Showing papers in "Bulletin of The World Health Organization in 1985"

Interventions for the control of diarrhoeal diseases among young children: improving water supplies and excreta disposal facilities.

Abstract: A theoretical model is proposed that relates the level of ingestion of diarrhoea-causing pathogens to the frequency of diarrhoea in the community. The implications of this model are that, in poor communities with inadequate water supply and excreta disposal, reducing the level of enteric pathogen ingestion by a given amount will have a greater impact on diarrhoea mortality rates than on morbidity rates, a greater impact on the incidence rate of severe diarrhoea than on that of mild diarrhoea, and a greater impact on diarrhoea caused by pathogens having high infectious doses than on diarrhoea caused by pathogens of a low infectious dose. The impact of water supply and sanitation on diarrhoea, related infections, nutritional status, and mortality is analysed by reviewing 67 studies from 28 countries. The median reductions in diarrhoea morbidity rates are 22% from all studies and 27% from a few better-designed studies. All studies of the impact on total mortality rates show a median reduction of 21%, while the few better-designed studies give a median reduction of 30%. Improvements in water quality have less of an impact than improvements in water availability or excreta disposal.

Field evaluation of vaccine efficacy.

Abstract: This paper describes the epidemiological techniques available for measuring vaccine efficacy and recommends a practical approach to their use. The efficacy of vaccines in clinical use can be determined by a variety of means including screening outbreak investigations secondary attack rates in families or clusters vaccine coverage assessment and case-control studies. They all offer a means of monitoring vaccine programs under conditions of day-to-day vaccine use. A table summarizes the different techniques for measuring efficacy. The screening technique is the most useful and rapid means of determining whether there is a problem with a vaccine. All that is required is a reliable estimate of the proportion of cases occurring in vaccinated individuals and an estimate of the vaccine coverage in the population at risk. If the estimated efficacy is within expected limits more detailed studies are not warranted. If the results suggest low efficacy more rigorous methods are necessary to assess the efficacy more accurately. Of the more accurate methods available outbreak investigation offers the simplest means of measuring vaccine efficacy and is the preferred technique if the situation permits. The biases inherent in the method can be minimized particularly if the disease incidence rate is high during the outbreak and accurate records exist. In large populations the underlying immunization status prior to the outbreak can be estimated using the same cluster sampling method used in coverage assessments. Calculation of secondary attack rates in families is also an excellent and accurate means of measuring vaccine efficacy and is an acceptable alternative to the outbreak investigation. Vaccine coverage methods in endemic areas are best suited to urban areas where the measles incidence rate is high after age 11 months and low before 12 months and maternal histories of disease are thought to be accurate. Case-control studies are best suited to areas where reliable personal immunization records may be difficult to find but other information such as clinic records may be available. No epidemiological method is perfect because it cannot exactly duplicate the experimental conditions of a prospective randomized clinical trial. The most accurate results will be obtained when biases are anticipated and corrective measures are taken whenever possible. Clinical vaccine efficacy determinations are carried out in order to assess whether the observed pattern of illness is consistent with the proper use of a highly effective vaccine. The components of a vaccine efficacy evaluation -- case definition case ascertainment and vaccination status determination -- apply to studies on all vaccines.

Interventions for the control of diarrhoeal diseases among young children: rotavirus and cholera immunization.

Abstract: The potential effects of rotavirus and cholera immunization (with an improved vaccine) on diarrhea morbidity and mortality among young children are reviewed using data from field studies and theoretical calculations. In developing countries rotavirus may be responsible for about 6% of all diarrhea episodes and 20% of all diarrhea deaths in children under 5 years of age. In industrial countries these proportions may be higher. Rotavirus immunization may reduce overall diarrhea morbidity rates by 2-3% and diarrhea mortality rates by 6-10% among children under 5 years of age in developing countries depending on vaccine efficacy and program coverage. The impact of improved cholera vaccines depends on the prominence of cholera as a cause of diarrhea and this varies greatly from country to country. Taking the extreme example of Bangladesh where cholera is endemic and may account for about 0.4% of all diarrhea episodes and 8% of all diarrhea deaths in children under 5 years of age cholera immunization might reduce overall diarrhea morbidity rates by 0.06-0.13% and diarrhea mortality rates by 1-2% among these children. The similar incidence rates in industrial and developing countries suggest that rotavirus diarrhea may not be controlled by improvements in water supply sanitation or hygiene. Control may depend upon the widespread of an effective vaccine. (author)

Rainfall and epizootic rift valley fever

Abstract: Epizootic Rift Valley fever (RVF) has occurred in Kenya four times over the last 30 years. Widespread, frequent, and persistent rainfall has been a feature of these epizootic periods. A composite statistic, based upon measurements of these rainfall characteristics, is positive during periods of epizootic Rift Valley fever. The heavy rainfall raises the level of the water table in certain areas, flooding the grassland depressions (dambos) that are the habitat of the immature forms of certain ground-pool-breeding mosquitos of the genus Aedes. RVF virus is probably transmitted transovarially in these species, very large numbers of which emerge under these damp conditions. This is when clinical signs of the disease are first seen.

Epidemiology of blindness in Nepal

Abstract: This report presents the major findings of the Nepal Blindness Survey, the first nationwide epidemiological survey of blindness, which was conducted in 1979-80. The survey was designed to gather data that could be used to estimate the prevalence and causes of blindness in the country. Ancillary studies were conducted to obtain information on socioeconomic correlates and other risk factors of blinding conditions and patterns of health care utilization.The nationwide blindness prevalence rate is 0.84%. Cataract is the leading cause of blindness, accounting for over 80% of all avoidable blindness. Trachoma is the most prevalent blinding condition, affecting 6.5% of the population. Very few cases of childhood blindness were detected.The implications of the survey findings for programme planning, health manpower development, and health education are discussed.

Biomass fuel combustion and health.

Abstract: Biomass fuels (wood, agricultural waste, and dung) are used by about half the world's population as a major, often the only, source of domestic energy for cooking and heating The smoke emissions from these fuels are an important source of indoor air pollution, especially in rural communities in developing countries These emissions contain important pollutants that adversely affect health—such as suspended particulate matter and polycyclic organic matter which includes a number of known carcinogens, such as benzo[a]pyrene, as well as gaseous pollutants like carbon monoxide and formaldehyde Exposure to large amounts of smoke may present a health risk that is of a similar order of magnitude to the risk from tobacco smoke The effects on health arising from exposure to air pollution are reviewed, based on what has been reported in the literature so far Further and more detailed information on exposures and on the epidemiological aspects is urgently required The persons most frequently affected are women who do the cooking for households in rural villages; they suffer from impaired health due to prolonged and repeated contact with these harmful pollutants When they are pregnant, the developing fetus may also be exposed and this leads to the risk of excess deaths In the developing countries, exposure to biomass fuel emissions is probably one of the most important occupational health hazards for women A conservatively estimated 300-400 million people worldwide, mostly in the rural areas of developing countries, are affected by these problems

Japanese encephalitis: current worldwide status.

Abstract: The changing epidemiological and distribution patterns of Japanese encephalitis in various southern and east Asian countries are described. Immunization is considered to be the only practical way to control the infection. Several vaccines have been developed and two types of inactivated vaccine are now available for use in man.

Circulation of influenza viruses and paramyxoviruses in waterfowl originating from two different areas of North America.

Abstract: Migratory waterfowl and shore birds harbour a wide range of influenza viruses, some of which have been implicated in influenza outbreaks in mammals and domestic birds. In the present study, a comparison was made of two marshalling areas for different migratory flyways of waterfowl in North America over a 6-8-year period. Virtually all known influenza subtypes were isolated and the predominant subtype changed from year to year. A marked difference between the two locations was that the predominant subtypes circulating were never the same, even though in both areas, most virus isolations were made from the same duck species (mallard duck). Isolations of paramyxovirus were characterized mainly as avian PMV-1.Viruses isolated from ducks included those antigenically related to viruses causing disease in birds and mammals, although the viruses did not necessarily appear in ducks immediately before they appeared in other species. For example, H5N2 isolates antigenically related to the virus causing severe disease outbreaks in chickens in the USA in 1983, were detected in ducks from both areas at different times (1976, 1980 and 1982). These studies indicate that ducks in different areas represent a continual source of orthomyxoviruses and paramyxoviruses of potential disease significance to other species.

Evaluation of chemotherapy with benznidazole and nifurtimox in mice infected with Trypanosoma cruzi strains of different types.

Abstract: A test was made of the susceptibility of 30 strains of Trypanosoma cruzi to chemotherapy with nifurtimox (Bay 2502) and benznidazole (Ro 7-1051). The strains had previously been classified as type I, II, or III according to their morphobiological and isoenzymic characteristics. Three type I strains, 14 type II strains, and 13 type III strains were studied. Mice were infected with 2 × 105 blood forms of these parasites and treated for 90 days with benznidazole or nifurtimox. All the surviving mice were submitted to parasitological tests (direct parasitaemia, xenodiagnosis, inoculation in new-born mice, and haemoculture) and serological tests (indirect immunofluorescence). As the latter remained positive in about 80% of the parasitologically negative animals, the cure rates were based on the more reliable parasitological tests. Type I strains displayed high susceptibility, type II strains showed medium to high susceptibility, and type III strains were highly resistant to both drugs. The fact that a particular strain type, with its own level of susceptibility, usually predominates in a given geographical area may explain the contradictory results after chemotherapy from different endemic areas.

The efficacy of DPT and oral poliomyelitis immunization schedules initiated from birth to 12 weeks of age.

Abstract: Infants should receive live trivalent oral poliovirus vaccine (TOPV) and DPT immunization as early in life as possible in order to minimize the time that they are at risk of contracting these vaccine-preventable diseases. Passively acquired circulating maternal antibodies provide protection in the 1st few weeks or months of life. Although these antibodies may modify or block the serum immune response during the 1st few weeks of life the 1st or priming dose of DPT can be given effectively after 4 weeks of age. TOPV administered to infants during the 1st week of life results in intestinal infections and local immune responses in 50-100% of infants and serum antibody responses in 30-70% of infants. The serum antibody response following TOPV administration at 4-8 weeks of age is as effective as vaccine administered to older infants. The WHO Program on Immunization recommends initiating DPT and TOPV schedules at 6 weeks of age. In countries where poliomyelitis has not been controlled TOPV should be given at birth or at 1st contact with the health services then at 6 weeks of age followed by 2 additional doses 4 weeks apart. (authors) (summary in FRE)

Rice-based oral rehydration solution decreases the stool volume in acute diarrhoea.

Abstract: A ramdomized trial using oral rehydration solutions (ORS) with rice or glucose was carried out in 342 patients with acute watery diarrhea in the outpatient ward of the International Centre for Diarrheal Disease Research Bangladesh during an epidemic of cholera between December 1982-March 1983. On admission 75% of these patients had severe dehydration and 70% were positive for Vibrio cholerae. There were 185 children aged under 10 years and 157 adults; 169 patients were treated with rice-ORS and 173 with glucose-ORS. Patients in both groups were comparable in age and body weight as well as the duration and severity of illness. Patients with severe dehydration were first rehydrated intravenously and then treated with ORS. Those with moderate dehydration received ORS from the start. The mean stool output in the first 24 hours in children treated with rice-ORS was less than that in those treated with glucose-ORS (155 vs 204 ml/kg 24h; P0.01). The same was the case for the adult patients the corresponding values for stool output being 115 versus 159 ml/kg24h (P0.05); the corresponding intakes in adult patients were respectively 180.5 and 247 ml/kg24 hours. A gain of about 10% of the body weight on admission was observed in all the groups. 6 cases (4 children and 2 adults) who failed to respond to oral rehydration after intravenous therapy all belonged to the glucose-ORS group. The study shows that even under epidemic conditions of severe cholera or in cholera-like diarrhea the glucose or sucrose solutions can be replaced by rice powder with improved results. Glucose and sucrose are manufactured products which are expensive and not always available in countries where diarrheal diseases are a problem. Rice a staple food in many of these countries reduces the fluid requirements when used in ORS and also provides increased nutrition even in the acute stage of illness.

Progress in enzyme immunoassays: production of reagents, experimental design, and interpretation.

Abstract: Enzyme immunoassays represent in many cases the preferred procedure for the detection of antigens or corresponding antibodies. However, many of the current procedures are performed suboptimally. This article reviews the available designs, auxiliary recognition systems, production and purification of antibodies, conjugation procedures, solid-phase materials, recording and interpretation of results, and quality control and standardization of procedures to improve the reproducibility of tests.

Detection, identification, and classification of mosquito larval habitats using remote sensing scanners in earth-orbiting satellites

Abstract: A method of identifying mosquito larval habitats associated with fresh-water plant communities, wetlands, and other aquatic locations at Lewis and Clark Lake in the states of Nebraska and South Dakota, USA, using remote sensing imagery obtained by multispectral scanners aboard earth-orbiting satellites (Landsat 1 and 2) is described. The advantages and limitations of this method are discussed.

Interventions for the control of diarrhoeal diseases among young children: weaning education.

Abstract: A review of data from 12 developing countries suggests that it is possible even in poor communities to improve substantially the nutritional status of infants and young children by weaning education Face-to-face communication by locally recruited workers reinforced by radio and other mass media may be the most effective channels for weaning education It is estimated that through its effect on nutritional status weaning education may reduce the diarrhea mortality rate among children under 5 years of age by 2-12% The possible impacts of weaning education on food hygiene and on feeding during and after diarrheal illness are not considered in this paper Preliminary estimates of cost-effectiveness suggest that weaning education may be an economically attractive intervention for reducing diarrhea mortality in some countries Several important aspects of weaning education and its relation to diarrhea need to be clarified by research (authors) (summary in FRE)

The ecology of trachoma: an epidemiological study in southern Mexico.

Abstract: A total of 1097 people in two communities in Chiapas, Mexico, were examined for trachoma, and information was obtained about personal and family hygiene. Trachoma was hyperendemic; approximately 25% of those under 10 years old were found to have significant inflammatory trachoma and almost 100% of those aged over 40 years had cicatricial trachoma, although the prevalence of trachoma differed significantly between the two communities. Risk factor analysis was performed by contingency table analysis and χ2 testing. The most important parameter associated with the occurrence and severity of inflammatory trachoma in children was the frequency of face washing. Children who washed their faces 7 or more times per week had significantly less trachoma than those who washed less often (χ22df = 28.7; P < 0.001). This effect was independent of age, use of clean water and soap, or use of clothes to dry the face. Children who washed infrequently and who used clothes to dry the face or clean the nose were more at risk for trachoma. No parameters of family hygiene or socioeconomic status correlated with the amount of trachoma in a family. These data confirm and quantify for the first time the long-held belief that trachoma is associated with poor personal hygiene and suggest potentially effective and efficient intervention strategies.

Comparative sensitivity of three mosquito cell lines for isolation of dengue viruses.

Abstract: Comparative studies were carried out on three mosquito cell lines (C6/36 clone of Aedes albopictus, AP-61 from A. pseudoscutellaris, and TRA-284 from Toxorhynchites amboinensis) to determine their sensitivity to dengue virus isolation, growth, and handling characteristics for immunofluorescent testing. Virus isolation rates from human sera were the highest in the TRA-284-SF (a line adapted to serum-free medium), followed by the TRA-284 parental line and AP-61. Virus isolation was the lowest in the C6/36 line. All 3 cell lines were comparable in terms of ease of handling, but C6/36 cells were preferable for detecting infected cells by the direct fluorescent antibody test (DFAT) because of frequent cell clumping in the AP-61 and TRA-284 lines. Early detection of viral antigen of all 4 serotypes in the infected cells by DFAT was dependent upon the virus titre in the serum. The AP-61 and TRA-284-SF cells were the best for early detection and identification of viral antigen. Similarly, both AP-61 and TRA-284 cells were more resistant than C6/36 cells to toxic effects of human sera. Based on the economy of using the serum-free medium, their higher sensitivity for dengue virus isolation, and their ease of handling, it is recommended that the TRA-284-SF cell line be used for routine dengue virus isolation in laboratories with cell culture capability.

Lyophilized combination pools of enterovirus equine antisera: new LBM pools prepared from reserves of antisera stored frozen for two decades.

Abstract: This paper describes the preparation and test procedures for a second batch of lyophilized LBM combination antiserum pools, A through H, used for identifying 42 enteroviruses. Each pool is selectively composed of 10 or 11 of 42 individual enterovirus equine sera so that it contains 500 antibody units of each serum component per 0.1 ml. The new pools have been constituted from equine monovalent antisera that were prepared during the period 1962-67 and then evaluated and standardized in a series of collaborative international studies. An essential aspect of preparing the new pools was ensuring that the individual sera had retained high antibody titres through the long period of storage. At the time of retesting, the original stocks of these monovalent sera had been stored frozen at -20°C for periods ranging from 16 to 20 years.

Case—control study to identify risk factors for paediatric endemic typhoid fever in Santiago, Chile

Abstract: Typhoid fever is an important endemic health problem in Santiago, Chile. Its incidence has more than doubled in recent years, during which access to potable water and sewage disposal in the home became almost universal in the city. A matched case-control study was carried out to identify risk factors and vehicles of transmission of paediatric typhoid fever; 81 children in the 3-14-years age group with typhoid fever were compared with controls, matched with respect to age, sex, and neighbourhood. It was found that case children more frequently bought lunch at school and shared food with classmates. Also, case children more often consumed flavoured ices bought outside the home; none of 41 other food items considered in the study was associated with a higher risk of typhoid fever. Only two food handlers for cases and one for controls were positive for Salmonella typhi, indicating that persons preparing food solely for their own family were not the main source of S. typhi infection. Rather, the risk factors identified in this study are consistent with the hypothesis that paediatric endemic typhoid fever in Santiago is largely spread by consumption of food-stuffs that are prepared outside the individual's home and are shared with or sold to children.

Boiling of drinking-water: can a fuel-scarce community afford it?

Abstract: In the prevention of diarrhoea, health professionals often advocate boiling as a method of choice to provide safe household drinking-water to villagers in the less developed countries. We have examined the financial feasibility of this recommendation in a village study in Bangladesh. Family income was categorized and the pattern of household fuel consumption was determined. Families in the lowest income quartile would have to spend approximately 22% of their yearly income on fuel, and those in the highest income bracket approximately 10%. Boiling of drinking-water would result in an 11% increase in the household budget (as a percentage of income) for a typical family in the lowest income quartile, compared with a 3% increase for a family in the highest income quartile. We conclude that recommendations concerning boiling of drinking-water in developing countries should not be made until their economic feasibility has been demonstrated.

BCG vaccination of children against leprosy: fourteen-year findings of the trial in Burma

Abstract: The value of BCG vaccination in preventing leprosy among children was studied in an area of high leprosy endemicity in Burma through a controlled trial; one group of 13 066 children received BCG and another group of 13 176 served as controls. The overall protective effect of BCG, which was only about 20% over the 14-year period, was found to vary with the batch of vaccine, as well as age, sex, and contact status of the children. BCG protection was found to be independent of the initial tuberculin status of the children. The protective effect of BCG against the lepromatous type of leprosy could not be measured because of the low incidence. Protection was observed throughout the fourteen years of the study except for the first year. The results are compared with those of three other major BCG trials in leprosy. The trial has shown that BCG provides only a very modest level of protection and that BCG vaccination is not likely to be an important solution for leprosy control.

Interventions for the control of diarrhoeal diseases among young children: prevention of low birth weight.

Abstract: The effect of low birth weight (LBW) on diarrhoea morbidity and mortality is analysed and interventions to increase birth weights are reviewed. Birth weight is a major determinant of infant mortality and, in developed countries at least, its effect on neonatal mortality is independent of socioeconomic status. We have located no satisfactory data on LBW as a determinant of diarrhoea mortality or morbidity. The strong association between LBW and mortality, however, makes it likely that there is an association between LBW and diarrhoea mortality in developing countries where diarrhoea is a major cause of infant death. Poor maternal nutrition, certain infections, pre-eclampsia, arduous work after mid-pregnancy, short birth intervals, and teenage pregnancy are likely to be causally associated with LBW in developing countries. Tobacco and alcohol consumption are additional risk factors.Of the interventions examined, maternal food supplementation has been the most studied. If targeted to mothers at nutritional risk, and if the food is consumed in addition to the usual diet, the prevalence of LBW can be expected to be reduced. However, food supplementation can be expensive and the results from carefully supervised feeding trials may be better than those that can be achieved in national programmes. The effect of supplementation with iron, zinc or folate requires further study. If it were possible to intervene in maternal nutrition, health and life-style in a developing country in a way that reduced the prevalence of LBW from around 30% to around 15%, a fall in the infant mortality rate of around 26% would be expected. The fall in infant diarrhoea mortality rate might be similar. The scarce data on relative risk of morbidity by birth weight do not allow any comparable computations for morbidity reductions to be made.This review confirms that whatever its association with diarrhoea, LBW is an important determinant of infant mortality. For the more general goal of reducing infant mortality it is necessary to know more about the nature, etiology, and prevention of LBW in developing countries.

Amoebiasis and its control

Abstract: On a global scale, 480 million people were recently estimated to be infected with Entamoeba histolytica and some 48 million people suffer from invasive amoebiasis. The latter, in the intestinal and extra-intestinal forms, accounts for 40 000 to 110 000 deaths annually. In view of this considerable mortality and morbidity, more research is urgently needed so that more effective control strategies may be introduced.This Update article reviews the magnitude of the problem, clinical and laboratory diagnosis, present treatment and prevention measures, possible control strategies, and research priorities.

Tubal infertility in the Gambia: chlamydial and gonococcal serology in women with tubal occlusion compared with pregnant controls.

Abstract: Levels of immunoglobulin G (IgG) antibodies to Chlamydia trachomatis and Neisseria gonorrhoeae were determined by enzyme-linked immunosorbent assay (ELISA) in 37 infertile Gambian women with bilateral fallopian tube occlusion and in 37 pregnant controls matched for age ethnic group and domicile. The infertile women had a significantly higher prevalence of antibodies to C. trachomatis serotype L1 (P=0.1) and to purified N. gonorrhoeae pili outer membrane and Lipopolysaccharide antigens (P0.01 in each case). Serological studies of immunoglobulin A (IgA) antibodies to C. trachomatis were less sensitive than the IgG studies in discriminating between the pregnant and infertile groups suggesting that much of the infertility due to chlamydiae was the result of past rather than current infection. Data suggest that both C. trachomatis and N. gonorrhoea are important causes of infertility due to tubal pathology in Gambian women. (authors) (summary in FRE)

Hepatitis virus non-A, non-B: the cause of a major public health problem in India

Abstract: Serological studies of hepatitis viruses A and B were carried out on 362 patients with acute viral hepatitis, 130 with fulminant hepatitis, and 56 with subacute hepatitis, and on samples of serum from 230 subjects during epidemics of viral hepatitis. A diagnosis of non-A, non-B viral hepatitis was made when serological tests showed that anti-HAV IgM and anti-HBc IgM were absent. Hepatitis virus non-A, non-B was the causative agent responsible for 58% of cases with acute viral hepatitis, 58% with fulminant hepatitis, 87% with subacute hepatitis, and 66% with epidemic hepatitis. A considerable proportion of patients (6-32%) were infected with both hepatitis virus non-A, non-B and hepatitis virus B. Viral hepatitis non-A, non-B is probably transmitted by infection of drinking-water and is the principal cause of hepatitis in India.

Evaluation of reagent strips in urine tests for detection of Schistosoma haematobium infection: a comparative study in Ghana and Zambia.

Abstract: The presence of haematuria and proteinuria, detected by reagent strips, was compared with Schistosoma haematobium egg counts in the urines of human subjects from two epidemiologically distinct areas in Ghana and Zambia. In children and adults in both areas, the individual or combined semiquantitative levels of proteinuria and haematuria were related directly to increasing urinary egg counts. In both areas the presence of blood in the urine was highly specific (greater than 85%) and sensitive, being positive in 97% of urine specimens with more than 64 eggs per 5-ml sample of urine. The sensitivity of the protein indicator was also high, but its specificity was less than the blood indicator. The specificity of combined proteinuria and haematuria was higher than either alone; on the other hand, the sensitivity was lower than either alone. At each level of proteinuria and haematuria, the geometric mean urinary egg count was higher in Ghana than in Zambia. This study confirms the necessity to evaluate indirect diagnostic techniques in each endemic country, in order to establish criteria for their interpretation, before wide-scale use.

Observations on the application of EPI cluster survey methods for estimating disease incidence.

Abstract: The present study attempted to assess the incidence of target diseases of the Expanded Programme on Immunization (poliomyelitis, tetanus, measles, pertussis, neonatal tetanus, diphtheria), using cluster samples and a household interview form. The results suggest that this method can indeed serve to estimate the incidence of these diseases with reasonable precision and may also be used to demonstrate reduction in incidence for the more common diseases. Analysis of 37 surveys for poliomyelitis and neonatal tetanus in India revealed a relative uniformity in the design effect (i.e., the ratio of the variance for the cluster estimate to the variance for the binomial estimate) for diseases with low incidence and prevalence. Diseases with higher prevalence tend to have a larger design effect, which may be indicative of the epidemic and “clustered” nature of the disease. A large design effect, therefore, does not necessarily indicate a need for a larger sample size, particularly if precision is acceptable. There is no one single design that is ideal for all surveys of disease incidence and decisions must be made in the light of local conditions and available resources.

Serial studies on the evolution of chloroquine resistance in an area of East Africa receiving intermittent malaria chemosuppression.

Abstract: Serial in vitro and in vivo tests for chloroquine sensitivity of Plasmodium falciparum were carried out from 1979 to 1982 in an area of E. Africa where chemosuppression with chloroquine had been attempted since 1977. Within 1½ years there were signs of a decreasing drug response. Chloroquine resistance was first detected in 1981 and this increased markedly in 1982. Other contributory causes for the rise of parasite rates in children were possibly a decline in the efficiency of the drug distribution system and also immunological factors. Evidence of resistance to pyrimethamine was also found. Observations were made of the heterogeneity of the parasites' responses with emerging resistance. Implications for the future are discussed.

Human tanapox in Zaire: clinical and epidemiological observations on cases confirmed by laboratory studies.

Abstract: Human tanapox, a mild disease characterized by a short febrile illness associated with one or more skin lesions, is important because of its possible confusion with smallpox. The article describes clinical and epidemiological features of 264 laboratory-confirmed tanapox cases observed in a geographically limited area in northern Zaire over the period 1979-83.

Indirect screening for Schistosoma haematobium infection: a comparative study in Ghana and Zambia.

Abstract: Four indirect approaches, based on inquiry into a past history of haematuria, visual inspection for blood in the urine specimens, and the use of reagent strips to detect haematuria and proteinuria, were evaluated to identify persons with Schistosoma haematobium infection. These approaches were applied individually and in three different screening sequences on two populations in Ghana and Zambia in order to identify infected children and adults for subsequent treatment in both areas. Detection of haematuria using reagent strips was the single approach with the highest sensitivity and specificity. The observation of gross haematuria (bloody urine), followed by detection of blood by reagent strips, identified 87% of infected children in both areas. This screening sequence showed the highest combined sensitivity and specificity in the identification of infected children as well as adults for treatment in both areas. Differences in the results between the two countries are discussed. This study emphasizes the need for evaluation of indirect screening procedures for the diagnosis of S. haematobium infection in each endemic area so as to establish criteria for their interpretation, prior to large-scale field application.

Bacteriological methods for distinguishing between human and animal faecal pollution of water: results of fieldwork in Nigeria and Zimbabwe

Abstract: Bacteriological techniques have traditionally been used to detect faecal pollution of drinking water supplies. Recently, methods have been developed to distinguish between human and animal faecal pollution in temperate climates. The present study assessed the applicability and practicality of these methods in tropical countries. Fieldwork in Nigeria and Zimbabwe has shown that animal faecal pollution can reliably be identified by the detection and enumeration of Rhodococcus coprophilus using modified M3 agar, whereas human faecal contamination can be identified by the detection of sorbitol-fermenting bifidobacteria. Each of these organisms was detected only in the faeces of the type (human or animal) that it was meant to indicate. Although Streptococcus bovis has been used in the past in mainly temperate countries to distinguish animal from human faecal contamination, the present study has shown that this organism is not a reliable indicator of animal pollution in the tropics because it was excreted by a proportion of the human population in both Nigeria and Zimbabwe. Water sources known to be contaminated by human or animal excreta were examined for these indicator organisms. The results correlated with the results obtained from examining human and animal faecal specimens for these organisms. The role of these bacteriological methods in water pollution control programmes is discussed.