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The Royal Free Hospital, Infectious Diseases Department, Coppetts Wood, Muswell Hill, London N10 1JN, England.

Prior to 1945 air travel was a luxury restricted to a few rich people and most travellers from the tropics came by sea to Western Europe or North America. The time taken for the voyage exceeded the incubation period of the major infectious diseases, such as smallpox, so afforded an effective period of quarantine. The speed of modern aircraft and the vast increase in the number of passengers have completely removed these protective barriers and have exposed Europe and North America to much greater risk from exotic diseases prevalent in remote parts of the tropics. Some idea of the size of the problem may be gained from the statistics of passengers using the major London airport at Heathrow, where a trickle of 1,400 passengers a day in 1950 had become a torrent of 100,000 a day in 1976. In 1976 more than 2,000 people arrived from Africa daily at the three airports serving London and well over 700 of these came directly from Tropical Africa where viral haemorrhagic fevers are endemic. This change in travelling pattern has been reflected in admissions to infectious diseases and tropical medicine units, where the problem of the feverish traveller has become all too common. The recognition of Lassa fever and the introduction of a few cases into London caused alarm and gave impetus to the provision of safe hospital accommodation for such patients. My own Department was made responsible for dealing with such admissions from a large area of southern England with a population of approximately 11 million.

It is common for travellers, who have recently arrived from Africa, to develop feverish illnesses and fall under suspicion because of the wide publicity given to Lassa fever, 'Green-monkey' disease and other newsworthy tropical infections. Needless to say the vast majority of these patients have minor respiratory tract infections or malaria and very few fall into the category of viral haemorrhagic fever. It is obviously impracticable and unnecessary to take stringent precautions with all these patients. Yet there is always the lurking possibility that some may be dangerous. Unfortunately there are no distinctive features in the early stages of viral haemorrhagic fevers to enable a firm diagnosis to be made on clinical grounds so judgement has to be made on epidemiological evidence.

We divide patients with unexplained fever, who have arrived from tropical Africa within the previous three weeks, into three categories and admit them to hospital accordingly :

1. Those who have come from major cities in Africa, where the risk of viral haemorrhagic fever is negligible, are admitted to standard isolation rooms with routine barrier nursing.

2. Patients from small towns in tropical Africa are regarded with more suspicion and are admitted to a high-security room with filtered negativepressure ventilation and separate facilities, where they are kept under observation while malaria is being excluded. If parasites are not found and pyrexia continues such patients are transferred to maximum security.

3. The last and potentially the most dangerous group of patients are those who have been living or working in rural areas, medical and nursing staff from country hospitals, contacts of known cases and laboratory workers handling dangerous material. Patients in this group are admitted directly into a Trexler negative-pressure isolator.

I do not propose to discuss in any detail our standard isolation facilities. Suffice it to say epidemiological studies have shown that they afford a high degree of protection against spread of routine infections. Our high-security room provides effective protection for the community but the staff come into direct contact with the patient and rely upon protective clothing as a defence against these dangerous infections for which there is at present no form of active immunization. The hazards to staff from such patients can be greatly reduced by using the Trexler isolator system (1,2). With this system the attend ants are separated physically from the patient by a barrier plastic film. Air filters attached to the isolator prevent contamination of the ventilation system and a negative pressure is maintained within the envelopes to prevent egress of airborne particles if the isolator is accidentally punctured. Over the past three to four years we have nursed a considerable number of patients in the Trexler isolator and in the past 18 months we have on average admitted a patient every six weeks. The patients have been mainly young adults but have included a child of 11 years. We have had no experience of nursing very young children or elderly patients in the isolator. Patients are generally aware of their predicament and accept the restrictions as a necessary precaution. The majority are removed within a few days though an occasional patient may spend a prolonged period within the isolator, especially while waiting for the results of clearance specimens. There have been no problems with temperature or humidity providing the isolator is not exposed to direct sunlight. Noise levels have been acceptable and have not interfered with sleep or listening to radio or television. The convalescent period can be trying because the space available for exercise is very restricted. Much can be achieved to alleviate boredom by reading, listening to the radio, watching television and maintaining a link with the outside world through a telephone.

Initially the nursing staff expressed some misgivings about looking after patients in the isolator but they gained confidence when it had been demonstrated that the techniques were practicable and patients could be effectively nursed within the isolator. Staff now appreciate the protection afforded by the system and prefer to nurse potentially dangerous patients in this manner. A team of 12 trained nurses is necessary to provide effective cover and constant training is essential to ensure proficiency. This can be achieved by weekly training sessions and by partnering a novice with an experienced nurse. The basic skills are usually acquired within two days.

I would not like to give the impression that a negative-pressure isolator by itself is the answer to safe hospitalisation of potentially dangerous patients or that an isolator can be set up in any ward. Ideally the isolator should be sited within a large room in a separate high-security unit to ensure safety in case there should be a major failure of equipment or faulty technique in disposing of contaminated waste. Moreover, there is always the remote possibility that the patient may have to be removed from the isolator in the event of a major emergency, such as fire. There should be direct access for admission of the patient to the isolator and suitable changing and shower rooms for the staff. The patient's room should be fitted with storage racks for supplies, which are replenished daily as necessary. The high-security area should be fully equipped for the disposal of infected material by incineration or sterilization and have facilities for entertainment during convalescence.

Before admission of a patient the isolator is inspected carefully to make sure there are no defects in the plastic envelopes or rubber gloves and the other equipment in the high-security area is tested. The isolator is stocked with sufficient supplies to last for 24 hours. Thereafter fresh supplies are introduced as required and all waste material removed in sealed bags for incineration or sterilization. The patient is usually brought in by special ambulance and placed directly into the isolator, in which case the ambulance crew and the admitting doctor wear full protective clothing. A patient arriving from abroad or from a distant part of England may be transferred in a transit isolator, which can be docked with the main isolator rather in the manner of a space craft, and the patient transferred directly into the main isolator without exposing the staff.

All routine nursing and medical procedures can be carried out with minimal interference by the physical barrier though it is not practicable at present to undertake artificial ventilation or haemodialysis. Blood and other samples can be taken within the isolator without exposing the staff to risk. The samples are removed in sealed plastic bags, welded into a second plastic bag and then packed in a metal box for despatch by special messenger to the appropriate laboratory. Used needles are placed in screw-topped hard plastic containers before removal and incineration.

When it is decided that a patient is not suffering from a dangerous infection the contents of the isolator are dealt with according to routine barrier nursing procedures. The envelopes are subsequently sprayed with a 1% hypochlorite solution and washed thoroughly before re-use. If it is confirmed that the patient has a dangerous infection all the contents of the isolator are removed for incineration or sterilization. The interior of the isolator and the adjacent highsecurity area are fumigated with formaldehyde. The envelopes are later detached from their frames and destroyed by incineration. The room is then refumigated. Should a patient die from a dangerous infection the body can be removed from the isolator into a large plastic bag which can be sealed and separated without contaminating the environment. The body in the bag can then be sealed in a coffin for cremation or burial.

Samples for investigation of dangerous pathogens are dispatched directly to the Microbiological Research Establishment at Porton Down where there are facilities for the safe processing of such material. Problems have arisen with other investigations for we have lacked adequate facilities for complex haematological or biochemical tests. In this age of specialization the laboratories with the necessary microbiological expertise have been deficient in other skills. This is now being rectified and the Public Health Laboratory Service has established a few centres where some of the simpler tests can be undertaken and blood films treated to render them safe for reference to malaria experts. In my view it will be necessary for more complex haematological and biochemical tests to be carried out by appropriate experts using safety cabinets under the supervision of trained microbiologists.

Another problem which has caused us a great deal of trouble is the vexed question of quarantine or surveillance of staff looking after these patients. In the case of the patient with Ebola infection the staff agreed to go into voluntary quarantine because of the evil reputation of the disease in Africa, the uncertainties about its mode of spread and the lack of scientific evidence about the relatively new techniques being used to contain the infection. Most of the nursing staff were married and the quarantine period of three weeks from last exposure caused a great deal of disruption of family life and some hardship. As a result many were subsequently reluctant to undertake this type of work, not because they had any qualms about the risks of infection but because they were not prepared to submit to quarantine. When you consider that they would be faced with the prospect approximately every six weeks I do not think that their attitude is unreasonable. Fortunately antibody studies after the Ebola episode 3 showed no evidence of infection amongst the 29 staff involved and laboratory investigations using bacteriophage have demonstrated that the isolator system is effective in containing small virus particles. As a result it has been accepted that less rigid measures will be sufficient.

The community physician is primarily responsible for the control of infection including hospital infection. Nevertheless, it has been agreed that we would be responsible for implementing surveillance of hospital staff and of keeping the community physician informed. We keep a register of all staff working in the high-security section and they are kept under daily surveillance for 21 days from last exposure or until the provisional diagnosis of viral haemorrhagic fever has been discounted. No restrictions are placed on the individual nurse or doctor apart from a daily recording of temperature. Should an individual be off-duty or away from home, he or she must telephone the Hospital each day to report the temperature. In the event of a mishap closer surveillance would be instituted. We have found this system to be acceptable to staff and to work well in practice. As far as contacts elsewhere are concerned, the responsibility for surveillance rests with the local community physician who visits twice daily to record the temperature and the appearance of the throat. Should a contact become ill, he is admitted for observation, either into the high-security room or into a Trexler isolator according to the assessed degree of risk.

Over the past four years, we have been gradually acquiring knowledge and experience in dealing with these complex problems. Obviously it is impossible to ensure absolute safety even at the expense of unacceptable curtailment of individual freedom. The measures I have outlined have proved effective in practice though they will no doubt need to be modified in the light of further experience.


I am grateful to Vickers Medical Ltd. for supplying the photograph of the Trexler isolator.

1. Emond, R.T.D. (1976) Postgraduate Medical Journal, 52, 563.
2. Trexler, P.C., et al. (1977) British Medical Journal, 2, 559.
3. Emond, R.T.D., et al. (1977) British Medical Journal, 2, 541.
K.M. Johnson : Dr. Emond, could you give us some more details on the criteria you do use in making a decision to discharge a patient from the isolator. I'm thinking here particularly of a person for example, who does not bleed and yet you are unable to make a specific diagnosis, how long would such a person have to stay there in terms of negativity on an antibody basis against all the potential bad agents ?
R.T.D. Emond : We find that for a considerable number of patients, the matter resolves itself. The temperature settles down within 48 hours, we keep them in the isolator for 48 hours and then take them out because the matter has resolved clinically. Or we may find malaria parasites in the blood film, treat them and when the temperature settles down, the patient is taken out. The most troublesome of course are the cases where the temperature does not settle down and where we are unable to find malarial parasites and where none of the other tests prove to be positive. In these circumstances, we have to wait until we obtain clearance from the Microbiological Research Establishment of Porton and with Lassa this takes about a week, with Marburg it my be two to three weeks or even more, it depends very much on the individual patient and the judgement has to be nude on clinical and also on microbiological grounds.
O.W. Prozesky : We have been confronted with the problem of those hematology and chemical pathology investigations. There are two ways out of it, one is to put a clinical pathologist in a laboratory attached to the unit, but this is costly since a special set of equipment is needed. The other one is to have these people acquainted with the procedures and work under the guidance of those familiar with the problems, but then the people on duty have to be doubled. So I don't think there is a really good answer. A practical contribution I can make is that the Coulter counter can be easily decontaminated with sodium hypochlorite.
R.T.D. Emond : Our problem in England is that our laboratories are so mechanized and our Laboratory technicians so specialized that no one nowadays has a general knowledge of pathology that existed ten, fifteen years ago, only the older technicians have the necessary skills to combine microbiology and biochemistry.
T.E. Woodward : Just a word of warning. I have seen patients with plague, typhoid, and typhus with malaria parasites in their blood, it is a little perplexing at times.
R.T.D. Emond : That is why I said that we wait after finding malaria parasites until the temperature responds to treatment. We had one patient transferred from the Hospital for Tropical Diseases found to have malaria parasites. He was treated, the parasites disappeared but the fever didn't. So he was transferred for further observation under conditions of security.
D.P. Francis : I don't want to disagree with anything that is done in the Western World to isolate these patients, I think that the bed isolator approach is very reasonable but I don't think that the people in the developing world should feel that they all have to have a hundred bed isolators. we have no evidence of any airborne transmission of this disease. Only very very close contacts, not even superficial contacts of these highly infected fatal cases, get infected. I think that they can be reasonably well dealt with on the open ward with simple barrier nursing.
J. Casals : What does one propose to do in this scheme of isolation of patients with Ebola, Marburg or Lassa, who may be excreting or secreting viruses for weeks after the clinical recovery? It is very difficult to consider to incarcerate the person for a month or two. How is one to decide when a negative constitutes a negative, do you have to take three sanples and find them all negative before you release him ?
R.T.D. Emond : Last year we had a man who had Lassa fever who was over the acute stage by the time we saw him, nevertheless, he was shedding virus in his urine and he did so for 42 days from the onset of illness. He was isolated not in a bed isolator but in a high security room. We allowed him to go out for walks on the grounds of the hospital still carrying his virus because he was a sensible fellow. Finally, we obtained three sets of negative specimens taken at weekly intervals, this took a month or so. The pressure of course comes on to us from the Public Health people who feel very unhappy about someone walking around the community knowing to be shedding virus, they are probably not unhappy about someone walking around the community not knowing to be shedding virus .

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