IMPORTANT. The specimens examined in the laboratory (stools, pus, sputum, blood, urine, etc.) are often infectious. After examination they must be treated in such a way that further risk of infection is avoided.
The specimens may be in:
• cardboard cartons or plastic pots that can be destroyed (stools, sputum); or
• glass jars and bottles that can be cleaned, sterilized and used again.
Most disposable containers should be used once only, but polypropylene pots and tubes can be sterilized, cleaned, and reused.
Specimen containers should be discarded into special disinfectant-filled containers (such as buckets), plastic disposal boxes, or hazardous waste bags. Reusable plastics, slides, and other materials should be kept separate from disposables for later decontamination and cleaning before reuse.
6.3.2 Methods of sterilization or decontamination
An incinerator is a device designed to completely burn up combustible materials, rendering them sterile ash. Simple but effective incinerators can be made on site in emergency situations.
Making such an incinerator and incineration are shown in Figures 6.1 and 6.2. Incineration should be done at least once a week, or as often as necessary.
1. Use an old metal petrol drum (200 litres/40 gallons).
2. Fix a strong metal grating (g) firmly about 1/3 of the way up the drum. Steel rods will keep it in place.
3. Cut a wide opening or vent (v) below the level of the grating.
4. Find a removable lid (l) for the drum.
Figure 6.1 Making an incinerator
1. At the end of each morning’s and afternoon’s work, place all used stool and sputum boxes on the grating of the incinerator.
2. Always keep the metal drum tightly closed (both lid and vent) except during incineration.
3. Fill the bottom of the drum with paper, sticks wood shavings, etc.
4. Remove the lid. Light the fire and keep it burning until all the infected material has been reduced to ash.
5. The ash produced is not dangerous and can be thrown on the refuse heap. The ash should be buried in a deep pit if it contains needles, lancets, etc.
Figure 6.2 Incineration
Anything can be sterilized in an autoclave. Heat-stable items such as glass containers, polypropylene tubes and cups, polycarbonate tubes and cups, cloth, instruments, etc. will survive autoclaving intact. These can be emptied, washed, and put back into service. Autoclaving is done at 121°C with pure steam (not a steam-air mixture) for 30 minutes.
Sputum pots, urine bottles, and blood sample containers can be autoclaved before being cleaned. A number of field autoclaves are commercially available (Figure 6.3). They can be heated by electricity, solar energy, gas burner, primus stove or cooking fire. Electrically-heated models consume a large amount of electricity and so are not usually suited to field laboratories. A pressure cooker designed for food preparation can also be used.
Figure 6.3 Autoclave
Boiling in detergent
When an autoclave is not available, boiling in detergent (Figure 6.4) is a satisfactory method of decontaminating most specimen containers. However, it does not kill spores and does not inactivate certain viruses. Boil specimen containers for 30 minutes in a large pail containing a strong solution of washing powder or sodium carbonate crystals (60 grams per litre of water).
Figure 6.4 Boiling in detergent
Burial (Figure 6.5) does not decontaminate infectious material but it does prevent the material from being a hazard.
1. Dig a pit 4-5 metres deep and 1-2 metres wide.
2. Make a lid that fits tightly over the pit. It is advisable to strengthen the upper rim of the pit by lining it with bricks and stones.
3. Throw stool or sputum boxes and other infected material into the pit twice a day. Replace the lid immediately.
4. Once a week, cover the refuse with a layer of quicklime. Alternatively, if quicklime is not available, cover the refuse with a layer of dried leaves (10 cm thick) once a week.
Figure 6.5 Burial of contaminated material
6.3.3 Disinfection of specific equipment
Reusable stool containers can be decontaminated by autoclaving or with strong disinfectant before cleaning. Autoclave at 121°C for 3 minutes or fill the jars containing stools with a 5 % solution of phenol or similar disinfectant. Leave for 24 hours. Empty into the lavatory*.
*NOTE. If the lavatory is connected to a septic tank, phenol or other antiseptic should not be put into the lavatory. Clean the jars with detergent and water (see Table 6.1). They can also be autoclaved before cleaning.
Reusable sputum pots and tubes of pus and CSF can be decontaminated by several methods before cleaning. In order of preference these are:
- boiling in detergent.
Follow the directions given for autoclaving or boiling.
Urine bottles should be emptied into the lavatory. Autoclave the bottles or fill them with a 1 % solution of commercial bleach, or 2 % solution of phenol. Leave them for at least 4 hours before cleaning them with detergent.
Blood sample containers should be autoclaved. Alternatively, they should be soaked overnight in a strong disinfectant, 5 % cresol or 1 % calcium hypochlorite, 1:2 V/V.
Containers of fresh blood collected the same day should be rinsed in cold water and left to soak in a soap or detergent solution.
Containers containing blood which has been kept for several days and in which organisms may have multiplied should be filled with a 1 % solution of commercial bleach and left for at least 6 hours before rinsing and cleaning.
Glass microscope slides used for tuberculosis should be soaked overnight disinfectant and then discarded.
Slides used for Gram stain and Romanovsky stain should be soaked overnight in disinfectant. The immersion oil should then be removed with xylene, washed in detergent and rinsed in several changes of clean water. The slides should then be air dried, or dried using a lint-free towel.