1. Allan Schapira Elimination course, Harare, 11/6/14
UNIT 5B: SURVEILLANCE: GEOGRAPHIC ASPECTS, FOCI DEFINITION, DELIMITATION, CLASSIFICATION
Allan Schapira
Elimination course, Harare, 11/6/14

2. Geographic information systems
Often equated with the choropleth maps, which are useful for presentation in the control phase, but not in the elimination phase.

3. In elimination phase, priority is to prepare and maintain maps as follows:
Large-scale maps of each malaria focus, showing:
Residence where cases have been detected
Minimum features of the cases, e.g. contracted at residence or elsewhere
Mosquito breeding sites and/or potential breeding sites
Boundaries and location of the focus
Small-scale maps of whole country or regions, showing
The dynamics of malaria foci year by year
Landscape characteristics, roads, health facilities, altitude cut-offs
Delineation of the initially malarious area of the country and/or areas of ecological risk (see Unit 3, Stratification), to have
Overview of potential risk areas
To include in the documentation for certification

4. The focus, and why do we need it?
Definition: “A circumscribed locality situated in a currently or formerly malarious area and containing the continuous or intermittent epidemiological factors necessary for malaria transmission.” I.e. there is not necessarily transmission, but humans and mosquito vectors must be present.
Purpose: To optimize targeting of a suitable package of interventions, which will interrupt transmission as rapidly as possible in a given area.
Requirements:
(a) it can be assessed, whether there is transmission, cases without transmission or no transmission;
(b) evidence-based geographic delimitation is possible.

5. The focus as an ecosystem
Note that we can talk about a focus even if there are no parasites at present. This will typically be a cleared up focus.

6. Purpose of working with foci
Where to search for cases
which may have been the source of infection for a local case;
which may have been infected from a first detected case (index case), which was detected after becoming infective ;
cases with a similar origin as the index case, whether local or imported (see diagram below);
identifies area, which should be covered by vector control to prevent any forward transmission from mosquitoes, which may have become or will become infected from the cases in the area (detected or not);
Identifies the human population, where malaria surveillance needs to be rigorous, so that (a) any new case is rapidly treated and (b) elimination from the focus can be documented.

7. Focus in practice
One or more cases are detected and classified in a particular area
Geo-reference the cases. Place of detection and most likely exact place of infection. Use GPS (e.g. cell phone) and/or paper or electronic map.
Identify potential/actual breeding places present now or in rainy season. Use field observation and/or map.
Delimit the focus based on the location of:
the cases (index case and others found in the area since by PCD or ACD)
Breeding sites (potential or actual)
Distribution of the population
Local population movement

8. Re 3. Identifying breeding sites
Based on knowledge of bionomics of local vectors
Consider that breeding sites may be absent at time of initial search, but may appear after rains start
Look for breeding sites, if entomologically trained person is available, otherwise potential breeding sites.
Use field observations, if possible, otherwise maps (these do not of course show rain-water puddles)
In most areas of Africa, where An.gambiae/arabiensis is main vector, breeding sites are ubiquitous after rains
If so, it may be reasonable to apply a radius of 1.5 to 3 km

9. Re 4. Delimit human habitations which should be included in the focus
If breeding sites are ubiquitous, this can be done by applying a radius of 1.5 – 3 km around a detected case. Shorter, if there is one imported case, longer, if there is an outbreak or ongoing transmission with several cases per year.
See, using field observation and/or maps, whether a village, a hamlet, a cluster of habitations will form a natural unit of human dwellings with breeding sites.
Then draw a line around the focus on a map.
Avoid automatically equating focus with village. It may be, but the focus may be smaller (when a subsection only is at risk) or larger, when several communities are epidemiologically connected.

10. Classification of foci
Characteristic
Main classification
Strategy
0 cases
Cleared up
Maintain 0
+ Cases,
0 transmission
Non-active: Residual or
new potential
Prevent transmission
+ Transmission
Active: Residual or new (or endemic)
Interrupt transmission

11. Geo-coordinates of Case 1, where cursor is placed
Attempted delimitation of a focus around an index case at Khorixa, Namibia using Google Earth.
Geo-coordinates of Case 1, where cursor is placed
1 km
Dried out streams, around which breeding sites could have formed. They are so widespread that they have not been delineated.
Human habitation is concentrated and limited.
White line: delineation of the focus made with the polygon tool.
Elevation a.s.l. of Case 1

12. Zooming out, you can see that there are really no more habitations within 5-8 km

13. Shapes of foci
The heavily interconnected micro-foci. Metapopulation is a better concept. Typical of forested areas in Southeast Asia
The well-rounded focus typically delimited by the distribution of human habitation
Humans
Vectors
The elongated focus or chain of microfoci, typically determined by a river

14. Use of maps to guide operations