SummaryThis paper discusses the distinction between the transmission of infectious diseases within the domestic domain (the area normally occupied by and under the control of a household) and that in the public domain, which includes public places of work, schooling, commerce and recreation as well as the streets and fields. Whereas transmission in the public domain can allow a single case to cause a large epidemic, transmission in the domestic domain is less dramatic and often ignored, although it may account for a substantial number of cases. Statistical methods are available to estimate the relative importance of the two. To control transmission in the public domain, intervention by public authorities is likely to be required. Two examples show how environmental interventions for disease control tend to address transmission in one or the other domain; interventions are needed in both domains in order to interrupt transmission. More than 20 years ago, Bradley and colleagues proposed the classification of water-related infections according to their mode of transmission, rather than the type of organism which caused them or their effect on the patient (White et al. 1972). This classification into water-borne, water-washed, water-based and water-related insect vector groups was a new paradigm which has stood the test of time with only a few modifications, and greatly helped to clarify our thinking about how environmental interventions such as water supply improvements affect disease. It has three advantages. First, it was so simple and (in retrospect) obvious that it was hard to argue with it or forget it. Second, it built on existing knowledge, and drew together the conclusions of a number of studies and authors in widely differing environments.Third, it helped to clarify the issues for the practitioner.The one significant improvement, made to the Bradley classification by Richard Feachem (rq77), was to consider it as a classification of transmission routes rather than of diseases, because (as Bradley had recognized) some diseases could be transmitted by more than one route. This helped to redouble the interest in the transmission process, which is the particular concern of those of us who seek to control disease by environmental modification rather than by immunization or the treatment of patients.We propose another division of transmission routes which cuts across the preceding categories and is complementary to that classification. It is not limited to the water related diseases and can apply to all infections. Our division is between transmission occurring within the domestic domain-the 27( j I996 Blackwell Science Ltd

A longitudinal prospective study of the effect of drainage and sewerage systems on diarrhoea in children aged < 5 years was conducted in 9 poor urban areas of the city of Salvador (population 2.44 million) in north-east Brazil in 1989-90. Due to complex political and administrative reasons, 3 areas had benefited from drainage improvements, 3 from both drainage and sewerage improvements, and 3 from neither. An extensive questionnaire was applied to collect information on each child and on the conditions of the household, and mothers recorded diarrhoea episodes in their children aged < 5 years daily for 1 year, using calendars. Fortnightly home visits were made to collect the data. The incidence of diarrhoea in children in neighbourhoods with drainage was less than two-thirds, and in neighbourhoods with drainage and sewerage less than one-third, of the incidence in neighbourhoods with neither. After controlling for potential confounders, the proportion of children with 'frequent diarrhoea' showed the same significant trend across the study groups. Though the groups were not exactly comparable, more than one child was monitored per household, and it was not possible to rotate fieldworkers between study groups, the study provides evidence that community sanitation can have an impact on diarrhoeal disease, even without measures to promote hygiene behaviour.

This cross-sectional study was conducted in 1989 among children aged between 5 and 14 years old living in nine poor urban areas of the city of Salvador (pop. 2.44 million), capital of Bahia State, in Northeast Brazil. Three of these areas had benefited from both drainage and sewerage, 3 from improved drainage only, and 3 from neither. The children studied thus belonged to 3 exposure groups regarding their level of sanitation infrastructure. An extensive questionnaire was applied to collect information on each child and on the conditions of the household, and stool examinations of the children 5-14 years old were performed to measure nematode infection. Comparison of the sewerage group with the drainage-only group and the latter with the control (no sewerage or drainage) group showed that, when the level of community sanitation was better, the prevalence of infection among children was less, but risk factors identified for infection were more numerous and more significant. Intensity of infection with Trichuris, but not with Ascaris or hookworm, was also less. The results suggest that sewerage and drainage can have a significant effect on intestinal nematode infections, by reducing transmission occurring in the public domain.

The association of infantile diarrhoea with the presence of garbage in the environment was investigated in Canabrava, a peripheral neighbourhood of Salvador, northeast of Brazil. A cross-sectional study was conducted with all the 184 children aged less than two years residing in Canabrava, which is located close to the city garbage dump. Variables selected for study included the method used for the disposal of excrement, type of floor, mother's education, unemployment of the head of the family, regularity of the water supply, presence of toilet, storage of garbage inside the house, age, gender, duration of breastfeeding, and the number of people per room. The estimated prevalence of diarrhoea was 21.2%. Exposure to garbage in the environment was found to be the most important factor associated with diarrhoea (adjusted odds ratio [AOR] = 3.98, 95% CI 1.56-10.13). Other important variables were the mother's education (AOR = 2.79, 95% CI 1.09-7.13), maternal breastfeeding (AOR = 2.30, 95% CI 1.05-5.04), and unemployment of the head of the family (AOR = 2.09, 95% CI 0.93-4.69). These findings indicate the necessity of adopting solutions in the public domain and of intersectorial policies for the reduction of diarrhoea.

The objective of this study was to identify target microorganisms as indicators of environmental contamination. The study evaluates the main environmental aspects and epidemiological chain related to such agents. Microorganisms were selected through key information about microbiological characterization of health care facilities' solid waste and evaluation of risk of infection from discarded sharps. The form of evaluation proposed for criteria adopted in the selection of contamination indicators included prior submission of a structured questionnaire to a network of specialists from the Federal District of Brazil. The specialists' multidisciplinary background, including professionals from the health field and an environmental microbiologist, helped define environmental contamination indicators by consensus. Pathogens such as Mycobacterium tuberculosis and hepatitis A and B viruses were specifically identified as capable of environmental survival or resistance.