Alternative Room Disinfection Modalities –Pros and Cons - Use of Biocidal Surfaces for Reduction of Healthcare Acquired Infections - page 195

One of the major reasons that researchers are exploring the use of additional
treatment modalities such as UVC irradiation and chemical fumigation is the belief
that spore forming microbes such as C. difficile may be difficult to control using
conventional environmental disinfection methods [ 30 , 33 ]. Microbial spores pre-
sent a particular challenge because their inner and outer coats are highly resistant to
inactivation by chemical and physical means. Furthermore, during sporulation, the
microbe may be able to repair the damage from the germicidal treatment [ 90 ].
Moeller et al. found that certain metabolites such as cysteine that are released
during sporulation, do reduce the ability of UVC to inactivate B. subtilis spores.
In addition, if these spores had been previously desiccated, the lowered RH in the
spores further reduced the effectiveness of the irradiation. The authors identified
similar problems when using HPV as the germicidal agent.
Recently efforts have been made to increase UV germicidal efficacy in water
and on surfaces by combining it with photocatalysts like TiO 2 or Ag [ 91 ].
Some researchers have found that even UVA has germicidal effects on vegetative
organisms in the presence of TiO 2 /Ag. This is an area of new research and as of this
writing; the mechanism is not well understood.
It has been long known that exposure to UV can cause deleterious effects to
the skin, eyes, and immune system [ 92 ]. It is also known that all forms of UV can
cause skin cancer [ 93 , 94 ]. However, it is important to note that UVC is the least
likely to cause skin cancer because the depth of penetration is so shallow, and the
radiation is absorbed in the outer layer of dead skin cells [ 68 ]. The primary health
effects of UVC overexposure are erythema of the skin, photoketaoconjunctivitis
and photokeratitis. Nevertheless, overexposure should be avoided because the
injuries such as sunburn, snow blindness, and “welder's flash” can be painful and
debilitating, at least in the short-term. As of this writing, there were no studies that
documented worker or patient exposures to UVC during surface disinfection;
however, First et al. measured 8-h doses to workers and patients from upper room
UV irradiation ranging from 7.9 to 34 mJ/cm 2 [ 81 ]. This exposure was well above
the Threshold Limit Value TM (TLV) for UVC of 3 mJ/cm 2 as an 8-h time weighted
average [ 61 ]. The authors concluded that this exposure was not a concern because
the position of the dosimeter significantly overestimated the actual dose, and they
believed that the TLV could be doubled and still be protective. It is important to
remember that the American Conference of Industrial Hygienists (ACGIH), the
association that publishes the TLVs, recommends against using their standards as a
basis of protecting members of the general public. Their reasons for making this
recommendation are that the members of the general public may be exposed for
more than an 8 h duration and because members of the general public may be more
susceptible to chemical or physical exposures than healthy workers. Patients in a
healthcare setting would be expected to be exposed for more than 8 h and to be
more susceptible to the deleterious effects of overexposure.
There are other concerns associated with the use of UVC as a germicidal
modality. Said et al. found that Escherichia coli exposed to UVC could be rendered
non cultivable but still viable [ 95 ]. Photoreactivation after exposure to UVC has
long been known to be a problem [ 96 ]. With photoreactivation, what appear to be