Mary J Hamel

KEMRI / CDC Research and Public Health Collaboration, Winam, Kisumu, Kenya

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Publications (70)311.15 Total impact

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    ABSTRACT: It has been speculated that widespread and sustained use of insecticide treated bed nets (ITNs) for over 10 years in Asembo, western Kenya, may have selected for changes in the location (indoor versus outdoor) and time (from late night to earlier in the evening) of biting of the predominant species of human malaria vectors (Anopheles funestus, Anopheles gambiae sensu stricto, and Anopheles arabiensis).
    Parasites & Vectors 08/2014; 7(1):380. · 3.25 Impact Factor
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    ABSTRACT: At least 39 sub-Saharan African countries have policies on preventing malaria in pregnancy (MIP), including use of long-lasting insecticidal nets (LLINs), intermittent preventive treatment with sulphadoxine-pyrimethamine (IPTp-SP) and case management. However, coverage of LLINs and IPTp-SP remains below international targets in most countries. One factor contributing to low coverage may be that MIP policies typically are developed by national malaria control programmes (NMCPs), but are implemented through national reproductive health (RH) programmes.
    Malaria Journal 06/2014; 13(1):212. · 3.49 Impact Factor
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    ABSTRACT: Historically, the malaria vectors in western Kenya have been Anopheles funestus, Anopheles gambiae s.s., and Anopheles arabiensis. Of these species, An. funestus populations declined the most after the introduction of insecticide-treated bed nets (ITNs) in the 1990s in Asembo, and collections of An. funestus in the region remained low until at least 2008. Contrary to findings during the early years of ITN use in Asembo, the majority of the Anopheles collected here in 2010 and 2011 were An. funestus. Female An. funestus had characteristically high Plasmodium falciparum sporozoite rates and showed nearly 100% anthropophily. Female An. funestus were found more often indoors than outdoors and had relatively low mortality rates during insecticide bioassays. Together, these results are of serious concern for public health in the region, indicating that An. funestus may once again be contributing significantly to the transmission of malaria in this region despite the widespread use of ITNs/long-lasting insecticidal nets (LLINs).
    The American journal of tropical medicine and hygiene 01/2014; · 2.53 Impact Factor
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    ABSTRACT: Recent global malaria burden modeling efforts have produced significantly different estimates, particularly in adult malaria mortality. To measure malaria control progress, accurate malaria burden estimates across age groups are necessary. We determined age-specific malaria mortality rates in western Kenya to compare with recent global estimates. We collected data from 148,000 persons in a health and demographic surveillance system from 2003-2010. Standardized verbal autopsies were conducted for all deaths; probable cause of death was assigned using the InterVA-4 model. Annual malaria mortality rates per 1,000 person-years were generated by age group. Trends were analyzed using Poisson regression. From 2003-2010, in children <5 years the malaria mortality rate decreased from 13.2 to 3.7 per 1,000 person-years; the declines were greatest in the first three years of life. In children 5-14 years, the malaria mortality rate remained stable at 0.5 per 1,000 person-years. In persons ≥15 years, the malaria mortality rate decreased from 1.5 to 0.4 per 1,000 person-years. The malaria mortality rates in young children and persons aged ≥15 years decreased dramatically from 2003-2010 in western Kenya, but rates in older children have not declined. Sharp declines in some age groups likely reflect the national scale up of malaria control interventions and rapid expansion of HIV prevention services. These data highlight the importance of age-specific malaria mortality ascertainment and support current strategies to include all age groups in malaria control interventions.
    PLoS ONE 01/2014; 9(9):e106197. · 3.73 Impact Factor
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    ABSTRACT: This study assesses full and timely vaccination coverage and factors associated with full vaccination in children ages 12-23 months in Gem, Nyanza Province, Kenya in 2003. A simple random sample of 1,769 households was selected, and guardians were invited to bring children under 5 years of age to participate in a survey. Full vaccination coverage was 31.1% among 244 children. Only 2.2% received all vaccinations in the target month for each vaccination. In multivariate logistic regression, children of mothers of higher parity (odds ratio [OR] = 0.27, 95% confidence interval [95% CI] = 0.13-0.65, P ≤ 0.01), children of mothers with lower maternal education (OR = 0.35, 95% CI = 0.13-0.97, P ≤ 0.05), or children in households with the spouse absent versus present (OR = 0.40, 95% CI = 0.17-0.91, P ≤ 0.05) were less likely to be fully vaccinated. These data serve as a baseline from which changes in vaccination coverage will be measured as interventions to improve vaccination timeliness are introduced.
    The American journal of tropical medicine and hygiene 12/2013; · 2.53 Impact Factor
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    ABSTRACT: In endemic regions of sub-Saharan Africa, malaria during pregnancy (MiP) is a major preventable cause of maternal and infant morbidity and mortality. Current recommended MiP prevention and control includes intermittent preventive treatment (IPTp), distribution of insecticide-treated bed nets (ITNs) and appropriate case management. This article explores the social and cultural context to the uptake of these interventions at four sites across Africa. A comparative qualitative study was conducted at four sites in three countries: Ghana, Malawi and Kenya. Individual and group interviews were conducted with pregnant women, their relatives, opinion leaders, other community members and health providers. Observations, which focused on behaviours linked to MiP prevention and treatment, were also undertaken at health facilities and in local communities. ITNs were generally recognized as important for malaria prevention. However, their availability and use differed across the sites. In Malawi and Kenya, ITNs were sought-after items, but there were complaints about availability. In central Ghana, women saved ITNs until the birth of the child and they were used seasonally in northern Ghana. In Kenya and central Ghana, pregnant women did not associate IPTp with malaria, whereas, in Malawi and northern Ghana, IPTp was linked to malaria, but not always with prevention. Although IPTp adherence was common at all sites, whether delivered with directly observed treatment or not, a few women did not comply with IPTp often citing previous side effects. Although generally viewed as positive, experiences of malaria testing varied across the four sites: treatment was sometimes administered in spite of a negative diagnosis in Ghana (observed) and Malawi (reported). Despite generally following the advice of healthcare staff, particularly in Kenya, personal experience, and the availability and accessibility of medication -- including anti-malarials -- influenced MiP treatment. Although ITNs were valued as malaria prevention, health messages could address issues that reduce their use during pregnancy in particular contexts. The impact of previous side effects on adherence to IPTp and anti-malarial treatment regimens during pregnancy also requires attention. Overtreatment of MiP highlights the need to monitor the implementation of MiP case management guidelines.
    Malaria Journal 11/2013; 12(1):427. · 3.49 Impact Factor
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    ABSTRACT: Results of a cluster randomized trial in rural western Kenya suggest a new form of malaria prevention, insecticide treated wall liner (ITWL) plus insecticide treated nets (ITNs), provide added benefit over that provided by ITN alone, reducing childhood malaria infection by 38% (95% confidence interval [CI], 23%-50%) overall and by 42% (95% CI=26%- 55%) in children aged 5-11 years. Prior studies have shown that malaria adversely affects children’s academic performance and school attendance. This supplemental study sought to determine whether children from the ITWL plus ITN (intervention) villages had reduced absenteeism when compared to children from the ITN alone (control) villages.We performed a retrospective analysis of attendance registers for children in standards (grades) 1 through 8 via comparison of school attendance in term 1 of the 2010 academic year (prior to ITWL) to term 3 (after ITWL). Data were available from 6 schools serving children from 8 of the 12 villages in the original trial. Using a multilevel mixed effects difference-in-differences regression model, we explored the effect of ITWL on attendance of pupils from intervention vs. control villages between terms 1 and 3. In order to adjust for registers with missing or incomplete recording of absences,mostly in the last weeks of each 13-week term, we choose to limit analysis to attendance from weeks 1-10 in each academic term. We adjusted for clustering by the inclusion of a village-level variable in the multilevel analysis; other covariates used in the analysis were categorical variables for standard, gender, village,and term. The resulting dataset had 1,126 observations, each representing the percentage of school days attended for one child for weeks 1-10 in a term. Overall recorded attendance averaged 90.1 percent (95% CI 88.9%-91.3%) over weeks 1-10 of term 1, so that recorded absenteeism averaged 9.9 percent. The interaction term in the regression showed that attendance improved (and absenteeism decreased) by 4.7 percentage points (95% CI 1.2%- 8.1%) for children in intervention compared to control villages (p=0.008), representing a halving of recorded absences. The main limitation was our inability to confirm the overall accuracy of entries from existing school attendance registers. Nevertheless, these favorable preliminary results suggest a beneficial impact on school attendance from adding ITWL to ITN.
    American Society of Tropical Medicine and Hygiene 62nd Annual meeting, Washington, DC; 11/2013
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    ABSTRACT: Although several studies have investigated the impact of reduced malaria transmission due to insecticide-treated bed nets (ITNs) on the patterns of morbidity and mortality, there is limited information on their effect on parasite diversity. Sequencing was used to investigate the effect of ITNs on polymorphisms in two genes encoding leading Plasmodium falciparum vaccine candidate antigens, the 19 kilodalton blood stage merozoite surface protein-1 (MSP-119kDa) and the Th2R and Th3R T-cell epitopes of the pre-erythrocytic stage circumsporozoite protein (CSP) in a large community-based ITN trial site in western Kenya. The number and frequency of haplotypes as well as nucleotide and haplotype diversity were compared among parasites obtained from children <5 years old prior to the introduction of ITNs (1996) and after 5 years of high coverage ITN use (2001). A total of 12 MSP-119kDa haplotypes were detected in 1996 and 2001. The Q-KSNG-L and E-KSNG-L haplotypes corresponding to the FVO and FUP strains of P. falciparum were the most prevalent (range 32--37%), with an overall haplotype diversity of > 0.7. No MSP-119kDa 3D7 sequence-types were detected in 1996 and the frequency was less than 4% in 2001. The CSP Th2R and Th3R domains were highly polymorphic with a total of 26 and 14 haplotypes, respectively detected in 1996 and 34 and 13 haplotypes in 2001, with an overall haplotype diversity of > 0.9 and 0.75 respectively. The frequency of the most predominant Th2R and Th3R haplotypes was 14 and 36%, respectively. The frequency of Th2R and Th3R haplotypes corresponding to the 3D7 parasite strain was less than 4% at both time points. There was no significant difference in nucleotide and haplotype diversity in parasite isolates collected at both time points. High diversity in these two genes has been maintained overtime despite marked reductions in malaria transmission due to ITNs use. The frequency of 3D7 sequence-types was very low in this area. These findings provide information that could be useful in the design of future malaria vaccines for deployment in endemic areas with high ITN coverage and in interpretation of efficacy data for malaria vaccines based on 3D7 parasite strains.
    Malaria Journal 08/2013; 12(1):295. · 3.49 Impact Factor
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    ABSTRACT: BACKGROUND: Operational vector sampling methods lack standardization, making quantitative comparisons of malaria transmission across different settings difficult. Human landing catch (HLC) is considered the research gold standard for measuring human-mosquito contact, but is unsuitable for large-scale sampling. This study assessed mosquito catch rates of CDC light trap (CDC-LT), Ifakara tent trap (ITT), window exit trap (WET), pot resting trap (PRT), and box resting trap (BRT) relative to HLC in western Kenya to 1) identify appropriate methods for operational sampling in this region, and 2) contribute to a larger, overarching project comparing standardized evaluations of vector trapping methods across multiple countries. METHODS: Mosquitoes were collected from June to July 2009 in four districts: Rarieda, Kisumu West, Nyando, and Rachuonyo. In each district, all trapping methods were rotated 10 times through three houses in a 3 x 3 Latin Square design. Anophelines were identified by morphology and females classified as fed or non-fed. Anopheles gambiae s.l. were further identified as Anopheles gambiae s.s. or Anopheles arabiensis by PCR. Relative catch rates were estimated by negative binomial regression. RESULTS: When data were pooled across all four districts, catch rates (relative to HLC indoor) for An. gambiae s.l (95.6% An. arabiensis, 4.4% An. gambiae s.s) were high for HLC outdoor (RR = 1.01), CDC-LT (RR = 1.18), and ITT (RR = 1.39); moderate for WET (RR = 0.52) and PRT outdoor (RR = 0.32); and low for all remaining types of resting traps (PRT indoor, BRT indoor, and BRT outdoor; RR < 0.08 for all). For Anopheles funestus, relative catch rates were high for ITT (RR = 1.21); moderate for HLC outdoor (RR = 0.47), CDC-LT (RR = 0.69), and WET (RR = 0.49); and low for all resting traps (RR < 0.02 for all). At finer geographic scales, however, efficacy of each trap type varied from district to district. CONCLUSIONS: ITT, CDC-LT, and WET appear to be effective methods for large-scale vector sampling in western Kenya. Ultimately, choice of collection method for operational surveillance should be driven by trap efficacy and scalability, rather than fine-scale precision with respect to HLC. When compared with recent, similar trap evaluations in Tanzania and Zambia, these data suggest that traps which actively lure host-seeking females will be most useful for surveillance in the face of declining vector densities.
    Malaria Journal 04/2013; 12(1):143. · 3.49 Impact Factor
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    ABSTRACT: Malaria in pregnancy can have devastating consequences for mother and baby. Coverage with the WHO prevention strategy for sub-Saharan Africa of intermittent-preventive-treatment (IPTp) with two doses of sulphadoxine-pyrimethamine (SP) and insecticide-treated-nets (ITNs) in pregnancy is low. We analysed household survey data to evaluate the effectiveness of antenatal clinics (ANC) to deliver IPTp and ITNs to pregnant women in Nyando district, Kenya. We assessed the systems effectiveness of ANC to deliver IPTp and ITNs to pregnant women and the impact on low birthweight (LBW). Logistic regression was used to identify predictors of receipt of IPTp and ITN use during pregnancy. Among 89% of recently pregnant women who attended ANC at least once between 4-9 months gestation, 59% reported receiving one dose of SP and 90% attended ANC again, of whom 57% received a second dose, resulting in a cumulative effectiveness for IPTp of 27%, most of whom used an ITN (96%). Overall ITN use was 89%, and ANC the main source (76%). Women were less likely to receive IPTp if they had low malaria knowledge (0.26, 95% CI 0.08-0.83), had a child who had died (OR 0.36, 95% CI 0.14-0.95), or if they first attended ANC late (OR 0.20, 95% CI 0.06-0.67). Women who experienced side effects to SP (OR 0.18, CI 0.03-0.90) or had low malaria knowledge (OR 0.78, 95% CI 0.11-5.43) were less likely to receive IPTp by directly observed therapy. Ineffective delivery of IPTp reduced its potential impact by 231 LBW cases averted (95% CI 64-359) per 10,000 pregnant women. IPTp presents greater challenges to deliver through ANC than ITNs in this setting. The reduction in public health impact on LBW resulting from ineffective delivery of IPTp is estimated to be substantial. Urgent efforts are required to improve service delivery of this important intervention.
    PLoS ONE 01/2013; 8(6):e64913. · 3.73 Impact Factor
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    ABSTRACT: Information on trauma-related deaths in low and middle income countries is limited but needed to target public health interventions. Data from a health and demographic surveillance system (HDSS) were examined to characterise such deaths in rural western Kenya. Verbal autopsy data were analysed. Of 11,147 adult deaths between 2003 and 2008, 447 (4%) were attributed to trauma; 71% of these were in males. Trauma contributed 17% of all deaths in males 15 to 24 years; on a population basis mortality rates were greatest in persons over 65 years. Intentional causes accounted for a higher proportion of male than female deaths (RR 2.04, 1.37-3.04) and a higher proportion of deaths of those aged 15 to 65 than older people. Main causes in males were assaults (n=79, 25%) and road traffic injuries (n=47, 15%); and falls for females (n=17, 13%). A significantly greater proportion of deaths from poisoning (RR 5.0, 2.7-9.4) and assault (RR 1.8, 1.2-2.6) occurred among regular consumers of alcohol than among non-regular drinkers. In multivariate analysis, males had a 4-fold higher risk of death from trauma than females (Adjusted Relative Risk; ARR 4.0; 95% CI 1.7-9.4); risk of a trauma death rose with age, with the elderly at 7-fold higher risk (ARR 7.3, 1.1-49.2). Absence of care was the strongest predictor of trauma death (ARR 12.2, 9.4-15.8). Trauma-related deaths were higher among regular alcohol drinkers (ARR 1.5, 1.1-1.9) compared with non-regular drinkers. While trauma accounts for a small proportion of deaths in this rural area with a high prevalence of HIV, TB and malaria, preventive interventions such as improved road safety, home safety strategies for the elderly, and curbing harmful use of alcohol, are available and could help diminish this burden. Improvements in systems to record underlying causes of death from trauma are required.
    PLoS ONE 01/2013; 8(11):e79840. · 3.73 Impact Factor
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    ABSTRACT: BACKGROUND: Antenatal care (ANC) is a key strategy to improve maternal and infant health. However, survey data from sub-Saharan Africa indicate that women often only initiate ANC after the first trimester and do not achieve the recommended number of ANC visits. Drawing on qualitative data, this article comparatively explores the factors that influence ANC attendance across four sub-Saharan African sites in three countries (Ghana, Kenya and Malawi) with varying levels of ANC attendance. METHODS: Data were collected as part of a programme of qualitative research investigating the social and cultural context of malaria in pregnancy. A range of methods was employed interviews, focus groups with diverse respondents and observations in local communities and health facilities. RESULTS: Across the sites, women attended ANC at least once. However, their descriptions of ANC were often vague. General ideas about pregnancy care - checking the foetus' position or monitoring its progress - motivated women to attend ANC; as did, especially in Kenya, obtaining the ANC card to avoid reprimands from health workers. Women's timing of ANC initiation was influenced by reproductive concerns and pregnancy uncertainties, particularly during the first trimester, and how ANC services responded to this uncertainty; age, parity and the associated implications for pregnancy disclosure; interactions with healthcare workers, particularly messages about timing of ANC; and the cost of ANC, including charges levied for ANC procedures - in spite of policies of free ANC - combined with ideas about the compulsory nature of follow-up appointments. CONCLUSION: In these socially and culturally diverse sites, the findings suggest that 'supply' side factors have an important influence on ANC attendance: the design of ANC and particularly how ANC deals with the needs and concerns of women during the first trimester has implications for timing of initiation.
    PLoS ONE 01/2013; 8(1):e53747. · 3.73 Impact Factor
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    ABSTRACT: Pregnancy-related (PR) deaths are often a result of direct obstetric complications occurring at childbirth. To estimate the burden of and characterize risk factors for PR mortality, we evaluated deaths that occurred between 2003 and 2008 among women of childbearing age (15 to 49 years) using Health and Demographic Surveillance System data in rural western Kenya. WHO ICD definition of PR mortality was used: "the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the cause of death". In addition, symptoms and events at the time of death were examined using the WHO verbal autopsy methodology. Deaths were categorized as either (i) directly PR: main cause of death was ascribed as obstetric, or (ii) indirectly PR: main cause of death was non-obstetric. Of 3,223 deaths in women 15 to 49 years, 249 (7.7%) were PR. One-third (34%) of these were due to direct obstetric causes, predominantly postpartum hemorrhage, abortion complications and puerperal sepsis. Two-thirds were indirect; three-quarters were attributable to human immunodeficiency virus (HIV/AIDS), malaria and tuberculosis. Significantly more women who died in lower socio-economic groups sought care from traditional birth attendants (p = 0.034), while less impoverished women were more likely to seek hospital care (p = 0.001). The PR mortality ratio over the six years was 740 (95% CI 651-838) per 100,000 live births, with no evidence of reduction over time (χ(2) linear trend = 1.07; p = 0.3). These data supplement current scanty information on the relationship between infectious diseases and poor maternal outcomes in Africa. They indicate low uptake of maternal health interventions in women dying during pregnancy and postpartum, suggesting improved access to and increased uptake of skilled obstetric care, as well as preventive measures against HIV/AIDS, malaria and tuberculosis among all women of childbearing age may help to reduce pregnancy-related mortality.
    PLoS ONE 01/2013; 8(7):e68733. · 3.73 Impact Factor
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    ABSTRACT: The human landing catch (HLC) has long been the gold standard for estimating malaria transmission by mosquitoes, but has come under scrutiny because of ethical concerns of exposing collectors to infectious bites. We estimated the incidence of Plasmodium falciparum malaria infection in a cohort of 152 persons conducting HLCs and compared it with that of 147 non-collectors in western Kenya. Participants were presumptively cleared of malaria with Coartem™ (artemether-lumefantrine) and tested for malaria every 2 weeks for 12 weeks. The HLC collections were conducted four nights per week for six weeks. Collectors were provided chemoprophylaxis with Malarone™ (atovaquone-proguanil) during the six weeks of HLC activities and one week after HLC activities were completed. The incidence of malaria was 96.6% and was lower in collectors than in non-collectors (hazard ratio = 0.034, P < 0.0001). Therefore, with proper prophylaxis, concern about increased risk of malaria among collectors should not be an impediment to conducting HLC studies.
    The American journal of tropical medicine and hygiene 12/2012; · 2.53 Impact Factor
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    ABSTRACT: Background. Although children <5 years old in sub-Saharan Africa are vulnerable to both malaria and influenza, little is known about coinfection.Methods. This retrospective, cross-sectional study in rural western Kenya examined outpatient visits and hospitalizations associated with febrile acute respiratory illness (ARI) during a 2-year period (July 2009-June 2011) in children <5 years old.Results. Across sites, 45% (149/331) of influenza-positive patients were coinfected with malaria, whereas only 6% (149/2408) of malaria-positive patients were coinfected with influenza. Depending on age, coinfection was present in 4%-8% of outpatient visits and 1%-3% of inpatient admissions for febrile ARI. Children with influenza were less likely than those without to have malaria (risk ratio [RR], 0.57-0.76 across sites and ages), and children with malaria were less likely than those without to have influenza (RR, 0.36-0.63). Among coinfected children aged 24-59 months, hospital length of stay was 2.7 and 2.8 days longer than influenza-only-infected children at the 2 sites, and 1.3 and 3.1 days longer than those with malaria only (all P < .01).Conclusions. Coinfection with malaria and influenza was uncommon but associated with longer hospitalization than single infections among children 24-59 months of age.
    The Journal of Infectious Diseases 09/2012; · 5.85 Impact Factor
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    ABSTRACT: The KEMRI/Centers for Disease Control and Prevention (CDC) Health and Demographic Surveillance System (HDSS) is located in Rarieda, Siaya and Gem Districts (Siaya County), lying northeast of Lake Victoria in Nyanza Province, western Kenya. The KEMRI/CDC HDSS, with approximately 220 000 inhabitants, has been the foundation for a variety of studies, including evaluations of insecticide-treated bed nets, burden of diarrhoeal disease and tuberculosis, malaria parasitaemia and anaemia, treatment strategies and immunological correlates of malaria infection, and numerous HIV, tuberculosis, malaria and diarrhoeal disease treatment and vaccine efficacy and effectiveness trials for more than a decade. Current studies include operations research to measure the uptake and effectiveness of the programmatic implementation of integrated malaria control strategies, HIV services, newly introduced vaccines and clinical trials. The HDSS provides general demographic and health information (such as population age structure and density, fertility rates, birth and death rates, in- and out-migrations, patterns of health care access and utilization and the local economics of health care) as well as disease- or intervention-specific information. The HDSS also collects verbal autopsy information on all deaths. Studies take advantage of the sampling frame inherent in the HDSS, whether at individual, household/compound or neighbourhood level.
    International Journal of Epidemiology 08/2012; 41(4):977-87. · 6.98 Impact Factor
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    ABSTRACT: Understanding the relationship between Plasmodium falciparum malaria transmission and health outcomes requires accurate estimates of exposure to infectious mosquitoes. However, measures of exposure such as mosquito density and entomological inoculation rate (EIR) are generally aggregated over large areas and time periods, biasing the outcome-exposure relationship. There are few studies examining the extent and drivers of local variation in malaria exposure in endemic areas. We describe the spatio-temporal dynamics of malaria transmission intensity measured by mosquito density and EIR in the KEMRI/CDC health and demographic surveillance system using entomological data collected during 2002-2004. Geostatistical zero inflated binomial and negative binomial models were applied to obtain location specific (house) estimates of sporozoite rates and mosquito densities respectively. Model-based predictions were multiplied to estimate the spatial pattern of annual entomological inoculation rate, a measure of the number of infective bites a person receive per unit of time. The models included environmental and climatic predictors extracted from satellite data, harmonic seasonal trends and parameters describing space-time correlation. Anopheles gambiae s.l was the main vector species accounting for 86% (n=2309) of the total mosquitoes collected with the remainder being Anopheles funestus. Sixty eight percent (757/1110) of the surveyed houses had no mosquitoes. Distance to water bodies, vegetation and day temperature were strongly associated with mosquito density. Overall annual point estimates of EIR were 6.7, 9.3 and 9.6 infectious bites per annum for 2002, 2003 and 2004 respectively. Monthly mosquito density and EIR varied over the study period peaking in May during the wet season each year. The predicted and observed densities of mosquitoes and EIR showed a strong seasonal and spatial pattern over the study area. Spatio-temporal maps of malaria transmission intensity obtained in this study are not only useful in understanding variability in malaria epidemiology over small areas but also provide a high resolution exposure surface that can be used to analyse the impact of transmission on malaria related and all-cause morbidity and mortality.
    Parasites & Vectors 04/2012; 5:86. · 3.25 Impact Factor
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    ABSTRACT: Resistance to sulphadoxine-pyrimethamine (SP) in Plasmodium falciparum parasites is associated with mutations in the dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes and has spread worldwide. SP remains the recommended drug for intermittent preventive treatment for malaria in pregnancy (IPTp) and information on population prevalence of the SP resistance molecular markers in pregnant women is limited. Temporal trends of SP resistance molecular markers were investigated in 489 parasite samples collected from pregnant women at delivery from three different observational studies between 1996 and 2009 in Kenya, where SP was adopted for both IPTp and case treatment policies in 1998. Using real-time polymerase chain reaction, pyrosequencing and direct sequencing, 10 single-nucleotide polymorphisms (SNPs) of SP resistance molecular markers were assayed. The prevalence of quintuple mutant (dhfr N51I/C59R/S108N and dhps A437G/K540E combined genotype) increased from 7% in the first study (1996-2000) to 88% in the third study (2008-2009). When further stratified by sample collection year and adoption of IPTp policy, the prevalence of the quintuple mutant increased from 2.4% in 1998 to 44.4% three years after IPTp policy adoption, seemingly in parallel with the increase in percentage of SP use in pregnancy. However, in the 1996-2000 study, more mutations in the combined dhfr/dhps genotype were associated with SP use during pregnancy only in univariable analysis and no associations were detected in the 2002-2008 and 2008-2009 studies. In addition, in the 2008-2009 study, 5.3% of the parasite samples carried the dhps triple mutant (A437G/K540E/A581G). There were no differences in the prevalence of SP mutant genotypes between the parasite samples from HIV + and HIV- women over time and between paired peripheral and placental samples. There was a significant increase in dhfr/dhps quintuple mutant and the emergence of new genotype containing dhps 581 in the parasites from pregnant women in western Kenya over 13 years. IPTp adoption and SP use in pregnancy only played a minor role in the increased drug-resistant parasites in the pregnant women over time. Most likely, other major factors, such as the high prevalence of resistant parasites selected by the use of SP for case management in large non-pregnant population, might have contributed to the temporally increased prevalence of SP resistant parasites in pregnant women. Further investigations are needed to determine the linkage between SP drug resistance markers and efficacy of IPTp-SP.
    Malaria Journal 04/2012; 11:134. · 3.49 Impact Factor
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    ABSTRACT: BACKGROUND: Targeted global efforts to improve survival of young adults need information on mortality trends; contributions from health and demographic surveillance system (HDSS) are required. METHODS AND FINDINGS: This study aimed to explore changing trends in deaths among adolescents (15-19 years) and young adults (20-24 years), using census and verbal autopsy data in rural western Kenya using a HDSS. Mid-year population estimates were used to generate all-cause mortality rates per 100,000 population by age and gender, by communicable (CD) and non-communicable disease (NCD) causes. Linear trends from 2003 to 2009 were examined. In 2003, all-cause mortality rates of adolescents and young adults were 403 and 1,613 per 100,000 population, respectively, among females; and 217 and 716 per 100,000, respectively, among males. CD mortality rates among females and males 15-24 years were 500 and 191 per 100,000 (relative risk [RR] 2.6; 95% confidence intervals [CI] 1.7-4.0; p<0.001). NCD mortality rates in same aged females and males were similar (141 and 128 per 100,000, respectively; p = 0.76). By 2009, young adult female all-cause mortality rates fell 53% (χ(2) for linear trend 30.4; p<0.001) and 61.5% among adolescent females (χ(2) for linear trend 11.9; p<0.001). No significant CD mortality reductions occurred among males or for NCD mortality in either gender. By 2009, all-cause, CD, and NCD mortality rates were not significantly different between males and females, and among males, injuries equalled HIV as the top cause of death. CONCLUSIONS: This study found significant reductions in adolescent and young adult female mortality rates, evidencing the effects of targeted public health programmes, however, all-cause and CD mortality rates among females remain alarmingly high. These data underscore the need to strengthen programmes and target strategies to reach both males and females, and to promote NCD as well as CD initiatives to reduce the mortality burden amongst both gender.
    PLoS ONE 01/2012; 7(11):e47017. · 3.73 Impact Factor
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    ABSTRACT: Both insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS) reduce malaria in high malaria transmission areas. The combined effect of these interventions is unknown. We conducted a non-randomized prospective cohort study to determine protective efficacy of IRS with ITNs (ITN + IRS) compared with ITNs alone (ITN only) in preventing Plasmodium falciparum parasitemia. At baseline, participants provided blood samples for malaria smears, were presumptively treated for malaria, and received ITNs. Blood smears were made monthly and at sick visits. In total, 1,804 participants were enrolled. Incidence of P. falciparum parasitemia in the ITN + IRS and ITN only groups was 18 and 44 infections per 100 persons-years at risk, respectively (unadjusted rate ratio = 0.41; 95% confidence interval [CI] = 0.31-0.56). Adjusted protective efficacy of ITN + IRS compared with ITN only was 62% (95% CI = 0.50-0.72). The combination of IRS and ITN might be a feasible strategy to further reduce malaria transmission in areas of persistent perennial malaria transmission.
    The American journal of tropical medicine and hygiene 12/2011; 85(6):1080-6. · 2.53 Impact Factor

Publication Stats

1k Citations
311.15 Total Impact Points

Institutions

  • 2013
    • KEMRI / CDC Research and Public Health Collaboration
      Winam, Kisumu, Kenya
  • 2008–2013
    • University of Amsterdam
      • Faculty of Medicine AMC
      Amsterdamo, North Holland, Netherlands
    • KEMRI-Wellcome Trust Research Programme
      Kilifi, Kilifi, Kenya
    • Harvard Medical School
      Boston, Massachusetts, United States
  • 2000–2013
    • Centers for Disease Control and Prevention
      • • Division of Parasitic Diseases and Malaria
      • • National Center for Emerging and Zoonotic Infectious Diseases
      Atlanta, Michigan, United States
  • 2012
    • Liverpool School of Tropical Medicine
      Liverpool, England, United Kingdom
  • 2011
    • Emory University
      Atlanta, Georgia, United States
  • 2009–2011
    • Kenya Medical Research Institute
      • Centre for Global Health Research
      Nairobi, Nairobi Province, Kenya
    • CRESIB Barcelona Centre for International Health Research
      Barcino, Catalonia, Spain
  • 2006–2011
    • Kenya Centers for Disease Control and Prevention
      Winam, Kisumu, Kenya
  • 2001
    • U.S. Department of Health and Human Services
      Washington, Washington, D.C., United States
    • National Institute of Allergy and Infectious Diseases
      Maryland, United States