Detecting Malaria Hotspots: A Comparison of Rapid Diagnostic Test, Microscopy, and Polymerase Chain Reaction

A combined school survey and reactive case detection reveals minimal local transmission of malaria in the Highlands Region of Papua New Guinea

BACKGROUND

The Highlands of Papua New Guinea are non-endemic for malaria compared to the rest of the country. This study aimed to explore the local transmission of malaria in the Highlands through a cross-sectional school survey coupled with reactive case detection.

METHODS

Between July and November 2019, 5575 schoolchildren and 1048 household members were screened for malaria using Rapid Diagnostic Tests, subsequently validated by light microscopy. In addition, an analysis of malaria cases (2017 to 2019) was conducted across 33 health facilities within the catchment areas of the surveyed schools and households.

RESULTS

Thirteen individuals were diagnosed with malaria: eleven with Plasmodium falciparum (five schoolchildren, six household members) and two with Plasmodium vivax (one student, one household member); all were aged ten years or older. Malaria prevalence was 0.09% [95% CI 0.03, 0.3] among schoolchildren and 1.7% [95% CI 0.3, 9.1] among household members. Eleven positive individuals (84%) reported recent travel, mainly to lower-altitude endemic areas. Long-Lasting Insecticidal Nets were used by 34.8% [95% CI 28.7, 40.8] of household members. The average annual malaria incidence in the catchment areas was 3.7 cases per 1000 [95% CI 2.6, 5.3] among the general population, while children under 15 years accounted for 19% [95% CI 14, 27] of the positive cases.

CONCLUSIONS

Local malaria transmission appears to be minimal in the surveyed Highlands areas. Strengthening surveillance-response system to control imported cases and stop local foci could support malaria elimination in PNG. However, effective operational triggers for reactive case finding remain to be determined.

Comparison of fine-scale malaria strata derived from population survey data collected using RDTs, microscopy and qPCR in South-Eastern Tanzania

BACKGROUND

Malaria-endemic countries are increasingly adopting data-driven risk stratification, often at district or higher regional levels, to guide their intervention strategies. The data typically comes from population-level surveys collected by rapid diagnostic tests (RDTs), which unfortunately perform poorly in low transmission settings. Here, a high-resolution survey of Plasmodium falciparum prevalence rate (PfPR) was conducted in two Tanzanian districts using rapid diagnostic tests (RDTs), microscopy, and quantitative polymerase chain reaction (qPCR) assays, enabling the comparison of fine-scale strata derived from these different diagnostic methods.

METHODS

A cross-sectional survey was conducted in 35 villages in Ulanga and Kilombero districts, south-eastern Tanzania between 2022 and 2023. A total of 7,628 individuals were screened using RDTs (SD-BIOLINE) and microscopy, with two thirds of the samples further analysed by qPCR. The data was used to categorize each district and village as having very low (PfPR < 1%), low (1%≤PfPR < 5%), moderate (5%≤PfPR < 30%), or high (PfPR ≥ 30%) parasite prevalence. A generalized linear mixed model was used to analyse infection risk factors. Other metrics, including positive predictive value (PPV), sensitivity, specificity, parasite densities, and Kappa statistics were computed for RDTs or microscopy and compared to qPCR as reference.

RESULTS

Significant fine-scale variations in malaria risk were observed within and between the districts, with village prevalence ranging from 0% to > 50%. Prevalence varied by testing method: Kilombero was low risk by RDTs (PfPR = 3%) and microscopy (PfPR = 2%) but moderate by qPCR (PfPR = 9%); Ulanga was high risk by RDTs (PfPR = 39%) and qPCR (PfPR = 54%) but moderate by microscopy (PfPR = 26%). RDTs and microscopy classified majority of the 35 villages as very low to low risk (18-21 villages). In contrast, qPCR classified most villages as moderate to high risk (29 villages). Using qPCR as the reference, PPV for RDTs and microscopy ranged from as low as < 20% in very low transmission villages to > 80% in moderate and high transmission villages. Sensitivity was 62% for RDTs and 41% for microscopy; specificity was 93% and 96%, respectively. Kappa values were 0.7 for RDTs and 0.5 for microscopy. School-age children (5-15 years) had higher malaria prevalence and parasite densities than adults (P < 0.001). High-prevalence villages also had higher parasite densities (Spearman r = 0.77, P < 0.001 for qPCR; r = 0.55, P = 0.003 for microscopy).

CONCLUSION

This study highlights significant fine-scale variability in malaria burden within and between the study districts and emphasizes the variable performance of the testing methods when stratifying risk at local scales. While RDTs and microscopy were effective in high-transmission areas, they performed poorly in low-transmission settings; and classified most villages as very low or low risk. In contrast, qPCR classified most villages as moderate or high risk. The findings emphasize that, where precise mapping and effective targeting of malaria are required in localized settings, tests must be both operationally feasible and highly sensitive. Furthermore, when planning microstratification efforts to guide local control measures, it is crucial to carefully consider both the strengths and limitations of the available data and the testing methods employed.

A versatile microfluidic platform for malaria infection screening and Plasmodium species genotyping

BACKGROUND

Malaria, a widespread parasitic disease caused by Plasmodium species, remains a significant global health concern. Rapid and accurate detection, as well as species genotyping, are critical for effective malaria control.

METHODS

We have developed a Flexible, Robust, Equipment-free Microfluidic (FREM) platform, which integrates recombinase polymerase amplification (RPA) and clustered regularly interspaced short palindromic repeats (CRISPR)-based detection, enabling simultaneous malaria infection screening and Plasmodium species genotyping. The microfluidic chip enabled the parallel detection of multiple Plasmodium species, each amplified by universal RPA primers and genotyped by specific crRNAs. The inclusion of a sucrose solution effectively created spatial separation between the RPA and CRISPR assays within a one-pot system, effectively resolving compatibility issues.

FINDINGS

Clinical assessment of DNA extracts from patients with suspected malaria demonstrates the FREM platform's superior sensitivity (98.41%) and specificity (92.86%), yielding consistent results with PCR-sequencing for malaria detection, which achieved a positive predictive agreement of 98.41% and a negative predictive agreement of 92.86%. Additionally, the accuracy of species genotyping was validated through concordance rates of 90.91% between the FREM platform and PCR-sequencing.

INTERPRETATION

The FREM platform offers a promising solution for point-of-care malaria screening and Plasmodium species genotyping. It highlights the possibility of improving malaria control efforts and expanding its applicability to address other infectious diseases.

FUNDING

This work was financially supported by International Joint Laboratory on Tropical Diseases Control in Greater Mekong Subregion, National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, Bill & Melinda Gates Foundation and National Research and Development Plan of China.

Key considerations, target product profiles, and research gaps in the application of infrared spectroscopy and artificial intelligence for malaria surveillance and diagnosis

Studies on the applications of infrared (IR) spectroscopy and machine learning (ML) in public health have increased greatly in recent years. These technologies show enormous potential for measuring key parameters of malaria, a disease that still causes about 250 million cases and 620,000 deaths, annually. Multiple studies have demonstrated that the combination of IR spectroscopy and machine learning (ML) can yield accurate predictions of epidemiologically relevant parameters of malaria in both laboratory and field surveys. Proven applications now include determining the age, species, and blood-feeding histories of mosquito vectors as well as detecting malaria parasite infections in both humans and mosquitoes. As the World Health Organization encourages malaria-endemic countries to improve their surveillance-response strategies, it is crucial to consider whether IR and ML techniques are likely to meet the relevant feasibility and cost-effectiveness requirements-and how best they can be deployed. This paper reviews current applications of IR spectroscopy and ML approaches for investigating malaria indicators in both field surveys and laboratory settings, and identifies key research gaps relevant to these applications. Additionally, the article suggests initial target product profiles (TPPs) that should be considered when developing or testing these technologies for use in low-income settings.

Factors Affecting the Performance of HRP2-Based Malaria Rapid Diagnostic Tests

The recent COVID-19 pandemic has profoundly impacted global malaria elimination programs, resulting in a sharp increase in malaria morbidity and mortality. To reduce this impact, unmet needs in malaria diagnostics must be addressed while resuming malaria elimination activities. Rapid diagnostic tests (RDTs), the unsung hero in malaria diagnosis, work to eliminate the prevalence of Plasmodium falciparum malaria through their efficient, cost-effective, and user-friendly qualities in detecting the antigen HRP2 (histidine-rich protein 2), among other proteins. However, the testing mechanism and management of malaria with RDTs presents a variety of limitations. This paper discusses the numerous factors (including parasitic, host, and environmental) that limit the performance of RDTs. Additionally, the paper explores outside factors that can hinder RDT performance. By understanding these factors that affect the performance of HRP2-based RDTs in the field, researchers can work toward creating and implementing more effective and accurate HRP2-based diagnostic tools. Further research is required to understand the extent of these factors, as the rapidly changing interplay between parasite and host directly hinders the effectiveness of the tool.

Spatial-temporal pattern of malaria in Burkina Faso from 2013 to 2020

Despite the implementation of different strategies to fight against malaria in Burkina Faso since 2005, it remains today the leading cause of hospitalization and death. Adapting interventions to the spatial and temporal distribution of malaria could help to reduce this burden. This study aims to determine the structure and stability of malaria hotspots in Burkina Faso, with the objective of adapting interventions at small geographical scales.

Data on malaria cases from 2013 to 2020 were acquired at municipalities level. Municipality-wise malaria endemicity levels were mapped through geographical information system (GIS) tools. Spatial statistical analysis using Kulldoff sweeps were carried out to identify malaria hotspots. Then we mapped the monthly malaria risk.

Malaria is endemic in all the municipalities of Burkina Faso. However, two stable main spatial clusters (South-Western and Eastern part of the country) are emerging with seasonal reinforcement.

Interventions targeting the identified clusters could significantly reduce the incidence of malaria in Burkina Faso. This also prompts for further studies to identify the local determinants of this high transmission for the future success of malaria control.

Comparison of diagnostic performance between conventional and ultrasensitive rapid diagnostic tests for diagnosis of malaria: A systematic review and meta-analysis

Background

Successful malaria treatment, control and elimination programs require accurate, affordable, and field-deployable diagnostic tests. A number of studies have directly compared diagnostic performance between the new ultrasensitive rapid diagnostic test (us-RDT) and conventional rapid diagnostic test (co-RDT) for detecting malaria. Thus, we undertook this review to directly compare pooled diagnostic performance of us-RDT and co-RDT for detection of malaria.

Methods

PubMed, Web of Science, Scopus, Embase, and ProQuest were searched from their inception until 31 January 2021 accompanied by forward and backward citations tracking. Two authors independently assessed the quality of included studies by RevMan5 software (using the QUADAS-2 checklist). Diagnostic accuracy estimates (sensitivity and specificity and others) were pooled using a random-effect model and 95% confidence interval (CI) in Stata 15 software.

Results

Fifteen studies with a total of 20,236 paired co-RDT and us-RDT tests were included in the meta-analysis. Molecular methods (15 studies) and immunoassay test (one study) were used as standard methods for comparison with co-RDT and us-RDT tests. The pooled sensitivity for co-RDT and us-RDT were 42% (95%CI: 25–62%) and 61% (95%CI: 47–73%), respectively, with specificity of 99% (95%CI: 98–100%) for co-RDT, and 99% (95%CI: 96–99%) for us-RDT. In asymptomatic individuals, the pooled sensitivity and specificity of co-RDT were 27% (95%CI: 8–58%) and 100% (95%CI: 97–100%), respectively, while us-RDT had a sensitivity of 50% (95%CI: 33–68%) and specificity of 98% (95%CI: 94–100%). In low transmission settings, pooled sensitivity for co-RDT was 36% (95%CI: 9 76%) and 62% (95%CI: 44 77%) for us RDT, while in high transmission areas, pooled sensitivity for co RDT and us RDT were 62% (95%CI: 39 80%) and 75% (95%CI: 57–87%), respectively.

Conclusion

The us-RDT test showed better performance than co-RDT test, and this characteristic is more evident in asymptomatic individuals and low transmission areas; nonetheless, additional studies integrating a range of climate, geography, and demographics are needed to reliably understand the potential of the us-RDT.

Challenges in Laboratory Diagnosis of Malaria in a Low-Resource Country at Tertiary Care in Eastern Nepal: A Comparative Study of Conventional vs. Molecular Methodologies

For ongoing malaria elimination programmes, available methods such as microscopy and rapid diagnostic tests (RDTs) cannot detect all malaria cases in acute febrile illness. These methods are entirely dependent on the course of infection, parasite load, and skilled technical resources. Our study objectives were to estimate the performance of light microscopy and a RDT as well as real-time PCR for the detection of the Plasmodium parasite. Altogether, 52 blood samples collected from patients with acute febrile illness were tested by microscopy, RDT, and real-time PCR. The results were compared in terms of sensitivity and specificity. Microscopy detected the malaria parasite in 5.8% of the blood samples whereas 13.5% were detected by the RDT and 27% by real-time PCR. Considering real-time PCR as the gold standard method, microscopy had a sensitivity of 21.4% and a specificity of 100%, and the RDT had a sensitivity of 28.6% and a specificity of 92.1%. Microscopy together with the RDT successfully detected malaria positive cases in blood samples of Ct value below 20, but both were unable to detect malaria cases between 26-40 Ct value ranges amplified by real-time PCR. Despite various diagnostic tools being available, microscopy still remains the method of choice for diagnosis, while the RDT is user-friendly when applied at the point of care. However, our preliminary results emphasize the need to implement the test with higher sensitivity and specificity in the context of a malaria elimination programme. Such programmes can be a crucial opportunity to understand the species prevalent in a low-endemic region. However, these results should be further verified with a large cohort study to document the submicroscopic infection.

Spatial-temporal clustering of malaria using routinely collected health facility data on the Kenyan Coast

BACKGROUND

The over-distributed pattern of malaria transmission has led to attempts to define malaria "hotspots" that could be targeted for purposes of malaria control in Africa. However, few studies have investigated the use of routine health facility data in the more stable, endemic areas of Africa as a low-cost strategy to identify hotspots. Here the objective was to explore the spatial and temporal dynamics of fever positive rapid diagnostic test (RDT) malaria cases routinely collected along the Kenyan Coast.

METHODS

Data on fever positive RDT cases between March 2018 and February 2019 were obtained from patients presenting to six out-patients health-facilities in a rural area of Kilifi County on the Kenyan Coast. To quantify spatial clustering, homestead level geocoded addresses were used as well as aggregated homesteads level data at enumeration zone. Data were sub-divided into quarterly intervals. Kulldorff's spatial scan statistics using Bernoulli probability model was used to detect hotspots of fever positive RDTs across all ages, where cases were febrile individuals with a positive test and controls were individuals with a negative test.

RESULTS

Across 12 months of surveillance, there were nine significant clusters that were identified using the spatial scan statistics among RDT positive fevers. These clusters included 52% of all fever positive RDT cases detected in 29% of the geocoded homesteads in the study area. When the resolution of the data was aggregated at enumeration zone (village) level the hotspots identified were located in the same areas. Only two of the nine hotspots were temporally stable accounting for 2.7% of the homesteads and included 10.8% of all fever positive RDT cases detected.

CONCLUSION

Taking together the temporal instability of spatial hotspots and the relatively modest fraction of the malaria cases that they account for; it would seem inadvisable to re-design the sub-county control strategies around targeting hotspots.

Clinical and Biological Factors Associated With Early Epstein-Barr Virus Infection in Human Immunodeficiency Virus-Exposed Uninfected Infants in Eastern Uganda

BACKGROUND

Immune control of Epstein-Barr virus (EBV) infection is impaired in individuals with HIV. We explored maternal factors associated with EBV acquisition in HIV-exposed uninfected (HEU) infants and the relationship between EBV infection and serious adverse events (SAEs) during the first year of life.

METHODS

201 HEU infants from Uganda enrolled in the ANRS 12174 trial were tested for antiviral capsid antigen (anti-VCA) antibodies at week 50. Date of infection was estimated by testing EBV DNA at weeks 1, 6, 14, 26, 38, and 50 postpartum on dried blood spots.

RESULTS

Eighty-seven (43%) infants tested positive for anti-VCA IgG at week 50. Among the 59 infants positive for EBV DNA, 25% were infected within the first 26 weeks. Almost half (12%) were infected before week 14. Shedding of EBV in breast milk was associated with EBV DNA in maternal plasma (P = .009), HIV RNA detection (P = .039), and lower CD4 count (P = .001) and correlated with plasma EBV DNA levels (P = .002). EBV infant infection at week 50 was associated with shedding of EBV in breast milk (P = .009) and young maternal age (P = .029). Occurrence of a clinical SAE, including malaria and pneumonia, was associated with higher levels of EBV DNA in infants (P = .010).

CONCLUSIONS

By assessing EBV infection in HEU infants we observed that infection during the first year is determined by HIV and EBV maternal factors and that EBV DNA levels were higher among infants with clinical SAEs.

CLINICAL TRIALS REGISTRATION

NCT00640263.

A Systematic Literature Review of Microscopy Methods Reported in Malaria Clinical Trials

Microscopy of stained blood films is essential for the diagnosis of malaria, differentiation of parasite species, and estimation of parasite density performed for assessments of antimalarial drug efficacy. The accuracy and comparability of these measures over time and space are vital to discern the emergence or spread of antimalarial drug resistance. Although evidence-based guidelines for malaria microscopy methods exist, the age-old microscopy techniques for parasitological assessments are subject to considerable methodological variations. The purpose of this review was to explore critically how microscopy methods were reported in published malarial studies between 2013 and 2017 with the focus on outlining the methodological differences and improving reporting standards in practice.

Prevalence and Epidemiological Characteristics of Asymptomatic Malaria Based on Ultrasensitive Diagnostics: A Cross-sectional Study

BACKGROUND

As the global public-health objectives for malaria evolve from malaria control towards malaria elimination, there is increasing interest in the significance of asymptomatic infections and the optimal diagnostic test to identify them.

METHOD

We conducted a cross-sectional study of asymptomatic individuals (N = 562) to determine the epidemiological characteristics associated with asymptomatic malaria. Participants were tested by rapid diagnostic tests (CareStart, Standard Diagnostics [SD] Bioline, and Alere ultrasensitive RDT [uRDT]), loop-mediated isothermal amplification (LAMP), and quantitative reverse transcription polymerase chain reaction (qRT-PCR) to determine malaria positivity. Hemoglobin values were recorded, and anemia was defined as a binary variable, according to World Health Organization guidelines.

RESULTS

Compared to reference qRT-PCR, LAMP had the highest sensitivity (92.6%, 95% confidence interval [CI] 86.4-96.5), followed by uRDT Alere Malaria (33.9%, 95% CI 25.5-43.1), CareStart Malaria (14.1%, 95% CI 8.4-21.5), microscopy (5.0%, 95% CI 1.8-10.5), and SD Bioline (5.0%, 95% CI 1.8-10.5). For Plasmodium falciparum specimens only, the sensitivity for uRDT Alere Malaria was 50.0% (95% CI 38.8-61.3) and SD Bioline was 7.3% (95% CI 2.7-15.3). Based on multivariate regression analysis with qRT-PCR as the gold standard, for every 3.2% increase in the prevalence of asymptomatic malaria, hemoglobin decreased by 1 gram per deciliter (prevalence ratio 0.968, 95% CI 0.940-0.997; P = .032). Deletions (4.8%) in hrp2 were noted.

CONCLUSIONS

While uRDT Alere Malaria has superior sensitivity to rapid diagnostic tests and microscopy in detecting asymptomatic malaria, LAMP is superior still. Ultrasensitive diagnostics provide the accurate prevalence estimates of asymptomatic malaria required for elimination.

Performance comparison of two malaria rapid diagnostic test with real time polymerase chain reaction and gold standard of microscopy detection method

Background

The diagnostic test for malaria is mostly based on Rapid Diagnostic Test (RDT) and detection by microscopy. Polymerase Chain Reaction (PCR) is also a sensitive detection method that can be considered as a diagnostic tool. The outcome of malaria microscopy detection depends on the examiner's ability and experience. Some RDT has been distributed in Indonesia, which needs to be evaluated for their results.

Objective

This study aimed to compare the performance of RightSign RDT and ScreenPlus RDT for detection of Plasmodium in human blood. We used specific real-time polymerase chain reaction abTESTMMalaria qPCRII) and gold standard of microscopy detection method to measure diagnostic efficiency.

Methods

Blood specimens were evaluated using RightSign RDT, ScreenPlus RDT, Microscopy detection, and RT-PCR as the protocol described. The differences on specificity (Sp), sensitivity (Sn), positive predictive value (PPV), and negative predictive value (NPV) were analyzed using McNemar and Kruskal Wallis analysis.

Results

A total of 105 subjects were recruited. Based on microscopy test, RightSign RDT had sensitivity, Specificity, PPV, NPV, 100%, 98%, 98.2%, 100%, respectively. ScreenPlus showed 100% sensitivity, 98% specificity, 98.2% PPV, 100% NPV. The sensitivity of both RDTs became lower (75%) and the specificity higher (100 %) when using real-time PCR. Both RDTs showed a 100% agreement. RTPCR detected higher mix infection when compared to microscopy and RDTs.

Conclusion

RightSign and ScreenPlus RDT have excellent performance when using microscopy detection as a gold standard. Real-time PCR method can be considered as a confirmation tool for malaria diagnosis.

Spatio-temporal variation of malaria hotspots in Central Senegal, 2008-2012

Background

In malaria endemic areas, identifying spatio-temporal hotspots is becoming an important element of innovative control strategies targeting transmission bottlenecks. The aim of this work was to describe the spatio-temporal variation of malaria hotspots in central Senegal and to identify the meteorological, environmental, and preventive factors that influence this variation.

Methods

This study analysed the weekly incidence of malaria cases recorded from 2008 to 2012 in 575 villages of central Senegal (total population approximately 500,000) as part of a trial of seasonal malaria chemoprevention (SMC). Data on weekly rainfall and annual vegetation types were obtained for each village through remote sensing. The time series of weekly malaria incidence for the entire study area was divided into periods of high and low transmission using change-point analysis. Malaria hotspots were detected during each transmission period with the SaTScan method. The effects of rainfall, vegetation type, and SMC intervention on the spatio-temporal variation of malaria hotspots were assessed using a General Additive Mixed Model.

Results

The malaria incidence for the entire area varied between 0 and 115.34 cases/100,000 person weeks during the study period. During high transmission periods, the cumulative malaria incidence rate varied between 7.53 and 38.1 cases/100,000 person-weeks, and the number of hotspot villages varied between 62 and 147. During low transmission periods, the cumulative malaria incidence rate varied between 0.83 and 2.73 cases/100,000 person-weeks, and the number of hotspot villages varied between 10 and 43. Villages with SMC were less likely to be hotspots (OR = 0.48, IC95%: 0.33–0.68). The association between rainfall and hotspot status was non-linear and depended on both vegetation type and amount of rainfall. The association between village location in the study area and hotspot status was also shown.

Conclusion

In our study, malaria hotspots varied over space and time according to a combination of meteorological, environmental, and preventive factors. By taking into consideration the environmental and meteorological characteristics common to all hotspots, monitoring of these factors could lead targeted public health interventions at the local level. Moreover, spatial hotspots and foci of malaria persisting during LTPs need to be further addressed.

Trial registration

The data used in this work were obtained from a clinical trial registered on July 10, 2008 at www.clinicaltrials.gov under NCT00712374.

Development and validation of serological markers for detecting recent Plasmodium vivax infection

A major gap in the Plasmodium vivax elimination toolkit is the identification of individuals carrying clinically silent and undetectable liver-stage parasites, called hypnozoites. This study developed a panel of serological exposure markers capable of classifying individuals with recent P. vivax infections who have a high likelihood of harboring hypnozoites. We measured IgG antibody responses to 342 P. vivax proteins in longitudinal clinical cohorts conducted in Thailand and Brazil and identified candidate serological markers of exposure. Candidate markers were validated using samples from year-long observational cohorts conducted in Thailand, Brazil and the Solomon Islands and antibody responses to eight P. vivax proteins classified P. vivax infections in the previous 9 months with 80% sensitivity and specificity. Mathematical models demonstrate that a serological testing and treatment strategy could reduce P. vivax prevalence by 59-69%. These eight antibody responses can serve as a biomarker, identifying individuals who should be targeted with anti-hypnozoite therapy.

Direct Estimation of Sensitivity of Plasmodium falciparum Rapid Diagnostic Test for Active Case Detection in a High-Transmission Community Setting

Community-based active case detection of malaria parasites with conventional rapid diagnostic tests (cRDTs) is a strategy used most commonly in low-transmission settings. We estimated the sensitivity of this approach in a high-transmission setting in Western Kenya. We tested 3,547 members of 912 households identified in 2013-2014 by index children with (case) and without (control) cRDT-positive malaria. All were tested for Plasmodium falciparum with both a cRDT targeting histidine-rich protein 2 and with an ultrasensitive real-time polymerase chain reaction (PCR). We computed cRDT sensitivity against PCR as the referent, compared prevalence between participant types, and estimated cRDT detectability as a function of PCR-estimated parasite density. Parasite prevalence was 22.9% by cRDTs and 61.5% by PCR. Compared with children aged < 5 years or adults aged > 15 years, geometric mean parasite densities (95% CI) were highest in school-age children aged 5-15 years (8.4 p/uL; 6.6-10.6). The overall sensitivity of cRDT was 36%; among asymptomatic household members, cRDT sensitivity was 25.5% and lowest in adults aged > 15 years (15.8%). When modeled as a function of parasite density, relative to school-age children, the probability of cRDT positivity was reduced in both children aged < 5 years (odds ratio [OR] 0.48; 95% CI: 0.34-0.69) and in adults aged > 15 years (OR: 0.35; 95% CI: 0.27-0.47). An HRP2-detecting cRDT had poor sensitivity for active P. falciparum case detection in asymptomatic community members, and sensitivity was lowest in highly prevalent low-density infections and in adults. Future studies can model the incremental effects of high-sensitivity rapid diagnostic tests and the impacts on transmission.

Strengthening Surveillance Systems for Malaria Elimination by Integrating Molecular and Genomic Data

Unprecedented efforts in malaria control over the last 15 years have led to a substantial decrease in both morbidity and mortality in most endemic settings. However, these progresses have stalled over recent years, and resurgence may cause dramatic impact on both morbidity and mortality. Nevertheless, elimination efforts are currently going on with the objective of reducing malaria morbidity and mortality by 90% and malaria elimination in at least 35 countries by 2030. Strengthening surveillance systems is of paramount importance to reach those targets, and the integration of molecular and genomic techniques into routine surveillance could substantially improve the quality and robustness of data. Techniques such as polymerase chain reaction (PCR) and quantitative PCR (qPCR) are increasingly available in malaria endemic countries, whereas others such as sequencing are already available in a few laboratories. However, sequencing, especially next-generation sequencing (NGS), requires sophisticated infrastructure with adequate computing power and highly trained personnel for data analysis that require substantial investment. Different techniques will be required for different applications, and cost-effective planning must ensure the appropriate use of available resources. The development of national and sub-regional reference laboratories could help in minimizing the resources required in terms of equipment and trained staff. Concerted efforts from different stakeholders at national, sub-regional, and global level are needed to develop the required framework to establish and maintain these reference laboratories.

A geostatistical framework for combining spatially referenced disease prevalence data from multiple diagnostics

Multiple diagnostic tests are often used due to limited resources or because they provide complementary information on the epidemiology of a disease under investigation. Existing statistical methods to combine prevalence data from multiple diagnostics ignore the potential overdispersion induced by the spatial correlations in the data. To address this issue, we develop a geostatistical framework that allows for joint modelling of data from multiple diagnostics by considering two main classes of inferential problems: (a) to predict prevalence for a gold-standard diagnostic using low-cost and potentially biased alternative tests; (b) to carry out joint prediction of prevalence from multiple tests. We apply the proposed framework to two case studies: mapping Loa loa prevalence in Central and West Africa, using miscroscopy, and a questionnaire-based test called RAPLOA; mapping Plasmodium falciparum malaria prevalence in the highlands of Western Kenya using polymerase chain reaction and a rapid diagnostic test. We also develop a Monte Carlo procedure based on the variogram in order to identify parsimonious geostatistical models that are compatible with the data. Our study highlights (a) the importance of accounting for diagnostic-specific residual spatial variation and (b) the benefits accrued from joint geostatistical modelling so as to deliver more reliable and precise inferences on disease prevalence.

Bayesian evaluation of the performance of three diagnostic tests for Plasmodium falciparum infection in a low-transmission setting in Kilifi County, Kenya

Background: Central to the successful elimination of Plasmodium falciparum malaria, are tests with superior capability of diagnosing low-density parasitaemias. Empirical evidence on the performance of the commonly available diagnostics (light microscopy (LM), rapid diagnostic tests (RDT) and polymerase chain reaction (PCR)) is needed to better inform case management and surveillance activities within primary health care settings where elimination of falciparum malaria is targeted. The objective of this study was to estimate the sensitivity (Se) and specificity (Sp) and predictive values of LM, RDT and PCR tests for P. falciparum infection in children, while evaluating the effect of specific covariates on the accuracy of the tests. Methods: The study enrolled 1,563 children presenting with fever (axillary temperature ≥ 37.5 0C) to the Ngerenya dispensary, Kilifi County between March and December 2014. A Bayesian latent class model (BLCM) was fitted to the participants' diagnostic data obtained from blood samples that were screened for the presence of P. falciparum using the three tests. Results: The PCR assay registered a higher Se (97.6% [92.0; 99.7]) than LM (84.0% [74.8; 91.0]) but similar to RDT (92.2% [84.4; 97.0]). However, the assay showed a similar Sp (98.9% [98.2; 99.4]) to both RDT (99.4% [98.9; 99.7]) and LM (99.5% [99.0; 99.8]). Regarding predictive values, the tests yielded statistically similar estimates of positive and negative predictive values (PPV and NPV). A serial interpretation of the results of RDT and LM raised the PPVs and NPVs to >98%. Conclusions: LM and RDT afford high Se and Sp in symptomatic care-seeking children in this low P. falciparum prevalence setting. A serial combination of the tests assures high PPV and NPV estimates. These elements, coupled with the wide deployment and affordability of the tests, lend the tests useful for guiding clinical care and surveillance activities for P. falciparum within elimination settings.

Spatiotemporal clustering of malaria in southern-central Ethiopia: A community-based cohort study

Introduction

Understanding the spatiotemporal clustering of malaria transmission would help target interventions in settings of low malaria transmission. The aim of this study was to assess whether malaria infections were clustered in areas with long-lasting insecticidal nets (LLINs) alone, indoor residual spraying (IRS) alone, or a combination of LLINs and IRS interventions, and to determine the risk factors for the observed malaria clustering in southern-central Ethiopia.

Methods

A cohort of 34,548 individuals residing in 6,071 households was followed for 121 weeks, from October 2014 to January 2017. Both active and passive case detection mechanisms were used to identify clinical malaria episodes, and there were no geographic heterogeneity in data collection methods. Using SaTScan software v 9.4.4, a discrete Poisson model was used to identify high rates of spatial, temporal, and spatiotemporal malaria clustering. A multilevel logistic regression model was fitted to identify predictors of spatial malaria clustering.

Results

The overall incidence of malaria was 16.5 per 1,000 person-year observations. Spatial, temporal, and spatiotemporal clustering of malaria was detected in all types of malaria infection (P. falciparum, P. vivax, or mixed). Spatial clustering was identified in all study arms: for LLIN + IRS arm, a most likely cluster size of 169 cases in 305 households [relative risk (RR) = 4.54, P<0.001]; for LLIN alone arm a cluster size of 88 cases in 103 households (RR = 5.58, P<0.001); for IRS alone arm a cluster size of 58 cases in 50 households (RR = 7.15, P<0.001), and for control arm a cluster size of 147 cases in 377 households (RR = 2.78, P<0.001). Living 1 km closer to potential vector breeding sites increased the odds of being in spatial clusters by 41.32 fold (adjusted OR = 41.32, 95% CI = 3.79–138.89).

Conclusions

The risk of malaria infection varied significantly between kebeles, within kebeles, and even among households in areas targeted for different types of malaria control interventions in low malaria transmission setting. The results of this study can be used in planning and implementation of malaria control strategies at micro-geographic scale.

Trial registration

PACT R2014 11000 882128 (8 September 2014).

Bayesian evaluation of the performance of three diagnostic tests for Plasmodium falciparum infection in a low-transmission setting in Kilifi County, Kenya

Background: Central to the successful elimination of Plasmodium falciparum malaria, are tests with superior capability of diagnosing low-density parasitaemias. Empirical evidence on the performance of the commonly available diagnostics (light microscopy (LM), rapid diagnostic tests (RDT) and polymerase chain reaction (PCR)) is needed to better inform case management and surveillance activities within primary health care settings where elimination of falciparum malaria is targeted. The objective of this study was to estimate the sensitivity (Se) and specificity (Sp) and predictive values of LM, RDT and PCR tests for P. falciparum infection in children, while evaluating the effect of specific covariates on the accuracy of the tests. Methods: The study enrolled 1,563 children presenting with fever (axillary temperature ≥ 37.50C) to the Ngerenya dispensary, Kilifi County between March and December 2014. A Bayesian latent class model (BLCM) was fitted to the participants' diagnostic data obtained from blood samples that were screened for the presence of P. falciparum using the three tests. Results: The PCR assay registered a higher Se (97.6% [92.0; 99.7]) than LM (84.0% [74.8; 91.0]) but similar to RDT (92.2% [84.4; 97.0]). However, the assay showed a similar Sp (98.9% [98.2; 99.4]) to both RDT (99.4% [98.9; 99.7]) and LM (99.5% [99.0; 99.8]). Regarding predictive values, the tests yielded statistically similar estimates of positive and negative predictive values (PPV and NPV). A serial interpretation of the results of RDT and LM raised the PPVs and NPVs to >98%. Conclusions: LM and RDT afford high Se and Sp in a low P. falciparum prevalence setting. A serial combination of the tests assures high PPV and NPV estimates. These elements, coupled with the wide deployment and affordability of the tests, lend the tests useful for guiding clinical care and surveillance activities for P. falciparum within elimination settings.

Bayesian evaluation of the performance of three diagnostic tests for Plasmodium falciparum infection in a low-transmission setting in Kilifi County, Kenya

Background: Central to the successful elimination of Plasmodium falciparum malaria, are tests with superior capability of diagnosing low-density parasitaemias. Empirical evidence on the performance of the commonly available diagnostics (light microscopy (LM), rapid diagnostic tests (RDT) and polymerase chain reaction (PCR)) is needed to better inform case management and surveillance activities within primary health care settings where elimination of falciparum malaria is targeted. The objective of this study was to estimate the sensitivity (Se) and specificity (Sp) and predictive values of LM, RDT and PCR tests for P. falciparum infection, while evaluating the effect of specific covariates on the accuracy of the tests. Methods: The study enrolled 1,563 children via a cross-sectional survey for asymptomatic malaria and those presenting with symptomatic malaria to the Ngerenya dispensary, Kilifi County between March and December 2014. A Bayesian latent class model (BLCM) was fitted to the participants' diagnostic data obtained from blood samples that were screened for the presence of P. falciparum using the three tests. Results: The PCR assay registered a higher Se (97.6% [92.0; 99.7]) than LM (84.0% [74.8; 91.0]) but similar to RDT (92.2% [84.4; 97.0]). However, the assay showed a similar Sp (98.9% [98.2; 99.4]) to both RDT (99.4% [98.9; 99.7]) and LM (99.5% [99.0; 99.8]). Regarding predictive values, the tests yielded statistically similar estimates of Positive and negative predictive values (PPV and NPV). A serial interpretation of the results of RDT and LM raised the PPVs and NPVs to >98%. Conclusions: LM and RDT tests afford high Se and Sp in a low P. falciparum prevalence setting. A serial combination of the tests assures high PPV and NPV estimates. These elements, coupled with the wide deployment and affordability of the tests, lend the tests useful for guiding clinical care and surveillance activities for P. falciparum within elimination settings.

Variation in the effectiveness of insecticide treated nets against malaria and outdoor biting by vectors in Kilifi, Kenya

Background: Insecticide treated nets (ITNs) protect humans against bites from the Anopheles mosquito vectors that transmit malaria, thereby reducing malaria morbidity and mortality. It has been noted that ITN use leads to a switch from indoor to outdoor feeding among these vectors. It might be expected that outdoor feeding would undermine the effectiveness of ITNs that target indoors vectors, but data are limited. Methods: We linked homestead level geospatial data to clinical surveillance data at a primary healthcare facility in Kilifi County in order to map geographical heterogeneity in ITN effectiveness and observed vector feeding behaviour using landing catches and CDC light traps in six selected areas of varying ITN effectiveness. We quantified the interaction between mosquitoes and humans to evaluate whether outdoor vector biting is a potential explanation for the variation in ITN effectiveness. Results: We observed 37% and 46% visits associated with positive malaria slides among ITN users and non-ITN-users, respectively; ITN use was associated with 32% protection from malaria (crude OR = 0.68, 95% CI: 0.64, 0.73). We obtained modification of ITN effectiveness by geographical area (p=0.016), and identified 6 hotspots using the spatial scan statistic. Majority of mosquitoes were caught outdoor (60%) and were of the An. funestus group (75%). The overall propensity to feed at times when most people were asleep was high; the vast majority of the Anopheles mosquitoes were caught at times when most people are indoors asleep. Estimates for the proportion of human-mosquito contact between the first and last hour when most humans were asleep was consistently high across all locations, ranging from 0.83 to 1.00. Conclusion: Our data do not provide evidence of an epidemiological association between microgeographical variations in ITN effectiveness and variations in the microgeographical distribution of outdoor biting.

Variation in the effectiveness of insecticide treated nets against malaria and outdoor biting by vectors in Kilifi, Kenya

Background: Insecticide treated nets (ITNs) protect humans against bites from the Anopheles mosquito vectors that transmit malaria, thereby reducing malaria morbidity and mortality. It has been noted that ITN use leads to a switch from indoor to outdoor feeding among these vectors. It might be expected that outdoor feeding would undermine the effectiveness of ITNs that target indoors vectors, but data are limited.

Methods: We linked homestead level geospatial data to clinical surveillance data at a primary healthcare facility in Kilifi County in order to map geographical heterogeneity in ITN effectiveness and observed vector feeding behaviour using landing catches and CDC light traps in six selected areas of varying ITN effectiveness. We quantified the interaction between mosquitoes and humans to evaluate whether outdoor vector biting is a potential explanation for the variation in ITN effectiveness.

Results: We observed 37% and 46% visits associated with positive malaria slides among ITN users and non-ITN-users, respectively; ITN use was associated with 32% protection from malaria (crude OR = 0.68, 95% CI: 0.64, 0.73). We obtained modification of ITN effectiveness by geographical area (p=0.016), and identified 6 hotspots using the spatial scan statistic. Majority of mosquitoes were caught outdoor (60%) and were of the An. funestus group (75%). The overall propensity to feed at times when most people were asleep was high; the vast majority of the Anopheles mosquitoes were caught at times when most people are indoors asleep. Estimates for the proportion of human-mosquito contact between the first and last hour when most humans were asleep was consistently high across all locations, ranging from 0.83 to 1.00.

Conclusion: Our data do not provide evidence of an epidemiological association between microgeographical variations in ITN effectiveness and variations in the microgeographical distribution of outdoor biting.

Variation in the effectiveness of insecticide treated nets against malaria and outdoor biting by vectors in Kilifi, Kenya

Background: Insecticide treated nets (ITNs) protect humans against bites from the Anopheles mosquito vectors that transmit malaria, thereby reducing malaria morbidity and mortality. It has been noted that ITN use leads to a switch from indoor to outdoor feeding among these vectors. It might be expected that outdoor feeding would undermine the effectiveness of ITNs that target indoors vectors, but data are limited. Methods: We linked homestead level geospatial data to clinical surveillance data at a primary healthcare facility in Kilifi County in order to map geographical heterogeneity in ITN effectiveness and observed vector feeding behaviour using landing catches and CDC light traps in six selected areas of varying ITN effectiveness. We quantified the interaction between mosquitoes and humans to evaluate whether outdoor vector biting is a potential explanation for the variation in ITN effectiveness. Results: We observed 37% and 46% visits associated with positive malaria slides among ITN users and non-ITN-users, respectively; ITN use was associated with 32% protection from malaria (crude OR = 0.68, 95% CI: 0.64, 0.73). We obtained significant modification of ITN effectiveness by geographical area (p=0.016), and identified significant hotspots using the spatial scan statistic. Majority of mosquitoes were caught outdoor (60%) and were of the An. funestus group (75%). The overall propensity to feed at times when most people are indoor was high; the vast majority of the Anopheles mosquitoes were caught at times when most people are indoor. Estimates for the proportion of human-mosquito contact between the first and last hour when most humans were indoor was consistently high, ranging from 0.83 to 1.00. Conclusion: Our data do not provide evidence of an epidemiological association between microgeographical variations in ITN effectiveness and variations in the microgeographical distribution of outdoor biting.

High proportions of pfhrp2 gene deletion and performance of HRP2-based rapid diagnostic test in Plasmodium falciparum field isolates of Odisha

BACKGROUND

With the documentation of cases of falciparum malaria negative by rapid diagnostic tests (RDT), though at low frequency from natural isolates in a small pocket of Odisha, it became absolutely necessary to investigate the status of HRP-2 based RDT throughout the state and in different seasons of the year.

METHODS

Suspected individuals were screened for malaria infection by microscopy and RDT in 25/30 districts of Odisha, India. Discrepancies in results were confirmed by PCR. False negative RDT samples for Plasmodium falciparum mono-infection were evaluated for detection of HRP2 antigen in ELISA and genotyped for pfhrp2, pfhrp3 and their flanking genes. Multiplicity of infection was ascertained based on msp1 and msp2 genotyping and parasitaemia level was determined by microscopy.

RESULTS

Of the total 1058 patients suspected for malaria, 384 were microscopically confirmed for P. falciparum mono-infection and RDT failure was observed in 58 samples at varying proportion in different regions of the state. The failure in detection was due to undetectable level of HRP-2. Although most of these samples were screened during rainy season (45/345), significantly high proportion (9/17) of RDT negative samples were obtained during the summer compared to rainy season (P = 0.0002; OR = 7.5). PCR genotyping of pfhrp2 and pfhrp3 in RDT negative samples showed 38/58 (65.5) samples to be pfhrp2 negative and 24/58 (41.4) to be pfhrp3 negative including dual negative in 17/58 (29.3). Most of the RDT negative samples (39/58) were with single genotype infection and high proportions of pfhrp2 deletion (7/9) was observed in summer. No difference in parasitaemia level was observed between RDT positive and RDT negative patients.

CONCLUSION

High prevalence of parasites with pfhrp2 deletion including dual deletions (pfhrp2 and pfhrp3) is a serious cause of concern, as these patients could not be given a correct diagnosis and treatment. Therefore, HRP2-based RDT for diagnosing P. falciparum infection in Odisha is non-reliable and must be performed in addition to or replaced by other appropriate diagnostic tools for clinical management of the disease.

Multiplicity of Infection Is a Poor Predictor of Village-Level Plasmodium vivax and P. falciparum Population Prevalence in the Southwest Pacific

Across 8101 individuals in 46 villages, the proportion of Plasmodium spp. multiple clone infections (0%–53.8%) did not reflect prevalence by quantitative polymerase chain reaction (qPCR; 1.9%–38.4%), except for P. vivax in Solomon Islands (P < .001). Thus this parameter was not informative to identify transmission foci. In contrast, prevalence by microscopy and qPCR correlated well.

When Should the Emphasis on Schistosomiasis Control Move to Elimination?

The stated goal of the World Health Organization’s program on schistosomiasis is paraphrased as follows: to control morbidity and eliminate transmission where feasible. Switching from a goal of controlling morbidity to interrupting transmission may well be currently feasible in some countries in the Caribbean, some areas in South America, northern Africa, and selected endemic areas in sub-Saharan Africa where there have been improvements in sanitation and access to clean water. However, in most of sub-Saharan Africa, where programmatic interventions still consist solely of annual mass drug administration, such a switch in strategies remains premature. There is a continued need for operational research on how best to reduce transmission to a point where interruption of transmission may be achievable. The level of infection at which it is feasible to transition from control to elimination must also be defined. In parallel, there is also a need to develop and evaluate approaches for achieving and validating elimination. There are currently neither evidence-based methods nor tools for breaking transmission or verifying that it has been accomplished. The basis for these statements stems from numerous studies that will be reviewed and summarized in this article; many, but not all of which were undertaken as part of SCORE, the Schistosomiasis Consortium for Operational Research and Evaluation.

Operational Performance of a Plasmodium falciparum Ultrasensitive Rapid Diagnostic Test for Detection of Asymptomatic Infections in Eastern Myanmar

In the Greater Mekong Subregion in Southeast Asia, malaria elimination strategies need to target all Plasmodium falciparum parasites, including those carried asymptomatically. More than 70% of asymptomatic carriers are not detected by current rapid diagnostic tests (RDTs) or microscopy.

In the Greater Mekong Subregion in Southeast Asia, malaria elimination strategies need to target all Plasmodium falciparum parasites, including those carried asymptomatically. More than 70% of asymptomatic carriers are not detected by current rapid diagnostic tests (RDTs) or microscopy. An HRP2-based ultrasensitive RDT (uRDT) developed to improve the detection of low-density infections was evaluated during prevalence surveys within a malaria elimination program in a low-transmission area of eastern Myanmar. Surveys were conducted to identify high-prevalence villages. Two-milliliter venous blood samples were collected from asymptomatic adult volunteers and transported to the laboratory. Plasmodium parasites were detected by RDT, uRDT, microscopy, ultrasensitive qPCR (uPCR), and multiplex enzyme-linked immunosorbent assay (ELISA). The sensitivity, specificity, and predictive positive and negative values of RDT and uRDT were calculated compared to uPCR and ELISA. Parasite and antigen concentrations detected by each test were defined using uPCR and ELISA, respectively. A total of 1,509 samples, including 208 P. falciparum-positive samples were analyzed with all tests. The sensitivity of the uRDT was twofold higher than that of RDT, 51.4% versus 25.2%, with minor specificity loss, 99.5% versus 99.9%, against the combined reference (uPCR plus ELISA). The geometric mean parasitemia detected by uRDT in P. falciparum monospecific infections was 3,019 parasites per ml (95% confidence interval [95% CI], 1,790 to 5,094; n = 79) compared to 11,352 parasites per ml (95% CI, 5,643 to 22,837; n = 38) by RDT. The sensitivities of uRDT and RDT dropped to 34.6% and 15.1%, respectively, for the matched tests performed in the field. The uRDT performed consistently better than RDT and microscopy at low parasitemias. It shows promising characteristics for the identification of high-prevalence communities and warrants further evaluation in mass screening and treatment interventions.

Spatio-temporal dynamic of malaria in Ouagadougou, Burkina Faso, 2011-2015

Background

Given the scarcity of resources in developing countries, malaria treatment requires new strategies that target specific populations, time periods and geographical areas. While the spatial pattern of malaria transmission is known to vary depending on local conditions, its temporal evolution has yet to be evaluated. The aim of this study was to determine the spatio-temporal dynamic of malaria in the central region of Burkina Faso, taking into account meteorological factors.

Methods

Drawing on national databases, 101 health areas were studied from 2011 to 2015, together with weekly meteorological data (temperature, number of rain events, rainfall, humidity, wind speed). Meteorological factors were investigated using a principal component analysis (PCA) to reduce dimensions and avoid collinearities. The Box–Jenkins ARIMA model was used to test the stationarity of the time series. The impact of meteorological factors on malaria incidence was measured with a general additive model. A change-point analysis was performed to detect malaria transmission periods. For each transmission period, malaria incidence was mapped and hotspots were identified using spatial cluster detection.

Results

Malaria incidence never went below 13.7 cases/10,000 person-weeks. The first and second PCA components (constituted by rain/humidity and temperatures, respectively) were correlated with malaria incidence with a lag of 2 weeks. The impact of temperature was significantly non-linear: malaria incidence increased with temperature but declined sharply with high temperature. A significant positive linear trend was found for the entire time period. Three transmission periods were detected: low (16.8–29.9 cases/10,000 person-weeks), high (51.7–84.8 cases/10,000 person-weeks), and intermediate (26.7–32.2 cases/10,000 person-weeks). The location of clusters identified as high risk varied little across transmission periods.

Conclusion

This study highlighted the spatial variability and relative temporal stability of malaria incidence around the capital Ouagadougou, in the central region of Burkina Faso. Despite increasing efforts in fighting the disease, malaria incidence remained high and increased over the period of study. Hotspots, particularly those detected for low transmission periods, should be investigated further to uncover the local environmental and behavioural factors of transmission, and hence to allow for the development of better targeted control strategies.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2280-y) contains supplementary material, which is available to authorized users.

Reactive case detection of Plasmodium falciparum in western Kenya highlands: effective in identifying additional cases, yet limited effect on transmission

Background

Identifying asymptomatic reservoirs of malaria parasites using index cases as entry points into the community is potentially a cost-effective way towards achieving malaria elimination.

Methods

Within 1 year, 1430 confirmed malaria cases were identified in Marani hospital, western Kenya. Fifty cases were followed up, and 108 index case household members and 612 neighbours within a 100 m radius were screened. As controls, samples were collected from 510 individuals matched with index cases and located at a distance of ≥ 500 m from them. Infections were diagnosed by microscopy and PCR while simultaneously collecting malaria vectors indoor using pyrethrum spray catches.

Results

In the index case and neighbour households, the prevalence of infection was approximately twice as high as in control households (by PCR: index cases households: 28.9%, neighbours: 25.3%, matched controls: 12.9%). In index case households, the indoor vector density (Anopheles gambiae and Anopheles funestus) was higher (0.46 female/house/night) than in neighbouring (0.31 f/h/n) and control houses (0.29 f/h/n).

Conclusions

Screening index case households and neighbours approximately doubles the chance to detect asymptomatic infections compared to randomly selected households. However, even if all cases were followed up, only a small proportion (˂ 10%) of the asymptomatic reservoir in the population would have been identified. Control programmes need to weigh the increased chance to find cases around index cases vs. the logistical challenges to target this subgroup within the population.

Variation in the effectiveness of insecticide treated nets against malaria and outdoor biting by vectors in Kilifi, Kenya

Background: Insecticide treated nets (ITNs) protect humans against bites from the Anopheles mosquito vectors that transmit malaria, thereby reducing malaria morbidity and mortality. It has been noted that ITN use leads to a switch from indoor to outdoor feeding among these vectors. It might be expected that outdoor feeding would undermine the effectiveness of ITNs that target indoors vectors, but data are limited. Methods: We linked homestead level geospatial data to clinical surveillance data at a primary healthcare facility in Kilifi County in order to map geographical heterogeneity in ITN effectiveness and observed vector feeding behaviour using landing catches and CDC light traps in six selected areas of varying ITN effectiveness. We quantified the interaction between mosquitoes and humans to evaluate whether outdoor vector biting is a potential explanation for the variation in ITN effectiveness. Results: We observed 37% and 46% visits associated with positive malaria slides among ITN users and non-ITN-users, respectively; ITN use was associated with 32% protection from malaria (crude OR = 0.68, 95% CI: 0.64, 0.73). We obtained significant modification of ITN effectiveness by geographical area (p=0.016), and identified significant hotspots using the spatial scan statistic. Majority of mosquitoes were caught outdoor (60%) and were of the An. funestus group (75%). The overall propensity to feed at times when most people are indoor was high; the vast majority of the Anopheles mosquitoes were caught at times when most people are indoor. Estimates for the proportion of human-mosquito contact between the first and last hour when most humans were indoor was consistently high, ranging from 0.83 to 1.00. Conclusion: Our data therefore do not support the hypothesis that outdoor biting limits the effectiveness of ITNs in our study area.