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Is cryotherapy treating or infecting?

Sepehr N Tabrizi and Suzanne M Garland
Med J Aust 1996; 164 (5): 263-264.
Published online: 4 March 1996

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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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. 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

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

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
Senior Research Officer
Department of Microbiology, The Royal Women's Hospital, Carlton, VIC.

Suzanne M Garland
Director of Microbiology
Department of Microbiology, The Royal Women's Hospital, Carlton, VIC.  

References
  1. Kuflick EG. Cryosurgery updated. J Am Acad Dermatol 1994; 31: 925-944.
  2. Kreyberg L. Local freezing. Proc R Soc Lond [Biol] 1957; 147: 546-547.
  3. Kreyberg L. Statis and necrosis. Scand J Clin Lab Invest Suppl 1963; 15 Suppl 71: S1-S26.
  4. Allington HV. Liquid nitrogen in the treatment of skin disease. Calif Med 1950; 72: 153-155.
  5. Camp FR, Ellis FR, Shields CE, Werline MM. Long-term preservation of biologicals for the forensic laboratory and their areas of application. J Forensic Sci 1968; 13: 419-432.
  6. Hildebrant RJ, Sever JL, Anderson B. Preservation of infectious cytomegalovirus. Proc Soc Exp Biol Med 1968; 129: 504-506.
  7. Jarvis JD, Wynne CD, Telfer ER. Storage of bacteria in liquid nitrogen. J Med Lab Technol 1967; 24: 312-314.
  8. Schafer TW, Everett J, Silver GH, Came PE. Biohazard potential: recovery of infectious virus from liquid nitrogen of a virus repository. Health Lab Sci 1976; 13: 23-24.
  9. Tedder RS, Zukerman MA, Goldstone AH, et al. Hepatitis B transmission from contaminated cryopreservation tank. Lancet 1995; 346: 137-140.
  10. Jones SK, Darville JM. Transmission of virus particles by cryotherapy and multi-use caustic pencils: a problem to dermatologists? Br J Dermatol 1989; 121: 481-486.
  11. Massing A, Epstein W. Natural history of warts; a two-year study. Arch Dermatol 1968; 87: 300-310.
  12. Charles CR, Sire DJ. Transmission of papovavirus by cryotherapy applicator. JAMA 1971; 218: 1435.
  13. Chant K, Lowe D, Rubin G, et al. Patient-to patient transmission of HIV in private surgical consulting rooms [letter]. Lancet 1993; 342: 1548-1549.
  14. Centers for Disease Control. Update: investigations of patients who have been treated by HIV-infected health-care workers. MMWR Morb Mortal Wkly Rep 1992; 41: 344-346.

Reprints: Dr S N Tabrizi, Department of Microbiology, The Royal Women's Hospital, Carlton, VIC 3053.

©MJA 1997

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