World Health • 49th Year, No.6, November-December 1996 9
Controlling epidemic diseases
David L. Heymann
Poor hygiene and crowding con turn a disease outbreak into an emergency.
Several outbreaks of infectious diseases developed into
international emergencies during the past decade. In each case the experience showed ways to improve the management and control of such outbreaks in the future.
N
atural and man-made disasters make ideal conditions for the spread of diseases, but an outbreak of an infectious disease can itself constitute an emergency.WHO works with its partners to contain outbreaks of infectious disease when local or national re- sources are insufficient. WHO's Division of Emerging and other Communicable Diseases Surveil- lance and Control was created in October 1995 to "strengthen national and international capacity in the surveillance and control of commu- nicable diseases, including those that represent new, emerging and re- emerging public health problems for which it will ensure a timely and effective response". The Division provides technical and medical
assistance in emergences caused by epidemics.
A cluster of deaths or of severely ill people does not necessarily make an epidemic. Yet against a back- ground of poverty, poor hygiene, crowding, fragmented communica- tion networks and weak structures for health care an outbreak has the potential to become an emergency.
Cases may go undetected, unreported or unattended even when there are unusual or severe symptoms and many deaths.
Several outbreaks of infectious diseases developed into international emergencies during the past decade.
In each case the experience showed ways to improve the management and control of outbreaks in the fu- ture.
Cholera in South America: The seventh cholera pandemic spread to Peru in 1991, causing over 300 000 cases and nearly 3000 deaths in that first year. Besides the impact on health, the epidemic led to enormous economic losses estimated for that year alone at US$ 770 million. The outbreak clearly illustrated a break- down in the application of Inter- national Health Regulations and the need for their revision.
Plague in India: The final count in the 1994 outbreak of plague in India was fewer than 1000 presump-
ti ve cases out of the 5000 initially suspected. The appearance of pneu- monic plague in Surat caused thou- sands to flee to other areas, at the risk of carrying the disease with them.
Fortunately that did not happen, but the outbreak led to tremendous economic disruption and worldwide concern. This outbreak showed the need to define signs and symptoms accurately at the start, to back up clinical diagnosis with laboratory investigations, and to communicate information to all concerned, includ- ing the general public.
Yellow fever in Kenya and Liberia: The 1992 yellow fever outbreak in Kenya was a challenge both logistically, as it occurred in remote terrain, and in terms of diag- nosis, since yellow fever had not been seen in Kenya for decades.
Vaccination of the people at risk brought the outbreak under control before 100 cases had occurred. This event illustrated the need to include yellow fever in disease surveillance programmes, to have funds quickly available for response to emergencies and to train local personnel in disease surveillance techniques. The out- break in Liberia struck a country tom apart by civil strife, with huge num- bers of people on the move. Despite the difficulties and dangers, over 80% of those at risk received a dose of the very effective yellow fever vaccine. Control of the Liberia out- break required strong partnership and cooperation across national bound- aries.
Ebola haemorrhagic fever in Africa: A total of316 cases, 245 of
them fatal, were traced after the outbreak of Ebola haemorrhagic fever in Zaire in 1995. Retrospective tracing of cases showed that the infection passed through chains of transmission from January of that year until the outbreak was declared in May. Other diseases with similar symptoms (such as shigella dysen- tery) occurred at the same time and
10
Peru, 1991. A health worker demonstrates how to prepare oral rehydration salts, which are used to replenish body Fluids lost through diarrhoea caused by cholera.
masked the Ebola outbreak. Poor sanitation and hygiene in hospitals and health centres amplified the spread, however, so that it was recog- nized. Although the initial situation was precarious, the outbreak was quickly halted by taking basic hy- giene precautions when dealing with infected patients, persons who had been in contact with the infection, and the dead. These lessons were applied in Gabon where it was possi- ble to contain an outbreak after only two waves of transmission thanks to the early detection and reporting of the infection. In Gabon, 37 people were infected and 21 died.
Diphtheria in the former Soviet Union: The epidemic of diphtheria in republics of the former Soviet Union caused 25 000 cases in the first six months of 1995. As many as 25% of those infected died; in one country about half of the affected children under two years of age died.
Inadequate surveillance of diseases, prevention and control methods, population migration, inflow of refugees from war areas, and short- ages of vaccine and antibiotics- all these contributed to the failure to halt the epidemic. The emergency under- lined how important it is to have effective control measures in the early phase of an epidemic, and to maintain good disease surveillance and mass immunization programmes.
The number of cases dropped sharply in 1996.
Dengue haemorrhagic fever in the Americas: Dengue returned to many countries of the Americas in the 1990s though they had been free of the disease for more than 50 years. In parallel came the poten- tially fatal haemorrhagic form of the disease. By the end of 1995, dengue haemorrhagic fever had been diag- nosed in 14 countries. The resur- gence of dengue and the emergence of dengue haemorrhagic fever were largely due to setbacks in
programmes to control the mosquito that carries the disease. A dengue vaccine is being developed but, until it becomes available, outbreaks of dengue and dengue haemorrhagic fever will continue to occur. The most effective defence is sanitation to bring the mosquito population under control.
Cerebrospinal meningitis:
Outbreaks of cerebrospinal meningi- tis occur in cycles every three to six years in Africa and parts of Asia. In the first four months of 1996, West Africa experienced a new cycle of outbreaks which infected many thousands of people and caused thousands of deaths. There is an effective vaccine which, while it cannot prevent outbreaks, can stop them from spreading if given in time. Outbreaks must be detected rapidly so that risk groups can be targeted for vaccination and vac- cines supplied in time.
World Health • 49th Yeor, No.6, November-December 1996
Improved WHO response
Ideally, disease outbreaks should be detected early, effective vaccines should be readily available, and people at risk should be vaccinated promptly. All too often, however, outbreaks are not recognized or reported until they have become emergencies, disease strains are resistant to the most affordable drugs, and mosquitos or other carri- ers spread the infection before it can be contained.
WHO's new approach to the control of epidemics is a proactive one. Staff with expertise and experi- ence in epidemic control and logistic support will assist countries to pre- pare for epidemics and will take part in containing epidemics when they occur. Once an epidemic has been contained, WHO will work with its national counterparts to identify the problems that led to the epidemic and take steps to detect and prevent future epidemics. Guidelines ex- plaining how to be prepared for and respond to specific disease epidemics will be used in national training courses. Equipment and supplies to accompany the guidelines will be stockpiled and maintained at regional offices and headquarters. •
Dr David L Heymann is Director of the Division of Emerging and other Communicable Diseases Surveillance and Control, World Health Organization, 121 I Geneva 27, Switzerland
The next issue of
World Health
joins in the celebration of the 1997 World Health Day with a special focus on emerging infectious diseases.
It will present in more detail
those emerging diseases that are a cause for particular concern. It will also describe the plans and activities of the Division of Emerging and other Communicable Diseases Surveillance and Control at WHO headquarters and its counterpart programmes in regional offices and countries.
