The Global Technical Strategy for Malaria advocates for “Malaria surveillance as a core intervention”; here we describe an effort of using the available data from the malaria surveillance system triangulated with other contextual information to analyse, characterize, and provide a response tailored to the malaria transmission dynamics at a very local level.
Over the past few years, pressure has been laid on the identification of epidemiological hotspots and tailoring of interventions.(23, 24) Several groups have explored potential approaches to stratify using high resolution risk maps created by using a comprehensive set of information. Use of these would have further improved the identification of hotspots in our work and to that end a risk map was developed in 2014 but could not be repeated annually. (25)We considered that the microstratification methodology should be replicable at least annually and by the local health staff; thus, tools available at their disposal were considered for our work. Additionally, there is considerable lack of information to guide tailored malaria interventions in an elimination setting.
In 2018, the WHO recommended a framework for stratifying malaria risk based on receptivity, vulnerability, epidemiological determinants, and interventions.(8). Cohen et al, suggest that optimal operational planning requires use of more than one aspect of risk assessment such as incidence. (26) Our work employed the use of all the factors recommended by WHO by operationalizing available information for risk stratification and tailoring interventions, albeit at a micro level, and moving away from use of a single aspect of risk – annual parasite incidence, as was done in previous years. It also shows how to employ the operative knowledge of MOH health personnel at the national and local level to develop a bottom-up response plan. (2)
A key aspect evidenced here is the increasing availability of malaria detection through RDT posts or microscopy in each micro-area. Given the socio-demographic characteristics, medical attention in Honduras is largely through rural health centres and a few tertiary level institutions. (15) The voluntary collaborator (ColVol, acronym in Spanish) network for malaria came into being in the late 20th century in Honduras and these were trained in attending patients and taking blood slides to be subsequently revised by the microscopist and treatment administered by the ColVol. Since 2014, they have been trained in using RDTs to ensure prompt diagnosis and treatment, especially in Gracias a Dios department (27). The ColVol network has been used by the country for other interventions like active case detection, distribution of LLINs and IRS, information, and education, among others. Our work provides information for better placement and orientation of this network to malaria endemic areas as malaria incidence declines.
The detailed study of health system factors at each locality and micro-area was vital for operational planning. Management of health systems is the Achille’s heel of all disease elimination programmes and the major reason for failures or exceptional delays.(28) Our approach takes the health system into account as vital parameter, analyses deficiencies, proposes solutions and local operational plans for their implementation.
Nonetheless the micro-stratification and the resulting operational planning is but an initial step towards improving response, the final goal. We consider that microstratification must be dynamic exercise that changes as determinants vary and should be revised and update by the local health personnel, preferably annually. This requires capacity development at the local level to both conduct as well as update the micro-stratification and micro-planification plan, and thus requires the methodology to be both simple yet encompassing the most important factors using information available to the local health staff.
Together with biological factors related to vector and parasites, human behaviour is considered key in the process of transmission on malaria-endemic settings across the world. (8, 29, 30) The correlation between infection risk and the human movement patterns is well established and several studies have tried to use information like census tracts, mobile phone use among other methods to understand this. However, given the low amount of data available at the granularity needed, this aspect is highly limited in low transmission malaria dynamics settings. (10, 25, 31–33) The use of local knowledge was an innovative way in our study to determine patterns of human movement and use it in conjunction with known malaria risk areas to determine vulnerability at the locality level. Undocumented migration both to and from Nicaragua as well as drug trafficking other than local socio-economic activities were also considered. However, it did not capture variations by seasons and other ad-hoc reasons like festivals, sports, or religious activities. Tools to measure vulnerability and temporal changes therein at the level of each locality are required.(34)
Among the limitations of this study are the availability and quality of data, and inherent biases in its generation. It is recognized that the national malaria program of Honduras has achieved tremendous advances on its pathway to elimination, as is demonstrated through the expansion of its diagnosis and treatment network via community health posts using RDTs and sustaining passive case detection by microscopy over the last ten years, case based surveillance and improving malaria case investigation capacity across the country.(4, 6, 7, 35) However, coverage of surveillance measured through number of suspected cases detected by geographical area and time was available at the level of locality was available for previous years but not for 2016. Geographical availability of diagnosis and treatment was used as a proxy for surveillance coverage. Nonetheless, we consider that highlighting this gap and demonstrating its need is a product of our approach. Need of more data or improvement in its quality should be a product of and not a pre-requisite for its use and analysis. Deficient information on site of infection, inability of mapping 15% of confirmed cases, combination of data from both passive and active case detection were also substantial limitations. These and other potential deficiencies of the national malaria surveillance system need be rectified for malaria elimination in Honduras. (2, 8, 9)
A limitation of this exercise was the lack of operational methods for receptivity characterization at the level of each locality. Receptivity was used as binary variable of being present or absent in our work. Data for adult entomological indicators were available from only one sentinel site in Gracias a Dios but information on breeding spots and larval density was available from most localities. The historic use of environmental methods for malaria control in Central America have led to extensive larval surveillance capacities and their implementation, further strengthened by various projects like the DDT/GEF project in 2004–2007.(36) However, no clear correlation between larval density or presence of breeding sites and the receptivity grade within a place currently exist. Further tools are required for the use of this information as well generally to establish receptivity gradient of a locality based on routine entomological surveillance information.
Data from the sentinel site in Puerto Lempira shows An. albimanus as the major malaria vector. This is are consistent with Escobar et al. who reported An albimanus as the most abundant and widespread anopheline specie in the country. (37) This, together with insecticide susceptibility surveillance data form Gracias a Dios, support the current national vector control strategy against major based on use of IRS and LLINS using mostly pyrethroids. (38, 39) Insect populations generally response as community individual, the basis of sentinel site surveillance. However, several studies have shown that some characteristics like insecticide resistance can be developed as a local event shaped by environmental variations. (40) This is a common characteristic found in African anophelines but not well studied on neotropical anophelines. (40, 41) As we get closer to elimination, improvement in coverage of entomological surveillance will be required to provide more evidence based tailored interventions. (8, 9, 38)
Our results show the viability of delimitation of micro areas in malaria-endemic areas of Honduras. Even when limitations could threaten the accuracy of this work, it is clear that this provides a more targeted strategy for diagnosis and treatment, surveillance and vector control and therefore, a clear way to malaria elimination in Honduras. The results of this methodology, beyond contributing to the scientific community, have served to reorient the activities and interventions included in the National Strategic plan for Malaria Elimination 2018–2023 of Honduras. (9, 15) This approach has been adopted by the Pan American Health Organization and has been adapted and applied in Central American countries for strategic and operational planning for malaria elimination. (42–44)The methodology provides the use of local available data to improve response and is especially useful in those countries where malaria incidence is high enough that each case can’t be followed individually yet the disease is concentrated in a few districts / municipalities.
Several methods have been used since 1950s to identify and prioritize malaria control intervention in endemic countries, from annual parasite incidence at state level to high resolution risk maps. Evidence-based decisions are the core recommendation of WHO guidelines; however, limited country evidence is published on this subject and moreover, scientific reports from the American countries are basically historical.(45) To the best of the authors’ knowledge, the results here are the first efforts to characterize local malaria transmission hotspots in Mesoamerica using an operational investigation approach based on available epidemiological and entomological data, human movement information, ecological and demographic parameters, and health system factors at the level of a locality. National malaria elimination programs must include a similar evidence-based approach using all available data for operational planning as a priority to achieve the global goal of malaria elimination.