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Interim Guidelines for Smallpox Response and Management in Scotland in the Post-Eradication era
Appendix 15: disinfection and decontamination
General principles
Heat is the most effective antimicrobial agent and viable counts of the virus are reduced within an hour or less to about 10
-7 of their initial value by exposure at atmospheric pressure to 60
oC. Therefore steam sterilisation is sufficient for articles that will withstand the treatment. For others, alternatives such as of chemical disinfection or incineration may be required.
In the early stages of the disease smallpox is infectious because of virus in respiratory discharges. Virus from this source is less protected by organic matter and is inactivated by liquid disinfectants or by formaldehyde in the form either of a vapour or of a liquid spray.
In the later stages of the disease smallpox is infectious because of virus dried on the skin and bedclothes and possibly contained within smallpox crusts or dried pus or blood. Smallpox crusts can be sterilized by exposure to dry heat at 160
o for 60 minutes or to steam under pressure at 121
o for 15 minutes, 126
o for 10 minutes or 134
o for 3 minutes, as in autoclaving.
Whichever method of disinfection is employed and whatever the stage of the illness,
persons engaged in disinfection must themselves be fully protected by vaccination and must wear suitable protective clothing.
Disinfection (concurrent or terminal) of articles
The order of preference is as follows:
Whenever possible the contaminated articles should be destroyed by burning.
If this cannot be done, articles should be autoclaved if this is practicable (MRC Working Party on Steam Disinfection).
If (a) and (b) are both impracticable, chemical disinfection should be considered.
Valuables may be disinfected by exposure to formaldehyde vapour or to ethylene oxide in a special chamber.
Decontamination of premises
If the patient has been removed from the premises in the early stages of disease, before the rash has become pustular, formaldehyde fumigation alone may be relied on (see paragraphs 8 and 9). However, if the patient has developed a pustular rash while in the premises, then the additional procedure outlined in paragraph 10 is recommended.
The most practical method for formaldehyde fumigation is the vaporisation of formaldehyde solution BP by boiling. This ensures the necessary high relative humidity. There are two methods of achieving this, chemical and electrical.
Electrical Method.
A stainless steel vessel of about 1.5 gallon (6.82 litres) capacity should be used, provided with an electric heating element and a thermostatic cutout to ensure automatic interruption of the current if the vessel boils dry. An additional precaution would be a time-switch set to open just before evaporation is completed. This apparatus is suitable for a room of about 3,000 cubic feet. For larger rooms a number of these units can be dispersed.
Mix 2 pints (1.14 litres) of water to 1 pint (O.57 litres) of formaldehyde solution BP (ie. 33% formaldehyde in water) for each 1,000 cubic feet (28.3 cubic metres) of space. The use of larger quantities than these is undesirable.
Seal the room and if possible maintain the temperature above 18
oC (64
oF). The exposure time should be not less than 6 hours, and fumigation is therefore best done overnight.
After fumigation the operator should enter the room wearing a service respirator or its equivalent and open all the windows. If insufficient ventilation is available to disperse the vapour quickly or the premises are required shortly a cloth impregnated with 0.25 pint (0.14 litres) of strong ammonia solution BP for each 1,000 cubic feet (28.3 cubic metres) of space may be suspended in the centre of the room for 2 hours.
Chemical Method
Used when the electrical method cannot be applied.
For each 1,000 cubic feet (28.3 cubic metres) of space a 0.5 gallon (2.27 litres) jar is required containing 1 pint (0.57 litres) of formaldehyde solution BP. The jar should stand in a bucket or on a large tray. The room should be sealed and 6 ounces (170 grammes) of permanganate of potash dropped into each vessel.
The operator should quickly withdraw and seal the door; within 10 seconds violent boiling begins. Extra water is not required because this is liberated during the chemical reaction. The exposure time is the same as for the electrical method.
When formaldehyde fumigation has been completed the following additional measures are necessary if the patient's rash had reached the pustular stage before his removal:
Wherever possible the rooms should be cleaned with a vacuum cleaner incorporating a disposable liner in the cloth bag. The cloth bag should be autoclaved after use but the liner and its contents must be burned. The vacuum cleaner should be one designated for hospital use, i.e. one provided with a dust filter at the air exit point.
The vacuum cleaner should be thoroughly wiped with a cloth soaked in a clear phenolic disinfectant 1 in 40 after making sure that it is detached from the electricity mains supply.
In addition to vacuum cleaning or where this is not possible, all horizontal surfaces should be washed and scrubbed with clear phenolic disinfectant 1 in 40 and the particulate matter thus collected should be burnt.
Decontamination of vehicles, ambulances and crews
Smallpox ambulances and their contents should normally be disinfected by their own crews. The crew must not discard their protective clothing until disinfection of the vehicle has been completed.
Articles that can be discarded should be sealed in stout paper bags and taken for immediate incineration; articles that can be autoclaved should be sealed in paper or cloth bags.
All removable fittings inside the vehicle, including loose floor coverings if any, should be removed, sprayed with a disinfectant and wiped dry.
Blankets and stretcher canvases used in the removal of the patient should be placed in a laundry bag with an alginate stitched lining and marked "smallpox", for laundering at the smallpox care centre.
The interior of the vehicle, including the driver's cabin, (particularly the steering wheel, brake and gear levers and other controls) should be sprayed systematically, first the floor, then the roof, and last the sides, front and rear, including the inside of the door. The handle on the outside of the door should also be sprayed. A suitable disinfectant solution is a clear phenolic 1 in 40.
It is preferable to use a power sprayer so that the work can be done thoroughly without entering the ambulance, but with weaker sprayers or other cleansing methods it will be necessary to enter the ambulance. In the absence of spraying apparatus, the same basic procedure may be carried out by wiping with a sponge soaked in disinfectant. After either procedure, the doors and windows of the vehicle are left open to the air for at least five minutes.
After disinfecting the ambulance the crew should:
Disinfect and remove their gumboots.
Disrobe with as little disturbance of the infected articles as possible.
Place the discarded clothing in a laundry bag with an alginate stitched lining and marked "smallpox", for laundering at the smallpox care centre.
Enter the cleansing room at the smallpox care centre and wash thoroughly paying particular attention to hands, face and hair.
Put on their clean clothing.
If necessary, the treated ambulance may now be dried out, using chamois leather (which should then be placed in a plastic bag and incinerated) or disposable wipes.
As many as possible of these recommendations should be incorporated in Standing Operating Procedures.
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