need for fecal indicator

  • most pathogens of water borne diseases originate from human or animal feces
  • it is impossible practically to detect all pathogens that cause diarrheal disease individually
  • so indicator species are used to identify feces contamination

ideal properties of indicator species

  • be universally present in feces of humans and animals
  • be present in higher numbers than fecal pathogens
  • not be actually pathogenic
  • be readily detected by simple inexpensive methods
  • persist in water in a similar manner to fecel pathogens
  • not multiply in natural waters
  • respond to treatment in a similar manner to fecal pathogens

common indicator species

  • total coliforms (TC)
    • bacterial species
    • ferment lactose and produce acid and gas at 35ºC
    • many families of coliforms
      • citrobacter
      • klebsiella
      • hafnia
      • enterobacter
      • e.coli
      • salmonella
      • shigella
      • yersinia
    • not a useful fecal indicator since there are many non-fecal sources for these bacteria
    • useful in monitoring effectiveness of water treatment
    • to test cleanliness and integrity in a water distribution system
  • thermotolerant coliforms (TTC)
    • a subset of TC
    • ferment lactose within 48 h at 44ºC
    • previously fecel coliforms

    • 10^6 - 10^9 cells per gram feces

    • some indication of non-fecal TTC
      • klebsiella, some enterobacter
    • may grow or die off at ambient temperature
  • escherichia coli (EC)
    • most suitable fecal indicator
    • some possibility of growth of environment
    • only moderately persistent, resistant
    • better options compared to the other
  • these indicator bacteria are reported in terms of
    • number of counts or colonies in a 100 mL sample
  • many drinking water standards and WHO guide
    • prescribe no detectable E Coli or thermotolerant coliform
  • water that has higher levels of indicator bacteria
    • has more fecal contamination
    • but there is no clear correlation between indicator bacteria and pathogens

  • water having more than 1000 count / mL is very risky for consumption

  • however, even water with no detectable e.coli is not perfectly safe
    • as e.coli is less persistent and robust in the environment compared to some pathogens
    • so the e.coli indicator should be used to complement some on-site inspection at the water source
      • not as the only metric to decide the safety of drinking water
      • on-site inspection identifies risk factor ratings

other fecel indicators

  • coliphage viruses: require bacteria for hosts
  • fecal streptococci: lower numbers than coliforms; more persistent, resistant
  • bacterial spores: similar to protozoa, highly persistent, resistant
    • clostrodium perfringens
    • bacillus spp

F-Diagram

  • pathogens in feces dont cause diseases unless they are ingested
  • the F-Diagram shows the path ways for pathogens to get to faces from feces
    • fluids: contaminated fluids going to the face
    • fingers: contaminated fingers going to the face
    • flies: flies transmitting by contact
    • fields: poor sanitation
    • floods: poor sanitation
    • food affected by all the above

opportunities for contamination

  • water resource itself:
    • by human or animal species
  • in the delivery system
    • if there isn’t enough pressure in the delivery system
    • contaminated water enters through pipes or joints
    • improperly constructed rising main on a borehole, or suction hand pumps
  • collection and transport
    • when the point of collection is outside the home
    • unclean hands
  • household storage
    • open containers
    • dust and insects
    • children and animals introduce pathogens
    • retrieved using unclean ladels
  • consumption
    • cups might be contaminated with fecal matter
    • cups might be wiped clean with hands
      • but this actually makes it dirtier
  • HWT aims to clean water targeting contamination introduced at all these opportunities