Geospatial data have been used in public health since John Snow mapped cholera cases around the Broad Street water pump during the London cholera epidemic of 1854. And, while global positioning system technologies (GPS) are so ubiquitous in the United States that virtually all new smartphones, tablets and cars have this technology embedded, in many areas of the world, health care workers in the field are often without the most basic two-dimensional paper maps. (At right: the author, Victoria Gammino, PhD, MPH, Epidemiologist, CDC Global Immunization Division)
So what do maps and map literacy have to do with polio? Polio is a crippling and potentially fatal infectious disease. There is no cure, but there are safe and effective vaccines. Therefore, the strategy to eradicate polio is based on preventing infection by immunizing every child to stop transmission of the virus that causes polio, and ultimately make the world polio free. The four pillars of polio eradication all rely on “microplans”— detailed logistical blueprints that guide the planning and implementation of vaccination campaigns, routine immunization outreach, and surveillance for polio cases by providing critical data on the size and location of the target population in a given geographic area. These target population numbers determine the amount of vaccine required, the number of health care workers and supervisors to deliver the vaccine, and the cost of transportation to get the vaccine and health care workers where they need to go.
In many countries, census data are out of date or are imprecise at sub-national levels. Political developments—for example the recent constitutional changes in Kenya that transferred authority to from five provincial to 47 county governments–can also create microplanning challenges as administrative boundaries are re-drawn and census estimates updated. In order to determine the number of vaccine delivery teams and their mode of transport (e.g., on foot, motorized vehicle, boat, camel, etc.) in a given area, or to estimate other microplanning or immunization-outreach resource requirements (e.g., the number of cold boxes or vaccine carriers needed), local knowledge of the terrain, seasonal weather patterns and geographic boundaries of an area are critical.
In urban areas characterized by high population density, vaccination teams visit many families, vaccinating upwards of 300+ children per day. In rural areas however, household compounds may be kilometers apart, with no road connecting them, forcing vaccinators to walk from house to house; in these instances, a team may only find and vaccinate 5 or 10 children in a day. In scenarios where nomadic pastoralist lifestyles prevail, the situation is more complex, as one considers tribe-specific migration patterns: season, type of livestock, family versus clan movement, the role of children in animal herding, and the location of livestock markets all figure into the microplanning process as variables that can impact a team’s ability to locate and vaccinate children.
It is also not unusual for some populations to assert tribal rather than national affiliations, and thus either be unfamiliar with, or indifferent to what they consider to be an arbitrary geopolitical boundary. Similarly, in low-density, remote or conflict areas, or in areas where administrative boundaries may be disputed, it is not always clear in what particular administrative jurisdiction a given village or cluster of homes may lie. Owing to the lack of access to either printed or digital maps, there can be ambiguity as to the jurisdiction of smaller, less densely populated settlements. This is where “social mapping” and geographic information systems (GIS) come in. Through an iterative dialogue with area residents, we create lists of inhabited areas and ask them to draw the key features of “their” area. We then compare these with two-dimensional printed maps and open sources of geographic information such as Google Earth to identify any areas that may have been overlooked during the community dialogue. The interstices or “no man’s land” between administrative jurisdictions are critical: in 2011, approximately one-half of wild polio cases in Kano and Jigawa States in Nigeria were within a few kilometers of an administrative boundary. Subsequent interviews with the teams confirmed that there was indeed confusion over the actual boundary, and consequently these villages may have been missed during campaigns, thereby creating potential immunity gaps.
A cow wears a GPS-enabled collar to monitor its daily grazing route in the Masai Mara, Kenya. Photo courtesy of Victoria Gammino/CDC. (click for larger image)
GIS has also become a critical tool to plan and support surveys. In order to create a statistically valid sample, one needs to have a sampling frame. For certain populations that are highly migratory, those data are elusive. GIS affords us the opportunity to sample a geographic area rather than a population, as well as alternative methods for estimating vaccination team coverage by measuring the amount of territory covered in contrast to the amount assigned to a team.
GIS is also a tool common to the veterinarians, agricultural extension workers, and other livestock experts with whom we collaborate in our effort to reach every last child. As GPS receivers allow the user to geo-reference specific locations (“geo-tag”) and sequences of geo-references (“tracks”), we can, for example, monitor the movement of animals in near-real time. This type of information–knowing the grazing radii of a cow versus a camel–can help us pinpoint where pastoralists may move with their livestock, and over what period of time relative to the availability of surface water.
Using Google maps to 'georeference' a hand drawn microplan in Nairobi, Kenya (click for larger image)
Recently, through a series of trainings in Ethiopia, Kenya, Nigeria and Burkina Faso, we have been learning how to adapt GIS tools and social mapping techniques to each country’s particular needs to improve microplanning, and thus improve immunization coverage. Through our collaborations with these host country governments, as well as multilateral partners such as WHO, UNICEF and FAO, we have worked to improve planning for seasonally mobile and border populations, as well as those living in conflict-torn areas where microplanning is a challenge and access is barred by insecurity. As long as polio remains anywhere in the world, all the world’s children are at risk – reaching every child can be difficult, but microplanning using GIS is one of the best tools in the eradication toolkit.
Reprinted from CDC Our Global Voices blog.