Water Quality Analysis Prioritisation
The Transmission cycle of disease
This study will focus on disease caused by pathogens, infectious agents, or the toxins that the
produce. For a pathogen to survive it must be able to leave an infected host, survive transmission in
the environment and develop or multiply in the newly infected host (DISEASE). This cycle is known
as the transmission cycle of disease.
Figure 1 Example Transmission Cycle
The pathogens which cause disease are generally split into several categories, Food-borne, Waterborne, Vector-borne and Water-washed. For this project we will be focussing on water-borne
pathogen cycles. (Water-washed are water related pathogens whose spread is reduced by
improvements in hygiene and as such fall outside the major scope of our project.)
The infectious dose of a pathogen is the number of pathogens that have to enter the body of a
susceptible person to cause infection. This is a characteristic mainly related to faecal-oral
transmission, of which many water-borne pathogens fall into.
`Health is improved by breaking the transmission cycle of diseases present in the project area
(DISEASE) and therefore, in order to design a system to improve health the pathogens and their
infectious doses must be established. This will allow us to decide the level of water quality we should
aim to treat to improve health.
Analysis of Pathogens
In order to establish which pathogens we wish to treat qualitative analysis has been performed to
give us a relative risk scale. The process followed can be seen in (FIGURE). The research undertaken
suggests that there is a health problem to be solved. This leads us to hazard identification and a risk
analysis. In order to do this each pathogen was assessed and rated against the following criteria
(TABLES 1, 2, 3) and a overall risk factor computed (TABLE 4).
Likelihood qualitative scale:
Score Exist
0
No
1
Yes
Description… in terms of chance of people getting sick upon ingestion
Problems and Disease not present in the area
Problems confirmed in the area by local dctors
Consequence (time) qualitative scale:

Time, not cost, is the parameter used to quantify hardship because interviews with locals did
not indicate money saving to be a priority.
 Consequences of pathogen ingestion will vary from person to person, given the scope and
level of detail of this analysis, each consequence score is chosen so as to describe the most
common scenarios we encountered in our research.
 Pathogen consequence score allocation will be backed up by medical articles/studies.
Score
Description… in terms of time lost from work for men and from school for
children
1
1 day
2
Less than 1 week
3
1-4 Weeks
4
Greater than a month
5
Long term health implications
Consequence (severity) qualitative scale:



Pathogen strains may vary, resulting in a wide range of severity
Pathogen consequence score allocation will be backed up by medical articles/studies.
Severity differs from time cost since some diseases may not result in huge loss of work, but
may occur over long periods of time, whilst some may occur over a short period of time, but
there is a chance of fatality.
Score
Description… in terms of possible health consequences of disease
1
Low
2
Low, very serious on rare occasions
3
Severe
4
Severe, higher chance of fatality amongst young, elderly etc.
5
High chance of fatality if untreated
Minerals
In the 1980s/1990s water quality problems due to chemicals begun to emerge. This occurred as
there was a switch to use of more ground water sources and also due to increased use of fertiliser
and pesticide use in both agricultural and industrial use, both potential problems in this area. WATER
AID. These minerals and their affects have been included TABLE 4, and rated using the same analysis
as the pathogens.
Disease
Bacterial enteritis,
Campylobacter enteritis,
Diarrhoea,
Gastroenteritis
Bacterial enteritis (Ecoli), Diarrhoea,
Gastroenteritis
Bacterial enteritis,
Salmonellosis,
Diarrhoea,
Gastroenteritis
Bacterial enteritis,
Yersiniosis,
Diarrhoea,
Gastroenteristis
Bacillary dysentry,
Shigellosis
Cholera
Viral enteritis,
Viral gastroenteritis,
Viral Diarrhoea,
Diarrhoea
Pathogen
Campylobacter Jejuni,
C. Coli
Infectious Dose
Likilihood
Consequence
(time)
Consequence
(severity)
Risk Factor
>500
1
2
2
5
low
1
3
4
8
v small to v high
1
2
3
6
med-high
1
3
3
7
10-100
1
2
4
7
2
5
Not Present
Escherichia coli
Salmonella
Yersina entercolitica,
Y.psuedotuberculosis
Shigella
Vibrio Cholera
Rotavirus
Dysentry (ameobic),
Ameobis
Entamoeba hostolytica
Giardia enmteritis,
Giardiasis
Cryptosporidiosis
Giardia lamblia
Cryptosporidium parvum
10^6 - 10^8
106 - 10^4
1
2
4
7
low
1
5
1
7
10-100
4
2
Not Present
low
3
1
Not Present
Dysentry (Balantidial),
Balantidiasis
Typhoid,
Enteric fever,
Typhoid fever,
Paratyphoid fever
Weil's disease,
Leptospirosis
Balantidium coli
Salmonella typhi,
Salmonella paratyphi
Leptospira
low
1
5
4
10
10^3 - 10^9
3
5
Not Present
low
3
2
Not Present
Fluoride
Digestive Disorders, Skin
Diseases,
Dental
Flurosis, Skeletal Flurosis
>1.5mg/l
1
5
3
9
>1mg/l
1
5
3
9
>100mg/l
1
5
3
9
1
5
3
9
Iron
Digestive Disorders, Skin
Diseases,
Dental
Problems, Poisonous in
High Doses
Methamoglobinemia,
Increase risk of cancer
Nitrate
Weakened immunity,
Abnormal multiplication
of cells
Pesticides
Is there a
Health
Problem?
System analysis
Computation of level of risk due
to each pathogen
HAZARD IDENTIFICATION:
LIKELIHOOD of EXPOSURE:
What are the main pathogens
present in the water?
What is the concentration
of each in local water when
it reaches houses?
RISK
CONSEQUENCE SCALE:
Is there
demand/need
for a solution?
PRA method
POPULATION VULNERABILITY:
How prepared is the
community to protect itself
against and recover from
contact with pathogen?
How severe are the
consequences, given
contact with pathogens?
n.b. hardship assessed
against comm. values
Determination of Adequate Level of Water Quality
Establishing adequacy of
design solution intervention