The pathogens described are:
Pathogenic bacteria:
Enterovirulent Escherichia coli group (EEC Group)
Parasitic protozoa and worms
Viruses
Natural toxins
Other pathogenic agents
External links:
... this case, the parabola does not intersect the x-axis at all.) Note that when computing roots numerically, the usual form of the quadratic formula is not ideal. See ...