|Public Health Action in Emergencies Caused by Epidemics (WHO - OMS, 1986, 285 p.)|
If the agent responsible for an outbreak and its mode of transmission from person to person are known, precautions can be taken against its excretion by both patients and healthy carriers. While the agent remains unidentified, the protection desirable should be based on the mode of transmission, the attack rate and the severity of the disease as judged by the case-fatality rate, sequelae ratio, or socioeconomic impact. The minimal protection procedures for diseases transmitted from person to person are known as standard precautions, but additional measures may be required, such as enteric or respiratory isolation or, exceptionally, strict isolation. The same levels of protection may also be required for medical evacuation.
A4.1 Standard precautions
A4.1.1 General principles
The purpose of standard precautions is to prevent the spread of a contagious agent to other patients, hospital personnel and visitors. Standard precautions should achieve this objective for moderately transmissible diseases without unnecessary waste of time and money.
This consists mainly of protective clothing, as follows:
- gown: should be of washable material, buttoned up at the back and protected if necessary by a plastic apron;
- gloves: cheap plastic gloves are available;
- mask: surgical masks made of cloth or paper may be used;
- caps and overshoes.
Other necessary equipment includes sinks for hand-washing (operated by foot), disinfectants (see Annex 7), plastic bags, an autoclave, and an incinerator.
Washing hands before and after each contact with potentially infected patients or materials is the most important and efficient precaution that can be taken. Rinsing hands with alcohol (700 ml/litre) or iodine solution in alcohol may cause skin damage and is not always necessary.
Warnings, in the form of coded colour cards fixed to the door or the bed, should indicate the specific type of precautions to be taken.
The double-bagging technique should be used whenever contagious material (including laboratory samples) is to be transported. Transparent plastic bags are used. The bag containing the contaminated material is placed in a second bag, which should be handled only with clean hands or a new pair of gloves; a label should be inserted between the bags to identify the material and indicate the precautions to be taken. Personnel should not smoke or eat while on duty.
Visitors are generally admitted (except for children, pregnant women and immunocompromised persons) after this has been authorized, but must be given advice on self-protection.
When indicated, gowns should be changed after each patient has been visited (individual gown technique).
Masks, whether of paper or cloth, are not effective when wet and should not be kept around the neck when not in use.
Standard precautions may be directed more specifically against excreta, secretions, skin discharges and blood, and appropriate procedures are indicated in Table A4.1.
Table A4.1. Procedures for protective precautions
Type of precautions
Excreta, secretions and skin discharges
Wearing gloves and/or hand-washing
Change gloves and gown after dealing with infective discharges
Mask when dealing with oral secretions
Excreta disposal with disinfection, or without, in communities with a modern sewage system (unsuitable for certain diseases-see Annex 3)
Oral secretions: same precautions as for excreta in certain diseases, e.g., poliomyelitis
Ocular secretions: when indicated, double-bagging techniques and incineration of contaminated material
Discharges and dressings: double-bagging techniques
Freshly soiled articles: double-bagging techniques and sterilization or incineration
Needle precautions to avoid creating bubbles in emptying the syringe
Contaminated articles: double-bagging and incineration or autoclaving
Private room (or ward for patients with same disease), isolated toilets
Change gloves and gown after dealing with infective material
Standard precautions for excreta and oral secretions, when indicated
Standard precautions for freshly soiled articles
Private room, negative pressure (exhaust fan), anteroom desirable
Discard gown, gloves, mask and cap after dealing with patient
Nasopharyngeal secretions: disinfection
Standard precautions for freshly soiled articles
Private room with anteroom and sink, airflow controlled by negative pressure and exhaust filtered (high efficiency particulate air (HEPA) filters)
Special devices for microbiological barrier:
-high-security, disposable, protective clothing and full-face or half-face microbiological mask, or positive-pressure hood-respirator; or plastic-film bed isolator (Trexlers tent type)
Decontamination of sewage and disinfection of excreta, discharges and blood
Medical personnel under surveillance
a A risk of transmission of hepatitis B may be present and should be borne in mind in handling blood.
A4.2 Enteric and respiratory isolation
A4.2.1 General principles
Isolation of a patient may become necessary when transmission of the agent is possible even when standard precautions are taken, as is the case with a limited number of diseases (see Annex 3 and Table 44). This procedure is time-consuming and increases the cost of hospitalization. However, under field conditions, there is room for improvisation, and simple techniques may be capable of limiting the spread of a disease by isolating the patient just as effectively. When the number of patients exceeds the number of hospital beds available, some improvisation will also be necessary to enable other rooms to be used. Field hospitals or fever clinics may also be set up temporarily with the same objective. The isolation techniques differ somewhat for patients with enteric as compared with respiratory diseases.
A private room is normally required when a patient has to be isolated. In emergency situations, at least temporarily, however, patients with enteric infections may be cared for on a ward rather than in a private room if all the patients admitted require the same care and precautions and are at the same stage of the disease. For respiratory isolation, grouping several patients together could expose them to cross-infections, thereby complicating the original disease.
In addition to gowns and gloves, masks, caps and overshoes may be necessary, a separate set being required for use in each individual patients room.
Enteric diseases that can spread easily require disinfection of excreta, even if the sewage system is considered safe, because of the quantity of agents that may be evacuated.
General procedures as described in section A4.1.3 are applicable. Additional special procedures are indicated in Table A4.1.
A4.3 Strict isolation
A4.3.1 General principles
Strict isolation is required for a small number of exceptionally highly contagious diseases (see Annex 3 and Table 44), and is designed to avoid any direct or indirect contact with the patient and to protect medical personnel and the community from possible transmission through droplet nuclei (aerosols) which might be carried some distance. It places a barrier around the patient that no microbial agent can pass through.
Even if it is known that the epidemic is caused by a highly contagious agent, it may be appropriate, for logistic reasons, to admit suspect patients initially to standard isolation facilities, either of the enteric or respiratory type, or even a combination of both, until the presence of the agent has been confirmed or is strongly suspected.
Although strict isolation requires special rooms and specially trained personnel, it is possible to improvise effective procedures whenever appropriate facilities are not available locally. It should not be forgotten that good barrier nursing practices provide a reliable level of safety.
Under field conditions, a practical solution is to isolate patients at home, providing protective equipment and giving the bare minimum of instruction to a member of the family, with supervision by medical personnel.
Facilities. Strict isolation requires a separate building or a completely separate part of a building without any common air flow. Strict isolation facilities consist of service rooms fitted with autoclaves and direct access to an incinerator, sewage decontamination systems, patients rooms with anterooms, and a direct entrance for ambulances, and a ventilation system providing an airflow from other areas to the anterooms, to the patients rooms and finally to an exhaust pipe fitted with a high efficiency particulate air (HEPA) filter. A HEPA filter retains 99.97% of particulates 0.3 mm in diameter.
Two systems have been in use for isolating patients from personnel. The first is the plastic-film bed isolator (Fig. A4.1), which is operated at a pressure below atmospheric and is equipped with HEPA filters and a lock system for evacuating contaminated material in sealed plastic bags. Nursing personnel do not need special suits, since the patient is surrounded by the microbiological barrier. In the second system, the patient is in a normal bed and personnel are protected by high-security protective clothing, i.e., the microbiological barrier is around the person who is taking care of the patient. The anteroom then plays an important role, and is divided into clean and contaminated areas. Contaminated articles are first placed in bags in the patients room and transferred to the contaminated area, where the health worker also leaves his contaminated suit in a bag. In between the two areas, the health worker decontaminates the outside of the bag containing contaminated material with hypochlorite solution, washes his hands, inserts the bag into another one taken from the clean area and moves into the clean area. The clean area contains a stock of material, and a basin for washing hands is located between the two areas. Both inside and outside doors of the anteroom should be locked. Glass windows are convenient since they permit personnel to see the patient from the corridor of the clean area. The patients room should be provided with a minimal amount of furniture, privies, bath, and alarm devices. All instruments such as thermometers, sphygmomanometers, etc., should be used only for one particular patient.
Protective clothing. Two types of protective clothing are available. The first (Fig. A4.2) is used for medical care and consists of gown, apron, hood and boots. The face is protected by a plastic visor, or goggles. Air is filtered through a surgical mask, or a half-face or full-face mask with a cartridge, which provides a microbiological barrier. A positive-pressure hood-respirator (Fig. A4.3) with a back-pack HEPA filter may also be used.
The second type (Fig. A4.4), consisting of an overall and boots, is used for high-risk operations, such as visiting a highly contagious patient at home, performing necropsies, taking laboratory specimens, or carrying out high-risk laboratory examinations. It should be made of waterproof fabric.
Disposable protective clothing may be incinerated after use, which avoids the problem of sterilization. It also permits new suits to be used as often as necessary. WHO keeps an emergency stock of such items. However, they are rather expensive and cotton equipment may also be used but must be sterilized before being washed.
Protective clothing may also be improvised with plastic materials, which will then also be disposable. Plastic bags of various sizes may be transformed into aprons, gloves, boots and hoods.
Whatever the material used for the protective clothing, the way that it is removed is of great importance in avoiding self-contamination. The procedure is described in Table A4.2. Potentially contaminated surfaces should never touch either the operator or any uncontaminated material.
These are indicated in Table A4.1.
A4.4 Medical evacuation
The level of precautions to be taken in the medical evacuation of acutely ill patients is shown in Table 44.
When strict isolation is recommended, all persons handling the patient or in close contact with him should be equipped with protective clothing and respirators or masks. The procedure for removing such clothing is shown in Table A4.2.
Pressurized stretcher transit isolators with HEPA filters are produced by commercial companies and provide the same microbiological barrier as the bed isolator (Fig. A4.5).
Medical care during evacuation will consist mainly of supportive treatment for the circulatory and respiratory functions. Ringer lactate infusions should be kept ready for use, but formation of bubbles in the ampoule resulting from the motion of the vehicles may present a difficulty.
Table A4.2 Procedure for removing protective clothing
1. In the contaminated area of the anteroom, rinse gloved hands in a sodium hypochlorite solution
2. Remove apron, head cover and overshoes and place in a plastic bag
3. Remove gown and gloves in a single operation, folding the gown and gloves inside out in doing so, or remove overall, gloves and overshoes in a single operation, turning the overall, gloves and overshoes inside out
4. Put on a fresh pair of gloves; place gown and contaminated gloves in a bag, or discard overall, gloves and overshoes into a plastic bag
5. Remove the respirator, sponge off with sodium hypochlorite solution and replace it in its container
6. Remove the second pair of gloves, place them in the bag and close it
7. Wash hands, move to the clean area of the anteroom and place the bags in an outer bag (double-bag technique) and label either for autoclaving, incineration or laboratory examination
The stretcher transit isolator is suitable for transferring patients by ambulance to the main hospital. Note the cones for tubes and wires and the evaginated sleeve for supporting an infusion bag.
Methods of disinfecting the vehicle, during transport or on arrival, are described in Annex 7.
Official arrangements for medical evacuation must be made with the hospital at the destination and with the local authorities at places where it is intended to stop en route.
CLAUSEN, L. ET AL. Isolation and handling of patients with dangerous infectious diseases. South African medical journal, 53: 238-242 (1978).
CONTROL OF INFECTION GROUP, NORTHWICK PARK HOSPITAL AND CLINICAL RESEARCH CENTRE. Isolation systems for general hospitals. British medical journal, 2: 41-44 (1974).
DUNSMORE, D. J. Safety measures for use in outbreaks of communicable disease. Geneva, World Health Organization, 1986.
EMOND, R. T. D. High security isolators. Postgraduate doctor - Middle East, (11): 473-478 (1981).
HUTCHINSON, J. G. ET AL. The safety of the Trexler isolator as judged by some physical and biological criteria: a report of experimental work at two centres. Journal of hygiene, 81: 311-319 (1978).
Isolation techniques for use in hospitals, Washington, DC, US Department of Health, Education, and Welfare, Centers for Disease Control, 1975 (DHEW Publication No. (CDC) 76-8314).
Laboratory biosafety manual. Geneva, World Health Organization, 1983.
Practical guide to the prevention of hospital-acquired infections. Unpublished WHO document, WHO/BAC/79.1.
TREXLER, P. C. ET AL. Negative pressure plastic isolator for patients with dangerous infections. British medical journal, 2: 559-561 (1977).