Each time a cluster of illness occurs there is a process to determine its cause. One of the first thing that comes to mind with clusters, broadly speaking, is determining whether an infectious disease is present or something else. "Something else" will include a list of things, chief of which is a common exposure to some toxin.
The recent cluster of illness (blurry vision, headache, alterations of conciousness) in Nigeria--which recently experienced several imported cases of Ebola--sparked concerns of Ebola, for obvious reasons. However, it appears that no infectious cause of illness is responsible for this event which has claimed the lives of 18.
Currently there are two competing explanations: methanol contaminated gin and the WHO's preliminary hypothesis: pesticides. Both are good explanations because they fit the symptomatology of the cases and are biologically plausible. Final diagnosis should be able to confirmed with laboratory testing.
The investigation of this event illustrates several aspects of public health investigations, the most important of which is the importance of surveillance. Without knowing what illnesses are occurring in an illness, it is impossible to detect unusual occurrences and place them in the context of what is the usual baseline mix of disease in an area.
Another aspect of this case is the possible link with pesticides (which may not turn out be the case). Though I am a big fan of pesticides as I value human life and the conditions required for our flourishing--such as an abundant supply of food--pesticides can be dangerous if the quantity ingested exceeds a threshold. Because of these limitations, alternatives to pesticides are actively sought. One such alternative are GMO crops that are resistant to plant pathogens. One would think that such a pathbreaking advance in genetics and agriculture would be embraced, yet it is not.
Why are GMOs feared? It is not because of any evidence of their danger for there really isn't any as no one has died or been harmed from GMO-poisoning (an oxymoron). Yet for those who seek an alternative to pesticides, which cause up to 20,000 illnesses yearly in the US, GMOs are often considered off-limits because of the vocal anti-science, anti-reason, anti-GMO movement which often resorts to threats, violence, and property destruction in their nihilistic quest.
Remember the corn we eat and the dogs we walk are all GMOs as artificial selection and breeding for specific traits are exactly the principles behind all genetic engineering.
You would think that people that scream "safety" would actually care about safety and embrace GMOs, but it isn't safety that motivates them, it is hatred of the human minds that made GMOs possible.