Advanced HIV disease (AHD) remains a significant burden, despite the widespread use of antiretroviral therapy (ART) programs. Individuals with AHD are at a high risk of death even after starting ART. We characterized treatment naïve and treatment experienced clients presenting with AHD in western Kenya to inform service delivery and program improvement. We conducted a retrospective study using routinely collected program data from October 2016 to September 2019 for AHD clients in eight facilities in Homa Bay County, Kenya. Demographic and clinical data were abstracted from the medical records of AHD clients, defined as HIV-positive clients aged ≥ 5 years with documented CD4 count < 200 cells/mm3 and/or WHO clinical stage II/IV. Associations were assessed using Pearson's chi-square and Mann-Whitney Rank-Sum tests at 5% level of significance. Of the 19,427 HIV clients at the eight facilities, 6649 (34%) had a CD4 count < 200 cells/mm3 or a WHO III/IV stage. Of these, 1845 were randomly selected for analysis. Over half (991) of participants were aged 45 + years and 1040 (56%) were female. The median age was 46.0 years (interquartile range: 39.2-54.5); 1553 (84%) were in care at county and sub-county hospitals; and 1460 (79%) were WHO stage III/IV at enrollment. At ART initiation, 241 (13%) had tuberculosis, 192 (10%) had chronic diarrhea, and 94 (5%) had Pneumocystis jiroveci pneumonia. At the time of data collection, 89 (5%) participants had died and 140 (8%) were lost to follow-up. Eighteen percent (330) of participants were ART-experienced (on ART for ≥ 3 months). The proportions of ART-experienced and -naïve clients regarding age, sex and marital status were similar. However, a higher proportion of ART-experienced clients received care at primary care facilities, (93(28%) vs. 199 (13%); P < .001); were WHO stage 3/4 at AHD diagnosis, 273 (84%) vs. 1187 (79%) (P = .041); and had died or been LTFU, (124 (38%) vs. 105 (7%); P < .001). With increasing prevalence of patients on ART, the proportion of AHD treatment-experienced clients may increase without effective interventions to ensure that these patients remain in care.

Following a four-year annual praziquantel treatment campaign the resulting prevalence of S. mansoni was seen to differ among individual villages along the Kenyan shore of Lake Victoria. We have investigated possible inherent differences in snail-related aspects of transmission among such 10 villages, including six persistent hotspot (PHS) villages (≤30% reduction in prevalence following repeated treatments) located along the west-facing shore of the lake, and four PZQ-responding (RESP) villages (&gt;30% prevalence reduction following repeated treatment) along Winam Gulf. When taking into account all sampling sites and times and water hyacinth presence/absence, shoreline-associated B. sudanica from PHS and RESP villages did not differ in relative abundance or prevalence of S. mansoni infection. Water hyacinth intrusions were associated with increased B. sudanica abundance. The deeper water snail Biomphalaria choanomphala was significantly more abundant in the PHS villages and prevalence of S. mansoni among villages both before and after control was positively correlated with B. choanomphala abundance. Worm recoveries from sentinel mice did not differ between PHS and RESP villages, and abundance of non-schistosome trematode species was not associated with S. mansoni abundance. Biomphalaria choanomphala provides an alternative, deepwater mode of transmission that may favor greater persistence of S. mansoni in PHS villages. As we found evidence for ongoing S. mansoni transmission in all 10 villages, we conclude conditions conducive for transmission and reinfection occur ubiquitously. This argues for an integrated, basin-wide plan for schistosomiasis control to counteract rapid reinfections facilitated by large snail populations and movements of infected people around the lake.

Despite large numbers of patients accessing antiretroviral treatment (ART) in Kenya, few studies have explored factors associated with virologic failure in Western Kenya, specifically. We undertook a study in Homa Bay County, Kenya to assess the extent of virologic treatment failure and factors associated with it. This was an observational retrospective study conducted from September 2020 to January 2021. Data were abstracted from the records of patients who had been on ART for at least six months at the time of data collection after systematic sampling stratified by age group at ART initiation (0-14 and 15+ years), using probability proportion to the numbers of patients attending the facility. Confirmed viral treatment failure was defined as viral load ≥1000 copies/ml based on two consecutive viral load measurements after at least three months of enhanced adherence counseling. Data were analyzed using descriptive statistics and Cox regression modeling. Of the 2,007 patients sampled, 160 (8.0%) had confirmed virologic treatment failure. Significantly higher virologic treatment failure rates were identified among male patients 78/830 (9.4%) and children 115/782 (14.7%). Factors associated with virologic treatment failure (VTF), were age 0-14 years, adjusted hazard ratio (AHR) 4.42, (95% Confidence Interval [CI], 3.12, 6.32), experience of treatment side effects AHD: 2.43, (95% CI, 1.76, 3.37), attending level 2/3 health facility, AHR: 1.87, (95% CI: 1.29, 2,72), and history of opportunistic infections (OIs), AHR: 1.81, (95% CI, 1.76, 3.37). Children, attendees of level 2/3 health facilities, patients with a history of OIs, and those experiencing treatment side-effects are at risk of VTF. Increased focus on children and adolescents on screening for drug resistance, administration of and adherence to medication, and on effective information and education on side-effects is critical. Additionally, there is need for increased training and support for health care workers at primary level care facilities.

INTRODUCTION: In 2020, Kenya had 19,000 new HIV infections among women aged 15+ years. Studies have shown sub-optimal oral pre-exposure prophylaxis (PrEP) use among sub-populations of women. We assessed the uptake and continuation of oral PrEP among women 15-49 years in two health facilities in Kisumu County, Kenya. METHODS: A retrospective cohort of 262 women aged 15-49 years, initiated into oral PrEP between 12 November 2019 and 31 March 2021, was identified from two health facilities in the urban setting of Kisumu County, Kenya. Data on baseline characteristics and oral PrEP continuation at months 1, 3 and 6 were abstracted from patient records and summarized using descriptive statistics. Missing data in the predictor variables were imputed within the joint modelling multiple imputation framework. Using logistic regression, we evaluated factors associated with the discontinuation of oral PrEP at month 1. RESULTS: Of the 66,054 women screened, 320 (0.5%) were eligible and 262 (82%) were initiated on oral PrEP. Uptake was higher among women 25-29 years as compared to those 15-24 years (77% vs. 33%). Oral PrEP continuation declined significantly with increasing duration of follow-up; 37% at month 1, 21% at month 3 and 12% at month 6 (p<0.05). In the adjusted analysis, women 15-24 years had lower adjusted odds of continuing at month 1 than women ≥25 years (adjusted odds ratio [aOR]: 0.41, 95% CI: 0.21-0.82). There was no association between being sero-discordant and continuation of oral PrEP at month 1 (aOR; 1.21, 95% CI 0.59-2.50). Women from the sub-county hospital were more likely to continue at month 1 of follow-up compared to women enrolled in the county referral hospital (aOR 5.11; 95% CI 2.24-11.70). CONCLUSIONS: The low eligibility for oral PrEP observed among women 15-49 years in an urban setting with high HIV prevalence calls for a review of the screening process to validate the sensitivity of the screening tool and its proper application. The low uptake and continuation among adolescent girls and young women underscores the need to identify and address specific patient- and facility-level barriers affecting different sub-populations at risk for HIV acquisition.

Viral suppression is suboptimal among children and adolescents on antiretroviral therapy (ART) in Kenya. We implemented and evaluated a standardized enhanced adherence counseling (SEAC) package to improve viral suppression in children and adolescents with suspected treatment failure in Homa Bay and Turkana. The SEAC package, implemented from February 2019 to September 2020, included: standard procedures operationalizing the enhanced adherence counseling (EAC) process; provider training on psychosocial support and communication skills for children living with HIV and their caregivers; mentorship to providers and peer educators on EAC processes; and individualized case management. We enrolled children and adolescents aged 0 to 19 years with suspected treatment failure (viral load [VL] >1000 copies/mL) who received EAC before standardization as well as those who received SEAC in a pre-post evaluation of the SEAC package conducted in 6 high-volume facilities. Pre-post standardization comparisons were performed using Wilcoxon-Mann-Whitney and Pearson's chi-square tests at a 5% level of significance. Multivariate logistic regression was performed to identify factors associated with viral resuppression. The study enrolled 741 participants, 595 pre- and 146 post-SEAC implementation. All post-SEAC participants attended at least 1 EAC session, while 17% (n = 98) of pre-SEAC clients had no record of EAC attendance. Time to EAC following the detection of high VL was reduced by a median of 8 days, from 49 (interquartile range [IQR]: 23.0-102.5) to 41 (IQR: 20.0-67.0) days pre- versus post-SEAC (P = .006). Time to completion of at least 3 sessions was reduced by a median of 12 days, from 59.0 (IQR: 36.0-91.0) to 47.5 (IQR: 33.0-63.0) days pre- versus post-SEAC (P = .002). A greater percentage of clients completed the recommended minimum 3 EAC sessions at post-SEAC, 88.4% (n = 129) versus 61.1% (n = 363) pre-SEAC, P < .001. Among participants with a repeat VL within 3 months following the high VL, SEAC increased viral suppression from 34.6% (n = 76) to 52.5% (n = 45), P = .004. Implementation of the SEAC package significantly reduced the time to initiate EAC and time to completion of at least 3 EAC sessions, and was significantly associated with viral suppression in children and adolescents with suspected treatment failure.

BACKGROUND: Adolescents living with HIV (ALHIV) experience higher mortality and are more likely to have poor antiretroviral therapy (ART) adherence and unsuppressed viral load (VL) compared to adults. Enhanced adherence counseling (EAC) is a client-centered counseling strategy that aims to identify and address barriers to optimal ART use and can be tailored to the unique needs of adolescents. This study aimed to better understand adherence barriers among ALHIV with suspected treatment failure and their experience with EAC to inform future programming. METHODS: A qualitative study was conducted in Homa Bay and Turkana counties, Kenya in 2019 with adolescents and caregivers of children and adolescents living with HIV with suspected treatment failure after 6months on ART and who had received 1 EAC sessions. Sixteen focus group discussions (FGDs) were conducted; five FGDs each were held with adolescents 12-14years (n=48) and 15-19years (n=36). Caregivers (n=52) participated in six FGDs. Additionally, 17 healthcare workers providing pediatric/adolescent HIV services participated in in-depth interviews. Audio recordings were transcribed and translated from Kiswahili or Dholuo into English and coded using MAXQDA software. Data were thematically analyzed by participant group. RESULTS: Participants identified adolescents' fear of being stigmatized due to their HIV status and their relationship with and level of support provided by caregivers. This underpinned and often undermined adolescents' ART-taking behavior and progress towards more independent medication management. Adolescents were generally satisfied with EAC and perceived it to be important in improving adherence and reducing VL. However, problems were noted with facility-based, individual EAC counseling, including judgmental attitudes of providers and difficulties traveling to and keeping EAC clinic appointments. Participant-suggested improvements to EAC included peer support groups in addition to individual counseling, allowing for greater flexibility in the timing and location of sessions and greater caregiver involvement. CONCLUSIONS: The findings provide opportunities to better tailor EAC interventions to promote improved ALHIV adherence and caregiver-supported disease management. Multi-prong EAC interventions that include peer-led and community approaches and target adolescent and caregiver treatment literacy may improve EAC delivery, address issues contributing to poor adherence, and position adolescents to achieve viral suppression. TRIAL REGISTRATION: ClinicalTrials.gov : NCT04915469.

BACKGROUND: Pregnant and breastfeeding adolescents and young women living with HIV (AYWLH) have lower retention in prevention of mother-to-child transmission (PMTCT) services compared to older women. METHODS: We evaluated a differentiated service model for pregnant and postnatal AYWLH at seven health facilities in western Kenya aimed at improving retention in antiretroviral treatment (ART) services. All pregnant AYWLH < 25 years presenting for antenatal care (ANC) were invited to participate in group ANC visits including self-care and peer-led support sessions conducted by health facility nurses per national guidelines. ART register data were used to assess loss to follow-up (LTFU) among newly-enrolled pregnant adolescent (< 20 years) and young women (20-24 years) living with HIV starting ART in the pre-period (January-December 2016) and post-period (during implementation; December 2017-January 2019). Poisson regression models compared LTFU incidence rate ratios (IRR) in the first six months after PMTCT enrollment and risk ratios compared uptake of six week testing for HIV-exposed infants (HEI) between the pre- and post-periods. RESULTS: In the pre-period, 223 (63.2%) of 353 pregnant AYWLH newly enrolled in ANC had ART data, while 320 (71.1%) of 450 in the post-period had ART data (p = 0.02). A higher proportion of women in the post-period (62.8%) had known HIV-positive status at first ANC visit compared to 49.3% in the pre-period (p < 0.001). Among pregnant AYWLH < 20 years, the incidence rate of LTFU in the first six months after enrollment in ANC services declined from 2.36 per 100 person months (95%CI 1.06-5.25) in the pre-period to 1.41 per 100 person months (95%CI 0.53-3.77) in the post-period. In both univariable and multivariable analysis, AYWLH < 20 years in the post-period were almost 40% less likely to be LTFU compared to the pre-period, although this finding did not meet the threshold for statistical significance (adjusted incidence rate ratio 0.62, 95%CI 0.38-1.01, p = 0.057). Testing for HEI was 10% higher overall in the post-period (adjusted risk ratio 1.10, 95%CI 1.01-1.21, p = 0.04). CONCLUSIONS: Interventions are urgently needed to improve outcomes among pregnant and postnatal AYWLH. We observed a trend towards increased retention among pregnant adolescents during our intervention and a statistically significant increase in uptake of six week HEI testing.

BACKGROUND: Understanding the missed opportunities in early infant HIV testing within the PMTCT program is essential to address any gaps. The study set out to describe the clinical and sociodemographic characteristics of the infants presenting late for early infant diagnosis in Kenya. METHODS: We abstracted routinely collected clinical and sociodemographic characteristics, in a cross-sectional study, on all HIV-infected infants with a positive polymerase chain reaction (PCR) test from 1,346 President's Emergency Plan for AIDS Relief (PEPFAR) supported health facilities for the period October 2016 to September 2018. We used multivariate logistic regression to examine the association of sociodemographic and clinical characteristics with late (>2 months after birth) presentation for infant HIV testing. RESULTS: Of the 4,011 HIV-infected infants identified, the median infant age at HIV diagnosis was 3 months [interquartile range (IQR), 1-16 months], and two-thirds [2,669 (66.5%)] presented late for infant HIV testing. Factors that were associated with late presentation for infant testing were: maternal ANC non-attendance, adjusted odds ratio (aOR) 1.41 (95% confidence interval (CI) 1.18 -1.69); new maternal HIV diagnosis, aOR 1.45, (95%CI 1.24 -1.7); and lack of maternal antiretroviral therapy(ART), aOR 1.94, (95% CI 1.64 - 2.30). There was a high likelihood of identifying HIV-infected infants among infants who presented for medical services in the outpatient setting (aOR 18.9; 95% CI 10.2 - 34.9) and inpatient setting (aOR 12.2; 95% CI 6.23-23.9) compared to the infants who presented late in maternity. CONCLUSION AND GLOBAL HEALTH IMPLICATIONS: Gaps in early infant HIV testing suggest the need to increase maternal pre-pregnancy HIV diagnosis, timely antenatal care, early infant diagnosis services, early identification of mothers who seroconvert during pregnancy or breastfeeding and improved HIV screening in outpatient and inpatient settings. Early referral from the community and access to health facilities should be strengthened by the implementation of national PMTCT guidelines.

INTRODUCTION: Young pregnant and postpartum women living with HIV (WLHIV) are at high risk of poor outcomes in prevention of mother-to-child transmission services. The aim of this systematic review was to collate evidence on strategies to improve retention in antenatal and/or postpartum care in this population. We also conducted a secondary review of strategies to increase attendance at antenatal care (ANC) and/or facility delivery among pregnant adolescents, regardless of HIV status, to identify approaches that could be adapted for adolescents and young WLHIV. METHODS: Selected databases were searched on 1 December 2020, for studies published between January 2006 and November 2020, with screening and data abstraction by two independent reviewers. We identified papers that reported age-disaggregated results for adolescents and young WLHIV aged <25 years at the full-text review stage. For the secondary search, we included studies among female adolescents aged 10 to 19 years. RESULTS AND DISCUSSION: Of 37 papers examining approaches to increase retention among pregnant and postpartum WLHIV, only two reported age-disaggregated results: one showed that integrated care during the postpartum period increased retention in HIV care among women aged 18 to 24 years; and another showed that a lay counsellor-led combination intervention did not reduce attrition among women aged 16 to 24 years; one further study noted that age did not modify the effectiveness of a combination intervention. Mobile health technologies, enhanced support, active follow-up and tracing and integrated services were commonly examined as standalone interventions or as part of combination approaches, with mixed evidence for each strategy. Of 10 papers identified in the secondary search, adolescent-focused services and continuity of care with the same provider appeared to be effective in improving attendance at ANC and/or facility delivery, while home visits and group ANC had mixed results. CONCLUSIONS: This review highlights the lack of evidence regarding effective strategies to improve retention in antenatal and/or postpartum care among adolescents and young WLHIV specifically, as well as a distinct lack of age-disaggregated results in studies examining retention interventions for pregnant WLHIV of all ages. Identifying and prioritizing approaches to improve retention of adolescents and young WLHIV are critical for improving maternal and child health.

Following a 4-year annual praziquantel (PZQ) treatment campaign, the resulting prevalence of Schistosoma mansoni was seen to differ among individual villages along the Kenyan shore of Lake Victoria. We have investigated possible inherent differences in snail-related aspects of transmission among such 10 villages, including six persistent hotspot (PHS) villages (</= 30% reduction in prevalence following repeated treatments) located along the west-facing shore of the lake and four PZQ-responding (RESP) villages (> 30% prevalence reduction following repeated treatment) along the Winam Gulf. When taking into account all sampling sites, times, and water hyacinth presence/absence, shoreline-associated Biomphalaria sudanica from PHS and RESP villages did not differ in relative abundance or prevalence of S. mansoni infection. Water hyacinth intrusions were associated with increased B. sudanica abundance. The deeper water snail Biomphalaria choanomphala was significantly more abundant in the PHS villages, and prevalence of S. mansoni among villages both before and after control was positively correlated with B. choanomphala abundance. Worm recoveries from sentinel mice did not differ between PHS and RESP villages, and abundance of non-schistosome trematode species was not associated with S. mansoni abundance. Biomphalaria choanomphala provides an alternative, deepwater mode of transmission that may favor greater persistence of S. mansoni in PHS villages. As we found evidence for ongoing S. mansoni transmission in all 10 villages, we conclude that conditions conducive for transmission and reinfection occur ubiquitously. This argues for an integrated, basin-wide plan for schistosomiasis control to counteract rapid reinfections facilitated by large snail populations and movements of infected people around the lake.

Despite dramatic global progress with implementing prevention of mother-to-child HIV transmission (PMTCT) programs, there were 160,000 new pediatric HIV infections in 2016. More than 50% of infant HIV infections now occur in the postpartum period, reflecting the relatively high coverage of interventions in the antenatal period and the need for greater attention to the breastfeeding mother and her HIV-exposed infant (HEI). Early diagnosis and treatment are critical to prevent morbidity and mortality in HIV-infected children; however, early infant HIV testing rates remain low in most high HIV-burden countries. Furthermore, systematic retention and follow-up of HEI in the postpartum period and ascertainment of final HIV status remain major program gaps. Despite multiple calls to action to improve infant HIV testing rates, progress has been marginal due to a lack of focus on the critical health care needs of HEI coupled with health system barriers that result in fragmented services for HIV-infected mothers and their families. In this paper, we describe the available evidence on the health outcomes of HEI, define a comprehensive care package for HEI that extends beyond early HIV testing, and describe successful examples of integrated services for HEI.

A rapid results initiative (RRI) aimed at increasing male involvement in prevention of mother-to-child transmission (PMTCT) and service uptake among pregnant women at 116 antenatal clinics in Western Kenya was compared at baseline, during the RRI, and 3-months post-RRI. Male involvement increased from 7.4 to 54.2% during RRI (risk difference [RD] 0.47, CI 0.45–0.48) then 43.4% post-RRI (RD 0.36, CI 0.35–0.37). Among HIV-infected women, facility delivery increased from 40.0 to 49.9% (RD 0.10, 95% CI 0.06–0.13) and 65.0% post-RRI (RD 0.25, 95% CI 0.22–0.28). HIV-infected pregnant women linkage to HIV care increased from 58.6 to 85.9% (RD 0.27, CI 0.24–0.30) and 97.3% post-RRI (RD 0.39, CI 0.36–0.41). Time to ART initiation reduced from 29 days (interquartile range [IQR] 6–56) to 14 days (IQR 0–28) to 7 days (IQR 0–20). A male-centered RRI can significantly increase men’s engagement in antenatal care leading to improved partner utilization of PMTCT and antenatal services.

AIM: This study evaluated potential changes in anti-schistosome immune responses in children from schools that received four rounds of annual mass drug administration (MDA) of praziquantel (PZQ). METHODS: In a repeated cross-sectional study design, 210 schistosome egg-positive children were recruited at baseline from schools in western Kenya (baseline group). Another 251 children of the same age range were recruited from the same schools and diagnosed for schistosome infection by microscopy (post-MDA group). In-vitro schistosome-specific cytokines and plasma antibody levels were measured by ELISA and compared between the two groups of children. RESULTS: Schistosome soluble egg antigen (SEA) and soluble worm antigen preparation (SWAP) stimulated higher IL-5 production by egg-negative children in the post-MDA group compared to the baseline group. Similarly, anti-SEA IgE levels were higher in egg negative children in the post-MDA group compared to the baseline group. Anti-SEA and anti-SWAP IgG4 levels were lower in egg negative children in the post-MDA group compared to baseline. This resulted in higher anti-SEA IgE/IgG4 ratios for children in the post-MDA group compared to baseline. CONCLUSION: These post-MDA immunological changes are compatible with the current paradigm that treatment shifts immune responses to higher anti-schistosome IgE:IgG4 ratios in parallel with a potential increase in resistance to reinfection. This article is protected by copyright. All rights reserved.

Introduction: Using spatial-temporal analyses to understand coverage and trends in elimination of mother-to-child transmission of HIV (e-MTCT) efforts may be helpful in ensuring timely services are delivered to the right place. We present spatial-temporal analysis of seven years of HIV early infant diagnosis (EID) data collected from 12 districts in western Kenya from January 2007 to November 2013, during pre-Option B+ use. Methods: We included in the analysis infants up to one year old. We performed trend analysis using extended Cochran-Mantel-Haenszel stratified test and logistic regression models to examine trends and associations of infant HIV status at first diagnosis with: early diagnosis ( < 8 weeks after birth), age at specimen collection, infant ever having breastfed, use of single dose nevirapine, and maternal antiretroviral therapy status. We examined these covariates and fitted spatial and spatial-temporal semiparametric Poisson regression models to explain HIVinfection rates using R-integrated nested Laplace approximation package. We calculated new infections per 100,000 live births and used Quantum GIS to map fitted MTCT estimates for each district in Nyanza region. Results: Median age was two months, interquartile range 1.5-5.8 months. Unadjusted pooled positive rate was 11.8% in the seven-years period and declined from 19.7% in 2007 to 7.0% in 2013, p < 0.01. Uptake of testing ≤ 8 weeks after birth was under 50% in 2007 and increased to 64.1% by 2013, p < 0.01. By 2013, the overall standardized MTCTrate was 447 infections per 100,000 live births. Based on Bayesian deviance information criterion comparisons, the spatial-temporal model with maternal and infant covariates was best in explaining geographical variation in MTCT. Discussion: Improved EID uptake and reduced MTCT rates are indicators of progress towards e-MTCT. Cojoined analysis of time and covariates in a spatial context provides a robust approach for explaining differences in programmatic impact over time. Conclusion: During this pre-Option B+ period, the prevention of mother to child transmission program in this region has not achieved e-MTCT target of ≤ 50 infections per 100,000 live births. Geographical disparities in program achievements may signify gaps in spatial distribution of e-MTCT efforts and could indicate areas needing further resources and interventions.

In Kenya, schistosomes infect an estimated 6 million people with >30 million people at risk of infection. We compared compatibility with, and ability to support and perpetuate, Schistosoma mansoni of Biomphalaria pfeifferi and Biomphalaria sudanica, 2 prominent freshwater snail species involved in schistosomiasis transmission in Kenya. Field-derived B. pfeifferi (from a stream in Mwea, central Kenya) and B. sudanica (from Nawa, Lake Victoria, in western Kenya) were exposed to S. mansoni miracidia isolated from fecal samples of naturally infected humans from Mwea or Nawa. Juvenile (<6 mm shell diameter), young adult (6-9 mm), and adult snails (>9 mm) were each exposed to a single miracidium. Schistosoma mansoni developed faster and consistently had higher infection rates (39.6-80.7%) in B. pfeifferi than in B. sudanica (2.4-21.5%), regardless of the source of S. mansoni or the size of the snails used. Schistosoma mansoni from Nawa produced higher infection rates in both B. pfeifferi and B. sudanica than did S. mansoni from Mwea. Mean daily cercariae production was greater for B. pfeifferi exposed to sympatric than allopatric S. mansoni (583-1,686 vs. 392-1,232), and mean daily cercariae production amongst B. sudanica were consistently low (50-590) with no significant differences between sympatric or allopatric combinations. Both non-miracidia exposed and miracidia-exposed B. pfeifferi had higher mortality rates than for B. sudanica, but mean survival time of shedding snails (9.3-13.7 weeks) did not differ significantly between the 2 snail species. A small proportion (1.5%) of the cercariae shedding B. pfeifferi survived up to 40 wk post-exposure. Biomphalaria pfeifferi was more likely to become infected and to shed more cercariae than B. sudanica, suggesting that the risk per individual snail of perpetuating transmission in Kenyan streams or lacustrine habitats may differ considerably. High infections rates exhibited by the preferential self-fertilizing B. pfeifferi relative to the out-crossing B. sudanica point out to the need to investigate further the role of host breeding systems in influencing transmission of schistosomiasis by snail hosts.