Is cryotherapy treating or infecting?
The preservation of microorganisms (especially viruses) in liquid nitrogen means that without adherence to proper infection control common cryotherapeutic procedures are an infection risk
MJA 1996; 164: 263
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©MJA1997
Of all the cryotherapeutic freezing agents, liquid nitrogen is the
agent of choice. The properties which have made liquid nitrogen
popular in clinical medicine include its low boiling point (-196oC) and inertness, relatively easy availability and
handling, affordability and good compliance. Liquid nitrogen
causes cellular death by formation of intracellular and
extracellular crystals (inducing dehydration), and damage to blood
vessels.2,3 Irreversible
vascular occlusion results from erythrocyte accumulation,
thrombus formation and diapedesis of blood elements, eventually
causing tissue necrosis.2,3
Other studies have also shown that infectious viruses can be isolated
from the liquid nitrogen in containers storing vials of preserved
virus and without any drop in viral titre.8,10 Transmission of viruses,
particularly human papillomavirus (HPV), via contaminated
inanimate objects has also been confirmed.11 Liquid nitrogen was implicated in
cases of HPV cross-infection when liquid nitrogen swabs were used to
treat patients with warts and then used to treat other patients with
non-infectious dermatological lesions.12
The risks of cross-infection in medical procedures have recently
become a critical public health issue in Australia after four people
were diagnosed HIV positive allegedly following simple surgical
procedures in a doctor's office,13
and in the United States where transmission of HIV from health
care worker to patient occurred in a dental practice.14 Therefore, it is essential that
all health care workers understand the principles of infection
control and practise them at all times.
Sepehr N Tabrizi
Suzanne M Garland
Reprints: Dr S N Tabrizi, Department of Microbiology, The Royal
Women's Hospital, Carlton, VIC 3053.
©MJA 1997
<URL: http://www.mja.com.au/>
© 1997 Medical Journal of Australia.
Cryotherapy has become an indispensable tool in the treatment of
benign dermatological lesions and some premalignant and malignant
lesions.1 As early as the
mid-1800s, clinicians used freezing agents as ablative therapy;
initially using a salt-ice mixture which was later replaced by
liquefied gases, such as air, oxygen and nitrogen. Other freezing
agents still in use include liquid refrigerants and solid carbon
dioxide.1 Of all the cryotherapeutic freezing agents,
liquid nitrogen is
the
agent of
choice.
In clinical practice, liquid nitrogen can be applied by various
methods: cryosurgical spray units, cryoprobes or cotton-tipped
swabs.4 Swabbing is the
simplest method of application, but cryospray units or cryoprobes
are more appropriate in settings where liquid nitrogen or nitrous
oxide is used more frequently.
It is often not recognised that, apart from causing tissue
necrosis, liquid nitrogen is also an excellent agent for cryo
preservation of biological material (e.g., for forensic analysis)5 and, in particular,
preservation of infectious microorganisms (including viruses).6-8 Therefore, without
adherence to correct infection control procedures when using
cryotherapy (and without adequate sterilisation of cryotherapy
accessories), staff could transmit infection from patient to
patient (see Box). For example, if a common receptacle filled
with liquid nitrogen is used for every patient throughout a clinic and
multiple swabs are dipped into it, the receptacle can be contaminated
with patients' microbial flora. Moreover, if any unused liquid
nitrogen is returned to the main storage container, the entire tank
can become contaminated. A recent study from the United Kingdom,9 where infection control
procedures broke down, reported hepatitis B virus contamination of a
cryopreservation tank used for storage of bone-marrow or stem cells.
Six patients developed icteric acute hepatitis B infection
subsequent to transplantation.9
Senior Research Officer
Department of Microbiology, The Royal Women's Hospital, Carlton,
VIC.
Director of Microbiology
Department of Microbiology, The Royal Women's Hospital, Carlton,
VIC.
References
- Sepehr N Tabrizi
- Suzanne M Garland