Back to home pageSwitzerland (Geneva) WORLD HEALTH STATISTICS QUARTERLY 1992 - VOLUME 45, NUMBER 2/3 COMMUNICABLE DISEASE EPIDEMIOLOGY AND CONTROL 93.77.01 - English - D.A.P. BUNDY, A. HALL, G.F. MEDLEY, WHO Collaborating Centre for the Epidemiology for Intestinal Parasitic Infections, Imperial College, London (U.K.), and L. SAVIOLI, Programme on Intestinal Parasitic Infections, Division of Communicable Diseases, WHO, Geneva (Switzerland) Evaluating Measures to Control Intestinal Parasitic Infections (p. 168-179) Intestinal parasitic infections are among the most common infections of human in developing countries, but the resources available for their control are severely limited. Careful evaluation of control measures is essential to ensure that they are cost-effective. The evaluation of the effects of control on intestinal helminths and intestinal protozoa requires an understanding of the different epidemiological patterns of these two groups of parasites. The transmission dynamics and morbidity associated with the major helminth infections are dependent on the size of the worm burdens. Thus the important parameter for evaluating the impact of control on morbidity and transmission is the intensity of infection, which can be assessed by determining the mean density of parasite eggs in faecal specimens. The estimation of intensity is exceptionally sensitive to the size and demographic structure of the population sample selected for assessment. With the major protozoan infections, an estimate of intensity is of little value and the central parameter for evaluation is prevalence. Prevalence does exhibit age and spatial heterogeneity, which may be species-specific, so there remains a need to ensure a consistent sample structure, although this is less critical than for the helminths. (DEVELOPING COUNTRIES, HEALTH, MORBIDITY) 93.77.02 - English - Michel GARENNE, Caroline RONSMANS, Center for Population and Development Studies, Harvard University, Cambridge, MA (U.S.A.), and Harry CAMPBELL, Consultant in Public Health (Child Health), Fife County Health Board, Scotland (U.K.) The Magnitude of Mortality from Acute Respiratory Infections in Children under 5 Years in Developing Countries (p. 180-191) This article reviews the available evidence of mortality from acute respiratory infections (ARI) among children aged under 5 years in contemporary developing countries and compares the findings with European populations before 1965. Deaths from ARI played a smaller role after 1950, when the use of antibiotics became generalized. In developing countries, the role of ARI mortality seems to be similar to the European experience. The age pattern is very marked. In absolute values, ARI mortality is highest in the neonatal period and decreases with age. ARI, mainly pneumonia, accounts for about 18% of underlying causes of death in developing countries. Pneumonia and other ARI are frequent complications of measles and pertussis; ARI is also commonly found after other infections and in association with severe malnutrition. Virtually no data are available in developing countries to prove final estimates of the role of ARI in mortality of children aged under 5 years. However, the WHO figure of 1 out of 3 deaths due to - or associated with - ARI may be close to the real range. (DEVELOPING COUNTRIES, WHO, YOUTH MORTALITY, PNEUMONIA) 93.77.03 - English - Gunther F. CRAUN, Virginia Polytechnic Institute and State University, Blacksburg, VA (U.S.A.) Waterborne Disease Outbreaks in the United States of America: Causes and Prevention (p. 192-199) During the past decade, 291 waterborne outbreaks were reported in community (43%) and noncommunity (33%) systems, and from the ingestion of contaminated water from recreational (14%) and individual (10%) water sources in the United States. Although several large waterborne outbreaks occurred, most were in small communities. The number of illnesses per outbreak in noncommunity systems is much larger than that reported during any previous period. The increased occurrence of outbreaks in disinfected groundwater systems may be due to (i) increased use of disinfection with little effort to reduce or eliminate sources of contamination, and (ii) not providing effective, continuous disinfection. In surface-water systems, outbreaks occur primarily because of inadequate or interrupted disinfection in systems that do not provide filtration, but a large increase in outbreaks has recently occurred in filtered systems. In community systems, most outbreaks were caused by inadequate disinfection of surface water (28%) and contamination of water in the distribution systems (24%), primarily through cross-connections and repairs of water mains. In noncommunity systems, almost all outbreaks (77%) were caused by contaminated groundwater. (UNITED STATES, WATER, WATER POLLUTION, MORBIDITY) 93.77.04 - English - F.-X. MESLIN, Veterinary Public Health, Division of Communicable Diseases, WHO, Geneva (Switzerland) Surveillance and Control of Emerging Zoonoses (p. 200-207) "Emerging zoonoses" are defined as zoonotic diseases caused either by apparently new agents, or by previously known microorganisms, appearing in places or in species in which the disease was previously unknown. Diseases associated with changing farming practices, trade and consumer habits. Bacterial enteric diseases due to Salmonella enteritidis and Echerichia coli 0:157 are examples of diseases associated with changing farming practices and consumer habits. Diseases associated with changing environmental conditions which influence reservoirs, vectors and/or victim species population parameters. Projects for the management of water resources (dams, irrigation) have brought Rift Valley fever to Rosso (Mauritania) and cutaneous leishmaniasis to countries of northern Africa. Human rabies outbreaks following contacts with infected vampire bats in Peru and Brazil are examples of changing vector and victim population parameters. Pathogens acquiring new properties through adaptation, mutation and recombination. Recently a new type of equine influenza viruses, antigenically different from circulating human and equine influenza strains, were detected in northern China. Early detection of emerging diseases requires reinforced surveillance on a global level. This could be achieved by strengthening the existing network of WHO collaborating centres and particularly those in developing tropical countries, by providing appropriate technology and training in detection and characterization of pathogenic agents. Highly specialized laboratories would serve as a backup reference resource. (DISEASES, MORBIDITY, WHO) 93.77.05 - French - Silvère SIMEANT, Division de la Surveillance épidémiologique et Appréciation de la Situation sanitaire et de ses Tendances, OMS, Genève (Switzerland) Cholera 1991 - An Old Enemy with a New Face (Choléra 1991 - vieil ennemi, nouveau visage) (p. 208-219) The cholera epidemics of the 19th century are described and reviewed. The extent, incidence and case-fatality rate for the disease in the seventh pandemic are described. The global epidemiological situation and its trend at the end of 1991 are analysed. A review of cholera epidemiology highlights the factors that might explain the less tragic nature of the disease today. The role of water, food and direct contagion in transmission of cholera over the last 20 years is considered in the light of recent studies and with special reference to the epidemic in Latin America, where the intense emotion aroused by the disease has prompted vigorous action that could produce significant and lasting progress in the health field. (LATIN AMERICA, CHOLERA, EPIDEMICS) 93.77.06 - English - James CHIN, Maria-Antonia REMENYI, Florence MORRISON, Forecasting and Impact Assessment Unit, Office of Research, Global Programme on AIDS, WHO, Geneva (Switzerland), and Rudolfo BULATAO, Population, Health and Nutrition Division, World Bank, Washington, DC (U.S.A.) The Global Epidemiology of the HIV/AIDS Pandemic and its Projected Demographic Impact in Africa (p. 220-227) The global epidemiology of HIV/AIDS has evolved to the point that the pandemic now predominantly affects heterosexuals, especially in developing countries. This article summarizes the status of the HIV/AIDS pandemic as of the early 1990s; provides estimates and short-term projections of AIDS mortality in a hypothetical country of sub-Saharan country; and describes the major problems associated with modelling the long-term demographic impact of this pandemic. (AFRICA, AIDS, EPIDEMICS, MORTALITY, MORBIDITY, PROJECTIONS) 93.77.07 - English - A. MEHEUS and G.M. ANTAL, Sexually Transmitted Diseases, Global Programme on AIDS, WHO, Geneva (Switzerland) The Endemic Treponematoses: Not Yet Eradicated (p. 228-237) The endemic treponematoses which comprise yaws, endemic syphilis (bejel) and pinta constitute a group of potentially disabling and disfiguring infections which primarily afflict children in tropical and subtropical areas. The failure of many countries to integrate active control measures into the functions of the rural health services led to the gradual build-up and extension of treponemal reservoirs and the resurgence of foci of increased disease transmission particularly in communities where standards of hygiene and health care had remained low. Central and West Africa are most severely affected by the resurgence of the endemic treponematoses. In recent years a number of countries (e.g. Ghana, Côte d'Ivoire and Mali) have launched renewed control efforts, often combining yaws or endemic syphilis control with other public health programmes. In Central Africa itinerant pygmy groups are still highly affected by yaws. In Chad, Sudan and Ethiopia, there is some evidence of persistent foci of endemic treponematoses. In the Eastern Mediterranean, bejel has been eliminated from most areas, but foci of infection have been reported in remote villages in Pakistan, and some endemic syphilis transmission might still prevail in nomadic people of the Arabian peninsula. Health officials in South-East Asia and the Pacific Islands have documented remaining foci of yaws in at least seven Member States. In Indonesia widely dispersed foci of infection still persist, particularly in Irian Jaya, the Moluccas, Sumatra and Kalimantan. In the Americas, yaws incidence is very low with very small foci remaining in Suriname, Guyana, Colombia and some islands of the Caribbean. (DEVELOPING COUNTRIES, ENDEMIC DISEASES, SYPHILIS, TROPICAL DISEASES, CHILDREN) 93.77.08 - English - Artur GALAZKA, Expanded Programme on Immunization, WHO, Geneva (Switzerland) Control of Pertussis in the World (p. 238-247) Available data indicate that pertussis remains an important disease during infancy and childhood, particularly among those who are inadequately immunized. Some problems have arisen in the industrialized world where pertussis had been well controlled previously. In developing countries, immunization coverage with primary series of three doses of DPT vaccine in infants exceeds 80%, but there are considerable differences in coverage rates between regions and between and within countries. Failures to reach and maintain high immunization coverage in developing countries are caused by multiple factors including weak management of immunization services, missing opportunities to immunize eligible children and ineffective information and motivation of mothers to return to complete the immunization series. More information on the present epidemiological pattern of pertussis, especially age distribution of pertussis cases in developing countries, is needed to develop the policy of booster doses of DPT vaccine in children >1 year. (CHILDHOOD, CONTAGIOUS DISEASES, VACCINATION) 93.77.09 - English - Cynthia WHITMAN, Expanded Programme on Immunization, WHO, Geneva (Switzerland) et al. Progress towards the Global Elimination of Neonatal Tetanus (p. 248-256) Neonatal tetanus (NT) claimed the lives of over 433 000 infants in 1991. It is endemic in 90 countries throughout the world. NT is still one of the most underreported notifiable diseases, and routine reporting systems identified only 4% of the NT cases estimated to have occurred in 1990. Based on WHO estimates, tetanus toxoid (TT) immunization and clean delivery practices prevented over 793 000 infant deaths in 1991. 80% of the newborns who died of NT in 1991 were born in South-East Asia or Africa. Of the 90 countries endemic for NT, 10% produce 80% of the world's NT deaths. Half the female population in developing countries risks unclean deliveries and infants dying of NT. WHO, in conjunction with the Centers for Disease Control (CDC), has developed a protocol to assist countries in the rapid assessment of suspected TT failures and in verifying their toxoid potency. (WHO, NOTIFIABLE DISEASES, NEONATAL MORTALITY, CHILDBIRTH) 93.77.10 - English - Division of Control of Tropical Diseases, WHO, Geneva (Switzerland) World Malaria Situation, 1990 (p. 257-266) Accurate information on the global incidence of malaria is difficult to obtain because reporting is particularly incomplete in areas known to be highly endemic. The global incidence of malaria is estimated to be nearly 120 million clinical cases each year, with nearly 300 million people carrying the parasite. Some 75% of cases are concentrated in 9 countries (in decreasing order): India, Brazil, Afghanistan, Sri Lanka, Thailand, Indonesia, Viet Nam, Cambodia and China. Furthermore, within these countries malaria is concentrated in certain areas. Of a total world population of about 5.3 billion people, 3.1 billion (59%) live in areas free of malaria; 1.7 billion people (32%) live in areas where endemic malaria was considerably reduced or even eliminated but transmission was reinstated and the situation is unstable or deteriorating. Areas where endemic malaria remains basically unchanged, and no national antimalaria programme was ever implemented, are inhabited by 500 million people (9%), mainly in tropical Africa. The vast majority of malaria deaths occur in Africa; estimates vary greatly: a figure of 800 000 deaths per year in African children has been quoted in 1991 by the WHO African Region. There are indications that mortality in children has fallen in some areas because of the widespread use of antimalarials, of social development and of better education. There are only a few countries from which the resistance to chloroquine has not been reported, and the rapid evolution of this resistance in Africa threatens to hamper the provision of adequate treatment in rural areas. Resistance to sulfadoxine/pyrimethamine has developed in South-East Asia, South America and focally in Africa. In Thailand, there are indications that up to 50% of cases in certain areas no longer respond to mefloquine therapy, while the sinsitivity to quinine is also diminishing in areas of Thailand and Viet Nam. (DEVELOPING COUNTRIES, MALARIA, TROPICAL DISEASES) 93.77.11 - English - P. DESJEUX, Trypanosomiases and Leishmaniases Control, Division of Control of Tropical Disease, WHO, Geneva (Switzerland) Human Leishmaniases: Epidemiology and Public Health Aspects (p. 267-275) The leishmaniases are parasitic diseases caused by different species of Leishmania, protozoa transmitted by sand flies, haematophagous biting insects. The reservoir hosts are man (anthroponotic cycle) and domestic or wild animals (zoonotic cycle). In man, the disease takes four main clinical forms: visceral, cutaneous, mucocutaneous and diffuse cutaneous. Leishmaniasis, which is now found on four continents, is endemic in 82 countries (21 in the New World and 61 in the Old). Annual incidence is estimated at some 600 000 new clinical cases, officially reported, with a global prevalence of 12 million cases and a population at risk of approximately 350 million. Nevertheless, it seems clear that official reporting of cases considerably underestimates the problem. The leishmaniases retard development and burden countries by weakening the labour force, calling for expensive treatment which often exceeds the total primary health care budget (US$ 60-120 per patient) and slowing down rural development. The leishmaniases can be controlled by tackling various elements of the transmission cycle. In all foci, passive case detection, followed by treatment and notification, should be the basis of the control program. (WHO, PARASITIC DISEASES) 93.77.12 - English - A. MONCAYO, Trypanosomiases and Leishmaniases Control, Division of Control of Tropical Disease, WHO, Geneva (Switzerland) Chagas Disease: Epidemiology and Prospects for Interruption of Transmission in the Americas (p. 276-279) American trypanosomiasis, or Chagas disease, is a parasitic disease caused by the haemoflagellate protozoa, Trypanosoma cruzi. The human infection occurs only in the Americas, where it is widely distributed in the periurban and rural areas of tropical and subtropical countries, from Mexico to Argentina and Chile. It is transmitted to man and other mammals mainly through insects, the triatomine bugs. The results of several serological surveys indicate an overall prevalence of 16-18 million infected individuals. Up to 30% of those infected will develop the cardiac and/or hollow viscera irreversible lesions that characterize chronic Chagas disease. The endemic countries can be divided into four groups according to several indicators such as the number of confirmed human cases, the prevalence of seropositive test in blood donors and population samples, the presence of infected vectors and reservoirs, and the existence or absence of coordinated actions towards the control of this disease. (MEXICO, ARGENTINA, CHILE, PARASITIC DISEASES, CHRONIC DISEASES) 93.77.13 - English - Harry F. HULL and Nicholas A. WARD, Expanded Programme on Immunization, WHO, Geneva (Switzerland) Progress towards the Global Eradication of Poliomyelitis (p. 280- 284) In 1988, the World Health Assembly set the goal of global eradication of poliomyelities by the year 2000. The current WHO strategy for eradication uses three primary activities beyond routine immunization with OPV. They are: (i) improved disease surveillance, (ii) building a global network of laboratories, and (iii) supplemental immunization strategies which include mass immunization campaigns with OPV at the national level, and targeted campaigns at the local level. Eradication of polio from the Region of the Americas is close and may have already been achieved. In other regions, the number of reported polio cases has declined, largely as a result of high immunization coverage. (WHO, POLIOMYELITIS, INFECTIOUS DISEASES) 93.77.14 - English - C. John CLEMENTS, Expanded Programme on Immunization, WHO, Geneva (Switzerland) et al. The Epidemiology of Measles (p. 285-291) Measles is a highly infectious disease which has a major impact on child survival, particularly in developing countries. The importance of understanding the epidemiology of this disease is underlined by its ability to change rapidly in the face of increasing immunization coverage. Much is still to be learned about its epidemiology and the best strategies for administering measles vaccines. However, it is clear that tremendous progress can be made in preventing death and disease from measles with existing knowledge about the disease, and by using the presently available vaccines and applying well-tried methods of treating cases. Research in the coming decade may provide more effective vaccines for use in immunization programmes. An understanding of the basic epidemiology of measles is a prerequisite for effective control measures. (CONTAGIOUS DISEASES, MEASLES, VACCINATION) 93.77.15 - English - Scott B. HALSTEAD, Rockefeller Foundation, New York, NY (U.S.A.) The 20th Century Dengue Pandemic: Need for Surveillance and Research (p. 292-298) By the last decade of 20th century Aedes aegypti and the four dengue viruses had spread to nearly all countries of the tropical world. Some two billion persons live in dengue-endemic areas with tens of millions infected annually. Dengue pandemics were also documented in the 18th and 19th centuries; they were contained by organized anti-Aedes aegypti campaigns and urban improvements. Nearly three million children have been hospitalized with this syndrome in the past three decades, mainly in South-East Asia. Recent outbreaks of DHF/DSS in the Pacific Islands, China, India, Sri Lanka, Cuba and Venezuela are indicators of the high intensity and rapid spread of dengue transmission. The magnitude of 20th century dengue pandemic requires urgent improvements in early warning surveillance by WHO Member States and the development of the capacity to study underlying mechanisms of the disease. A key research question is why does DHF/DSS not occur with all second dengue infections? Two answers have been suggested: (1) a human resistance gene; (2) the existence of dengue "biotypes". How does a second dengue infection cause severe disease? A recent study in Thailand suggests that when antibody residual from the first infection is able to neutralize a second virus type, even weakly, a secondary infection will occur, but its severity is down- regulated and the disease mild. (WHO, TROPICAL DISEASES, ENDEMIC DISEASES, EPIDEMICS) 93.77.16 - English - Akira IGARASHI, Department of Virology, Institute of Tropical Medicine, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852 (Japan) Epidemiology and Control of Japanese Encephalitis (p. 299-305) Japanese encephalitis (JE) remains endemo-epidemic in several countries in East, South-East and South Asia. The disease has been under control in Japan since the 1970s owing to mass immunization using mouse-brain-derived inactivated vaccine and to reduced vector mosquito populations. The vector density which was once reduced by wide spraying of insecticides in rice fields showed an increasing trend after the 1980s as a result of mosquito resistance. In the Republic of Korea, the number of JE cases showed a significant decrease after 1983 also because of mass immunization using mouse-brain-derived vaccine. On the other hand, large outbreaks of JE continued to occur in China, Viet Nam, Thailand, India, Nepal and Sri Lanka. In China, a hamster-kidney cell-derived vaccine was developed and used for human immunization. Besides human JE, the fatal outcome of equine JE is an economic problem in China. The technology of mouse-brain- derived inactivated JE vaccine production was transferred from Japan to India, Thailand and Viet Nam. (ASIA, JAPAN, EPIDEMICS, VACCINATION, EPIDEMIOLOGY) 93.77.17 - English - Y. GHENDON, Microbiology and Immunology Support Services, Division of Communicable Diseases, WHO, Geneva (Switzerland) Influenza - Its Impact and Control (p. 306-311) Epidemics spread rapidly from country to country and may affect as many as 500 million people across the world in a moderate influenza year. The disease, particularly influenza A, kills and the new influenza viruses which appeared in 1957 (Asian influenza) and 1968 (Hong Kong) are estimated to have caused at least 100 000 deaths in the United States of America. Deaths from influenza also occur in years when there is no new virus; at least 10 000 excess deaths have been documented in the United States during each of 18 different epidemics recorded from 1957 to 1985. As many as 79-80% of influenza cases can be prevented when the virus inducing the outbreak and the virus used in the influenza vaccine are closely related. Preventing 80% of cases would correspond in the United States to a saving of US$ 2.5 billion. The strategy for influenza control must be based on the mechanisms of immunity to influenza in humans. Influenza surveillance plays an important part in the control of the disease. The emphasis of the WHO influenza programme established in 1947 is on the rapid isolation and characterization of new strains needed for effective vaccines. It is based on a network of 110 WHO-recognized national institutions for influenza designated by governments in 79 countries and three WHO collaborating centres for reference and research on influenza. Each year at the end of February, WHO issues recommendations for the composition of influenza vaccines to be used in the forthcoming epidemiological season. (WHO, EPIDEMICS, INFLUENZA, VACCINATION)
Back to home page