Long-term blood pressure trajectories and associations with age and body mass index among urban women in South Africa.

BACKGROUND: Blood pressure (BP) is known to increase inevitably with age. Understanding the different ages at which great gains could be achieved for intervention to prevent and control BP would be of public health importance. METHODS: Data collected between 2003 and 2014 from 1 969 women aged 22 to 89 years were used in this study. Growth curve models were fitted to describe intra- and inter-individual trajectories. For BP tracking, the intra-class correlation coefficient (ICC) was used to measure dependency of observations from the same individual. RESULTS: Four patterns were identified: a slow decrease in BP with age before 30 years; a period of gradual increase in midlife up to 60 years; a flattening and slightly declining trend; and another increase in BP in advanced age. These phases persisted but at slightly lower levels after adjustment for body mass index. Three groups of increasing trajectories were identified. The respective number (%) in the low, medium and highly elevated BP groups were 1 386 (70.4%), 482 (24.5%) and 101 (5.1%) for systolic BP; and 1 167 (59.3%), 709 (36.0%) and 93 (4.7%) for diastolic BP. The ICC was strong at 0.71 and 0.79 for systolic and diastolic BP, respectively. CONCLUSIONS: These results show that BP preventative and control measures early in life would be beneficial for control later in life, and since increase in body mass index may worsen hypertension, it should be prevented early and independently.

Transitions between body mass index categories, South Africa.

OBJECTIVE: To profile the prevalence of the three body mass index (BMI) categories by sociodemographic characteristics, and to calculate the percentage transitioning (or not) from one BMI category to another, to inform South African health policy for the control of obesity and noncommunicable diseases. METHODS: We used data from the National Income Dynamics Study, including sociodemographic characteristics and BMI measurements collected in 2008, 2010, 2012, 2014 and 2017. For each data collection wave and each population group, we calculated mean BMI and prevalence by category. We also calculated the percentage making an upwards transition (e.g. from overweight to obese), a downwards transition or remaining within a particular category. We used a multinomial logistic regression model to estimate transition likelihood. FINDINGS: Between 2008 and 2017, mean BMI increased by 2.3 kg/m2. We calculated an increased prevalence of obesity from 19.7% (3686/18 679) to 23.6% (3412/14 463), with the largest increases in prevalence for those aged 19-24 years and those with at least high school education. The percentages of upwards transitions to overweight or obese categories increased sharply between the ages of 19 and 50 years. Once overweight or obese, the likelihood of transitioning to a normal BMI is low, particularly for women, those of higher age groups, and those with a higher income and a higher level of education. CONCLUSION: In the development of national strategies to control obesity and noncommunicable diseases, our results will allow limited public health resources to be focused on the relevant population groups.

Geographical influence on the distribution of the prevalence of hypertension in South Africa: a multilevel analysis.

BACKGROUND: As a response to the growing burden of non-communicable diseases, the South African government has set targets to reduce the prevalence of people with raised blood pressure, through lifestyle changes and medication, by 20% by the year 2020. It has also recognised that the prevalence varies at local administrative level. The study aim was to determine the geographical variation by district of the prevalence of hypertension among South African adults aged 15 years and above. METHODS: Data from all five waves of the National income Dynamics Study, a panel survey, were used for estimation by both design-based and multilevel analysis methods. In the multilevel analysis, a three-level hierarchy was used with panel participants in the first level, repeated measurements on patients in the second level, and districts in the third level. RESULTS: After accounting for demographic, behavioural, socio-economic and environmental factors, significant variation remained in the prevalence of hypertension at the district level. Districts with higher-than-average prevalence were found mostly in the south-western part of the country, while those with a prevalence below average were found in the northern area. Age, body mass index and race were the individual factors found to have a strong effect on hypertension prevalence for this sample. CONCLUSIONS: There were significant differences in hypertension prevalence between districts and therefore the method of analysis and the results could be useful for more targeted preventative and control programmes.

Microbiological investigation for tuberculosis among HIV-infected children in Soweto, South Africa.

SETTING: A paediatric human immunodeficiency virus (HIV) clinic in an academic hospital in Soweto, South Africa. OBJECTIVES: 1) To describe and compare the clinical, immunological and virological characteristics of HIV-infected children co-treated for tuberculosis (TB), and 2) to compare those investigated microbiologically with those who were not, with a description of the results of the microbiological TB investigation. DESIGN: Retrospective analysis of TB-HIV-infected children aged <15 years treated for TB between 1 October 2007 and 15 March 2009. RESULTS: Anti-tuberculosis treatment was initiated in 616/3358 (18%) children during the study period. Microbiological TB investigation results were available for 399/616 (65%), among whom culture-confirmed TB was diagnosed in 49 (12%). Drug susceptibility testing was performed in 29/49 (59%) children: 5/29 (17%) were isoniazid-resistant, and 3 had multidrug-resistant TB. Children aged >8 years and those between 3 and 8 years were more likely to have culture-confirmed TB than those aged <3 years (aOR 9.4, 95%CI 2.26-39.08 vs. aOR 6.7, 95%CI 1.60-27.69), as were those with CD4 count <200 cells/mm(3) compared to those with >500 cells/mm(3) (aOR 3.95, 95%CI 1.23-12.72). CONCLUSION: Our study in HIV-infected children showed a high TB case rate, a low rate of definite TB and a high rate of drug-resistant TB based on World Health Organization case definitions. Increased uptake of available TB tests and availability of new diagnostic tests remains a priority in high TB-HIV burden settings.

A survey for Echinococcus spp. of carnivores in six wildlife conservation areas in Kenya.

To investigate the presence of Echinococcus spp. in wild mammals of Kenya, 832 faecal samples from wild carnivores (lions, leopards, spotted hyenas, wild dogs and silver-backed jackals) were collected in six different conservation areas of Kenya (Meru, Nairobi, Tsavo West and Tsavo East National Parks, Samburu and Maasai Mara National Reserves). Taeniid eggs were found in 120 samples (14.4%). In total, 1160 eggs were isolated and further analysed using RFLP-PCR of the nad1 gene and sequencing. 38 of these samples contained eggs of Echinococcus spp., which were identified as either Echinococcus felidis (n=27) or Echinococcus granulosus sensu stricto (n=12); one sample contained eggs from both taxa. E. felidis was found in faeces from lions (n=20) and hyenas (n=5) while E. granulosus in faeces from lions (n=8), leopards (n=1) and hyenas (n=3). The host species for two samples containing E. felidis could not be identified with certainty. As the majority of isolated eggs could not be analysed with the methods used (no amplification), we do not attempt to give estimates of faecal prevalences. Both taxa of Echinococcus were found in all conservation areas except Meru (only E. felidis) and Tsavo West (only E. granulosus). Host species identification for environmental faecal samples, based on field signs, was found to be unreliable. All samples with taeniid eggs were subjected to a confirmatory host species RLFP-PCR of the cytochrome B gene. 60% had been correctly identified in the field. Frequently, hyena faeces were mistaken for lion and vice versa, and none of the samples from jackals and wild dogs could be confirmed in the tested sub-sample. This is the first molecular study on the distribution of Echinococcus spp. in Kenyan wildlife. The presence of E. felidis is confirmed for lions and newly reported for spotted hyenas. Lions and hyenas are newly recognized hosts for E. granulosus s.s., while the role of leopards remains uncertain. These data provide the basis for further studies on the lifecycles and the possible link between wild and domestic cycles of cystic echinococcosis in eastern Africa.

Changing mother's hygiene and sanitation practices in resource constrained communities: case study of Turkana District, Kenya.

Lack of adequate sanitation, hygiene and safe portable water are serious global health problems that contribute to deaths of many children under the age of 5 years annually, mainly due to diarrhoeal diseases. This study was set out to determine the extent to which sanitation and hygiene promotion influenced mothers' and children's health in Turkana District; one of the arid Northern frontier Districts of Kenya. A repeat cross-sectional study design with multi-stage sampling method was used. A total of 300 mothers were randomly sampled for interviews in a baseline survey carried out in 2007 and in a post-intervention survey carried out in 2008. Data were collected using questionnaires and analyzed using SPSS for frequencies, cross tabulations and regression amongst other tests. Significant improvements were observed in hand washing practice, presence of hand washing soap at household and refuse pit ownership. In Kakuma Division the proportion of those who washed hands regularly increased from 48.8 to 91.3 % (χ(2) = 7.28, P = 0.122), in Lodwar Central, those who wash hands regularly increased from 85.5 to 89.9 % (χ² = 10.85, P = 0.028) while in Lokichogio, the proportions increased from 77.5 to 93.8 % (χ² = 15.56, P = 0.004). For hand washing soap at household, there was an increase in proportion of those who wash hands with soap from 65 to 78 % (χ² = 3.87, P = 0.049) within the group with no formal education. There was significant reduction of diarrhoea prevalence in children aged less than 5 years. Sanitation and hygiene promotion based on community participatory approaches can lead to significant reduction of diarrhoea in children.

Effects of hygiene and sanitation interventions on reducing diarrhoea prevalence among children in resource constrained communities: case study of Turkana District, Kenya.

Worldwide, lack of access to safe drinking water together with inadequate sanitation and hygiene is an overwhelming contributor to approximately 4 billion cases of illness annually. This study was set out to understand the effects of hygiene and sanitation interventions on targeted health outcomes including diarrhoeal prevalence in children's of Turkana District, Kenya. The interventions undertaken included capacity building and empowerment approach to trigger communities to demand hygiene and sanitation facilities. Three hundred mothers were randomly sampled in a baseline survey carried out in 2007 and in a post-intervention survey carried out in 2008 (a repeat cross-sectional study design). Specimens were collected for microbiological tests of key diarrhoea related pathogens. Overall, Faecal coliform counts per 100 ml sample had significant variations between 2007 and 2008; in Kakuma, reduced from 88 to 30.2 colony units (P = 0.005), Lodwar Central where the number reduced from 91 to 17.3 units (P = 0.003), and in Lokichogio Division, the number reduced from 63.8 to 23.6 units (P = 0.006). From the 230 stool samples examined, the proportion of children from whom infectious pathogens of Proteus spp. was isolated reduced from 16 to 7 % while Escherichia coli reduced from 54 to 41 %. Overall, prevalence of diarrhoea related microbes in children aged <5 years reduced from 91.3 % in 2007 to 78.3 % after intervention (2008). It is notable that sanitation and hygiene promotion leads to significant reduction of diarrhoea prevalence in children aged <5 years. Its application should therefore be up-scaled in resource constrained areas.

NIMART rollout to primary healthcare facilities increases access to antiretrovirals in Johannesburg: an interrupted time series analysis.

INTRODUCTION: South Africa has made remarkable progress in rolling out antiretroviral therapy (ART), with the largest number of people (more than 1.4 million) enrolled on antiretroviral in the world. Decentralisation of services to primary health centres (PHCs) has strengthened retention of patients on ART and reduced the burden of managing uncomplicated cases at referral hospitals. METHODS: This was a ten-step Nurse Initiation Management of Antiretroviral Treatment (NIMART) rollout intervention in which nurses from 17 primary healthcare facilities of Region F, City of Johannesburg, South Africa, were trained and mentored in NIMART by the Wits Reproductive Health and HIV Research Institute (WRHI) to commence patients on ART in their PHCs. A total of 20 535 patients initiated ART during the 30-month study period. Monthly initiations at both PHCs and referral clinics were monitored. To test the statistical significance of the impact of NIMART rollout on the referral hospital initiations and Region F monthly initiations, interrupted time series analysis was applied. FINDINGS: Ten-step NIMART was applied, with the first step being establishment of NIMART as a priority in order to obtain primary buy-in by the Department of Health (DoH) and City of Johannesburg (CoJ). Forty-five professional nurses were trained in NIMART by WRHI quality improvement mentors. By the end of September 2011, all 17 PHCs in Region F were initiating patients on ART. Total initiations significantly increased by 99 patients immediately after NIMART rollout (p=0.013) and continued to increase by an average of 9 every month (p=0.013), while referral facility initiations decreased by 12 (p=0.791) immediately after NIMART and then decreased by an average of 18 every month (p=0.01). CONCLUSION: In this study, decentralisation of ART initiation by professional nurses was shown to increase ART uptake and reduce workload at referral facilities, enabling them to concentrate on complicated cases. However, it is important to ensure capacity building, training and mentoring of nurses to integrate HIV services in order to reduce workload and provide a comprehensive package of care to patients. Engaging and having buy-in from DoH/CoJ partners in rolling out NIMART was crucial in increasing outputs as well as for sustainability of the NIMART programme.

Modifiable factors associated with active pulmonary tuberculosis in a Kenyan prison.

OBJECTIVES: To establish modifiable factors associated with active pulmonary tuberculosis (PTB) among prisoners. DESIGN: Retrospective matched case-control study. SETTING: Nakuru GK prison in Kenya. SUBJECTS: A total of 144 subjects (48 cases and 96 controls) were recruited into the study. Cases were adult prisoners who had at least two initial sputum specimens being Acid Fast Bacilli-positive (AFB+) on direct smear microscopy and hence recruited to PTB WHO DOTS Programme. Controls were adults with no chronic cough and not on PTB treatment six months prior to the study. RESULTS: Independent factors significantly associated with active PTB disease were: self reported HIV+ status (OR=11; 95% CI = 2.42-47.77), evidence of BCG vaccination (OR = 0.20; 95% CI = 0.05-0.60), contact with PTB case (OR = 7.0; 95% CI = 1.17-38.23), unemployment (OR = 9.0; 95% CI = 1.84-43.97) and sharing linen (OR = 4.32; 95%CI = 1.08-17.29). CONCLUSIONS: Modifiable factors associated with active PTB in Nakuru G.K prison are: HIV status, BCG vaccination, PTB case contact, poverty and poor personal hygiene. We recommend HIV counselling and testing of all PTB patients, screening for TB upon prison entry and TB contact investigation and improving personal hygiene of prisoners.

Hepatosplenomegaly associated with chronic malaria exposure: evidence for a pro-inflammatory mechanism exacerbated by schistosomiasis.

In sub-Saharan Africa, chronic hepatosplenomegaly, with palpable firm/hard organ consistency, is common, particularly among school-aged children. This morbidity can be caused by long-term exposure to malaria, or by Schistosoma mansoni, and it is exacerbated when these two occur together. Although immunological mechanisms probably underlie the pathogenic process, these mechanisms have not been identified, nor is it known whether the two parasites augment the same mechanisms or induce unrelated processes that nonetheless have additive or synergistic effects. Kenyan primary schoolchildren, living in a malaria/schistosomiasis co-transmission area, participated in cross-sectional parasitological and clinical studies in which circulating immune modulator levels were also measured. Plasma IL-12p70, sTNF-RII, IL-10 and IL-13 levels correlated with relative exposure to malaria, and with hepatosplenomegaly. Soluble-TNF-RII and IL-10 were higher in children infected with S. mansoni. Hepatosplenomegaly caused by chronic exposure to malaria was clearly associated with increased circulating levels of pro-inflammatory mediators, with higher levels of regulatory modulators, and with tissue repair cytokines, perhaps being required to control the inflammatory response. The higher levels of regulatory modulators amongst S. mansoni infected children, compared to those without detectable S. mansoni and malarial infections, but exposed to malaria, suggest that S. mansoni infection may augment the underlying inflammatory reaction.

Intestinal polyparasitism in a rural Kenyan community.

BACKGROUND: Polyparasitism seems to be a common feature in human populations in sub-Saharan Africa. However, very little is known about its epidemiological significance, its long term impact on human health or the types of interactions that occur between the different parasite species involved. OBJECTIVES: To determine the prevalence and co-occurrence of intestinal parasites in a rural community in the Kibwezi, Makueni district, Kenya. DESIGN: A cross sectional study. SETTING: Kiteng'ei village, Kibwezi, Makueni district, between May and September 2006. SUBJECTS: One thousand and forty five who comprised of 263 adult males, 271 adult females > 15 years of age and 232 boys, and 279 girls <15 years of age. INTERVENTIONS: All infected members of the community were offered Praziquantel (at dosages of 40 mg/kg body weight) for Schistosomiasis and Albendazole (600 mg) for soil transmitted helminths. RESULTS: A total of ten intestinal parasite species (five protozoan and five helminth parasite species) were present in this community and polyparasitsm was common in individuals 5-24 years of age with no gendar related differences. Most of the infections were mild. The protozoan parasites of public health significance present were Entamoeba histolytica and Giardia lamblia with prevalence of 12.6% and 4.2%, respectively. The helminth parasites of public health significance in the locality were Schistosoma mansoni with a prevalence of 28%, and hookworms prevalence of 10%. About 53% of the study population harboured intestinal parasite infections, with 31% of the infected population carrying single parasite species infections, and 22% harbouring two or more intestinal parasite species per individual. Significant positive associations (p values <0.05) were observed between S. mansoni and hookworms, hookworms and Hymenolepis. nana and Entamoeba histolytica and Entamoeba coli. CONCLUSION: Intestinal polyparasitism was common in the Kiteng'ei community, particularly in individuals aged of 5-24 years old. An integrated control programme of approach would be recommended for the control of S. mansoni, hookworms and Entamoeba histolytica for this community.

Hydrological modelling of snail dispersal patterns in Msambweni, Kenya and potential resurgence of Schistosoma haematobium transmission.

Urinary schistosomiasis is an important source of human morbidity in Msambweni, Kenya, where the intermediate host snail, Bulinus nasutus is found in ponds and water pools. In the past, aquatic habitats in the area have been studied separately; however, recent collections of B. nasutus snails and shells indicated that many of these ponds are in fact connected during and following sufficient rains. Satellite imagery and a geographical information system (GIS) were used to survey the main water courses and potential drainage routes, to locate potential source populations of snails and to determine probable snail dispersal routes. The 2 water bodies implicated as being the most important Schistosoma haematobium transmission foci in the area were found to differ in their degree of connectivity to other B. nasutus source habitats. One pond becomes connected even after normal rains, while the other pond requires prolonged rains or flooding to become connected with source habitats. Consequently, the transmission foci differ in their susceptibility to snail population control measures. Spatially explicit dispersal models that consider the spatial and temporal patterns of connectivity between aquatic habitats will contribute to improved snail surveillance and more focused control for urinary schistosomiasis at a local level.

Hepatosplenic morbidity in two neighbouring communities in Uganda with high levels of Schistosoma mansoni infection but very different durations of residence.

Peri-portal fibrosis can be a serious sequelae of Schistosoma mansoni infection. Age or duration of exposure have been identified as important risk factors, but their relative importance cannot be easily separated. Here, we have compared two cohorts, aged 6-50 years and resident for ten years or since birth, from two neighbouring villages (Booma and Bugoigo) on the eastern shore of Lake Albert, Uganda. Parasitological measurements were similar, whereas the prevalence of peri-portal fibrosis was 5-fold higher in Booma. Data from the cohorts were pooled to assess the relative contribution of age and duration of residency on the risk of disease. Amongst adults, duration of residency was the critical risk factor--individuals aged 17-31 years resident for more 22 years had an almost 12-fold increased risk of fibrosis than those resident for less than 15 years. Height-standardised Splenic Vein Diameter (SVD), Portal Vein Diameter (PVD), Para-sternal Liver Length (PLL) and Spleen Length (SL) values were all higher in Booma, and each organometric parameter except PLL increased with the severity of fibrosis. Our results clearly demonstrate that duration of exposure is a critical risk factor for the development of peri-portal fibrosis and its sequelae in adults. This parameter should therefore be a routine measurement during epidemiological surveys of S. mansoni.

Schistosoma haematobium-induced urinary tract morbidity correlates with increased tumor necrosis factor-alpha and diminished interleukin-10 production.

This study examined the hypothesis that the nature of the host cellular immune response to schistosome ova is a risk factor for urinary tract morbidity in areas in which Schistosoma haematobium is endemic. S. haematobium-infected children and adolescents with bladder pathology assessed by ultrasonography had 54-fold greater tumor necrosis factor (TNF)-alpha production and a 120-fold greater ratio of TNF-alpha to interleukin (IL)-10 release by peripheral blood mononuclear cells in response to egg antigens, in comparison with control children and adolescents matched by age, sex, and infection severity. Mycobacterial antigens also stimulated 7-fold more TNF-alpha among subjects with bladder morbidity than in control subjects, which suggests an innate predisposition to enhanced TNF-alpha production. Levels of egg antigen-induced IL-4 and -5 and interferon-gamma were equivalent in subjects with and without bladder pathology. Thus, children and adolescents predisposed to increased TNF-alpha production to S. haematobium infection are more likely to develop an exaggerated granulomatous response to ova trapped in the bladder wall, with associated urinary tract pathology.

A comparative study of different albendazole and mebendazole regimens for the treatment of intestinal infections in school children of Usigu Division, western Kenya.

A clinical trial to compare the effectiveness of 4- and 6-mo repeated treatment with albendazole 600 mg (Zentel, SmithKline Beecham) or mebendazole 600 mg (Vermox, Janssen) on geohelminth infections was carried out on children in 6 primary schools; the study included 1,186 children, ages 4 to 19 yr. Kato-Katz examination was performed on stool samples before and after treatment. Overall, albendazole produced better cure rates and egg reduction rates for geohelminths. The cure rates for albendazole were 92.4% for hookworm infection, 83.5% for Ascaris lumbricoides, and 67.8% for Trichuris trichiura. Mebendazole given either 2 or 3 times in a year had cure rates of 50 and 55.0% (respectively) for hookworm, 79.6 and 97.5% for A. lumbricoides, and 60.6 and 68.3% for T. trichiura infection. The geometric mean intensity of hookworm eggs per gram (epg) of stool decreased by 96.7% after albendazole treatment compared with 66.3 and 85.1%, respectively, for 2 or 3 doses of mebendazole (P < 0.05) over the same period. Reductions in epg for A. lumbricoides and T. trichiura were comparable for both drugs. Our results indicate that treatment with albendazole at a 6-mo interval was more effective than mebendazole regimens and may be the best choice for use in the control of the 3 geohelminths.

Prevalence and familial aggregation of schistosomal liver morbidity in Kenya: evaluation by new ultrasound criteria.

Severe periportal fibrosis is not an inevitable consequence of infection with Schistosoma mansoni. Genetic predisposition may be a deciding factor in the development of disease. To assess the contribution of genetic factors in the severity of hepatic fibrosis, the degree of familial aggregation was determined in a Kenyan population. Schistosomal fibrosis was identified with hepatic ultrasound and newly proposed World Health Organization criteria, which include both qualitative and quantitative observations. These 2 aspects of the criteria correlated well with one another. The peak prevalence of ultrasound proven fibrosis trailed 5-10 years behind peak prevalence of infection and declined sharply after age 50 years. This pattern was consistent with either resolution of severe fibrosis over 10-20 years or early death of those severely affected. Genetic predisposition appears to be a weak factor in the development of severe disease in this population, since no household or familial aggregation could be identified.

Evidence against rapid emergence of praziquantel resistance in Schistosoma haematobium, Kenya.

We examined the long-term efficacy of praziquantel against Schistosoma haematobium, the causative agent of urinary schistosomiasis, during a school-based treatment program in the Msambweni area of Coast Province, Kenya, where the disease is highly endemic. Our results, derived from treating 4,031 of 7,641 children from 1984 to 1993, indicate substantial year-to- year variation in drug efficacy. However, the pattern of this variation was not consistent with primary or progressive emergence of praziquantel resistance. Mathematical modeling indicated that, at current treatment rates, praziquantel resistance will likely take 10 or more years to emerge.

A school-based approach to the control of urinary schistosomiasis and intestinal helminth infections in children in Matuga, Kenya: impact of a two-year chemotherapy programme on prevalence and intensity of infections.

A school- and chemotherapy-based urinary schistosomiasis and intestinal helminth infection control programme was conducted in Matuga Division, Kwale District, Coast Province with teachers taking care of diagnosis, treatment and health education. More than 12,000 children in 36 primary schools were included in the 2-year programme. Results for 20 evaluation schools are presented. Children with haematuria were treated with praziquantel (40 mg/kg) once a year. Within 2 years, the prevalence of haematuria in the schools was reduced from 28% (range 8-68%) to 11.4% (range 3-23%). More than 80% of the schoolchildren were infected with one or more intestinal helminths at baseline. After one year with levamisole mass chemotherapy, single dose (2.5 mg/kg) three times a year (once per school term), the prevalence of Ascaris infection was reduced by 83% from 18% to 3%, but there was no change in pretreatment prevalences of hookworm (57%) and Trichuris (56%) infections. In the second year of the programme, albendazole 600 mg once every six months was administered to the children in 10 randomly selected schools. This resulted in 52% and 23% reductions in prevalences of hookworm and Trichuris infections, respectively, in these schools and a reduction in mean intensity of infection of 52.8% and 50.3%, respectively.

Dynamics and control of Schistosoma haematobium transmission in Kenya: an overview of the Msambweni Project.

Ecologic modeling of Schistosoma transmission in endemic communities has suggested that antiparasite therapy targeted at the most heavily infected segment of the human population (i.e., school-age children) should have a significant impact on local parasite transmission. Our 1984-1991 experience with age-targeted therapy in the Msambweni area of Kenya has shown an overall decrease in area transmission within 1-2 years following initiation of annual treatment of school-age groups. Snail monitoring confirmed a continuing but variable reduction of vector infection rates. However, subgroup analysis showed significant differences in transmission suppression between more developed coastal villages with piped-water kiosks and villages with only limited access to safe water supplies. Villages without piped water were marked by higher initial prevalences of S. haematobium infection, greater prevalence among adults, longer and more frequent contact with high-risk water sources, and persistently high transmission despite compliance with parasitologic screening or drug therapy. We conclude that targeted therapy had a significant impact on S. haematobium transmission in some areas, but that more extensive or more prolonged coverage is necessary to reduce the rate of new infection in high-risk villages. Defining field-use algorithms, based on decision analysis of economic and ecologic parameters, should provide effective guidelines for selective versus mass treatment in expanded control areas.