Public Health Action in Emergencies Caused by Epidemics (WHO - OMS, 1986, 285 p.): ANNEX 5 - Collection and shipment of laboratory specimens

Public Health Action in Emergencies Caused by Epidemics (WHO - OMS, 1986, 285 p.)

		(introduction...)
		Acknowledgements
		1. Introduction
		2. Explanation of terms and general lines of action
		3. Organization of an emergency health service
		4. Procedures for epidemiological investigations
		5. Analysis of investigation data
		6. General measures for the control of outbreaks
		7. Follow-up of control measures
		ANNEX 1 - Explanation of epidemiological terms1
		ANNEX 2 - Procedures for assembling epidemiological data and formulating and testing hypotheses of causation
		ANNEX 3 - Diseases that may cause epidemics1
		ANNEX 4 - Standard precautions, isolation and medical evacuation for diseases with person-to-person transmission
		ANNEX 5 - Collection and shipment of laboratory specimens
		ANNEX 6 - Identification of arthropod and rodent vectors of communicable diseases and use of insecticides and rodenticides
		ANNEX 7 - Decontamination procedures
		ANNEX 8 - Informal Consultation on Strategies for the Control of Emergencies Caused by Epidemics of Communicable Disease, 9-13 November 1981
		Where to Purchase WHO Publications
		Back Cover

ANNEX 5 - Collection and shipment of laboratory specimens

As mentioned in sections 4.1.5 and 4.2.6, the correct collection of specimens for laboratory examination is an important part of any investigation. Specimen collection should be carefully planned; this requires consideration of the selection of appropriate samples, the preferred method of collection, safety precautions, requirements for packaging and shipment, and the competence of the laboratory to which the specimens will be sent.

A5.1 Collection of specimens

A5.1.1 Human population

If it is not clear what disease has caused the outbreak, specimens should be taken as outlined in Table A5.1.

The specimens required when certain specific agents are suspected are indicated in Table A5.2. It should be noted that liver biopsy is contraindicated in yellow fever and haemorrhagic fevers because of the risk of internal bleeding.

Methods for the collection of specimens are outlined in Table A5.3 and shown for blood in Fig. A5.1.

A5.1.2 Food-borne diseases

Advice on collecting clinical specimens and samples of suspected foods is given in Table A5.4. It is most important to collect remnants of suspected food but it may also be wise to take samples of all other foods, even though they do not seem to be contaminated, and even if there is only a remote possibility that they have caused the outbreak.

A5.1.3 Vertebrate animals

The collection of specimens may present hazards from contact with the sick animal or infectious aerosols produced by it; whenever this possibility exists, the safety precautions described above are recommended. Blood may be taken with vacuum blood-collecting tubes from the jugular vein in large animals, with a syringe from the humeral vein in birds, with a capillary tube from the ocular sinus in small rodents, or by cardiac puncture in post-mortem examinations. Serum from animals that have been shot is often anticomplementary in complement-fixation tests. Parasites may be found in faeces, but their immature stages in animals may be different morphologically from the mature forms in man, and vice versa.

Special techniques are required for certain diseases. For rabies in a dog, the animal should be killed and the head removed and placed in a plastic bag in a container packed with wet ice. For plague, rodents should be captured in a cage-type trap, which should then be sent to the laboratory so as not to lose the rodent’s arthropod parasites. Snap traps are not recommended since infected fleas would leave the dead rodent.

A few hints on rodent identification are given in Annex 6.

Table A5.1. Specimens to be collected according to the disease or the principal body system affected

	Specimens required^a
Disease or affected system	For direct examination	For isolation^b	For serology
General	Thick and thin blood films	Heparinized blood, throat swabs, faeces	Paired sera^c (blood without additive or with heparin)
Exanthems	Skin lesions	Heparinized blood, throat swabs, skin lesions, faeces
Lymphadenopathy	Pus from gland, or tissue taken with a biopsy needle	Heparinized blood, bubo fluid
Haemorrhagic fever (strict safety precautions)	Heparinized blood (taken aseptically) (electron microscopy)	Heparinized blood, urine (taken aseptically)
Nervous system	Cerebrospinal fluid, corneal impressions	Heparinized blood, cerebrospinal fluid, throat swabs, faeces
Respiratory tract	Nasopharyngeal aspirates, throat swabs	Throat swabs
Gastrointestinal tract	Faeces, vomit	Faeces, heparinized blood
Jaundice	-	Heparinized blood
Eye infections	Conjunctival scrapings or swabs	Conjunctival scrapings or swabs, heparinized blood

^a Adequate safety precautions are necessary in collecting all specimens. Blood for isolation should be taken aseptically.
^b Some specimens require enrichment or transport media.
^c For some diseases, detection of IgM antibody in a single serum specimen taken early after onset is sufficient.

Table A5.2. Laboratory specimens required for tests for particular causative agents

Suspected agent or disease	Specimen	Test
Arbovirus	Blood or brain (- 70°C)	Isolation
	Blood or serum (+ 4°C)	Serology
Cholera	Rectal swabs or stool specimens in transport medium, as recommended by the laboratory	Culture
Gastroenteritis	Stool	Culture (bacterial, viral), electron-microscopy, ELISA^a
	Blood or serum (+4°C)	Serology
Hepatitis	Serum (+4°C)	ELISA^a
Legionella	Blood, sputum in enrichment broth	Culture; FA^b
Malaria	Blood (thick and thin smears)	Staining
Meningococcal meningitis	Spinal fluid, blood, pharyngeal swabs (all on transport media)	Culture, counterimmunoelectrophoresis
Plague	Bubo fluid, blood (in broth or on blood agar slants)	Culture, FA^b
Rabies	Brain (-70°C)	FA^b and isolation
Salmonella typhi	Blood (early in disease) in enrichment broth	Culture
Shigella	Faecal specimens or rectal swabs in enrichment broth	Culture
Typhus	Blood Serum (+4°C)	Inoculation Serology
Varicella and suspected smallpox	Lesion fluid, crusts	Electron-microscopy, cell culture

^a Enzyme-linked immunosorbent assay.
^b Fluorescent antibody test.

Table A5.3. Methods to be employed in collecting specimens

A. Safety precautions

Purpose

Precautions

Protection of operator

Depending on estimated risk: surgical mask, gloves, gown, plastic apron, and goggles or face shield

Decontamination of material

Disposable material: place in plastic bags and send for incineration

Reusable material:

- syringes: draw up hypochlorite or 1% formaldehyde solution into the needle and syringe; leave for 20 minutes, wash, sterilize
- other instruments: immerse in disinfectant solution, leave for 20 minutes

Vials containing specimens: wash outside with cotton soaked in disinfectant or immerse in disinfectant solution

B. Collection of blood^a

Method or type of blood	Equipment and procedure
Venepuncture	Equipment - 10-ml vacuum blood-collecting tubes, 21/22 gauge needle, with or without heparin (see Fig. A5.1) - 5-10-ml syringes (preferably disposable), 21/22 gauge needle - plastic screw-cap vials Procedure - As usual for venepuncture - For serum separation: clot formation, 1 hour at room temperature clot retraction, 4 hours at + 4°C or room temperature aspirate serum with another Vacutainer, syringe, or pipette with bulb (do not use mouth pipette) - Storage: heparinized blood at + 4°C (unless otherwise specified) serum at + 4°C clot at + 4°C for inoculation
Capillary blood	Equipment - disposable sterile lancets - tubes Procedure - Adults: clean skin of finger or ear with alcohol, allow to evaporate, and prick skin - Babies under 6 months of age: prick on side of heel (Fig. A5.1), about 2 mm deep, cutting very slightly sideways - Older infants: prick on thumb - Collect blood either in heparinized capillary tube or on strip of absorbent paper - If absorbent paper (Whatman No. 3 for chromatography) is used, cut strips of 14 × 9 cm, allow drops of blood to fall on the paper, mark spots with reference number; collect drops from other patients sufficiently far away on the strip (samples from up to 5 suspects may be collected on one strip), allow strips to dry, standing on their sides inside a covered bowl at room temperature before transport; dry thoroughly later on for long storage and keep at + 4°C or - 20°C in polythene bags.
Blood for parasitology or haematology	Prepare thick and thin blood films as usual (heparinized blood may be used for cell counts); observe filariasis microfilariae in a drop of fresh blood diluted with normal saline solution

^a Aseptic precautions are necessary for blood inoculation or cultivation and good preservation of serum.

C. Specimens of skin lesions^a

Stage or purpose	Procedure
Macular-papular stage	Scrape the lesions with a lancet until the surface becomes moist but without blood. The material on the lancet should be rubbed on to slides, and further material absorbed on a swab which is then placed in a screw-cap vial
Vesiculo-pustular stage	Open the lesions with the lancet. Absorb the fluid from at least 6 lesions on the swab. Place the swab and lancet in the plastic container and screw the top on securely. If no plastic container is available: - fill at least 4 capillary tubes and seal the ends with plasticine - take the contents of 3-4 vesicles with a swab with wooden applicator, rub the swab on 2 slides with a circular motion, covering an area about 1 cm in diameter
Crusting stage	With the lancet, take off a minimum of 6 crusts and place them in a plastic screw-top bottle
Parasitology	Observe trichinellosis parasites in muscle biopsy and onchocerciasis microfilariae in cutaneous snip

^a Specimens for direct examination and cultivation can be taken directly from skin lesions of vesicular rashes. In other exanthemata (macular/papular). the agent may be isolated more easily from blood, throat swabs or faeces than from skin lesions. The WHO specimen collection kit (Fig. A5.3) may be used. particularly for suspected varicella, monkeypox or smallpox lesions (with strict safety precautions).

D. Respiratory tract specimens

Purpose

Procedure

Bacteriology, mycology or parasitology

Direct examination of sputum: thin smear on a slide for Gram staining

Cultivation: make a cough swab. Fragile bacteria require special media and particular precautions (ask laboratory for guidance)

Virology

Direct examination by immunofluorescence: cough swab transported in Hanks’ medium at + 4°C, or preferably nasopharyngeal aspirate obtained with a suction apparatus

Cultivation: same specimens. Fragile viruses require special media and particular precautions (ask laboratory for guidance)

E. Specimens of faeces

Purpose	Procedure
All examinations	3 ml (or equivalent in solid) in screw-cap “bijou” bottle (capacity 7 ml). Store at +4°C or normal temperature
Parasitology	3 parts of 10% formaldehyde solution are added to 1 part of stool for dispatch
Bacteriology	Use special transport medium for cholera, other vibrios, Salmonella, Shigella, etc.; store at room temperature in shade, not in refrigerator. If medium not available, consult laboratory
Virology	A suitable virus transport medium may be provided by the laboratory

F. Specimens of cerebrospinal fluid^a

Purpose	Procedure
All examinations	Collect in 2 tubes, one containing 6-7 ml, the other 2 ml; transfer contents of latter tube aseptically to a sterile bijou bottle
Cytology, biochemistry, or parasitology	Use specimen from first tube (examine without delay)
Bacteriology or virology	Use bijou bottle, do not put in refrigerator, keep at + 37°C if possible, in shade. Transport medium is needed for meningococci (ask laboratory), but not for viruses

^a Like the viruses of most encephalitides, the rabies virus cannot be isolated from the CSF; cutaneous biopsy in the retroauricular region and corneal impressions may give rapid results by immunofluorescence.

G. Eye specimens

Purpose	Procedure
Direct examination	Conjunctival scraping with a fine spatula, smear on clean dry microscope slide for staining to check for bacteria and chlamydiae
Cultivation	Bacteria and viruses require special media for transport (ask laboratory for guidance)

H. Specimens of urine

Purpose	Procedure
Parasitology, bacteriology, or virology	After centrifugation, parasites may be observed; the pellet can be cultivated if it has been obtained aseptically

I. Post-mortem specimens^a

Specimen or disease	Procedure
Blood	The most important sample needed, it can be taken from the heart cavities
Liver	The second sample needed and obtainable without autopsy by use of a biopsy needle. Several fragments are needed, some in fixative for histopathology,^b others in saline (aseptically) for bacteria and viruses
Spleen, kidneys, lungs, heart	If necessary, pieces of these organs may be prepared both for histopathology^b and for bacteria and viruses, as for liver
Encephalitides	Pieces of brain (cortex, thalamus, Ammon’s horn) should be taken aseptically for isolation, and a cortical smear made for detection of Plasmodium falciparum

^a Safety precautions must be taken when death is due to a communicable disease and must be strict for septicaemia, encephalitides and haemorrhagic fevers; direct contact and aerosol transmission must be avoided. Virus titres decline rapidly after death while bacteria rapidly increase in number. Post mortem material should therefore be collected as soon as possible.
^b The fixative fluid (saline formol) for use in histopathology is made up as follows:

Formol, commercial grade	120 ml
Distilled water	880 ml
Sodium chloride	9 g

Material fixed in saline formol can be utilized in electron microscopy.

A5.1.4 Arthropods

Arthropods are best captured and identified by an entomologist. Table A5.5 gives some brief advice on methods of capture; some information on identifying arthropods is given in Annex 6.

Fig. A5.1. Collection of blood (by courtesy of Becton-Dickinson, Vacutainer Systems Europe, Meylan, France)

(a) Use of vacuum blood-collecting tubes.

A-evacuated tube (sterile interior)
B-protected sterile needle
C-holder

Figure

II. Screw protected needle into holder; insert tube into holder, making sure that the needle is slightly embedded in the stopper (the stopper then meets the guideline on the holder).

Figure

III. When the needle is in the vein, push the tube to insert the needle through the stopper; the blood flows. It is possible to fill several tubes, keeping the needle and holder in place. To obtain drops, hold the tube vertically and tap the bottom of the tube. To transfer serum, insert a second tube as if performing a venepuncture, or remove stopper and collect serum with a syringe or pipette.

Figure

(b) Collection of capillary blood from babies under 6 months of age.

IV. Prick the foot where indicated in the diagram.

Figure

Table A5.4. Food-borne diseases: methods of collecting specimens

A. Body products and organs

Type of specimen	Method^a
Blood	Collect specimens for isolation of agent and serology as for bacteriology (see Table A5.3B)
Vomit	Collect 50-200 g with a sterile spoon; put into a sterile jar
Faeces	Place 2-ml or 2-g (bean-size) portion in two sterile screw-cap bottles, one containing transport medium for bacteria and one for viruses (ask laboratory for special transport medium)
Urine	Collect 50 ml of mid-stream urine, and preserve with a few drops of diluted formalin (40g/l formaldehyde solution)
Autopsy	Collect the stomach and its contents (tightly bound at both extremities), the liver, kidney, brain; samples of fat may be useful and can be taken with a biopsy needle

^a The collection of specimens for use in official inquiries may be governed by legal provisions.

B. Food and other materials

Type of specimen	Method
Liquid food	Shake, pour 200 ml into a sterile container, refrigerate but do not freeze
Solid or mixed food	Separate portions with sterile knife, transfer to a sterile glass jar (e.g., jam jar); take samples from periphery to central laboratory; refrigerate
Meat and poultry	Cut portion of meat or skin aseptically from different parts of carcass; alternatively, wipe large portions of carcass with sterile gauze squares or swabs; place in transport medium
Water	See Table A5.6
Other	Collect any fabric, e.g. sheets or towels, known or suspected to contain poison, vomit, urine, faeces

Table A5.5. Capture of arthropods

A. Mosquitos

Stage

Method of capture

Adults

Collection in resting places in houses, with a collecting tube (aspirator) or after knock-down with pyrethrum insecticide spray

Biting collections on volunteer human “bait”

Light-trap collections, with or without carbon dioxide

Animal bait trap collections

Mosquito-net collections in grassland

Larvae^a

Collection in breeding places by using dipper in water that has collected in jars, cisterns, refuse (old tyres, bottles, cans), rocks, plant and tree holes, ponds, banks of streams, etc., or in ovitraps (container in which Aedes females lay eggs)

^a The following special density indexes are used for domestic Aedes aegypti:

- house index = percentage of houses positive for larvae;
- container index = percentage of water-holding containers positive for larvae;
- Breteau index = number of positive containers per 100 houses.

B. Other arthropods

Arthropod	Method of capture and characteristics
Bed bugs	Inspection of mattresses and corners of bed-frames, cracks in walls
Biting midges (Culicoides)	Pests of man and livestock. Great diversity of larval breeding habitats (soil, sandy beaches, low-humus-content or high-organic muck, saltwater beaches, swamps, tidal pools, freshwater bogland, rice fields, pools, small streams, whether polluted or not, edges of larger streams and lakes, crab holes, tree holes, plant axils, decomposing plants). Collection of adults with hand-operated sweep nets, light traps with carbon dioxide
Blackflies (Simulium)	Feed on man, domestic and wild animals, birds. Adults 1.5 mm long. Immature stages in slow- to fast-flowing streams, attached to plant axils. Adults fly in swarms. Capture with standard insect net
Fleas	Collect by brushing the animal over a white enamelled basin, probing rodent burrows with a rubber rod covered with white flannel or introducing a “sentinel” mouse attached to a long string. A “sentinel” guinea pig can be released in human dwellings, or a white enamelled tray containing water may be placed on the floor, with a piece of brick in the middle and a lighted candle placed on it
Horse flies	Collect with hand-net
Houseflies	Collect with sticky fly paper
Sandflies (phlebotomines)	Adults are active from dusk to dawn. During daylight they rest in a variety of well protected sites: tree trunks, animal burrows, tree holes, crevices in walls and in the ground, piles of rocks, animal shelters, forest litter. Light traps and sticky paper are most useful for their capture
Ticks	Worldwide, two families: Argasidae (soft ticks) which feed on multiple hosts (up to 3 at each developmental stage) and Ixodidae (hard ticks) which feed on a single host. Collect parasitic stage on animal skin and free-living stages by dragging a square piece of flannel across the ground
Tsetse flies	In Africa only. Attracted by movement, e.g., by people on foot or on bicycles, or by slowly moving vehicles. Capture with hand-net when they alight

A5.1.5 Environment

Investigations of diseases thought to have originated in the environment should cover:

- sources of water used for drinking and other domestic purposes at the point where contamination may have originated;
- water for recreational or agricultural use;
- facilities for faeces disposal;
- unusual situations, such as large amounts of bird droppings, caves inhabited by bats, contamination of ventilation/air-conditioning systems, etc.

Methods of collecting water samples are shown in Table A5.6. However, the detection of pathogens in water, air, dust and ground samples calls for complicated procedures and sometimes for special devices and is better achieved with the cooperation of a laboratory. Water and other specimens to be sent to the laboratory should preferably be kept at the temperature of wet ice.

A5.2 Shipment of infectious substances

A5.2.1 Packaging

Packaging must comply with national and international safety regulations for the transport of infectious material by air freight, airmail or surface mail; a suitable package fulfilling these requirements is shown in Fig. A5.2. The principle is to provide material that will absorb liquids in case of leakage and protect against shocks, as described in Table A5.7.

Fig. A5.2. Packaging for transport of infectious material and diagnostic specimens

WHO 761006

A:	Ampoule containing the specimen: screw-capped vial (illustrated) with a nontoxic rubber liner and taped shut, or flame-sealed glass ampoule.	Primary receptacle
B:	Absorbent material - e.g., tissue paper or absorbent cotton wool-sufficient to absorb all the specimen should leakage occur.	Secondary packaging
C:	Plastic bag, heat-sealed or taped over (not stapled).
D:	Shock-absorbing padding - e.g., loosely packed paper or absorbent cotton wool.	Outer packaging
E:	Rigid waterproof outer container.
F:	Tight-fitting lid - e.g., screw-on or push-on (paint-can type) - taped shut or clipped.

Table A 5.6. Collection of water samples^a

Type of water	Method of collection
Tap-water	(1) Disinfect the mouth of the tap with a burning cotton wool swab soaked in 700 ml/litre alcohol (2) Let the water flow for 2 minutes (3) Fill the bottle
Well-water	Weight a sterile bottle with a sterile stone attached with sterile string and dip into well
Open water^b	Plunge the bottle neck down into the water and then turn it upwards with the mouth facing the current

^a Water should be collected in sterile bottles (1-5 litres).
^b Water from springs, streams, rivers and lakes.

A special kit is available from WHO for the collection and transport of material suspected of containing varicella, monkeypox or smallpox viruses (see Fig. A5.3).

Table A5.7. Instructions for packaging infectious material

Item	Instructions
Primary container	Use watertight test tube or vial (screw cap fixed with adhesive tape), or flame-sealed ampoule, together with absorptive material
Secondary container	Use watertight container (metal or sealed plastic bag) which may contain several primary containers if there is no risk of shock and breakage
Outer shipping container	Must be waterproof, rigid to resist crushing; use expanded polystyrene to provide adequate thermal insulation (picnic box)
Refrigerant	Place outside secondary container; use dry ice (will leave space after melting) or wet ice in sealed plastic bag (vacuum jars are not recommended as they often break)
Labels	Should include both sender’s and receiver’s name and carry the special tag for infectious material (see Fig. A5.4)
Letter	Include list of specimens in a sealed plastic bag and mail a duplicate list separately

Fig. A5.3. WHO specimen collection kit used for material suspected of containing varicella, monkeypox or smallpox viruses

1. Lancet (sterile); 2. Sterile swabs; 3. Plastic specimen collection container; 4. Metal tin; 5. Outer cardboard mailing container.

A5.2.2 Refrigeration

In general, infectious agents should be kept at a low temperature during storage and transport. The types of refrigeration required to achieve various temperatures are as follows:

Temperature (°C)	Type of refrigeration
+10	Domestic refrigerator
+ 4	Wet ice or frozen pads (cold dogs)
- 8	Freezer of domestic refrigerator
- 20	Freezer cabinet
- 70	Deep freezer or dry ice
-163	Liquid nitrogen

Repeated freezing and thawing should be avoided as this rapidly kills all living agents. Some respiratory viruses cannot be kept under cold conditions and special instructions should be sought from the receiving laboratory. Whole blood should not be frozen as this will haemolyse the red blood-cells.

The different methods of refrigeration during shipping have various advantages and disadvantages, as shown in Table A5.8.

Table A5.8. Advantages and disadvantages of refrigeration methods

Refrigeration method	Advantages	Disadvantages
Wet ice	Universally available, replenishment easy	Melts rapidly, messy unless in sealed plastic bag
Frozen pads (cold dogs)	Pads are dry	Refrigerate for a short time; freezing the pads takes a long time
Dry ice (solid carbon dioxide)	Material may be kept for several days at -70°C	Gives off carbon dioxide gas which is noxious to some agents (the receptacle used for the specimen must be airtight and space must be left in the package for the carbon dioxide gas produced to evaporate)
Liquid nitrogen	Material may be kept for a long period at -160°C	Special container (open) for transport, not accepted by all airlines

A5.2.3 Air-freight and airmail requirements

A package containing infectious substances must be identified by means of a special label, as shown in Fig. A5.4.

The sender should fill in the form for air-freight or airmail required by the International Air Transport Association (see Fig. A5.5).

Both the sender and the receiver of packages containing infectious material have certain responsibilities. The sender must:

- obtain the agreement of the transport company;
- contact the laboratory by telephone or cable to confirm acceptance and obtain advice on arrangements for shipment and refrigeration;
- obtain an import permit, if required;
- notify the receiver of the transportation data (company, flight, transit point(s), airway bill number, estimated time of arrival);
- avoid sending packages during holiday periods;
- send separately a description of the material concerned;
- ensure that the refrigerant is replenished in transit, if necessary.

Similarly, the receiver must:

-obtain the agreement of the national authorities, if necessary;
-send the import permit;
-arrange for prompt delivery by the transportation company and customs;
-check the acceptability of transit points;
-inform the receptionist, give instructions for cold storage;
-send an acknowledgement of receipt to the sender.

Fig. A5.4. Label for packages containing infectious substances

Regulations governing shipments by airmail and air-freight are very strict. Even when these have been complied with, difficulties may be encountered with airlines if the pilot refuses to carry infectious material on a passenger aircraft. WHO can assist with transportation, particularly of highly dangerous materials to be sent to the WHO collaborating centres for special pathogens.

A5.3 Shipment of other materials

A5.3.1 Shipment of specimens collected in connection with food-borne diseases

Refrigeration is necessary to preserve samples from putrefaction; unpreserved samples may undergo chemical changes that may interfere with the identification of the poison. It should be noted that a number of plastics and rubbers contain impurities that may be difficult to distinguish chemically from certain toxic substances; glass receptacles are therefore preferred. However, imperfect specimens are better than none at all.

Specimens should be carefully labelled and should indicate the nature of the material, the weight of the sample, the time and date of collection, the nature of the transport medium, etc. Those suspected to be heavily contaminated should be kept apart from others.

Samples that may be of medicolegal importance must be sealed in the presence of a representative of the law and transported with great care.

Fig. A5.5. Form to be completed for shipment of infectious substances by air

A5.3.2 Shipment of arthropods

Arthropods may be shipped in Barraud cages made of muslin and nylon organdie suspended on a wire frame. Cages, which should contain some food (slices of fruit with sugar), should be placed inside insulators containing wet towels. Tin cans provided with a screened hole for ventilation and plaster of Paris as a humidifier may also be used.

BIBLIOGRAPHY

DEPARTMENT OF HEALTH AND SOCIAL SECURITY. Code of practice for the prevention of infection in clinical laboratories and post-mortem rooms. London, HMSO, 1978.

GOMPERTS, E. D. ET AL. Handling of highly infectious material in a clinical pathology laboratory and in a viral diagnostic unit. South African medical journal, 53: 243-248 (1978).

Guidelines for biological safety cabinets. Unpublished WHO document, CDS/SMM/81.21.

Laboratory classification. Unpublished WHO document, CDS/SMM/79.11.

Laboratory safety for arboviruses and certain other viruses of vertebrates. American journal of tropical medicine and hygiene, 29: 1359-1381 (1980).

MADELEY, C. R. Guide to the collection and transport of virological specimens. Geneva, World Health Organization, 1977.

Manual for rapid laboratory viral diagnosis. Geneva, World Health Organization, 1979 (WHO Offset Publication, No. 47).

Rapid diagnosis in acute bacterial respiratory infections. Unpublished WHO document, WHO/BAC/ARI/81.5.

VAN DER GROEN, G. ET AL. Negative-pressure flexible film isolator for work with class IV viruses in a maximum security laboratory. Journal of infection, 2: 165-170 (1980).

WHO/CAMR meeting on guidelines for laboratory facilities and containment equipment and isolation facilities for persons infected with dangerous pathogens. Unpublished WHO document, WHO/SMM/80.17.