubercle
bacilli from the suction material generated during embalming. This information can
be applied to the practice of autopsy, as stated by Nolte in a paper on autopsy
biosafety: “Given the uniform use of oscillating saws and spray and aspirator hoses
by prosectors, a fair assumption is that all autopsies generate potentially infectious
Jerome Smith, MD, a pathologist at the University of Texas stated that,
“Some mighty pathologists of yore succumbed to the disease (tuberculosis) that they
had presumably contracted at the autopsy table.”(6) Although a routine, diagnostic
and educational tool used in the practice of Pathology, the autopsy procedure may be
the greatest source of TB exposure and subsequent infections that members of the
pathology profession encounter. Nonparticipating observers are at risk as well if they
share the same air space as the cadaver. As Nolte states, “An autopsy is an
exceptionally efficient method of transmitting tuberculosis from decedent to those
present in the dissection room.”(11) This statement may sound facetious, but it is
most unfortunately factual.
Several papers have demonstrated that even a brief exposure to TB during an
autopsy on an infectious individual carries a high risk of infection.(11-13) A report
of MDR-TB (multi-drug resistant tuberculosis) transmission on persons exposed in a
New York medical examiner’s office showed an increased rate (28%) of skin test
conversion to PPD positive status among workers involved in autopsies on MDR-TB
positive patients.(14) In a study on nosocomial (hospital acquired) transmission of
TB, it was reported that three of five employees present during an autopsy on an
individual with unsuspected disease had skin test conversions after the procedure.(5)
Another autopsy worker who had a prior BCG vaccination (which causes skin test
results to always read positive) developed active TB five months after the infectious
autopsy which is clinically consistent with becoming infected at the time of the
autopsy. An even more frightening article in the Annals of Internal Medicine
reported that none of the workers caring for a particular patient with unsuspected
disease before his death showed a skin test conversion later on; while after a three
hour autopsy on this patient, all five previously negative employees present during
the autopsy subsequently converted to positive PPD status.(13) All five of these
employees used double tie standard surgical masks during the autopsy. Two of the
autopsy workers had positive sputum cultures eight weeks after the autopsy. The
cultures from these two workers and the source patient yielded identical DNA
fingerprints. Fortunately, all five of the skin test converters were treated with
isoniazid or isoniazid and rifampin and did not develop active TB. The article
concludes: “A patient who did not transmit tuberculosis before death released a
prodigious number of tubercle bacilli during autopsy.” The data discussed here
should certainly alert the reader to the immense need for awareness to and personal
protection against TB during all autopsies.
Is formalin fixation adequate protection from infection?
When dealing with infectious tissues and specimens containing blood and
body fluids, a popular practice is to “throw it in formalin” based on the assumption
that formalin is toxic and will kill or disable whatever pathogens are present within
the tissue and associated blood and body fluids. Formaldehyde is a toxic chemical,
which is known to be bactericidal and virucidal against certain pathogens, but should
not be taken for granted as an effective weapon against all infectious agents,
including TB. Collins writes, “It is generally assumed that M. tuberculosis is not
viable in formalin fixed material, including lung tissue from tuberculosis patients,
and that such material may therefore be handled without risk of infection. The data
supporting this assumption are however, very weak.”(12) A 1951 study reported
cultures from embalmed bodies yielding isolates of M. tuberculosis as long as 60
hours after fixation.(15) In the most recent study of the effect of formalin on M.
tuberculosis, the authors were not able to culture TB in formalin-fixed tissue,
however, they concluded, “…the true disinfection efficacy of formalin for tissues
infected with M. tuberculosis is unclear. Larger, prospective studies…are needed to
establish guidelines to ensure the safety for those handling infected, fixed tissue.”(16)
Jerome Smith gives us an even more descriptive scenario to consider: “Dense
fibrocaseous lesions seen in old chronic active intrapulmonary or plural tuberculosis
may provide sanctuaries in which tubercle bacilli can survive fixation and
decontamination…”(6) Considering the available data, it seems prudent to be
cautious even with formalin-fixed tuberculous specimens, and to consider “fixed” TB
specimens as potentially infectious as fresh specimens containing the disease.
What is the government doing to protect us?
At the time of this writing, “Guidelines for Preventing the Transmission of
Mycobacterium tuberculosis in Health-Care Facilities, 1994”, has been published by
the CDC.(4) This publication consists of recommendations and reports—not laws or
requirements. In 1996, OSHA published a directive entitled, “Enforcement
Procedures and Scheduling for Occupational Exposure to Tuberculosis”.(17) This
directive requires employers to schedule routine PPD testing and medical follow-up
for employees exposed to TB; but there are not any laws yet requiring employers to
help prevent and protect health-care workers from initial exposure to TB. The OSHA
rule on occupational exposure has been in the proposed stage since 1997.(3) There is
a need for increased infection control guidelines and enforcement procedures within
autopsy rooms and health-care facilities in general. The United Kingdom requires
that cultures and specimens containing TB, as well as autopsies on known TB
patients be handled in Containment Level 3 laboratories.(12) The U.S. has no such
requirements, and most hospital laboratories in this country are only Level 2
Biosafety facilities. Our current CDC guidelines are in place but are not necessarily
being followed. OSHA states: “…in every recent TB outbreak investigated by the
CDC, noncompliance with CDC’s TB control guidelines was evident.”(18)
Guidelines alone are not enough to combat the TB epidemic; rules and enforcement
procedures are desperately needed as well.
OSHA’s Proposed Rule:
The proposed standard on occupational exposure to TB covers workers in a
variety of occupational settings, including health-care facilities. The standard
recognizes the danger of TB, the role of HIV infection in increasing the efficacy and
frequency of TB transmission, and the additional danger of multi-drug resistant
TB.(18) The standard calls for employers to adhere to several important and urgently
needed measures, including: identifying all employees at risk of TB exposure and
listing job tasks which involve higher risks of transmission (autopsy is recognized in
this document as a high-hazard procedure), developing an exposure control plan
which includes TB education and training for employees, prompt identification of
individuals with infectious TB, and providing employees with routine skin testing.
The standard also requires employers to utilize proper work practices and engineering
controls in places where patients with TB or their specimens can be found. These
types of controls include maintaining negative pressure isolation rooms, and
providing employees who may be exposed to TB with acceptable respirators;
specifically either NIOSH approved HEPA (high efficiency particulate air) masks, or
N95 respirators. The standard also recommends but does not require additional anti-
TB controls, including HEPA filtration to clean air systems in which TB is carried,
and UVGI (ultra violet germicidal irradiation) systems to kill or inactivate airborne
What can we do to protect ourselves?
It is more than evident that we as pathologists’ assistants cannot take a
passive role in the fight against TB exposure or wait for directives and new policies
to be handed down to us from our employers or the state and federal governments.
We must be proactive in protecting ourselves against this microscopic, insidious, and
practically ubiquitous infectious organism. There are several types of actions we can
take in order to lessen TB exposure from specimens and autopsy cases that we may
face at any time due to the nature of our specific occupational duties. The easiest and
most obvious form of protection is the use of personal respirators. Wearing a mask is
appropriate whenever exposure to TB is even remotely anticipated. Standard surgical
masks are not adequate protection against TB, as we have seen from the Templeton
study(13). N95 respirators are practical and less costly than HEPA masks, and are
efficient in filtering the infectious droplet nuclei from the air we breathe.(4) These
masks require fit testing before wearing, and your facility should provide this service
as well as providing the masks for employee use. Other work practices we can utilize
to guard against TB include cutting specimens under a hood or very close to a vent,
and by not using gas coolant during frozen sections, as discussed earlier. It is also
important to comply with scheduled TB skin testing, which every health-care facility
is required to provide (17), and to report any confirmed or suspected TB exposure of
employees or others to the immediate head of your department and to infection
control services. We should also try to be active in educating other staff of the
dangers of TB transmission, and to try to become involved in developing TB
prevention plans and policies for the laboratory and autopsy room. Misconceptions
or ignorance of the modes of TB transmission discussed in this paper are prevalent
and must be overcome.
Perhaps the most important defenses against TB are heightened awareness
and your own common sense. For example, if you receive a surgical specimen for
frozen section that you determine to be suspicious, relay your fears to the pathologist
on duty. The surgeon can be asked for additional information, and the frozen section
may be deferred, or another procedure such as smear or touch-preparation of the
lesion can be performed. Any lesion which is soft, granulomatous-appearing, and
especially caseous-appearing (resembling crumbly or liquefied cheese) should be
treated as suspicious, even if it is not from the lung.
As health-care workers, M. tuberculosis is a danger we face from a variety of
sources; it does not matter whether we work in busy city hospitals or facilities located
in sparsely populated areas. As Pathologists’ Assistants, we face unique and serious
risks of TB transmission during virtually every step of human tissue examination and
processing. If the government and health-care facilities in general have shown less
recognition and given less emphasis to these risks, then conversely we should be
more motivated to promote awareness of these risks and increase our own
responsibilities regarding protection of our coworkers and ourselves. Facts regarding
specific TB transmission in the pathology lab and autopsy room should become part
of our ongoing collective professional knowledge. Educating others, improving our
work practices, and contributing to new policies in order to lessen the risk of
exposure to TB will make our work areas much safer places. This in turn will enable
us to provide better patient care, thereby making us all the more valuable as
professionals who represent the field of Pathology.
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incidence, prevalence, and mortality by country: WHO Global Surveillance and
Monitoring Project. JAMA 1999; 282:677-686.
3. Occupational exposure to tuberculosis-Proposed Rule. OSHA Federal Register
62:54159-54309; 29 CFR Part 1910. October 17, 1997.
4. Centers for Disease Control. Guidelines for preventing the transmission of
Mycobacterium tuberculosis in health-care facilities, 1994. Morbidity and
Mortality Weekly Report 1994; 43:1-132.
5. Kantor HS, Poblete R, Pusateri SL. Nosocomial transmission of tuberculosis from
unsuspected disease. The American Journal of Medicine 1988; 84:833-838.
6. Smith JH. The hazard to pathologists from tuberculous specimens. Human
Pathology 1996; 27:1251-1252.
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Morbidity and Mortality Weekly Report 1981; 30:73-74.
8. Duray PH, Flannery B, Brown S. Tuberculosis infection from preparation of
frozen sections. New England Journal of Medicine 1981; 305:167.
9. Sterling TR, Pope DS, Bishai WR, et al. Transmission of Mycobacterium
tuberculosis from a cadaver to an embalmer. New England Journal of Medicine
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tuberculosis to a funeral director during routine embalming. Chest 2001; 119: 640-
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13. Templeton GL, Illing LA, Young L, et al. The risk of transmission of
Mycobacterium. Annals of Internal Medicine 1995; 122:922-955.
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17. Enforcement procedures and scheduling for occupational exposure to tuberculosis.
OSHA directives CPL 2.106. February 9, 1996.
18. Occupational exposure to tuberculosis. Unified Agenda 1218-AB46-2038. OSHA
CFR Citation: 29 CFR 1910.1035. December 5, 2001.