Sibling familial risk ratio of meningococcal disease in UK Caucasians.

To quantify the host genetic component of meningococcal disease (MD) susceptibility, the sibling risk ratio (lambdaS) was calculated as the ratio of observed MD cases among 845 siblings of 443 UK Caucasian cases to that expected, calculated from age-calendar year specific rates for England and Wales. Twenty-seven siblings contracted MD compared with an expected 0.89, generating a lambdaS value of 30.3. Overestimation of lambdaS due to Neisseria meningitidis exposure was minimized by excluding siblings with MD onset within set time points of the index case. Irrespective of whether siblings contracted MD more than 1, 3, 6, 9 or 12 months after the index case, the lambdaS varied slightly (lambdaS range: 8.2-11.9), suggesting that host genetic factors may contribute approximately one third of the total lambdaS. Social class distribution did not differ between MD cases and the general population of England and Wales. This study is the first to calculate lambdaS for MD and establishes that susceptibility to MD has a significant host genetic component.

A computer simulation of household sampling schemes for health surveys in developing countries.

BACKGROUND: Cluster sample surveys of health and nutrition in rural areas of developing countries frequently utilize the EPI (Expanded Programme on Immunization) method of selecting households where complete enumeration and systematic or simple random sampling (SRS) is considered impractical. The first household is selected by choosing a random direction from the centre of the community, counting the houses along that route, and picking one at random. Subsequent households are chosen by visiting that house which is nearest to the preceding one. METHODS: Using a computer, and data from a survey of all children in 30 villages in Uganda, we simulated the selection of samples of size 7, 15 and 30 children from each village using SRS, the EPI method, and four different modifications of the EPI method. RESULTS: The choice of sampling scheme for households had very little effect on the precision or bias of estimates of prevalence of malnutrition, or of recent morbidity, with EPI performing as well as SRS. However, the EPI scheme was inefficient and showed bias for variables relating to child care and for socioeconomic variables. Two of the modified EPI schemes (taking every fifth house and taking separate EPI samples in each quarter of the community) performed in general much better than EPI and almost as well as SRS. CONCLUSIONS: These results suggest that the unmodified EPI household sampling scheme may be adequate for rapid appraisal of morbidity prevalence or nutritional status of communities, but that it may not be appropriate for surveys which cover a wider range of topics such as health care, or seek to examine the association of health or nutrition with explanatory factors such as education and socioeconomic status. Other factors such as cost and the ability to monitor interviewers' performance should also be taken into account.

Determinants of water quality, availability and use in Kurunegala, Sri Lanka.

Between January 1987 and February 1988, 4590 homes of children under five years of age were visited in three areas of Kurunegala district, Sri Lanka and data were collected on water related practices. 60% of the population used protected wells, 30% used unprotected sources and 10% used handpumps on boreholes or piped supplies. 90% of households had a source less than 1 km away. Mean water consumption was above 25 litres per capita per day and did not correlate with the distance to source. Samples of drinking water were collected and faecal coliform levels were determined in samples of stored water from 3092 households and in samples from the water sources used by 1043 of these households. The absence or presence of organisms in each sample, and the geometric mean count in samples with organisms were used as indices of contamination. Both indices changed with season and varied between areas and between types of water source. The proportion of positive source samples was uniformly high with the exception of piped supplies and handpumps. The mean count was highest for unprotected sources. There was no evidence that ground water contamination occurred in boreholes. With stored samples, boiling appeared to reduce contamination markedly. The proportion of positive stored water samples was also lower with the use of different vessels for collection and storage, with storage inside the house, and with use of a storage container other than an earthenware pot. Because surface water pollution appears to be important it is proposed that headwalls and drainage aprons be built around unprotected sources. Faecal contamination at the source may have more public health significance than contamination of stored water. In this respect public hygiene may play an important role in reducing water pollution at handpumps or protected wells.

Risk of malaria in British residents returning from malarious areas.

OBJECTIVES: To identify which British residents travelling abroad are at greatest risk of malaria infection, and to determine the efficacy of malaria chemoprophylaxis for preventing P falciparum infections in tropical Africa. DESIGN: Prospective cohort study (case-base linkage) with routine national surveillance systems. Denominators (base population) were obtained from monitoring a random sample of returning British travellers with the international passenger survey. Numerators (cases) were obtained from reports of malaria infections in British residents, through the Malaria Reference Laboratory network. SETTING: International passenger survey conducted at passport control of international airports in Britain. Malaria reports received nationally were collated centrally in London. SUBJECTS: 2948 British residents (0.2%) returning to Britain in 1987 randomly selected and questioned and 1052 British residents with microscopically confirmed malaria infections in 1987, whose case reports were reviewed and on whom additional data were collected by postal survey. MAIN OUTCOME MEASURES: Annual incidence subdivided by categories of risk. Chemoprophylactic efficacy for east and west Africa by principal regimens and compliance. RESULTS: Annual rates of reported infection per 100,000 travellers to Oceania were 4100; to west and east Africa were 375 and 172 respectively; to Latin America, the Far East, and the Middle East were 12, 2, and 1 respectively. Immigrants visiting friends and relatives in Ghana and Nigeria were at greatest risk (1303 and 952 per 100,000 respectively) in west Africa. Business travellers to Kenya experienced the highest attack rates in east Africa (465 per 100,000). Age-sex specific attack rates varied by region. No prophylaxis was reported to have been used by 23% of British visitors to west Africa, 17% to east Africa, 46% to central or southern Africa, and 58% visiting south Asia. The efficacy of chloroquine plus proguanil against P falciparum infection was 73% and 54% in west and east Africa respectively. Lower values were obtained for chloroquine alone and proguanil alone. The efficacy of Maloprim (pyrimethamine-dapsone) was 61% in west Africa, but only 9% in east Africa. Visitors to west Africa who did not comply with their chemoprophylactic regimen were at a 2.5-fold higher risk of infection than fully compliant users. Non-compliant visitors to east Africa had similar rates of infection as non-drug users. CONCLUSIONS: In 1987 chloroquine plus proguanil was the preferred chemoprophylactic regimen for P falciparum infection in Africa; antimalarial drugs must be taken regularly to be effective.

Morbidity in relation to the clinical forms and to intensity of infection in Schistosoma mansoni infections in the Sudan.

A study of morbidity in Schistosoma mansoni infection was made in 593 Sudanese patients seen in a four-year period in Khartoum Civil Hospital. Clinical and laboratory findings were compared in three egg-count groups and in four clinical forms of the infection. Patients were divided into three levels of intensity of infection: light (up to 100 eggs/gram of stool), moderate (101--400 eggs/g) and heavy (more than 400 eggs/g). According to the presence or absence of visceral enlargement, infected subjects were divided into one of four clinical forms: intestinal, hepatic, hepatosplenic and splenic. Among the symptoms only the passage of blood in the stools was significantly related to intensity of infection, and fever was significantly related to the presence of hepatosplenic disease. Hepatomegaly and splenomegaly were significantly more frequent in the heavy infection group. Anaemia, eosinophilia, raised ESR and an increase in both serum alkaline phosphatase and serum globulins were significantly related to the intensity of infection. On the other hand, haematological and biochemical changes, as well as histopathological changes, were more marked and severe in patients with hepatosplenic disease. For comparison, the findings of 117 patients with S. haematobium infections and of 41 with dual S. mansoni/S. haematobium infections are included.